- Email: [email protected]
How close is artificial biochar aging to natural biochar aging in fields? A meta-analysis
Geoderma 352 (2019) 96–103
Contents lists available at ScienceDirect
Geoderma journal homepage: www.elsevier.com/locate/geoderma
How close is artificial biochar aging to natural biochar aging in fields? A meta-analysis
T
Haixiao Lia,b, , Xueqiang Lua,b, , Yan Xuc,d, Haitao Liue ⁎
⁎
a
College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China Tianjin Key Laboratory of Environmental Technology for Complex Trans-Media Pollution, Nankai University, Tianjin 300350, China c Quebec Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd., Quebec City, QC G1V 2J3, Canada d Department of Soils and Agri-Food Engineering, Paul Comtois Bldg., Laval University, Quebec, QC G1K 7P4, Canada e Shaanxi Provincial Land Engineering Construction Group Baoji Branch, No.7 Guangtai Road, Xi'an 710075, Shaanxi, China b
ARTICLE INFO
ABSTRACT
Handling Editor: David Laird
Biochar is used as a soil amendment to improve soil quality and fertility. The performance of biochar changes as it ages in fields. Artificial biochar aging methods (i.e. chemical oxidation) are considered proxies for natural biochar aging and help to evaluate the long-term effects of biochar amendment in soil. However, few studies have focused on how close artificial biochar aging methods are to biochar aging in fields. A meta-analysis of 42studies was conducted to quantitatively compare the effects of soil incubation (natural field biochar aging), chemical oxidation (chemical biochar aging) and freeze-thaw cycling (freeze-thaw biochar aging) on biochar properties, including surface and bulk element compositions (C, H, O, N), specific surface area, cation exchange capacity and pH. The results showed that the artificial biochar aging methods cannot yet simulate biochar aging in the soil. In comparison with natural field aging, chemical aging tended to have a higher degree of oxidation at the surface of the aged biochar and posed the problems of oxidation inside the biochar and the import of exogenous elements from oxidants to the biochar. Freeze-thaw aging changed only the porous structure of the biochar with no significant alterations to element compositions, in contrast with natural aging.
Keywords: Soil incubation Chemical oxidation Freeze-thaw cycling Surface/bulk element composition Cation exchange capacity Specific surface area
1. Introduction Biochar is a carbon-rich solid material made from the pyrolysis of biological residues in an oxygen-limited environment. Used as a soil amendment, biochar contributes to improving soil fertility (Yao et al., 2012), water retention (Laird et al., 2010), aggregate stability (Soinne et al., 2014) and microorganism diversity (Lehmann et al., 2011). Biochar also helps to mitigate climate change via carbon sequestration (Matovic, 2011). The performance of biochar in soil depends mainly on the biochar's properties as a result of the feedstock and the pyrolysis process and on the biochar's interaction with soil constituents (Joseph et al., 2010; Ronsse et al., 2013; Sun et al., 2014; Suliman et al., 2016a). Moreover, biochar's performance changes as the biochar progressively ages in soil, through chemical reactions, water erosion, and microbial decomposition (Mia et al., 2017a; de la Rosa et al., 2018). For instance, the breakdown of aromatic moieties and the oxidation at the biochar surface could generate carboxylic functional groups, making the biochar more interactive with soil minerals, nutrients, and contaminants (Rechberger et al., 2019). Moreover, Gronwald et al. 2015) reported
⁎
that 7 months of field aging decreased the adsorption capacity of biochar by 60% to 80%. It is time-consuming to study the long-term effects of biochar on soil, since the natural biochar aging process is very slow. Uras et al. (2012) pointed out that the half-life of biochar in soil could be in excess of 1000-years. In this case, artificial aging methods such as chemical oxidation and freeze-thaw cycling have been developed as proxies for natural biochar aging (Frišták et al., 2014; Su et al., 2015; Jin et al., 2017). These methods help to accelerate biochar aging, cutting the time from months or years to days or hours. However, few studies have considered the extent to which artificial biochar aging is able to simulate biochar aging under soil conditions. Meta-analysis would be a useful tool to address that concern using published data to obtain a conclusion, as has been done for other aspects of biochar research (Jeffery et al., 2011; Cayuela et al., 2014; Thomas and Gale, 2015). Herein a bibliometric work and a meta-analysis have been conducted to compare the alterations of biochar properties (surface and bulk element contents, specific surface area [SSA], cation exchange capacity [CEC], and pH) under different aging
Corresponding authors at: College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China. E-mail addresses: [email protected] (H. Li), [email protected] (X. Lu).
https://doi.org/10.1016/j.geoderma.2019.06.006 Received 24 February 2019; Received in revised form 31 May 2019; Accepted 3 June 2019 Available online 12 June 2019 0016-7061/ © 2019 Elsevier B.V. All rights reserved.
Geoderma 352 (2019) 96–103
H. Li, et al.
processes, namely, soil incubation (natural biochar aging [NA]), chemical oxidation (chemical biochar aging [CA]), and freeze-thaw cycling (freeze-thaw biochar aging [FA]). The results would show whether biochar properties change in a similar pattern under artificial aging as under natural aging.
(ni 1) SDi2 (n i 1)
SDpooled =
(1)
where SDpooled is the pooled standard deviation for a certain biochar property value, ni is the number of biochar property measurements in the i-th comparison, and SDi is the presented standard deviation of a certain biochar property value in the i-th comparison.
2. Material and methods 2.1. Data collection
2.2. Data screening
The keywords “biochar,” “aging,” “ageing,” “oxidation,” “soil incubation,” “freeze-thaw,” “drying-wetting,” and “weathering” were combined with one another and entered into the Google Scholar, Baidu Scholar, and Web of Science search engines to identify relevant studies for the meta-analysis. Studies had to meet the following criteria to be included in the analysis: (a) a randomized design was used; (b) the term pair “fresh biochar” and “aged biochar” appeared, and “aged biochar” was produced via the same process as “fresh biochar” in all aspects apart from biochar aging; and (c) replicated samples were considered. However, it should be noted that, in general, the analyses of biochar surface element composition, bulk element composition, and SSA were quite accurate, such that most publications accepted the measurements without replication. Hence, to avoid the specific selection of studies, these relatively accurate data without replication should not be simply ignored and could also be included in the meta-analysis (Quemada et al., 2013). In addition to these criteria, studies containing results reported repeatedly by the same research group were counted as one study. Each study contained the measured data for at least one biochar property out of surface element contents, bulk element contents, SSA, CEC, and pH. In total, 42 studies were selected (Table 1). The distribution of the studies across time is presented in Fig. 1, which shows an increasing interest in biochar aging research, with more published articles in the period from 2016 to 2018. The number of comparisons of “fresh biochar” versus “aged biochar” for each biochar property is presented in Fig. 2. Of the 42 studies, 19 studies aged biochar through soil incubation in fields or in pots for periods varying from 1 month to 5 years, 15 studies aged biochar by chemical oxidation using H2O2, HNO3, and HNO3/H2SO4 solutions, and 9 studies conducted biochar aging via freeze-thaw cycling of different sequences. In those studies, the biochars aged by soil incubation were generally separated manually from soil with sieves and tweezers and then washed with deionized water and air-dried, although Heitkötter and Marschner (2015) and Lin et al. (2018) collected the biochar particles directly from the polyamide mesh bags buried in soil. The biochars aged by chemical oxidation were collected by draining them through sieves and then washing and airdrying the particles. The biochars aged through freeze-thaw cycling were air-dried before analysis. The biochar surface element compositions were measured using X-ray photoelectron spectroscopy (XPS) or scanning electron microscope electron diffraction analysis (SEM-EDX). The bulk element compositions were determined with an elemental analyzer. Biochar CEC was measured by the replacement methods described in Mukherjee et al. (2014) or by other similar methods. Biochar SSA was determined by either the Brunauer, Emmett, and Teller (BET) N2-sorption method or the CO2-sorption method (Donne, 2011; Jagiello and Thommes, 2004). When both the N2-sorption SSA and the CO2sorption SSA were used in one study, only the results of the N2-sorption SSA were included. The data for biochar properties together with their standard deviations or standard errors were collected from the tables in manuscripts or from the figures using DataThief software where possible. The collected standard errors were then converted to standard deviations for the corresponding study. When there were no standard deviations or standard errors for the presented data in a study, a pooled standard deviation calculated from the obtained standard deviations via Eq. (1) will be used instead (Furukawa et al., 2006).
Data screening was conducted to exclude extreme values. The boxplots of biochar property values for fresh biochars under NA, CA, and FA are presented in Fig. 3. The separated points were observed for surface C, O, and N contents and for bulk H, O, and N contents (Fig. 3-a, c, d, f, g, h). However, since the values are within the range reported in other biochar literature, the data were included for the meta-analysis. Extremely low bulk C contents (< 20%) were observed for the fresh biochars under NA and CA (Fig. 3-e), because the biochars were made from chicken manure (Jin et al., 2017) and sewage sludge (de la Rosa et al., 2018) rather than from plant residues. These low bulk C content values for fresh biochar were eliminated from the analysis. Biochar SSA and CEC vary a great deal according to the literature. Hence, even though separate points were observed for SSA and CEC (Fig. 3-i, j), all data were retained for the analysis. Extremely low biochar pH values (pH = 3 and 3.5) were found with the fresh biochars under NA (Fig. 3k). As there was no elucidation for the low pH data for oak- and pinederived biochars pyrolyzed at 250 °C (Mukherjee et al., 2014), the data were eliminated from the meta-analysis. 2.3. Data analysis The meta-analysis was conducted using Review Manager-5 software (RevMan-5, Cochrane Community, London, UK) under the random effect model because there was heterogeneity among the studies. The standardized mean difference (SMD) between fresh biochar properties and aged biochar properties was used to compare the effects of different biochar aging methods on biochar alteration. According to the statistical algorithms (Deeks and Higgins, 2007), the SMD calculation implemented in the software was Hedges' adjusted g with an adjustment for small sample bias:
SMDi =
m1i
m2i si
1
3 4Ni 9
(2)
with standard error calculated as follows:
SEi =
SMDi2 Ni + n1i n2i 2(Ni 3.94)
(3)
where SMDi is the standardized mean difference of the i-th comparison; SEi is the standard error of the i-th comparison; m1i and m2i are the means of the biochar property for aged and fresh biochar groups of the i-th comparison; si is the pooled standard deviation across two groups of the i-th comparison; and n1i, n2i and Ni are the numbers of biochar property measurements for aged biochar, fresh biochar, and all biochars, respectively, of the i-th comparison. Once the SMD's 95% confidence intervals (CIs) did not overlap zero, which indicated that the P-value of the overall effect test was smaller than 0.05, the effect of the biochar aging method on a biochar property was deemed significant. Similarly, SMDs for the different aging methods were considered significantly different from one another when their 95% CIs did not overlap with one another.
97
98
Fan et al. (2018) Huang et al. (2018) Kumar et al. (2018)
Lin et al. (2018)
Nguyen et al. (2018) Oleszczuk and Kołtowski (2018) Wang et al. (2018) (Chinese) Cao et al. (2017)
Dong et al. (2017) Güzel et al. (2017) Jin et al. (2017)
Lin et al. (2017) (Chinese) Luo et al. (2017) Mia et al. (2017a,b) Wang et al. (2017) (Chinese) Bakshi et al. (2016)
Chen et al. (2016) (Chinese)
Huff and Lee (2016) Lawrinenko et al. (2016)
Ren et al. (2016) Sorrenti et al. (2016) Trigo et al. (2016) Wang et al. (2016a)
Wei et al. (2016) Wen et al. (2016) (Chinese) Ghaffar et al. (2015) Heitkötter and Marschner (2015) Su et al. (2015) Wang et al. (2015) Frišták et al. (2014) Mukherjee et al. (2014)
Prendergast-Miller et al. (2014) Qian and Chen (2014)
Trigo et al. (2014) Kim et al. (2013) Liu et al. (2013) Spokas (2013) Lin et al. (2012) Hale et al. (2011) Joseph et al. (2010)
3 4 5
6
7 8
9 10
11 12 13
14 15 16 17 18
19
20 21
22 23 24 25
26 27 28 29
34 35
36 37 38 39 40 41 42
30 31 32 33
Rechberger et al. (2019) de la Rosa et al. (2018)
Reference
1 2
No.
Macadamia nut shells Switchgrass Oak, bamboo, straw Hardwood, wood pellet, macadamia nut shell Poultry manure and papermill sludge Corn stover Chicken litter, papermill waste, and greenwaste
Miscanthus giganteus and Salix sp. Rice straw
Pine chips Maple wood Beech wood chips and garden green waste residues Oak, pine, and grass
Rice husk Straw Peanut shells Pine chips and corn degistate
Pig manure Chipped hardwood of peach and grapevine Macadamia nut shells, wood chips Maple tree
Pinewood Alfalfa, cellulose, and maize stover
Mushroom substrate waste Weeds Rice straw, wheat straw, maize straw, swine manure, cow manure, and chicken manure Peanut shells Maize Eucalyptus wood Yak dung Hardwood, soybean, switchgrass, corn stover, and macadamia nut shell Rice straw
Maize straw Rice hull
Eucalyptus saligna Wheat straw, elephant grass
Poultry manure and drying sludge
Mixed wood chips Pine wood, paper sludge, wheat husks, sewage sludge, vineyard, mixed wood chips Wheat straw Rice husk Grain husk and cattle manure
Feedstock
Table 1 List of references for the data collected in the meta-analysis.
400 °C 500 and 700 °C
350 °C
400 °C 300 and 500 °C 550 °C 300, 450 and 600 °C 500–850 °C
400 °C for 4 h 500 °C for 1 h 450 °C for 1 h
400 °C for 2 h 500 °C for 30 min
550 °C for 30 min 650 °C
500 °C for 2 h
450 °C 350 and 550 °C for 2 h 450 °C
525 °C for 1 h –
– 450, 600 and 800 °C for 30s 600 °C for oak and bamboo; 300 °C for straw 500–550 °C 550 °C for 30 and 60 min 600 °C 450 and 550 °C
450 and 700 °C 350, 500, and 700 °C
500 and 700 °C for 2 h 500 °C for 30 min 500 °C for 2 h 250, 400, and 600 °C for 3 h
300, 500, and 700 °C 550 °C for 30 min 550 and 850 °C 300, 400, 500, 600, 700 °C for 30 min; 500 °C for 5, 60, 120, 400, and 800 min 400 °C for 30 min 200 and 500 °C 300 and 700 °C for 4 h 400 and 600 °C
Pyrolysis
Freeze-thaw sequences of 20 °C (20 h) and −20 °C (4 h) for 30 days Oxidation by 15 and 30% H2O2 for 0.25–350 h at 30 °C 20 freeze-thaw sequences of 25 °C (12 h) and −18 °C (12 h) Incubation in the soil of Gainesville, Florida without macrofauna and sunlight for 15 months 200 freeze-thaw sequences between 30 and −10 °C Oxidation by 20, 40, or 60% HNO3/H2SO4 solution (1/3) at 70 °C for 6h Incubation in Waukegan silt loam for 1 and 2 years Oxidation by HNO3 (pH = 3, 5, and 7) for 24 h Oxidation by 65% HNO3 at 80 °C for 48 h Incubation in a Waukegan silt loam soil (pH = 6.4) for 3 years Incubation in a highly weathered acidic ferrosol 42 freeze-thaw sequences of 20 °C (19 h) and −70 °C (5 h) Incubation in a Ferrosol for 1 and 2 years
25 freeze-thaw sequences of 30 °C (10 days) and −20 °C (10 days) Oxidation by 20% H2O2 for 1 to 7 days Oxidation by HNO3/H2SO4 solution (1/3) at 70 °C for 6 h Incubation in historical kiln soil and a control soil for 100 days
Oxidation by 20% HNO3/H2SO4 (1/3) at 70 °C for 6 h Incubation in soil at 25 °C with 75% of water holding capacity Oxidation by 5, 10 and 15% H2O2 (1:30, m/v) at 80 °C for 6 h 30 freeze-thaw sequences of 35 °C (16 h) and − 20 °C (8 h) 30% H2O2 with 1 M HCl at 40 °C; incubation in agricultural fields in Minnesota and South Dakota Freeze-thaw sequence of 20 °C (5 h) and −78 °C (19 h) with 40% water content for 2 months Oxidation by 1, 3, 10, 20 and 30% H2O2 Oxidation by 30% H2O2 weekly with 1 M NaOH for 10 min within 4 months Incubation in quartz sand for wheat root substrate for 90 days Incubation in a sandy loam inceptisol soil (pH = 8.08) for 4 years Incubation in silt loam soil for 1, 4 and 5 years Oxidation by 30% H2O2 (v/v) at 30 °C for two weeks
Freeze-thaw sequences of 25 °C (19 h) and − 18 °C (5 h) for 50 days Incubation in red soil, sandy soil, and coastal solonchak for 1 and 13 months Incubation in Fluvisol for 5 years Oxidation by 20, 40, and 65% HNO3 at 80 °C for 1 h Oxidation by 25% HNO3 at 90 °C for 4 h
40 and 60% HNO3/H2SO4 (1/3) solution; 30% H2O2 with 1 M NaOH Incubation in quartz sand for 100, 200, and 300 days Incubation in a red, non-calcareous, iron oxide-coated quartz sand soil for 60 days Incubation in a typic udic ferrisol with 60% water hold capacity for 3 months Incubation in red Ferralsol for 9 years Freeze-thaw sequences of 20 °C (7d) and −20 °C (7d) for 14 months
Incubation in an acidic sandy loam Planosol for 15 months Incubation in calcareous sandy clay loam soil for 6, 12 and 24 months
Aging method
H. Li, et al.
Geoderma 352 (2019) 96–103
Geoderma 352 (2019) 96–103
H. Li, et al.
6
of −1.76) and a significant bulk O increase (SMD of 1.95) (Table 2, Fig. 4-e, f, g). In addition, CA tended to increase biochar bulk N content, with an SMD of 1.01 and a P-value close to 0.05 (P = 0.06) (Table 2, Fig. 4-h). Similar to biochar surface element contents, FA did not show a significant effect on biochar bulk element contents (Table 2, Fig. 4-e, f, g, h).
4
3.3. Biochar SSA, CEC, and pH
12
Number of studies
10 8
The meta-analysis results showed that CA significantly decreased biochar SSA (SMD of −0.91), whereas FA relatively increased biochar SSA (SMD of 0.59 and P-value of 0.08) (Table 2, Fig. 4-i). In addition, NA had no effects on biochar SSA. In terms of biochar CEC, the NA, CA, and FA methods tended to slightly increase biochar CEC with SMDs of 2.27, 0.93, and 1.45, respectively (Fig. 4-j). However, there were no significant effects observed (Table 2). The CA method had the most significant effect on decreasing biochar pH (SMD of −7.47), followed by NA (SMD of −2.90) (Table 2, Fig. 4-k), whereas FA showed no significant effects on biochar pH but also tended to decrease pH.
2 0 2010
2012
2014
2016
2018
2020
Years Fig. 1. Distribution along time of studies on biochar aging collected for metaanalysis.
3. Results 3.1. Biochar surface element contents
4. Discussion
The NA method significantly decreased biochar surface C content (SMD of −2.29) and increased surface H, O, and N contents (SMDs of 0.76, 3.36, and 3.72, respectively) (Table 2, Fig. 4-a, b, c, d). The CA method significantly decreased biochar surface C content (SMD of −0.99) and increased surface O content (SMD of 3.72) (Table 2, Fig. 4-a, c), but no significant effects of CA on surface H and N contents were observed (Table 2, Fig. 4-b, d). In comparison with NA, CA decreased biochar surface C less but increased surface O content to a similar level. The FA method seemed to cause no differences in surface element contents between fresh and aged biochars (Table 2, Fig. 4-a, c). However, we still need other data to verify the effect on biochar surface H and N.
4.1. Biochar aging in soil The high content of aromatic structures in biochar makes it stable and recalcitrant in the soil. However, variable amounts of aliphatic C exist in biochar as either bridges between aromatic moieties or branches of the aromatic layer (Mia et al., 2017a,b). On a molecular scale, once the aliphatic C decomposes, disconnected and intact aromatic moieties could break down through soil constituent interactions and microbial decomposition (Shi et al., 2015). With oxidation of the aromatic backbone yielding carboxylic groups, biochar C would be depleted, and O content would tend to increase. This natural aging process would take place first at the biochar surface, leading to decreased surface C content and increased surface O content, as shown by the meta-analysis results (Fig. 4-a, c). The increased surface H and N contents of the aged biochar under NA would be due to adsorption of organic matters and mineral nutrients on biochar surface (Fig. 4-b, d), although the washing of the biochar during the separation from soil might mitigate this effect. In addition to the adsorption of labile organic matter, the porous structure of biochar would create a favorable habitat for soil microorganisms, which play an important role in biochar stability (Ameloot et al., 2013).
3.2. Biochar bulk element contents The biochars aged by NA had significantly lower bulk C content (SMD of −0.88) and higher bulk H content (SMD of 1.59) than the fresh biochars (Table 2, Fig. 4-e, f) but there was little effect on biochar bulk O and N contents (Table 2, Fig. 4-g, h). In comparison with NA, CA depleted significantly more biochar bulk C, with an SMD of −1.47, and had a significant bulk H decrease (SMD
Fig. 2. Numbers of “fresh biochar” vs “aged biochar” comparisons for each biochar properties in the meta-analysis. 99
Geoderma 352 (2019) 96–103
H. Li, et al.
Fig. 3. Box-plots for biochar surface element contents (C, H, O, N), bulk element contents (C, H, O, N), specific surface area (SSA), cation exchange capacity (CEC) and pH of fresh biochars under chemical aging (CA), natural aging (NA), and freeze-thaw aging (FA).
Microorganisms could assimilate the soil organic matter adsorbed on biochar surface, the labile C in the biochar, and even the resistant C in it. According to Kuzyakov et al. (2014), higher organic matter content and higher microorganism activities in soil would accelerate the biochar decomposition rate. In contrast to the way that it increased surface O, NA had few effects on biochar bulk O content. That finding likely indicates an aerobic environment inside biochar. The blockage of biochar pores by organic matter, clay particles and pore-filling water could be the main reason that there was less oxidation inside the biochar (Wang et al., 2012; Inyang and Dickenson, 2015). However, soil constituents, microorganisms, and biochar could also interact aerobically inside biochar, possibly altering biochar bulk C and H contents under NA, as observed in the meta-analysis (Fig. 4-e, f). The carboxylic and phenolic groups generated from biochar surface oxidation might increase biochar CEC (Fig. 4-j), as hydroxyls (−OH) in carboxylic and phenolic groups would form carboxylate and phenolate with cations in the soil while releasing H+ (Uchimiya et al., 2011). That phenomenon also explains why naturally aged biochar had a lower pH than fresh biochar did (Fig. 4-k). In terms of SSA, the blockage of biochar pores by organic matter was considered to decrease biochar SSA (Kong et al., 2014). On the other hand, erosion, dissolution and transport by water fluxes in the soil were also reported to contribute to biochar aging (de la Rosa et al., 2018). Once the volatile organic compounds and ash in the blocked pores are washed by fluxes, biochar porosity and SSA might be increased (Suliman et al., 2016b). These counteracting processes would contribute to biochar SSA alteration in the soil. Our results showed that biochar SSA changed insignificantly during aging in the soil (NA) (Table 2).
incubation period, which ranges from 1 month to 9 years, most chemical oxidation treatments took only several hours (Table 1). That method accelerated biochar aging a great deal but caused different alterations to biochar properties. Similar to NA, CA also decreased biochar surface C (Fig. 4-a). However, CA increased surface O only, whereas NA increased biochar surface O, H, and N. This difference probably indicates that aged biochar has a higher degree of surface oxidation in the oxidizing agent (i.e. H2O2 or HNO3) solution. The mild oxidation and microbial activities in the soil generate the carboxyl, phenolic, and carbonyl groups on the biochar surface (Mia et al., 2017a), whereas chemical oxidation might not only turn biochar surface functional groups into carboxylic groups but also oxidize phenolic hydroxyl possibly into other structures such as quinones (Mia et al., 2017b). Additionally, structures such as quinones make no contribution to biochar CEC, which probably explains why CA increased biochar CEC less than NA did (SMDs of 0.93 and 2.27, respectively). Severe liquid phase oxidation could destroy biochar pores and decrease biochar SSA (Yakout et al., 2015). Without pore blockage in solution, chemical oxidizing agents could oxidize the interior of biochar. One of the principal differences between NA and CA might be that CA could increase biochar bulk O (Fig. 4-g). This phenomenon might be questionable, since the fresh CA biochars had larger SSA than the fresh NA biochars did (Fig. 3-i), which might make it easier to oxidize the interior of the biochar. However, there were actually only four studies (Ghaffar et al., 2015; Wang et al., 2015, 2016a; Mia et al., 2017b) with both data for biochar bulk O and large biochar SSA values (> 100 m2 g−1). Regardless of these bulk O data with large SSA, the bulk O SMD for CA was even higher, at 2.92 in comparison with 1.95 as shown in Fig. 4-g. That finding might thus confirm that CA method oxidized more of the interior of the biochar than NA did. In terms of SSA, we observed that the SMD of biochar with large SSA values (> 100 m2 g−1) under CA was −2.91, whereas the SMD of biochar with small SSA values (< 100 m2 g−1) under CA was 0.34 (data not shown). That finding indicates that the CA probably decreased the SSA
4.2. Chemical oxidation versus soil incubation Chemical oxidation (CA) is the most commonly used method to simulate biochar oxidation during aging. In comparison to the soil 100
Geoderma 352 (2019) 96–103
H. Li, et al.
4.3. Freeze-thaw cycling versus soil incubation
Table 2 Overall effect results (P-value) of the meta-analysis for biochar aging effects on biochar property alterations. Biochar properties Surface NA CA FA Surface NA CA FA Surface NA CA FA Surface NA CA FA Bulk C NA CA Bulk H NA CA FA Bulk O NA CA FA Bulk N NA CA FA SSA NA CA FA CEC NA CA FA pH NA CA FA
C
H
O
N
Freeze-thaw cycling is another common method used to accelerate biochar aging. Although that method takes more time than chemical oxidation treatments do, it rarely requires more than two months, according to the selected studies (Table 1). Our results showed that FA had no effects on biochar element compositions and pH (Table 2), apparently because of the weak oxidation and microbial activities under extremely low temperatures and the lack of exogenous element inputs. The FA method affected biochar mainly by resulting in a larger SSA and higher CEC in the aged biochar (Fig. 4-i, j). Freezing-thawing could increase biochar SSA probably by creating more pore space: ice crystal of the water infiltrated biochar pores would grow and expand intrapore size during freezing and would end up breaking biochar particles (Liu et al., 2018). This process would create more small biochar particles, which have larger SSA values than large particles do, similar to the case for soil particles (Xiao et al., 2014). Meanwhile, the CEC increase could be related to the SSA increase. However, further study is needed to determine whether FA could also break the biochar skeletal structure, causing the compaction of aged biochar and the reduction of SSA and CEC.
P < 0.0001⁎ 0.03⁎ 0.72 0.03⁎ 0.91 0.85 0.001⁎ < 0.00001⁎ 0.62 0.0001⁎ 0.58 0.73 0.0006⁎ < 0.00001⁎ 0.002⁎ < 0.00001⁎ 0.48
4.4. Perspectives
0.78 < 0.00001⁎ 0.77
Biochar aging in fields is complex and includes various processes, such as abiotic oxidation, carbonate dissolution, chemisorption, soil constituent interaction, physical disintegration, microbial degradation, macrofauna activity, water erosion, freeze-thaw cycling, and swellshrink (wet-dry) cycling (Wang et al., 2016b). Even though it is impossible to simulate all the biochar aging processes that occur in soil, artificial biochar aging could be adjusted to be as close to natural biochar aging as possible. According to our results, aging biochar by liquid phase chemical oxidation might lead to a high degree of oxidation at the biochar surface, which might not be attained by abiotic oxidation or microbial degradation. Controlling the oxidizing agent concentration can be a way to solve this problem and has already been done in several studies (Qian and Chen, 2014; Huff and Lee, 2016; Fan et al., 2018). Reducing the oxidation period and heating temperature could also reduce the degree of biochar oxidation. Solution turbulence during chemical oxidation may favor the infiltration of oxidizing agents into the interior of the biochar. To prevent the oxidation inside the biochar, a higher ratio of biochar to solution or solid phase oxidation could be considered. Moreover, in order to simulate natural biochar aging, chemical oxidation should not bring too many unique exogenous elements to the biochar. In this case, H2O2 could be a better oxidizing agent than KMnO4 and HNO3 (or an HNO3/H2SO4 mixture) are. In addition, H2O2 could oxidize biochar in both acidic and alkaline environments and could therefore be used to simulate biochar aging in different soil types. Freeze-thaw cycling is an effective way to change the porous structure of biochar, but that method did not induce elemental alterations in the biochar. Thus, freeze-thaw cycling should be used as a supplemental treatment with other artificial biochar aging methods. Other supplemental treatments have also been developed to improve artificial biochar aging. In the study by Bakshi et al. (2016), a laboratory-aged biochar was made by means of oxidation by H2O2/HCl, washing with CaCl2 solution, incubating with a dissolved organic compound solution for comparison with field-aged biochar. More studies on combined artificial biochar aging methods are necessary and should be encouraged in the future.
0.79 0.06 0.91 0.23 0.03⁎ 0.08 0.17 0.11 0.07 < 0.00001⁎ < 0.00001⁎ 0.15
⁎ When P < 0.05, it indicates that biochar aging method could significantly alter the biochar property.
of the biochar with large SSA values, but worked similarly to NA in increasing the SSA of the biochar with small SSA values. However, to analyze whether CA and NA worked similarly on the SSA of the biochar with large SSA values, more SSA data for biochar with large SSA values under NA are needed. Moreover, CA decreased biochar pH. Unlike the formation of acidic groups under NA, the much lower pH under CA was attributed to the use of an acidic solution in most of the selected studies. Chemical oxidation of biochar could also be conducted in an alkaline environment (i.e. NaOH solution) (Lawrinenko et al., 2016) or by other agents such as O3 and KMnO4 (Xiu et al., 2017). Lawrinenko et al. (2016) mentioned that oxidation of biochar by various oxidizing agents yielded changes unique to the oxidant. Using HNO3 as the oxidizing agent seemed to be the main reason that CA tended to increase biochar bulk N. Calculated from the data, bulk N SMD for HNO3 oxidation was 11.32, versus only 0.19 for H2O2 oxidation (data not shown). The increased biochar bulk N would lead to a higher C/N ratio and would thus influence biochar stability, the priming effect on soil organic matter, and soil nitrogen dynamics (K. Yin and Xu, 2009; Cayuela et al., 2013). Therefore, the selection of the oxidizing agent is relevant to biochar property alteration under CA.
5. Conclusion Studying biochar aging via artificial aging methods is important for evaluating the long-term performance of biochar in soil for agricultural 101
Geoderma 352 (2019) 96–103
H. Li, et al.
Fig. 4. Standard mean differences (SMDs) of biochar surface element contents (C, H, O, N), bulk element contents (C, H, O, N), specific surface area (SSA), cation exchange capacity (CEC) and pH under all biochar aging methods, chemical aging (CA, red), natural aging (NA, green), and freeze-thaw aging (FA, blue). The horizontal bars are the 95% confidence intervals of the SMDs. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
activities or soil contamination treatments. Our meta-analysis showed that current artificial aging methods such as chemical oxidation and freeze-thaw cycling are not yet able to simulate biochar aging in the soil. In comparison with aging in the soil, the chemical oxidation method tended to have a higher degree of oxidation at the surface of the aged biochar and posed the problems of bulk biochar oxidation and the import of exogenous elements from oxidants to the biochar. For its part, freeze-thaw cycling changed only the porous structure of the biochar with no alterations to biochar elemental compositions. Based on the meta-analysis, we have identified several perspectives for improving the artificial biochar aging, including the careful selection of oxidizing agents and the combination of artificial biochar aging methods. However, in order for a compound evaluation of artificial biochar aging to be performed, yet other factors that influence biochar aging (i.e. biochar feedstock, pyrolysis conditions) need to be taken into account, and other biochar property data (i.e. anion exchange capacity, bulk density, microporosity, biochar mass loss) need to be collected. More studies comparing artificially-aged biochar and field-aged biochar for specific sites are therefore required.
or by other similar methods Ameloot, N., Graber, E.R., Verheijen, F.G.A., De Neve, S., 2013. Interactions between biochar stability and soil organisms: review and research needs: biochar stability and soil organisms. Eur. J. Soil Sci. 64, 379–390. Bakshi, S., Aller, D.M., Laird, D.A., Chintala, R., 2016. Comparison of the physical and chemical properties of laboratory and field-aged biochars. Journal of Environment Quality 45, 1627. Cao, T., Chen, W., Yang, T., He, T., Liu, Z., Meng, J., 2017. Surface characterization of aged biochar incubated in different types of soil. Bioresources 12, 6366–6377. Cayuela, M.L., Sánchez-Monedero, M.A., Roig, A., Hanley, K., Enders, A., Lehmann, J., 2013. Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions? Sci. Rep. 3. Cayuela, M.L., van Zwieten, L., Singh, B.P., Jeffery, S., Roig, A., Sánchez-Monedero, M.A., 2014. Biochar's role in mitigating soil nitrous oxide emissions: a review and metaanalysis. Agric. Ecosyst. Environ. 191, 5–16. Chen, Y., Liang, Y., Zheng, Z., Shi, W., 2016. Effect of aging on Cd adsorption ability by rice-straw derived biochar. Environ. Chem. 35, 2337–2343. de la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Effects of aging under field conditions on biochar structure and composition: implications for biochar stability in soils. Sci. Total Environ. 613–614, 969–976. Deeks, J.J., Higgins, J.P., 2007. Statistical Algorithms in Review Manager 5. Dong, X., Li, G., Lin, Q., Zhao, X., 2017. Quantity and quality changes of biochar aged for 5 years in soil under field conditions. Catena 159, 136–143. Donne, S., 2011. Specific surface area and porosity measurements. Biochar: A Guide to 463 Analysitical Methods. CSIRO Publishing, VIC, Australia, pp. 297–299. Fan, Q., Sun, J., Chu, L., Cui, L., Quan, G., Yan, J., Hussain, Q., Iqbal, M., 2018. Effects of chemical oxidation on surface oxygen-containing functional groups and adsorption behavior of biochar. Chemosphere 207, 33–40. Frišták, V., Frieslhanl, W., Pipíška, M., Soja, G., 2014. The response of artificial aging to sorption properties of biochar for potentially toxic heavy metals. Nova Biotechnologica et Chimica 13, 137–147. Furukawa, T.A., Barbui, C., Cipriani, A., Brambilla, P., Watanabe, N., 2006. Imputing missing standard deviations in meta-analyses can provide accurate results. J. Clin. Epidemiol. 59, 7–10. Ghaffar, A., Ghosh, S., Li, F., Dong, X., Zhang, D., Wu, M., Li, H., Pan, B., 2015. Effect of biochar aging on surface characteristics and adsorption behavior of dialkyl
Acknowledgement This study was supported by Major Science and Technology Program for Water Pollution Control and Treatment of China (2018ZX07110-007).
102
Geoderma 352 (2019) 96–103
H. Li, et al. phthalates. Environ. Pollut. 206, 502–509. Gronwald, M., Don, A., Tiemeyer, B., Helfrich, M., 2015. Effects of fresh and aged chars from pyrolysis and hydrothermal carbonization on nutrient sorption in agricultural soils. SOIL, 1, 475–489. Güzel, F., Sayğılı, H., Sayğılı, G.A., Koyuncu, F., Yılmaz, C., 2017. Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye methylene blue from aqueous solution. J. Clean. Prod. 144, 260–265. Hale, S., Hanley, K., Lehmann, J., Zimmerman, A., Cornelissen, G., 2011. Effects of chemical, biological, and physical aging as well as soil addition on the sorption of pyrene to activated carbon and biochar. Environmental Science & Technology 45, 10445–10453. Heitkötter, J., Marschner, B., 2015. Interactive effects of biochar ageing in soils related to feedstock, pyrolysis temperature, and historic charcoal production. In: EGU General Assembly Conference, pp. 56–64. Huang, Z., Hu, L.C., Zhou, Q., Guo, Y., Tang, W., Dai, J., 2018. Effect of aging on surface chemistry of rice husk-derived biochar. Environ. Prog. Sustain. Energy 37 (1), 410–417. Huff, M.D., Lee, J.W., 2016. Biochar-surface oxygenation with hydrogen peroxide. J. Environ. Manag. 165, 17–21. Inyang, M., Dickenson, E., 2015. The potential role of biochar in the removal of organic and microbial contaminants from potable and reuse water: a review. Chemosphere 134, 232–240. Jagiello, J., Thommes, M., 2004. Comparison of DFT characterization methods based on N, Ar, CO, and H adsorption applied to carbons with various pore size distributions. Carbon 165, 1227–1232. Jeffery, S., Fga, V., Van, der V.M., Bastos, A.C., 2011. A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis. Agric. Ecosyst. Environ. 144, 175–187. Jin, J., Sun, K., Wang, Z., Han, L., Du, P., Wang, X., Xing, B., 2017. Effects of chemical oxidation on phenanthrene sorption by grass- and manure-derived biochars. Sci. Total Environ. 598, 789. Joseph, S.D., Camps-Arbestain, M., Lin, Y., Munroe, P., Chia, C.H., Hook, J., van Zwieten, L., Kimber, S., Cowie, A., Singh, B.P., Lehmann, J., Foidl, N., Smernik, R.J., Amonette, J.E., 2010. An investigation into the reactions of biochar in soil. Aust. J. Soil Res. 48, 501. K. Yin, C., Xu, Z., 2009. Biochar: nutrient properties and their enhancement, in: biochar for environmental management. Earthscan 67–84. Kim, P., Johnson, A.M., Essington, M.E., Radosevich, M., Kwon, W.-T., Lee, S.-H., Rials, T.G., Labbé, N., 2013. Effect of pH on surface characteristics of switchgrass-derived biochars produced by fast pyrolysis. Chemosphere 90, 2623–2630. Kong, L.L., Liu, W.T., Zhou, Q.X., 2014. Biochar: An Effective Amendment for Remediating Contaminated Soil. Springer International Publishing. Kumar, A., Joseph, S., Tsechansky, L., Privat, K., Schreiter, I.J., Schüth, C., Graber, E.R., 2018. Biochar aging in contaminated soil promotes Zn immobilization due to changes in biochar surface structural and chemical properties. Sci. Total Environ. 626. Kuzyakov, Y., Bogomolova, I., Glaser, B., 2014. Biochar stability in soil: decomposition during eight years and transformation as assessed by compound-specific 14C analysis. Soil Biol. Biochem. 70, 229–236. Laird, D., Fleming, P., Wang, B., Horton, R., Karlen, D., 2010. Biochar impact on nutrient leaching from a Midwestern agricultural soil. Geoderma 158, 436–442. Lawrinenko, M., Laird, D.A., Johnson, R.L., Jing, D., 2016. Accelerated aging of biochars: impact on anion exchange capacity. Carbon 103, 217–227. Lehmann, J., Rillig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., Crowley, D., 2011. Biochar effects on soil biota – a review. Soil Biol. Biochem. 43, 1812–1836. Lin, Q., Xu, X., Chen, Q., Fang, J., Shen, X., Zhang, L., 2018. Changes in structural characteristics and metal speciation for biochar exposure in typic udic ferrisols. Environ. Sci. Pollut. Res. 25, 153–162. Liu, Z., Demisie, W., Zhang, M., 2013. Simulated degradation of biochar and its potential environmental implications. Environ. Pollut. 179, 146–152. Liu, Z., Dugan, B., Masiello, C.A., Wahab, L.M., Gonnermann, H.M., Nittrouer, J.A., 2018. Effect of freeze-thaw cycling on grain size of biochar. PLoS One 13, e0191246. Luo, L., Lv, J., Chen, Z., Huang, R., Zhang, S., 2017. Insights into the attenuated sorption of organic compounds on black carbon aged in soil. Environ. Pollut. 231, 1469–1476. D., Matovic, 2011. Biochar as a viable carbon sequestration option: global and Canadian perspective. Energy, 36 (4), 2011–2016. Mia, S., Dijkstra, F.A., Singh, B., 2017a. Chapter one–long-term aging of biochar: a molecular understanding with agricultural and environmental implications. Adv. Agron. 141, 1–51. Mia, Shamim, Dijkstra, F.A., Singh, B., 2017b. Aging induced changes in biochar's functionality and adsorption behavior for phosphate and ammonium. Environmental Science & Technology 51, 8359–8367. Mukherjee, A., Zimmerman, A.R., Hamdan, R., Cooper, W.T., 2014. Physicochemical changes in pyrogenic organic matter (biochar) after 15 months field-aging. Solid Earth 5, 693–704 5,2(2014-07-23). Nguyen, T.T.N., Wallace, H.M., Xu, C.-Y., Zwieten, L.V., Weng, Z.H., Xu, Z., Che, R., Tahmasbian, I., Hu, H.-W., Bai, S.H., 2018. The effects of short term, long term and reapplication of biochar on soil bacteria. Sci. Total Environ. 636, 142–151. Oleszczuk, P., Kołtowski, M., 2018. Changes of total and freely dissolved polycyclic aromatic hydrocarbons and toxicity of biochars treated with various aging processes. Environ. Pollut. 237, 65–73. Prendergast-Miller, M.T., Duvall, M., Sohi, S.P., 2014. Biochar-root interactions are mediated by biochar nutrient content and impacts on soil nutrient availability: biochar-root interactions. Eur. J. Soil Sci. 65, 173–185. Qian, L., Chen, B., 2014. Interactions of aluminum with biochars and oxidized biochars: implications for the biochar aging process. Journal of Agricultural & Food Chemistry
62, 373–380. Quemada, M., Baranski, M., Nobel-de Lange, M.N.J., Vallejo, A., Cooper, J.M., 2013. Meta-analysis of strategies to control nitrate leaching in irrigated agricultural systems and their effects on crop yield. Agric. Ecosyst. Environ. 174, 1–10. Rechberger, M.V., Kloss, S., Wang, S.-L., Lehmann, J., Rennhofer, H., Ottner, F., Wriessnig, K., Daudin, G., Lichtenegger, H., Soja, G., Zehetner, F., 2019. Enhanced Cu and Cd sorption after soil aging of woodchip-derived biochar: what were the driving factors? Chemosphere 216, 463–471. Ren, X., Sun, H., Wang, F., Cao, F., 2016. The changes in biochar properties and sorption capacities after being cultured with wheat for 3 months. Chemosphere 144, 2257–2263. Ronsse, F., van Hecke, S., Dickinson, D., Prins, W., 2013. Production and characterization of slow pyrolysis biochar: influence of feedstock type and pyrolysis conditions. Global Change Biology Bioenergy 5, 104–115. Shi, K., Xie, Y., Qiu, Y., 2015. Natural oxidation of a temperature series of biochars: opposite effect on the sorption of aromatic cationic herbicides. Ecotoxicol. Environ. Saf. 114, 102–108. Soinne, H., Hovi, J., Tammeorg, P., Turtola, E., 2014. Effect of biochar on phosphorus sorption and clay soil aggregate stability. Geoderma 219–220, 162–167. Sorrenti, G., Masiello, C.A., Dugan, B., Toselli, M., 2016. Biochar physico-chemical properties as affected by environmental exposure. Sci. Total Environ. 563–564, 237–246. Spokas, K.A., 2013. Impact of biochar field aging on laboratory greenhouse gas production potentials. Global Change Biology Bioenergy 5, 165–176. Su, D.-L., Hu, Q.-H., Peng Wang, S.-J., Yin, Y.-Z., 2015. The simulated effects of freezing and thawing on properties and sorption characteristics for carbamazepine of biochar. In: Energy, Environmental & Sustainable Ecosystem Development. Presented at the 2015 International Conference on Energy, Environmental & Sustainable Ecosystem Development (EESED 2015), World Scientific, Yunnan, Kunming, China. Suliman, W., Harsh, J.B., Abu-Lail, N.I., Fortuna, A.M., Dallmeyer, I., Garcia-Perez, M., 2016a. Influence of feedstock source and pyrolysis temperature on biochar bulk and surface properties. Biomass Bioenergy 84, 37–48. Suliman, W., Harsh, J.B., Abu-Lail, N.I., Fortuna, A.M., Dallmeyer, I., Garcia-Perez, M., 2016b. Modification of biochar surface by air oxidation: role of pyrolysis temperature. Biomass Bioenergy 85, 1–11. Sun, Y., Gao, B., Yao, Y., Fang, J., Zhang, M., Zhou, Y., Chen, H., Yang, L., 2014. Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties. Chem. Eng. J. 240, 574–578. Thomas, S.C., Gale, N., 2015. Biochar and forest restoration: a review and meta-analysis of tree growth responses. New For. 46, 931–946. Trigo, C., Spokas, K.A., Cox, L., Koskinen, W.C., 2014. Influence of soil biochar aging on sorption of the herbicides MCPA, nicosulfuron, terbuthylazine, indaziflam, and fluoroethyldiaminotriazine. J. Agric. Food Chem. 62, 10855–10860. Trigo, C., Spokas, K.A., Hall, K.E., Cox, L., Koskinen, W.C., 2016. Metolachlor sorption and degradation in soil amended with fresh and aged biochars. J. Agric. Food Chem. 64, 3141–3149. Uchimiya, M., Chang, S., Klasson, K.T., 2011. Screening biochars for heavy metal retention in soil: role of oxygen functional groups. J. Hazard. Mater. 190, 432–441. Uras, Ümit, Carrier, M., Hardie, A.G., Knoetze, J.H., 2012. Physico-chemical characterization of biochars from vacuum pyrolysis of South African agricultural wastes for application as soil amendments. Journal of Analytical & Applied Pyrolysis 98, 207–213. Wang, T.-T., Cheng, J., Liu, X.-J., Jiang, W., Zhang, C.-L., Yu, X.-Y., 2012. Effect of biochar amendment on the bioavailability of pesticide chlorantraniliprole in soil to earthworm. Ecotoxicol. Environ. Saf. 83, 96–101. Wang, B., Lehmann, J., Hanley, K., Hestrin, R., Enders, A., 2015. Adsorption and desorption of ammonium by maple wood biochar as a function of oxidation and pH. Chemosphere 138, 120–126. Wang, B., Lehmann, J., Hanley, K., Hestrin, R., Enders, A., 2016a. Ammonium retention by oxidized biochars produced at different pyrolysis temperatures and residence times. RSC Adv. 6, 41907–41913. Wang, J., Xiong, Z., Kuzyakov, Y., 2016b. Biochar stability in soil: meta-analysis of decomposition and priming effects. GCB Bioenergy 8, 512–523. Wang, Y., Hou, J., Guo, J., Huang, B., Luo, Z., Chen, L., 2017. Effects of freeze-thaw cycles on ammonium-nitrogen adsorption of yak dung biochar. Journal of AgroEnvironment Science 36, 566–573 (Chinese). Wang, C., Chen, S., Zhang, F., Cui, J., Hongyan, L.I., 2018. Effects of aged maize strawderived biochars on ammonia oxidation in an alkaline farmland soil. Ecology & Environmental Sciences 27 (1), 31–39. Wei, M., Xiao, Y.C., Meng, J., Liang, T., 2016. Ageing of rice husk biochar along a freezethaw cycles. MATEC Web of Conferences 63, 04013 2016. Wen, F., Chen, J., Tian, L., Liang, N., Zhang, D., Wu, M., 2016. Chemical oxidation of biochars and the impact on bisphenol A sorption. Asian Journal of Ecotoxicology 11, 628–635 (Chinese). Xiao, D., Feng, W., Zhang, Z., 2014. The changing rule of loess's porosity under freezingthawing cycles. J. Glaciol. Geocryol. 907–912, 36 (Chinese). Xiu, S., Shahbazi, A., Li, R., 2017. Characterization, modification and application of biochar for energy storage and catalysis: a review. Trends in Renewable Energy 3, 86–101. Yakout, S.M., Daifullah, A.E.H.M., El-Reefy, S.A., 2015. Pore structure characterization of chemically modified biochar derived from rice straw. Environmental Engineering & Management Journal 14, 473–480. Yao, Y., Gao, B., Zhang, M., Inyang, M., Zimmerman, A.R., 2012. Effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. Chemosphere 89, 1467–1471.
103
Contents lists available at ScienceDirect
Geoderma journal homepage: www.elsevier.com/locate/geoderma
How close is artificial biochar aging to natural biochar aging in fields? A meta-analysis
T
Haixiao Lia,b, , Xueqiang Lua,b, , Yan Xuc,d, Haitao Liue ⁎
⁎
a
College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China Tianjin Key Laboratory of Environmental Technology for Complex Trans-Media Pollution, Nankai University, Tianjin 300350, China c Quebec Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd., Quebec City, QC G1V 2J3, Canada d Department of Soils and Agri-Food Engineering, Paul Comtois Bldg., Laval University, Quebec, QC G1K 7P4, Canada e Shaanxi Provincial Land Engineering Construction Group Baoji Branch, No.7 Guangtai Road, Xi'an 710075, Shaanxi, China b
ARTICLE INFO
ABSTRACT
Handling Editor: David Laird
Biochar is used as a soil amendment to improve soil quality and fertility. The performance of biochar changes as it ages in fields. Artificial biochar aging methods (i.e. chemical oxidation) are considered proxies for natural biochar aging and help to evaluate the long-term effects of biochar amendment in soil. However, few studies have focused on how close artificial biochar aging methods are to biochar aging in fields. A meta-analysis of 42studies was conducted to quantitatively compare the effects of soil incubation (natural field biochar aging), chemical oxidation (chemical biochar aging) and freeze-thaw cycling (freeze-thaw biochar aging) on biochar properties, including surface and bulk element compositions (C, H, O, N), specific surface area, cation exchange capacity and pH. The results showed that the artificial biochar aging methods cannot yet simulate biochar aging in the soil. In comparison with natural field aging, chemical aging tended to have a higher degree of oxidation at the surface of the aged biochar and posed the problems of oxidation inside the biochar and the import of exogenous elements from oxidants to the biochar. Freeze-thaw aging changed only the porous structure of the biochar with no significant alterations to element compositions, in contrast with natural aging.
Keywords: Soil incubation Chemical oxidation Freeze-thaw cycling Surface/bulk element composition Cation exchange capacity Specific surface area
1. Introduction Biochar is a carbon-rich solid material made from the pyrolysis of biological residues in an oxygen-limited environment. Used as a soil amendment, biochar contributes to improving soil fertility (Yao et al., 2012), water retention (Laird et al., 2010), aggregate stability (Soinne et al., 2014) and microorganism diversity (Lehmann et al., 2011). Biochar also helps to mitigate climate change via carbon sequestration (Matovic, 2011). The performance of biochar in soil depends mainly on the biochar's properties as a result of the feedstock and the pyrolysis process and on the biochar's interaction with soil constituents (Joseph et al., 2010; Ronsse et al., 2013; Sun et al., 2014; Suliman et al., 2016a). Moreover, biochar's performance changes as the biochar progressively ages in soil, through chemical reactions, water erosion, and microbial decomposition (Mia et al., 2017a; de la Rosa et al., 2018). For instance, the breakdown of aromatic moieties and the oxidation at the biochar surface could generate carboxylic functional groups, making the biochar more interactive with soil minerals, nutrients, and contaminants (Rechberger et al., 2019). Moreover, Gronwald et al. 2015) reported
⁎
that 7 months of field aging decreased the adsorption capacity of biochar by 60% to 80%. It is time-consuming to study the long-term effects of biochar on soil, since the natural biochar aging process is very slow. Uras et al. (2012) pointed out that the half-life of biochar in soil could be in excess of 1000-years. In this case, artificial aging methods such as chemical oxidation and freeze-thaw cycling have been developed as proxies for natural biochar aging (Frišták et al., 2014; Su et al., 2015; Jin et al., 2017). These methods help to accelerate biochar aging, cutting the time from months or years to days or hours. However, few studies have considered the extent to which artificial biochar aging is able to simulate biochar aging under soil conditions. Meta-analysis would be a useful tool to address that concern using published data to obtain a conclusion, as has been done for other aspects of biochar research (Jeffery et al., 2011; Cayuela et al., 2014; Thomas and Gale, 2015). Herein a bibliometric work and a meta-analysis have been conducted to compare the alterations of biochar properties (surface and bulk element contents, specific surface area [SSA], cation exchange capacity [CEC], and pH) under different aging
Corresponding authors at: College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China. E-mail addresses: [email protected] (H. Li), [email protected] (X. Lu).
https://doi.org/10.1016/j.geoderma.2019.06.006 Received 24 February 2019; Received in revised form 31 May 2019; Accepted 3 June 2019 Available online 12 June 2019 0016-7061/ © 2019 Elsevier B.V. All rights reserved.
Geoderma 352 (2019) 96–103
H. Li, et al.
processes, namely, soil incubation (natural biochar aging [NA]), chemical oxidation (chemical biochar aging [CA]), and freeze-thaw cycling (freeze-thaw biochar aging [FA]). The results would show whether biochar properties change in a similar pattern under artificial aging as under natural aging.
(ni 1) SDi2 (n i 1)
SDpooled =
(1)
where SDpooled is the pooled standard deviation for a certain biochar property value, ni is the number of biochar property measurements in the i-th comparison, and SDi is the presented standard deviation of a certain biochar property value in the i-th comparison.
2. Material and methods 2.1. Data collection
2.2. Data screening
The keywords “biochar,” “aging,” “ageing,” “oxidation,” “soil incubation,” “freeze-thaw,” “drying-wetting,” and “weathering” were combined with one another and entered into the Google Scholar, Baidu Scholar, and Web of Science search engines to identify relevant studies for the meta-analysis. Studies had to meet the following criteria to be included in the analysis: (a) a randomized design was used; (b) the term pair “fresh biochar” and “aged biochar” appeared, and “aged biochar” was produced via the same process as “fresh biochar” in all aspects apart from biochar aging; and (c) replicated samples were considered. However, it should be noted that, in general, the analyses of biochar surface element composition, bulk element composition, and SSA were quite accurate, such that most publications accepted the measurements without replication. Hence, to avoid the specific selection of studies, these relatively accurate data without replication should not be simply ignored and could also be included in the meta-analysis (Quemada et al., 2013). In addition to these criteria, studies containing results reported repeatedly by the same research group were counted as one study. Each study contained the measured data for at least one biochar property out of surface element contents, bulk element contents, SSA, CEC, and pH. In total, 42 studies were selected (Table 1). The distribution of the studies across time is presented in Fig. 1, which shows an increasing interest in biochar aging research, with more published articles in the period from 2016 to 2018. The number of comparisons of “fresh biochar” versus “aged biochar” for each biochar property is presented in Fig. 2. Of the 42 studies, 19 studies aged biochar through soil incubation in fields or in pots for periods varying from 1 month to 5 years, 15 studies aged biochar by chemical oxidation using H2O2, HNO3, and HNO3/H2SO4 solutions, and 9 studies conducted biochar aging via freeze-thaw cycling of different sequences. In those studies, the biochars aged by soil incubation were generally separated manually from soil with sieves and tweezers and then washed with deionized water and air-dried, although Heitkötter and Marschner (2015) and Lin et al. (2018) collected the biochar particles directly from the polyamide mesh bags buried in soil. The biochars aged by chemical oxidation were collected by draining them through sieves and then washing and airdrying the particles. The biochars aged through freeze-thaw cycling were air-dried before analysis. The biochar surface element compositions were measured using X-ray photoelectron spectroscopy (XPS) or scanning electron microscope electron diffraction analysis (SEM-EDX). The bulk element compositions were determined with an elemental analyzer. Biochar CEC was measured by the replacement methods described in Mukherjee et al. (2014) or by other similar methods. Biochar SSA was determined by either the Brunauer, Emmett, and Teller (BET) N2-sorption method or the CO2-sorption method (Donne, 2011; Jagiello and Thommes, 2004). When both the N2-sorption SSA and the CO2sorption SSA were used in one study, only the results of the N2-sorption SSA were included. The data for biochar properties together with their standard deviations or standard errors were collected from the tables in manuscripts or from the figures using DataThief software where possible. The collected standard errors were then converted to standard deviations for the corresponding study. When there were no standard deviations or standard errors for the presented data in a study, a pooled standard deviation calculated from the obtained standard deviations via Eq. (1) will be used instead (Furukawa et al., 2006).
Data screening was conducted to exclude extreme values. The boxplots of biochar property values for fresh biochars under NA, CA, and FA are presented in Fig. 3. The separated points were observed for surface C, O, and N contents and for bulk H, O, and N contents (Fig. 3-a, c, d, f, g, h). However, since the values are within the range reported in other biochar literature, the data were included for the meta-analysis. Extremely low bulk C contents (< 20%) were observed for the fresh biochars under NA and CA (Fig. 3-e), because the biochars were made from chicken manure (Jin et al., 2017) and sewage sludge (de la Rosa et al., 2018) rather than from plant residues. These low bulk C content values for fresh biochar were eliminated from the analysis. Biochar SSA and CEC vary a great deal according to the literature. Hence, even though separate points were observed for SSA and CEC (Fig. 3-i, j), all data were retained for the analysis. Extremely low biochar pH values (pH = 3 and 3.5) were found with the fresh biochars under NA (Fig. 3k). As there was no elucidation for the low pH data for oak- and pinederived biochars pyrolyzed at 250 °C (Mukherjee et al., 2014), the data were eliminated from the meta-analysis. 2.3. Data analysis The meta-analysis was conducted using Review Manager-5 software (RevMan-5, Cochrane Community, London, UK) under the random effect model because there was heterogeneity among the studies. The standardized mean difference (SMD) between fresh biochar properties and aged biochar properties was used to compare the effects of different biochar aging methods on biochar alteration. According to the statistical algorithms (Deeks and Higgins, 2007), the SMD calculation implemented in the software was Hedges' adjusted g with an adjustment for small sample bias:
SMDi =
m1i
m2i si
1
3 4Ni 9
(2)
with standard error calculated as follows:
SEi =
SMDi2 Ni + n1i n2i 2(Ni 3.94)
(3)
where SMDi is the standardized mean difference of the i-th comparison; SEi is the standard error of the i-th comparison; m1i and m2i are the means of the biochar property for aged and fresh biochar groups of the i-th comparison; si is the pooled standard deviation across two groups of the i-th comparison; and n1i, n2i and Ni are the numbers of biochar property measurements for aged biochar, fresh biochar, and all biochars, respectively, of the i-th comparison. Once the SMD's 95% confidence intervals (CIs) did not overlap zero, which indicated that the P-value of the overall effect test was smaller than 0.05, the effect of the biochar aging method on a biochar property was deemed significant. Similarly, SMDs for the different aging methods were considered significantly different from one another when their 95% CIs did not overlap with one another.
97
98
Fan et al. (2018) Huang et al. (2018) Kumar et al. (2018)
Lin et al. (2018)
Nguyen et al. (2018) Oleszczuk and Kołtowski (2018) Wang et al. (2018) (Chinese) Cao et al. (2017)
Dong et al. (2017) Güzel et al. (2017) Jin et al. (2017)
Lin et al. (2017) (Chinese) Luo et al. (2017) Mia et al. (2017a,b) Wang et al. (2017) (Chinese) Bakshi et al. (2016)
Chen et al. (2016) (Chinese)
Huff and Lee (2016) Lawrinenko et al. (2016)
Ren et al. (2016) Sorrenti et al. (2016) Trigo et al. (2016) Wang et al. (2016a)
Wei et al. (2016) Wen et al. (2016) (Chinese) Ghaffar et al. (2015) Heitkötter and Marschner (2015) Su et al. (2015) Wang et al. (2015) Frišták et al. (2014) Mukherjee et al. (2014)
Prendergast-Miller et al. (2014) Qian and Chen (2014)
Trigo et al. (2014) Kim et al. (2013) Liu et al. (2013) Spokas (2013) Lin et al. (2012) Hale et al. (2011) Joseph et al. (2010)
3 4 5
6
7 8
9 10
11 12 13
14 15 16 17 18
19
20 21
22 23 24 25
26 27 28 29
34 35
36 37 38 39 40 41 42
30 31 32 33
Rechberger et al. (2019) de la Rosa et al. (2018)
Reference
1 2
No.
Macadamia nut shells Switchgrass Oak, bamboo, straw Hardwood, wood pellet, macadamia nut shell Poultry manure and papermill sludge Corn stover Chicken litter, papermill waste, and greenwaste
Miscanthus giganteus and Salix sp. Rice straw
Pine chips Maple wood Beech wood chips and garden green waste residues Oak, pine, and grass
Rice husk Straw Peanut shells Pine chips and corn degistate
Pig manure Chipped hardwood of peach and grapevine Macadamia nut shells, wood chips Maple tree
Pinewood Alfalfa, cellulose, and maize stover
Mushroom substrate waste Weeds Rice straw, wheat straw, maize straw, swine manure, cow manure, and chicken manure Peanut shells Maize Eucalyptus wood Yak dung Hardwood, soybean, switchgrass, corn stover, and macadamia nut shell Rice straw
Maize straw Rice hull
Eucalyptus saligna Wheat straw, elephant grass
Poultry manure and drying sludge
Mixed wood chips Pine wood, paper sludge, wheat husks, sewage sludge, vineyard, mixed wood chips Wheat straw Rice husk Grain husk and cattle manure
Feedstock
Table 1 List of references for the data collected in the meta-analysis.
400 °C 500 and 700 °C
350 °C
400 °C 300 and 500 °C 550 °C 300, 450 and 600 °C 500–850 °C
400 °C for 4 h 500 °C for 1 h 450 °C for 1 h
400 °C for 2 h 500 °C for 30 min
550 °C for 30 min 650 °C
500 °C for 2 h
450 °C 350 and 550 °C for 2 h 450 °C
525 °C for 1 h –
– 450, 600 and 800 °C for 30s 600 °C for oak and bamboo; 300 °C for straw 500–550 °C 550 °C for 30 and 60 min 600 °C 450 and 550 °C
450 and 700 °C 350, 500, and 700 °C
500 and 700 °C for 2 h 500 °C for 30 min 500 °C for 2 h 250, 400, and 600 °C for 3 h
300, 500, and 700 °C 550 °C for 30 min 550 and 850 °C 300, 400, 500, 600, 700 °C for 30 min; 500 °C for 5, 60, 120, 400, and 800 min 400 °C for 30 min 200 and 500 °C 300 and 700 °C for 4 h 400 and 600 °C
Pyrolysis
Freeze-thaw sequences of 20 °C (20 h) and −20 °C (4 h) for 30 days Oxidation by 15 and 30% H2O2 for 0.25–350 h at 30 °C 20 freeze-thaw sequences of 25 °C (12 h) and −18 °C (12 h) Incubation in the soil of Gainesville, Florida without macrofauna and sunlight for 15 months 200 freeze-thaw sequences between 30 and −10 °C Oxidation by 20, 40, or 60% HNO3/H2SO4 solution (1/3) at 70 °C for 6h Incubation in Waukegan silt loam for 1 and 2 years Oxidation by HNO3 (pH = 3, 5, and 7) for 24 h Oxidation by 65% HNO3 at 80 °C for 48 h Incubation in a Waukegan silt loam soil (pH = 6.4) for 3 years Incubation in a highly weathered acidic ferrosol 42 freeze-thaw sequences of 20 °C (19 h) and −70 °C (5 h) Incubation in a Ferrosol for 1 and 2 years
25 freeze-thaw sequences of 30 °C (10 days) and −20 °C (10 days) Oxidation by 20% H2O2 for 1 to 7 days Oxidation by HNO3/H2SO4 solution (1/3) at 70 °C for 6 h Incubation in historical kiln soil and a control soil for 100 days
Oxidation by 20% HNO3/H2SO4 (1/3) at 70 °C for 6 h Incubation in soil at 25 °C with 75% of water holding capacity Oxidation by 5, 10 and 15% H2O2 (1:30, m/v) at 80 °C for 6 h 30 freeze-thaw sequences of 35 °C (16 h) and − 20 °C (8 h) 30% H2O2 with 1 M HCl at 40 °C; incubation in agricultural fields in Minnesota and South Dakota Freeze-thaw sequence of 20 °C (5 h) and −78 °C (19 h) with 40% water content for 2 months Oxidation by 1, 3, 10, 20 and 30% H2O2 Oxidation by 30% H2O2 weekly with 1 M NaOH for 10 min within 4 months Incubation in quartz sand for wheat root substrate for 90 days Incubation in a sandy loam inceptisol soil (pH = 8.08) for 4 years Incubation in silt loam soil for 1, 4 and 5 years Oxidation by 30% H2O2 (v/v) at 30 °C for two weeks
Freeze-thaw sequences of 25 °C (19 h) and − 18 °C (5 h) for 50 days Incubation in red soil, sandy soil, and coastal solonchak for 1 and 13 months Incubation in Fluvisol for 5 years Oxidation by 20, 40, and 65% HNO3 at 80 °C for 1 h Oxidation by 25% HNO3 at 90 °C for 4 h
40 and 60% HNO3/H2SO4 (1/3) solution; 30% H2O2 with 1 M NaOH Incubation in quartz sand for 100, 200, and 300 days Incubation in a red, non-calcareous, iron oxide-coated quartz sand soil for 60 days Incubation in a typic udic ferrisol with 60% water hold capacity for 3 months Incubation in red Ferralsol for 9 years Freeze-thaw sequences of 20 °C (7d) and −20 °C (7d) for 14 months
Incubation in an acidic sandy loam Planosol for 15 months Incubation in calcareous sandy clay loam soil for 6, 12 and 24 months
Aging method
H. Li, et al.
Geoderma 352 (2019) 96–103
Geoderma 352 (2019) 96–103
H. Li, et al.
6
of −1.76) and a significant bulk O increase (SMD of 1.95) (Table 2, Fig. 4-e, f, g). In addition, CA tended to increase biochar bulk N content, with an SMD of 1.01 and a P-value close to 0.05 (P = 0.06) (Table 2, Fig. 4-h). Similar to biochar surface element contents, FA did not show a significant effect on biochar bulk element contents (Table 2, Fig. 4-e, f, g, h).
4
3.3. Biochar SSA, CEC, and pH
12
Number of studies
10 8
The meta-analysis results showed that CA significantly decreased biochar SSA (SMD of −0.91), whereas FA relatively increased biochar SSA (SMD of 0.59 and P-value of 0.08) (Table 2, Fig. 4-i). In addition, NA had no effects on biochar SSA. In terms of biochar CEC, the NA, CA, and FA methods tended to slightly increase biochar CEC with SMDs of 2.27, 0.93, and 1.45, respectively (Fig. 4-j). However, there were no significant effects observed (Table 2). The CA method had the most significant effect on decreasing biochar pH (SMD of −7.47), followed by NA (SMD of −2.90) (Table 2, Fig. 4-k), whereas FA showed no significant effects on biochar pH but also tended to decrease pH.
2 0 2010
2012
2014
2016
2018
2020
Years Fig. 1. Distribution along time of studies on biochar aging collected for metaanalysis.
3. Results 3.1. Biochar surface element contents
4. Discussion
The NA method significantly decreased biochar surface C content (SMD of −2.29) and increased surface H, O, and N contents (SMDs of 0.76, 3.36, and 3.72, respectively) (Table 2, Fig. 4-a, b, c, d). The CA method significantly decreased biochar surface C content (SMD of −0.99) and increased surface O content (SMD of 3.72) (Table 2, Fig. 4-a, c), but no significant effects of CA on surface H and N contents were observed (Table 2, Fig. 4-b, d). In comparison with NA, CA decreased biochar surface C less but increased surface O content to a similar level. The FA method seemed to cause no differences in surface element contents between fresh and aged biochars (Table 2, Fig. 4-a, c). However, we still need other data to verify the effect on biochar surface H and N.
4.1. Biochar aging in soil The high content of aromatic structures in biochar makes it stable and recalcitrant in the soil. However, variable amounts of aliphatic C exist in biochar as either bridges between aromatic moieties or branches of the aromatic layer (Mia et al., 2017a,b). On a molecular scale, once the aliphatic C decomposes, disconnected and intact aromatic moieties could break down through soil constituent interactions and microbial decomposition (Shi et al., 2015). With oxidation of the aromatic backbone yielding carboxylic groups, biochar C would be depleted, and O content would tend to increase. This natural aging process would take place first at the biochar surface, leading to decreased surface C content and increased surface O content, as shown by the meta-analysis results (Fig. 4-a, c). The increased surface H and N contents of the aged biochar under NA would be due to adsorption of organic matters and mineral nutrients on biochar surface (Fig. 4-b, d), although the washing of the biochar during the separation from soil might mitigate this effect. In addition to the adsorption of labile organic matter, the porous structure of biochar would create a favorable habitat for soil microorganisms, which play an important role in biochar stability (Ameloot et al., 2013).
3.2. Biochar bulk element contents The biochars aged by NA had significantly lower bulk C content (SMD of −0.88) and higher bulk H content (SMD of 1.59) than the fresh biochars (Table 2, Fig. 4-e, f) but there was little effect on biochar bulk O and N contents (Table 2, Fig. 4-g, h). In comparison with NA, CA depleted significantly more biochar bulk C, with an SMD of −1.47, and had a significant bulk H decrease (SMD
Fig. 2. Numbers of “fresh biochar” vs “aged biochar” comparisons for each biochar properties in the meta-analysis. 99
Geoderma 352 (2019) 96–103
H. Li, et al.
Fig. 3. Box-plots for biochar surface element contents (C, H, O, N), bulk element contents (C, H, O, N), specific surface area (SSA), cation exchange capacity (CEC) and pH of fresh biochars under chemical aging (CA), natural aging (NA), and freeze-thaw aging (FA).
Microorganisms could assimilate the soil organic matter adsorbed on biochar surface, the labile C in the biochar, and even the resistant C in it. According to Kuzyakov et al. (2014), higher organic matter content and higher microorganism activities in soil would accelerate the biochar decomposition rate. In contrast to the way that it increased surface O, NA had few effects on biochar bulk O content. That finding likely indicates an aerobic environment inside biochar. The blockage of biochar pores by organic matter, clay particles and pore-filling water could be the main reason that there was less oxidation inside the biochar (Wang et al., 2012; Inyang and Dickenson, 2015). However, soil constituents, microorganisms, and biochar could also interact aerobically inside biochar, possibly altering biochar bulk C and H contents under NA, as observed in the meta-analysis (Fig. 4-e, f). The carboxylic and phenolic groups generated from biochar surface oxidation might increase biochar CEC (Fig. 4-j), as hydroxyls (−OH) in carboxylic and phenolic groups would form carboxylate and phenolate with cations in the soil while releasing H+ (Uchimiya et al., 2011). That phenomenon also explains why naturally aged biochar had a lower pH than fresh biochar did (Fig. 4-k). In terms of SSA, the blockage of biochar pores by organic matter was considered to decrease biochar SSA (Kong et al., 2014). On the other hand, erosion, dissolution and transport by water fluxes in the soil were also reported to contribute to biochar aging (de la Rosa et al., 2018). Once the volatile organic compounds and ash in the blocked pores are washed by fluxes, biochar porosity and SSA might be increased (Suliman et al., 2016b). These counteracting processes would contribute to biochar SSA alteration in the soil. Our results showed that biochar SSA changed insignificantly during aging in the soil (NA) (Table 2).
incubation period, which ranges from 1 month to 9 years, most chemical oxidation treatments took only several hours (Table 1). That method accelerated biochar aging a great deal but caused different alterations to biochar properties. Similar to NA, CA also decreased biochar surface C (Fig. 4-a). However, CA increased surface O only, whereas NA increased biochar surface O, H, and N. This difference probably indicates that aged biochar has a higher degree of surface oxidation in the oxidizing agent (i.e. H2O2 or HNO3) solution. The mild oxidation and microbial activities in the soil generate the carboxyl, phenolic, and carbonyl groups on the biochar surface (Mia et al., 2017a), whereas chemical oxidation might not only turn biochar surface functional groups into carboxylic groups but also oxidize phenolic hydroxyl possibly into other structures such as quinones (Mia et al., 2017b). Additionally, structures such as quinones make no contribution to biochar CEC, which probably explains why CA increased biochar CEC less than NA did (SMDs of 0.93 and 2.27, respectively). Severe liquid phase oxidation could destroy biochar pores and decrease biochar SSA (Yakout et al., 2015). Without pore blockage in solution, chemical oxidizing agents could oxidize the interior of biochar. One of the principal differences between NA and CA might be that CA could increase biochar bulk O (Fig. 4-g). This phenomenon might be questionable, since the fresh CA biochars had larger SSA than the fresh NA biochars did (Fig. 3-i), which might make it easier to oxidize the interior of the biochar. However, there were actually only four studies (Ghaffar et al., 2015; Wang et al., 2015, 2016a; Mia et al., 2017b) with both data for biochar bulk O and large biochar SSA values (> 100 m2 g−1). Regardless of these bulk O data with large SSA, the bulk O SMD for CA was even higher, at 2.92 in comparison with 1.95 as shown in Fig. 4-g. That finding might thus confirm that CA method oxidized more of the interior of the biochar than NA did. In terms of SSA, we observed that the SMD of biochar with large SSA values (> 100 m2 g−1) under CA was −2.91, whereas the SMD of biochar with small SSA values (< 100 m2 g−1) under CA was 0.34 (data not shown). That finding indicates that the CA probably decreased the SSA
4.2. Chemical oxidation versus soil incubation Chemical oxidation (CA) is the most commonly used method to simulate biochar oxidation during aging. In comparison to the soil 100
Geoderma 352 (2019) 96–103
H. Li, et al.
4.3. Freeze-thaw cycling versus soil incubation
Table 2 Overall effect results (P-value) of the meta-analysis for biochar aging effects on biochar property alterations. Biochar properties Surface NA CA FA Surface NA CA FA Surface NA CA FA Surface NA CA FA Bulk C NA CA Bulk H NA CA FA Bulk O NA CA FA Bulk N NA CA FA SSA NA CA FA CEC NA CA FA pH NA CA FA
C
H
O
N
Freeze-thaw cycling is another common method used to accelerate biochar aging. Although that method takes more time than chemical oxidation treatments do, it rarely requires more than two months, according to the selected studies (Table 1). Our results showed that FA had no effects on biochar element compositions and pH (Table 2), apparently because of the weak oxidation and microbial activities under extremely low temperatures and the lack of exogenous element inputs. The FA method affected biochar mainly by resulting in a larger SSA and higher CEC in the aged biochar (Fig. 4-i, j). Freezing-thawing could increase biochar SSA probably by creating more pore space: ice crystal of the water infiltrated biochar pores would grow and expand intrapore size during freezing and would end up breaking biochar particles (Liu et al., 2018). This process would create more small biochar particles, which have larger SSA values than large particles do, similar to the case for soil particles (Xiao et al., 2014). Meanwhile, the CEC increase could be related to the SSA increase. However, further study is needed to determine whether FA could also break the biochar skeletal structure, causing the compaction of aged biochar and the reduction of SSA and CEC.
P < 0.0001⁎ 0.03⁎ 0.72 0.03⁎ 0.91 0.85 0.001⁎ < 0.00001⁎ 0.62 0.0001⁎ 0.58 0.73 0.0006⁎ < 0.00001⁎ 0.002⁎ < 0.00001⁎ 0.48
4.4. Perspectives
0.78 < 0.00001⁎ 0.77
Biochar aging in fields is complex and includes various processes, such as abiotic oxidation, carbonate dissolution, chemisorption, soil constituent interaction, physical disintegration, microbial degradation, macrofauna activity, water erosion, freeze-thaw cycling, and swellshrink (wet-dry) cycling (Wang et al., 2016b). Even though it is impossible to simulate all the biochar aging processes that occur in soil, artificial biochar aging could be adjusted to be as close to natural biochar aging as possible. According to our results, aging biochar by liquid phase chemical oxidation might lead to a high degree of oxidation at the biochar surface, which might not be attained by abiotic oxidation or microbial degradation. Controlling the oxidizing agent concentration can be a way to solve this problem and has already been done in several studies (Qian and Chen, 2014; Huff and Lee, 2016; Fan et al., 2018). Reducing the oxidation period and heating temperature could also reduce the degree of biochar oxidation. Solution turbulence during chemical oxidation may favor the infiltration of oxidizing agents into the interior of the biochar. To prevent the oxidation inside the biochar, a higher ratio of biochar to solution or solid phase oxidation could be considered. Moreover, in order to simulate natural biochar aging, chemical oxidation should not bring too many unique exogenous elements to the biochar. In this case, H2O2 could be a better oxidizing agent than KMnO4 and HNO3 (or an HNO3/H2SO4 mixture) are. In addition, H2O2 could oxidize biochar in both acidic and alkaline environments and could therefore be used to simulate biochar aging in different soil types. Freeze-thaw cycling is an effective way to change the porous structure of biochar, but that method did not induce elemental alterations in the biochar. Thus, freeze-thaw cycling should be used as a supplemental treatment with other artificial biochar aging methods. Other supplemental treatments have also been developed to improve artificial biochar aging. In the study by Bakshi et al. (2016), a laboratory-aged biochar was made by means of oxidation by H2O2/HCl, washing with CaCl2 solution, incubating with a dissolved organic compound solution for comparison with field-aged biochar. More studies on combined artificial biochar aging methods are necessary and should be encouraged in the future.
0.79 0.06 0.91 0.23 0.03⁎ 0.08 0.17 0.11 0.07 < 0.00001⁎ < 0.00001⁎ 0.15
⁎ When P < 0.05, it indicates that biochar aging method could significantly alter the biochar property.
of the biochar with large SSA values, but worked similarly to NA in increasing the SSA of the biochar with small SSA values. However, to analyze whether CA and NA worked similarly on the SSA of the biochar with large SSA values, more SSA data for biochar with large SSA values under NA are needed. Moreover, CA decreased biochar pH. Unlike the formation of acidic groups under NA, the much lower pH under CA was attributed to the use of an acidic solution in most of the selected studies. Chemical oxidation of biochar could also be conducted in an alkaline environment (i.e. NaOH solution) (Lawrinenko et al., 2016) or by other agents such as O3 and KMnO4 (Xiu et al., 2017). Lawrinenko et al. (2016) mentioned that oxidation of biochar by various oxidizing agents yielded changes unique to the oxidant. Using HNO3 as the oxidizing agent seemed to be the main reason that CA tended to increase biochar bulk N. Calculated from the data, bulk N SMD for HNO3 oxidation was 11.32, versus only 0.19 for H2O2 oxidation (data not shown). The increased biochar bulk N would lead to a higher C/N ratio and would thus influence biochar stability, the priming effect on soil organic matter, and soil nitrogen dynamics (K. Yin and Xu, 2009; Cayuela et al., 2013). Therefore, the selection of the oxidizing agent is relevant to biochar property alteration under CA.
5. Conclusion Studying biochar aging via artificial aging methods is important for evaluating the long-term performance of biochar in soil for agricultural 101
Geoderma 352 (2019) 96–103
H. Li, et al.
Fig. 4. Standard mean differences (SMDs) of biochar surface element contents (C, H, O, N), bulk element contents (C, H, O, N), specific surface area (SSA), cation exchange capacity (CEC) and pH under all biochar aging methods, chemical aging (CA, red), natural aging (NA, green), and freeze-thaw aging (FA, blue). The horizontal bars are the 95% confidence intervals of the SMDs. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
activities or soil contamination treatments. Our meta-analysis showed that current artificial aging methods such as chemical oxidation and freeze-thaw cycling are not yet able to simulate biochar aging in the soil. In comparison with aging in the soil, the chemical oxidation method tended to have a higher degree of oxidation at the surface of the aged biochar and posed the problems of bulk biochar oxidation and the import of exogenous elements from oxidants to the biochar. For its part, freeze-thaw cycling changed only the porous structure of the biochar with no alterations to biochar elemental compositions. Based on the meta-analysis, we have identified several perspectives for improving the artificial biochar aging, including the careful selection of oxidizing agents and the combination of artificial biochar aging methods. However, in order for a compound evaluation of artificial biochar aging to be performed, yet other factors that influence biochar aging (i.e. biochar feedstock, pyrolysis conditions) need to be taken into account, and other biochar property data (i.e. anion exchange capacity, bulk density, microporosity, biochar mass loss) need to be collected. More studies comparing artificially-aged biochar and field-aged biochar for specific sites are therefore required.
or by other similar methods Ameloot, N., Graber, E.R., Verheijen, F.G.A., De Neve, S., 2013. Interactions between biochar stability and soil organisms: review and research needs: biochar stability and soil organisms. Eur. J. Soil Sci. 64, 379–390. Bakshi, S., Aller, D.M., Laird, D.A., Chintala, R., 2016. Comparison of the physical and chemical properties of laboratory and field-aged biochars. Journal of Environment Quality 45, 1627. Cao, T., Chen, W., Yang, T., He, T., Liu, Z., Meng, J., 2017. Surface characterization of aged biochar incubated in different types of soil. Bioresources 12, 6366–6377. Cayuela, M.L., Sánchez-Monedero, M.A., Roig, A., Hanley, K., Enders, A., Lehmann, J., 2013. Biochar and denitrification in soils: when, how much and why does biochar reduce N2O emissions? Sci. Rep. 3. Cayuela, M.L., van Zwieten, L., Singh, B.P., Jeffery, S., Roig, A., Sánchez-Monedero, M.A., 2014. Biochar's role in mitigating soil nitrous oxide emissions: a review and metaanalysis. Agric. Ecosyst. Environ. 191, 5–16. Chen, Y., Liang, Y., Zheng, Z., Shi, W., 2016. Effect of aging on Cd adsorption ability by rice-straw derived biochar. Environ. Chem. 35, 2337–2343. de la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Effects of aging under field conditions on biochar structure and composition: implications for biochar stability in soils. Sci. Total Environ. 613–614, 969–976. Deeks, J.J., Higgins, J.P., 2007. Statistical Algorithms in Review Manager 5. Dong, X., Li, G., Lin, Q., Zhao, X., 2017. Quantity and quality changes of biochar aged for 5 years in soil under field conditions. Catena 159, 136–143. Donne, S., 2011. Specific surface area and porosity measurements. Biochar: A Guide to 463 Analysitical Methods. CSIRO Publishing, VIC, Australia, pp. 297–299. Fan, Q., Sun, J., Chu, L., Cui, L., Quan, G., Yan, J., Hussain, Q., Iqbal, M., 2018. Effects of chemical oxidation on surface oxygen-containing functional groups and adsorption behavior of biochar. Chemosphere 207, 33–40. Frišták, V., Frieslhanl, W., Pipíška, M., Soja, G., 2014. The response of artificial aging to sorption properties of biochar for potentially toxic heavy metals. Nova Biotechnologica et Chimica 13, 137–147. Furukawa, T.A., Barbui, C., Cipriani, A., Brambilla, P., Watanabe, N., 2006. Imputing missing standard deviations in meta-analyses can provide accurate results. J. Clin. Epidemiol. 59, 7–10. Ghaffar, A., Ghosh, S., Li, F., Dong, X., Zhang, D., Wu, M., Li, H., Pan, B., 2015. Effect of biochar aging on surface characteristics and adsorption behavior of dialkyl
Acknowledgement This study was supported by Major Science and Technology Program for Water Pollution Control and Treatment of China (2018ZX07110-007).
102
Geoderma 352 (2019) 96–103
H. Li, et al. phthalates. Environ. Pollut. 206, 502–509. Gronwald, M., Don, A., Tiemeyer, B., Helfrich, M., 2015. Effects of fresh and aged chars from pyrolysis and hydrothermal carbonization on nutrient sorption in agricultural soils. SOIL, 1, 475–489. Güzel, F., Sayğılı, H., Sayğılı, G.A., Koyuncu, F., Yılmaz, C., 2017. Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye methylene blue from aqueous solution. J. Clean. Prod. 144, 260–265. Hale, S., Hanley, K., Lehmann, J., Zimmerman, A., Cornelissen, G., 2011. Effects of chemical, biological, and physical aging as well as soil addition on the sorption of pyrene to activated carbon and biochar. Environmental Science & Technology 45, 10445–10453. Heitkötter, J., Marschner, B., 2015. Interactive effects of biochar ageing in soils related to feedstock, pyrolysis temperature, and historic charcoal production. In: EGU General Assembly Conference, pp. 56–64. Huang, Z., Hu, L.C., Zhou, Q., Guo, Y., Tang, W., Dai, J., 2018. Effect of aging on surface chemistry of rice husk-derived biochar. Environ. Prog. Sustain. Energy 37 (1), 410–417. Huff, M.D., Lee, J.W., 2016. Biochar-surface oxygenation with hydrogen peroxide. J. Environ. Manag. 165, 17–21. Inyang, M., Dickenson, E., 2015. The potential role of biochar in the removal of organic and microbial contaminants from potable and reuse water: a review. Chemosphere 134, 232–240. Jagiello, J., Thommes, M., 2004. Comparison of DFT characterization methods based on N, Ar, CO, and H adsorption applied to carbons with various pore size distributions. Carbon 165, 1227–1232. Jeffery, S., Fga, V., Van, der V.M., Bastos, A.C., 2011. A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis. Agric. Ecosyst. Environ. 144, 175–187. Jin, J., Sun, K., Wang, Z., Han, L., Du, P., Wang, X., Xing, B., 2017. Effects of chemical oxidation on phenanthrene sorption by grass- and manure-derived biochars. Sci. Total Environ. 598, 789. Joseph, S.D., Camps-Arbestain, M., Lin, Y., Munroe, P., Chia, C.H., Hook, J., van Zwieten, L., Kimber, S., Cowie, A., Singh, B.P., Lehmann, J., Foidl, N., Smernik, R.J., Amonette, J.E., 2010. An investigation into the reactions of biochar in soil. Aust. J. Soil Res. 48, 501. K. Yin, C., Xu, Z., 2009. Biochar: nutrient properties and their enhancement, in: biochar for environmental management. Earthscan 67–84. Kim, P., Johnson, A.M., Essington, M.E., Radosevich, M., Kwon, W.-T., Lee, S.-H., Rials, T.G., Labbé, N., 2013. Effect of pH on surface characteristics of switchgrass-derived biochars produced by fast pyrolysis. Chemosphere 90, 2623–2630. Kong, L.L., Liu, W.T., Zhou, Q.X., 2014. Biochar: An Effective Amendment for Remediating Contaminated Soil. Springer International Publishing. Kumar, A., Joseph, S., Tsechansky, L., Privat, K., Schreiter, I.J., Schüth, C., Graber, E.R., 2018. Biochar aging in contaminated soil promotes Zn immobilization due to changes in biochar surface structural and chemical properties. Sci. Total Environ. 626. Kuzyakov, Y., Bogomolova, I., Glaser, B., 2014. Biochar stability in soil: decomposition during eight years and transformation as assessed by compound-specific 14C analysis. Soil Biol. Biochem. 70, 229–236. Laird, D., Fleming, P., Wang, B., Horton, R., Karlen, D., 2010. Biochar impact on nutrient leaching from a Midwestern agricultural soil. Geoderma 158, 436–442. Lawrinenko, M., Laird, D.A., Johnson, R.L., Jing, D., 2016. Accelerated aging of biochars: impact on anion exchange capacity. Carbon 103, 217–227. Lehmann, J., Rillig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., Crowley, D., 2011. Biochar effects on soil biota – a review. Soil Biol. Biochem. 43, 1812–1836. Lin, Q., Xu, X., Chen, Q., Fang, J., Shen, X., Zhang, L., 2018. Changes in structural characteristics and metal speciation for biochar exposure in typic udic ferrisols. Environ. Sci. Pollut. Res. 25, 153–162. Liu, Z., Demisie, W., Zhang, M., 2013. Simulated degradation of biochar and its potential environmental implications. Environ. Pollut. 179, 146–152. Liu, Z., Dugan, B., Masiello, C.A., Wahab, L.M., Gonnermann, H.M., Nittrouer, J.A., 2018. Effect of freeze-thaw cycling on grain size of biochar. PLoS One 13, e0191246. Luo, L., Lv, J., Chen, Z., Huang, R., Zhang, S., 2017. Insights into the attenuated sorption of organic compounds on black carbon aged in soil. Environ. Pollut. 231, 1469–1476. D., Matovic, 2011. Biochar as a viable carbon sequestration option: global and Canadian perspective. Energy, 36 (4), 2011–2016. Mia, S., Dijkstra, F.A., Singh, B., 2017a. Chapter one–long-term aging of biochar: a molecular understanding with agricultural and environmental implications. Adv. Agron. 141, 1–51. Mia, Shamim, Dijkstra, F.A., Singh, B., 2017b. Aging induced changes in biochar's functionality and adsorption behavior for phosphate and ammonium. Environmental Science & Technology 51, 8359–8367. Mukherjee, A., Zimmerman, A.R., Hamdan, R., Cooper, W.T., 2014. Physicochemical changes in pyrogenic organic matter (biochar) after 15 months field-aging. Solid Earth 5, 693–704 5,2(2014-07-23). Nguyen, T.T.N., Wallace, H.M., Xu, C.-Y., Zwieten, L.V., Weng, Z.H., Xu, Z., Che, R., Tahmasbian, I., Hu, H.-W., Bai, S.H., 2018. The effects of short term, long term and reapplication of biochar on soil bacteria. Sci. Total Environ. 636, 142–151. Oleszczuk, P., Kołtowski, M., 2018. Changes of total and freely dissolved polycyclic aromatic hydrocarbons and toxicity of biochars treated with various aging processes. Environ. Pollut. 237, 65–73. Prendergast-Miller, M.T., Duvall, M., Sohi, S.P., 2014. Biochar-root interactions are mediated by biochar nutrient content and impacts on soil nutrient availability: biochar-root interactions. Eur. J. Soil Sci. 65, 173–185. Qian, L., Chen, B., 2014. Interactions of aluminum with biochars and oxidized biochars: implications for the biochar aging process. Journal of Agricultural & Food Chemistry
62, 373–380. Quemada, M., Baranski, M., Nobel-de Lange, M.N.J., Vallejo, A., Cooper, J.M., 2013. Meta-analysis of strategies to control nitrate leaching in irrigated agricultural systems and their effects on crop yield. Agric. Ecosyst. Environ. 174, 1–10. Rechberger, M.V., Kloss, S., Wang, S.-L., Lehmann, J., Rennhofer, H., Ottner, F., Wriessnig, K., Daudin, G., Lichtenegger, H., Soja, G., Zehetner, F., 2019. Enhanced Cu and Cd sorption after soil aging of woodchip-derived biochar: what were the driving factors? Chemosphere 216, 463–471. Ren, X., Sun, H., Wang, F., Cao, F., 2016. The changes in biochar properties and sorption capacities after being cultured with wheat for 3 months. Chemosphere 144, 2257–2263. Ronsse, F., van Hecke, S., Dickinson, D., Prins, W., 2013. Production and characterization of slow pyrolysis biochar: influence of feedstock type and pyrolysis conditions. Global Change Biology Bioenergy 5, 104–115. Shi, K., Xie, Y., Qiu, Y., 2015. Natural oxidation of a temperature series of biochars: opposite effect on the sorption of aromatic cationic herbicides. Ecotoxicol. Environ. Saf. 114, 102–108. Soinne, H., Hovi, J., Tammeorg, P., Turtola, E., 2014. Effect of biochar on phosphorus sorption and clay soil aggregate stability. Geoderma 219–220, 162–167. Sorrenti, G., Masiello, C.A., Dugan, B., Toselli, M., 2016. Biochar physico-chemical properties as affected by environmental exposure. Sci. Total Environ. 563–564, 237–246. Spokas, K.A., 2013. Impact of biochar field aging on laboratory greenhouse gas production potentials. Global Change Biology Bioenergy 5, 165–176. Su, D.-L., Hu, Q.-H., Peng Wang, S.-J., Yin, Y.-Z., 2015. The simulated effects of freezing and thawing on properties and sorption characteristics for carbamazepine of biochar. In: Energy, Environmental & Sustainable Ecosystem Development. Presented at the 2015 International Conference on Energy, Environmental & Sustainable Ecosystem Development (EESED 2015), World Scientific, Yunnan, Kunming, China. Suliman, W., Harsh, J.B., Abu-Lail, N.I., Fortuna, A.M., Dallmeyer, I., Garcia-Perez, M., 2016a. Influence of feedstock source and pyrolysis temperature on biochar bulk and surface properties. Biomass Bioenergy 84, 37–48. Suliman, W., Harsh, J.B., Abu-Lail, N.I., Fortuna, A.M., Dallmeyer, I., Garcia-Perez, M., 2016b. Modification of biochar surface by air oxidation: role of pyrolysis temperature. Biomass Bioenergy 85, 1–11. Sun, Y., Gao, B., Yao, Y., Fang, J., Zhang, M., Zhou, Y., Chen, H., Yang, L., 2014. Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties. Chem. Eng. J. 240, 574–578. Thomas, S.C., Gale, N., 2015. Biochar and forest restoration: a review and meta-analysis of tree growth responses. New For. 46, 931–946. Trigo, C., Spokas, K.A., Cox, L., Koskinen, W.C., 2014. Influence of soil biochar aging on sorption of the herbicides MCPA, nicosulfuron, terbuthylazine, indaziflam, and fluoroethyldiaminotriazine. J. Agric. Food Chem. 62, 10855–10860. Trigo, C., Spokas, K.A., Hall, K.E., Cox, L., Koskinen, W.C., 2016. Metolachlor sorption and degradation in soil amended with fresh and aged biochars. J. Agric. Food Chem. 64, 3141–3149. Uchimiya, M., Chang, S., Klasson, K.T., 2011. Screening biochars for heavy metal retention in soil: role of oxygen functional groups. J. Hazard. Mater. 190, 432–441. Uras, Ümit, Carrier, M., Hardie, A.G., Knoetze, J.H., 2012. Physico-chemical characterization of biochars from vacuum pyrolysis of South African agricultural wastes for application as soil amendments. Journal of Analytical & Applied Pyrolysis 98, 207–213. Wang, T.-T., Cheng, J., Liu, X.-J., Jiang, W., Zhang, C.-L., Yu, X.-Y., 2012. Effect of biochar amendment on the bioavailability of pesticide chlorantraniliprole in soil to earthworm. Ecotoxicol. Environ. Saf. 83, 96–101. Wang, B., Lehmann, J., Hanley, K., Hestrin, R., Enders, A., 2015. Adsorption and desorption of ammonium by maple wood biochar as a function of oxidation and pH. Chemosphere 138, 120–126. Wang, B., Lehmann, J., Hanley, K., Hestrin, R., Enders, A., 2016a. Ammonium retention by oxidized biochars produced at different pyrolysis temperatures and residence times. RSC Adv. 6, 41907–41913. Wang, J., Xiong, Z., Kuzyakov, Y., 2016b. Biochar stability in soil: meta-analysis of decomposition and priming effects. GCB Bioenergy 8, 512–523. Wang, Y., Hou, J., Guo, J., Huang, B., Luo, Z., Chen, L., 2017. Effects of freeze-thaw cycles on ammonium-nitrogen adsorption of yak dung biochar. Journal of AgroEnvironment Science 36, 566–573 (Chinese). Wang, C., Chen, S., Zhang, F., Cui, J., Hongyan, L.I., 2018. Effects of aged maize strawderived biochars on ammonia oxidation in an alkaline farmland soil. Ecology & Environmental Sciences 27 (1), 31–39. Wei, M., Xiao, Y.C., Meng, J., Liang, T., 2016. Ageing of rice husk biochar along a freezethaw cycles. MATEC Web of Conferences 63, 04013 2016. Wen, F., Chen, J., Tian, L., Liang, N., Zhang, D., Wu, M., 2016. Chemical oxidation of biochars and the impact on bisphenol A sorption. Asian Journal of Ecotoxicology 11, 628–635 (Chinese). Xiao, D., Feng, W., Zhang, Z., 2014. The changing rule of loess's porosity under freezingthawing cycles. J. Glaciol. Geocryol. 907–912, 36 (Chinese). Xiu, S., Shahbazi, A., Li, R., 2017. Characterization, modification and application of biochar for energy storage and catalysis: a review. Trends in Renewable Energy 3, 86–101. Yakout, S.M., Daifullah, A.E.H.M., El-Reefy, S.A., 2015. Pore structure characterization of chemically modified biochar derived from rice straw. Environmental Engineering & Management Journal 14, 473–480. Yao, Y., Gao, B., Zhang, M., Inyang, M., Zimmerman, A.R., 2012. Effect of biochar amendment on sorption and leaching of nitrate, ammonium, and phosphate in a sandy soil. Chemosphere 89, 1467–1471.
103