Release characteristics and control of nitrogen, phosphate, organic matter from spent mushroom compost amended soil in a column experiment

Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 417–423

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Release characteristics and control of nitrogen, phosphate, organic matter from spent mushroom compost amended soil in a column experiment Zimo Lou, Jin Zhu, Zhuoxing Wang, Shams Ali Baig, Li Fang, Baolan Hu, Xinhua Xu ∗ Department of Environmental Engineering, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, Zhejiang, People’s Republic of China

a r t i c l e

i n f o

a b s t r a c t

Article history:

Spent mushroom compost (SMC) is a co-product of edible mushroom which contains abun-

Received 18 July 2015

dant nutrients including organics, nitrogen (N) and phosphorous (P). This study is related

Received in revised form 25

to the release potential of nitrogen, phosphate and organic matter from SMC amended soil

September 2015

in column-based experiments. Results showed that due to SMC application, NH4 + –N and

Accepted 6 October 2015

NO3 − –N concentrations in leachate decreased by 92.5% and 76.3%, respectively, while EC and

Available online 22 October 2015

CODCr concentrations increased by 84.2% and 481.9%, respectively, as compared to chemical

Keywords:

good nutrient retention capacity. Leaching test results demonstrated that the mixed appli-

fertilizers. Moreover, a minor loss of TNcum (65%) and TPcum (almost equal value) exhibited Spent mushroom compost

cation of SMC and chemical fertilizers could alleviate excessive CODCr level in SMC leachate.

Column test

The release process of nutrients in SMC amended soil could be described by first/first order

Nitrogen

mixed model, indicating that nutrients leached from SMC follow a two-stage pattern.

Phosphate

© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Organic matter

1.

Introduction

Agricultural solid wastes, including forest residues and unutilized cellulose based industrial residues, may cause environmental problems, such as occupying vast area, dispersing stink odors, and ground water pollution (Garg and Gupta, 2009). Spent mushroom substrate (SMS), an organic waste, has traditionally been incinerated or deposited in landfills, which would further produce large amounts of greenhouse gases and occupy valuable agricultural land (Zhang and Sun, 2014). In China, more than 22.6 million tons of edible mushrooms are reported to be produced every year. Thus, a considerable amount of SMS requires proper disposal technique for minimizing its environmental effects as soon as possible. A number of reports have demonstrated the beneficial application of SMS

∗

in environmental friendly methods (Zhu et al., 2012) and most concentrated on composting treatment. Composting is a process of biological decomposition and stabilization of wastes, which could transform organic matter into stable products (Zhang and Sun, 2014). Mushroom production has become the biggest solid-state-fermentation in the world (Soccol and Vandenberghe, 2003) and SMS derived compost, which is defined as spent mushroom compost (SMC) has turned out to be an appropriate organic fertilizer (Ribas et al., 2009). SMC contains abundant nutrients including organic substances, sulphur, potassium, calcium, magnesium, nitrogen and phosphorous (Jordan et al., 2008; Zhang and Sun, 2014). Moreover, it is generally regarded as a neutral soil amendment in agriculture production and ecosystem restoration (Chong et al., 1991; Guo, 2005). SMC will neither add a great

Corresponding author. Tel.: +86 571 88982031; fax: +86 571 88982031. E-mail address: [email protected] (X. Xu). http://dx.doi.org/10.1016/j.psep.2015.10.003 0957-5820/© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

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Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 417–423

Table 1 – Physico-chemical characteristics of SMS/SMC. Parameters

SMS

SMC

C (%) H (%) N (%) P (%) C/N Ash (%) Protein (mg/g) Polysaccharide (mg/g) Moisture (%) pH EC value (ds/m) TDS (mg/L) Lignin (%) Cellulose (%) Hemiscellulose (%)

32.1 4.4 1.7 – 18.4 14.3 22.4 9.7 42.3 6.2 45.3 22.5 11.6 29.1 7.3

15.3 2.1 1.1 0.2 13.6 12.7 11.2 2.0 41.6 7.2 36.5 18.2 12.1 29.8 7.0

amount of the macronutrients such as nitrogen, phosphorous, and potassium (N, P, K) to the soil nor tie up nutrients (Curtis and Suess, 2006). Excessive chemical fertilizers application would cause over fertilization, which will not lead to any extra yield of grain (Zarabi and Jalali, 2012). Consequently, many researchers worldwide have reported serious NO3 − –N pollution in surface and groundwater due to chemical fertilizers (Angelopoulos et al., 2009; Chen et al., 2007; Shomar et al., 2008). Therefore, as a slow-release source of nitrogen (Stewart et al., 1998), SMC is becoming a potential alternate for soil amendment. Recent studies have investigated the release of nutrient from SMC amended soil under laboratorial and field conditions (Stewart et al., 1997, 1998). Besides, the slow nitrogen mineralization rate from SMC and the necessary addition of inorganic-N fertilizer for rapid plant growth were also clarified in reported studies. However, no report has systematically compared the nutrients loss between chemical fertilizers and SMC. This study was undertaken under four broad categories including: (1) Physico-chemical characteristics of SMC were studied with the objective of determining the applied rate that could contribute to soil enrichment. (2) Heavy metal content was measured to evaluate the safety of SMC application. (3) The soil columns study was performed to compare the leachate components between chemical fertilizers, SMC and mixed fertilizer. (4) Several releasing models were applied to describe the leaching characteristics of SMC amended soil.

2.

Materials and methods

2.1.

Spent mushroom compost

2.1.1.

Physical and chemical characteristics

SMC samples were obtained from an edible mushroom Industrial Ltd., located in Qingyuan (Zhejiang, China), consisted mainly of Pleurotus ostreatus degraded straws. Meanwhile, raw composting material (SMS) samples were also collected for a comparative study. Both the fresh samples were airdried under an environment without sunlight or ventilation, and crushed into granules (<2 mm) for component analysis. Selected physicochemical properties were measured before leaching experiment (Table 1). pH, EC and TDS were determined for slurry in a ratio of 1:5 (w/v) consisting of dry material: distilled water. Lignin, cellulose and hemicellulose were measured according to the Van-Soest method in Agricultural Hand Book (No. 379). Protein was measured using

Coomassie light blue (Sedmak and Grossberg, 1977); Polysaccharide with phenol-sulfuric acid (Masuko et al., 2005). C, H and N contents were analyzed by a Flash EA 1112 Thermo Finnigan elemental analyzer. Total P was measured colorimetrically by UV spectrophotometry.

2.1.2.

Heavy metal content

In order to conduct risk assessments of SMC application, heavy metal concentrations in SMC samples were analyzed by inductively coupled plasma emission spectrometry (ICP6000, Thermo Fisher Scientific). Table 2 illustrates the test outcome. Although it was not known if these contents were within acceptable range as no heavy metal limits have been standardized for SMC in China, there are limits to implement for organic fertilizer. According to the NY525-2012 organic fertilizer standard carried out in China, Cr, Cd, Pb and As contents of SMC were well within the recommended range and should not be concerned in application. Compared to the proposed legal heavy metal levels in Germany and Netherlands, Cu, Ni and Zn obtained by SMC were also significantly lower than the permissible limits.

2.2.

Leaching experiment

The experiment was conducted using subtropical cropland soils collected in Hangzhou city, Zhejiang Province, China (30◦ 18 20 N, 120◦ 4 21 E) (Zhao et al., 2014; Zhao and Xing, 2009). A series of PVC columns with 10 cm diameter and 20 cm length were employed for leaching-incubation experiments. As described by Zhao et al. (2014) and Xu et al. (2012), each column was fixed with a porous baffle and pretreated quartz was loaded above the baffle. Quartz sand used in this experiment was pretreated with 1 M HCl and distilled water until the solution was neutral. For comparison, SMC was in contrast with SMS, chemical fertilizers and compound fertilizer, respectively. Table 3 describes the treatment details. For control treatments, each column contained 600 g 2 mm-sieved soil. As typical N, P fertilizers, urea and calcium superphosphate were used to provide nitrogen and phosphate in chemical fertilizers treatment (CF). The application rates of SMS and SMC in treatments were equivalent to the application of 300 mg N/kg, which was comparable with 550–600 kg N/ha per year in an actual field (Ju et al., 2009). After packing the column with the mixture of soil and amendments, the surface of the mixture was covered with 1 cm of quartz stone in order to make a uniform distribution of leachates. The well-packed columns were incubated at 25 ◦ C inside an incubator throughout the whole experiment (Qian and Cai, 2007) and DI water was added to adjust the soil moisture content to 65% WHC (Water holding capacity) (Novak et al., 2009). On incubation day 1, 8, 15, 22, 29, 36, 43, and 50, respectively, 320 mL of DI water was added to the top of each column and leaching occurred through gravitational force. The total amounts of water were determined depending on the average annual rainfall recorded on Li Shui Water Resources Bulletin. The constant flow rate of DI water was controlled by a peristaltic pump. After a 60-min equilibrium time, the leachates were completely collected while all the columns were returned to the incubator to start the next cycle. We call this process a leaching event. DI water was added as a supplement of water evaporation between adjacent leaching events.

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Table 2 – Heavy metal contents of SMC (a according to Li and Liu, 2006). Heavy metal contents

SMC

Cr (mg/kg) Cd (mg/kg) Cu (mg/kg) Ni (mg/kg) Pb (mg/kg) Zn (mg/kg) As (mg/kg)

15.2 2.8 25.3 7.9 49.4 97.0 3.0

Limits in Germanya

Limits in China (NY525-2012) ≤150 ≤3 – – ≤50 – ≤15

Limits in Netherlandsa

≤100 ≤1.5 ≤100 ≤50 ≤150 ≤400 –

≤200 ≤2 ≤300 ≤50 ≤140 ≤400 ≤25

Table 3 – Details of treatments in column experiment. Treatments

Dosage

Abbreviation

No addition Chemical fertilizers addition Spent mushroom substrate addition Spent mushroom compost addition Compound fertilizer addition

– 0.16 g calcium superphosphate; 0.386 g urea 10.26 g SMS 15.75 g SMC 0.08 g calcium superphosphate; 7.88 g SMC; 0.193 g urea

CK CF SMS SMC SMC/CF

Table 4 – Selected kinetics models that have been used to describe release of nutrient before. (1) (2)

Y = M (1 − e−k1 t ) Y = M (1− e−k1 t ) +k0 t

(3)

Y = M1

−ke t 1

+ M2

CK

CF

SMS

SMC

SMC/CF

8.2



−kr t 1



8.0

1−e

7.8

pH value

1−e

8.4

7.6 7.4 7.2

2.3.

Chemical analysis

7.0

Several parameters including pH, TDS, EC, TN, NH4 + –N, NO3 − –N, TP, PO4 3− –P, CODCr were analyzed to describe the characteristics of leachates. pH, TDS and EC was measured using a Mettler Toledo pH meter and a conductivity meter (DDBJ-350, LeiCi, China). Total nitrogen, NH4 + –N, NO3 − –N, Total phosphate and PO4 3− –P were determined by a UV spectrophotometer (TU-1810, Persee). CODCr was determined by a COD analyzer (5B-3A, Lianhua, China).

2.4.

6.8 6.6 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43

Days Fig. 1 – Temporal pattern of pH values in leachate.

3.

Results and discussion

3.1.

pH and EC of leachate

Cumulative releasing models

To describe the nutrients release from SMC amended soils, three nonlinear regression mathematical models were applied, as shown in Table 4: where Y is the amount of cumulative nutrients leached (mg/kg) over a period of time t; t (days) is the time since the start of leaching-incubation experiment; M is the maximum amount of leachable nutrient; M1 is the easily leachable fraction of nutrient; M2 is the resistant leachable fraction of nutrient; k0 , k1 are zero, first order exponential model rate parameters, respectively; k1 e , k1 r are rate parameters for M1 and M2 , respectively. Eq. (1) is a first order model which has been mainly used to describe the release of nutrients from soil columns (Stewart et al., 1997; Zarabi and Jalali, 2012), while the first/zero order model (Eq. (2)) is a composite model developed for a constant and linear rate of nutrient release (Stewart et al., 1997). However, the first/first order mixed model (Eq. (3)) has two rate constants, which could be considered more flexible (Brunner and Focht, 1984). As a result, all the three models were employed and the parameters were obtained by fitting experimental data to the models using OriginPro 8.0.

Fig. 1 presents pH variations in different treatments. The initial pH value of all the leachate ranged from 7.6 to 7.9 except for SMC group. Compared to the control group, the initial pH of SMC treatment decreased from 7.8 to 7.2, which could be attributed to the relatively low pH value of SMC as shown in the research (Table 1) and other reports (Jordan et al., 2008; Stewart et al., 1997). Since SMC could stimulate the nitrification of soil, more hydrogen ion would be released through the reaction, which could cause soil acidification (Zhou et al., 2014). Minor differences were recorded among all the pH values in 50-day leachates. This result could be attributed to the dilution of large amounts of DI water and the buffering action ˜ of calcium carbonate, as reported by Santibánez et al. (2007). Based on the specified quality levels of groundwater provided in China (GB/T 14848-93), both pH values of SMC and SMC/CF leachates during the leaching events meet the demands of class I (6.5 < pH < 8.5). As shown in Fig. 2, the EC of all the leachates ranged from 650 to 1700 ␮S/cm at the beginning. According to the standards

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Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 417–423

1800 1600 CK

CF

SMS

SMC

SMC/CF

1400

EC( S/cm)

1200 1000 800 600 400 200 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43

Days Fig. 2 – Temporal pattern of electrical conductivity in leachate. provided by the Food and Agricultural Organization of the United Nations, it was within the normal range for irrigation water (0–3000 ␮S/cm). However, a slight decrease was found in SMC leachate in day 8, which was similar to the result reported by Zarabi and Jalali (2012), suggesting that the reduction of soluble salt could be caused by the leaching event (Civeira and Lavado, 2008). Though EC level in SMC leachate in day 50 (536 ␮S/cm) differed a lot from the initial value (1667 ␮S/cm), it remained in the same level with EC in SMS leachate (569 ␮S/cm on day 50). As a result, it suggests that the composting process from SMS to SMC doesn’t lead to an obvious EC reduction in leachates. As evidence, EC values of SMS/SMC itself are also similar (Table 1). In contrast, SMC/CF treatment displayed a notable lower EC value (1055 ␮S/cm) than SMC in day 1, indicating that the mixed application of chemical fertilizers and SMC could lead to EC reduction in leachate.

3.2.

Nitrogen in leachate

Fig. 3 presents the distribution of mineral nitrogen and NO3 − –N was the dominant mineral nitrogen form in leachate.

NO3 − –N in all treatments ranged from 5.75 to 35.84 mg/L, while NH4 + –N ranged from 0.63 to 21.70 mg/L in day 1. Ammonium performed a lower leaching rate than nitrate in soil, as reported by Zarabi and Jalali (2012), which could be ascribed to the fact that negatively-charged clay particles and functional groups of soil organic matter tend to hold cations, such as ammonium by electrostatic forces. As compared to SMS group, NO3 − –N in SMC group decreased from ∼34.57 mg/L to ∼8.50 mg/L, while NH4 + –N did not show a significant difference in Day 1. The phenomenon might be resulted from the larger proportion of NO3 − –N in SMC, coinciding with the evaluation method that mature compost has a higher NO3 − content and relatively lower NH4 + content (Das et al., 2011; Zhang and Sun, 2014). Therefore, composting treatment is considered to be an effective method to reduce the nutrients loss in SMS. The temporal curve of SMC/CF group showed a continuing decline during the whole leaching process and the initial NO3 − –N content is also considered to be the peak value (21.97 mg/L). However, the maximum value of SMC/CF group could only account for 61.3% of CF group, thus indicating that the mixed application of nitrogenous fertilizer and SMC would conserve nitrogen more efficiently. Cumulative amounts of total N leached from soil columns were significantly affected by SMC addition (Fig. S1). The value of TNcum in SMC group was found to be 3.96 times higher than that of the control. Among different treatments, the application of chemical fertilizers resulted in the greatest leaching amounts of TNcum (89.17 mg N), followed by SMC/CF and SMC. When subtracting the TNcum of control group from other groups, the leached TNcum of CF, SMC and SMC/CF were equivalent to 45.1%, 13.0% and 16.7%, of the applied nitrogen, respectively. Compared SMC with CF, it could be clearly observed that application of SMC as soil amendment may cause nitrogen immobilization in soil (Stewart et al., 1998). The mixture of SMC/CF could serve as nitrogen fertilizer retention method, which could be explained by the phenomenon that high C/N ratio would lead to the immobilization of ammonium and reduction of leachable ammonium (Kim et al., 2008).

3.3.

Phosphate in leachate

Fig. 4 depicts the variations of phosphate concentrations in leachate. It can be seen that the total phosphate variation 0.8

Phosphate in leachate (mg/l)

0.7

CK

CF TP 3PO4 -P

SMC

SMS TP 3PO4 -P

TP 3PO4 -P

TP 3PO4 -P

SMC/CF TP 3PO4 -P

0.6 0.5 0.4 0.3 0.2 0.1 0.0 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43

Days Fig. 3 – Temporal pattern of mineral nitrogen in leachate.

Fig. 4 – Temporal pattern of phosphate in leachate.

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Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 417–423

2200

CK

CF

SMS

SMC

SMC/CF

2000

Table 5 – TDS, Mineral N, TP, CODCr release model parameters and r2 values. Parameter Model

1800 1600

Eq. (1)

CODCr(mg/l)

1400 1200

Eq. (2)

1000 800 Eq. (3)

600 400 200

M k1 r2 M k1 k0 r2 M1 M2 k1 e k1 r r2

TDS

Mineral N

TP

CODCr

971 0.06 0.915 310 667 14 0.989 980 −7.6E−4 0.05 9.23E−7 0.865

9.24 0.10 0.915 5.25 0.88 0.10 0.989 7.17 3.67 0.04 1.59 0.999

0.42 0.03 0.977 0.08 0.68 0.006 0.999 0.08 113 0.68 5.4E−5 0.999

792 0.12 0.902 361 100 12.5 0.958 672 341 0.032 1.47 0.999

0 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43 1 15 29 43

Days Fig. 5 – Temporal pattern of CODCr in leachate. curve of SMC treatment was similar to the reported study (Chen et al., 2003) with the application of dredged sediment. Thus, the total phosphate in leachate increased during the first week, but decreased to a nearly unchangeable value in the subsequent leaching events. Two factors were regarded as the major “blocks” of phosphate migration in soil, including soil colloid adsorption like Fe/Mn oxides or organic matter and precipitation with CaCO3 (Lv et al., 1999). However, the continuous leaching events would lead the soil column to an anaerobic condition, resulting in the reduced adsorption between phosphate and Fe/Mn oxides, which caused the temporary increase of phosphate (Jensen et al., 1999). Temporary pattern of SMC treatment suggested that the total phosphate and soluble phosphate at the first leaching event could only account for 20.1% and 35.2% in CF treatment, indicating that SMC could be a slow-released origin of phosphate. This result could be explained by the slow decomposition of phosphorus containing organics in SMC. Fig. S2 shows the cumulative amounts of leaching phosphate. According to application rate (Table 3) and phosphorus content in SMC (Table 1), the initial phosphate in column could be obtained as 52.5 mg P/kg. Similarly, the initial phosphate in CF treatment equaled to 70.5 mg P/kg. After subtracting the background value from control group, the leached TPcum of CF, SMC, and SMC/CF could account for 0.71%, 0.75%, and 0.35% of the initial applied phosphate, respectively. Therefore, the mixture of SMC/CF was also an effective phosphorus retention method in compost application. In general, addition of SMC did not show a difference in comparison to chemical fertilizers, verifying that both the leaching of phosphate in SMC and CF amended soil were a slow-release process. Calculations also show that the PO4 3− –P/TP ratio in all treatments was 37%, 34.8% and 18.7%, respectively, illustrating that PO4 3− –P did not serve as the main existence form of leached phosphate in all amended soil columns.

3.4.

CODCr in leachate

CODCr temporal pattern described the leaching organic matters from soil columns, which correlated with other nutrients (Fig. 5). When fertilizers were applied, leached CODCr in CF group showed a slight increase than that in control group. After a week of incubation, CODCr concentration decreased to

the level of control group gradually, which could be attributed to a low application rate of fertilizer dosage and negligible CODCr increment caused by urea and calcium superphosphate. However, the addition of SMC led to a sharp increase as compared to control group. The SMC/CK ratio of CODCr concentration ranged from ∼19.7 in day 1 to ∼1.4 in day 43. SMC contains organic compounds, such as polysaccharide and protein, which resulted in the increase of CODCr . It is noteworthy that the CODCr concentration ratio of SMS/SMC varied from ∼5.0 in day 1 to ∼1.7 in day 43, suggesting that SMS acted as an easier leachable origin of organics. SMS is reasonable to release more organic matters as the precursor of SMC, since composting process can transform organics into stable final inorganics (Zhang and Sun, 2014). Moreover, a blend of SMC/CF gave rise to a lower CODCr content in leachate, which could weaken the excessive organics. It has been observed that the application of excessive SMC could assimilate more nutrients in soil and may result in groundwater pollution (Curtis and Suess, 2006), including adding higher concentration of dry OM from leachate (Guo et al., 2001). In order to solve this problem, several suggestions have been recommended by other authors. For instance, Zhang and Sun (2014) have reported an enhanced degradation of organic matter in co-composting process with SMC and biochar and Guo (2005) mentioned that SMC should be stacked in the field for two years of weathering before application. Moreover, the Pennsylvania State Law has stated the detailed parameters of field-weathering, while the same field cannot be used for additional SMC weathering. Furthermore, leachate collected during weathering could be reused as liquid fertilizer (Guo, 2005). According to the leaching experiment results, reduction in the application rate of SMC and combination SMC with chemical fertilizers should also be considered as effective methods to control the excessive CODCr concentration in leachate.

3.5.

Nutrient release kinetics

The leached TDS, mineral N, total P and CODCr from SMC treatment were accurately described by first order model, first/zero order model and first/first order model, as shown in Figs. S3–S6. All the parameters including M, M1 , M2 , k0 , k1 , k1 e , k1 r were listed in Table 5. Since M in Eq. (1) denotes the predicted maximum leachable value (Stewart et al., 1998), the cumulative leached TDS, mineral N, total P and CODCr up to day 50 could account for 99%, 106.8%, 122.1%, and 105.5% of the estimated value, respectively. However, it could be observed from

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Process Safety and Environmental Protection 9 8 ( 2 0 1 5 ) 417–423

Eq. (2) fitting curves that rapid nutrients leaching from soil column were observed initially, but decreased in subsequent leachate fractions. Eq. (3) satisfactorily shows the two distinct sections during the leaching event: (1) the initial section with a rapid leaching and (2) the later section with a slow leaching (Zarabi and Jalali, 2012), indicating that all the leached components including TDS, mineral N, total P and CODCr comply with the two-stage pattern. Among the applied models, Eq. (3) had a coefficient of determination r2 (0.999) for all the cumulative compositions except for TDS. TDS consists of K+ , Ca2+ , Na+ etc., thus should have been considered individually before fitting (Stewart et al., 1997). In addition, different M2 values in Eq. (3) revealed that there were fractions of nutrients resistant to be leached. The first/first order model could be a reasonable model in nutrient leaching description of SMC amended soil column.

4.

Conclusions

Physico-chemical characteristics of SMC, risk assessments of SMC application, nutrients loss of SMC amended soil and the description of nutrient release in leachate were presented in this paper. Results suggested that SMC contains protein, polysaccharide, lignocellulose as well as other nutrients. Heavy metal contents of SMC could meet the safe levels at different standards. Comparative analyses were performed with the possibilities of nutrient release from SMC and chemical fertilizers as well as mixed fertilizers during leaching test. SMC was regarded as better fertilizers than chemical fertilizers, which could hold 65% nitrogen Moreover, mixed application of SMC and chemical fertilizers could effectively reduce the excessive organic matter in leachate. Thus, SMC could be promising in agriculture application and has also the advantage of its nutrient retention characteristic.

Acknowledgement The authors would like to acknowledge the National Key Technology Research and Development Program, China (Grant No. 2013BAC16B03) for the financial support for this study.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. psep.2015.10.003.

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