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Efficiency of various sewage sludges and their biochars in improving selected soil properties and growth of wheat (Triticum aestivum)
Journal of Environmental Management 223 (2018) 607–613
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Efficiency of various sewage sludges and their biochars in improving selected soil properties and growth of wheat (Triticum aestivum)
T
Rabia Abdur Rehmana, Muhammad Rizwanb, Muhammad Farooq Qayyuma,∗, Shafaqat Alib, Muhammad Zia-ur-Rehmanc, Muhammad Zafar-ul-Hyea, Farhan Hafeezd, Muhammad Fasih Iqbala a
Department of Soil Science, Faculty of Agricultural Sciences & Technology, Bahauddin Zakariya University Multan, Pakistan Department of Environmental Sciences and Engineering, Government College University, Allama Iqbal Road, 38000 Faisalabad, Pakistan c Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Pakistan d Department of Environmental Sciences, COMSATS University Islamabad, Abbottabad Campus, Pakistan b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sewage sludge Biochar Wheat Phosphorus
Due to increasing demand of P fertilizers and gradual decrease in P resources, recyclable P is the focus of researchers in recent years. Sewage sludge (SS) is a municipal waste that contains appreciable amounts of P and probably other nutrients. In present study, the effects of various SS and their biochars (450 °C for 2 h) were investigated on soil properties and P uptake in wheat (Triticum aestivum) with and without P fertilizer. The biomass of plants and grain yield were significantly increased with application of SS and their biochars as compared to the control treatment either without or with P application. Moreover, there was significant interaction between treatments and P application for the concentration of K, and P in shoots and roots of wheat. Shoot P concentration was not significantly affected with SS than biochars whereas root P concentration was higher in SS treatments than respective biochars. Higher increase in Olsen's P concentration was observed in populated area sludge applied-soil as compared to disposal sludge and their biochars. Overall, it is observed that SS application increased the wheat yield and P concentrations in plants than control depending upon SS types whereas biochar application decreased the P concentration in roots. Grain yield and P concentration in shoots were not significantly affected for the treatment with P fertilizers than without P. Sewage sludge and their biochars might be a potential source of P but further research is needed to recommend the use of modified SSbiochars as source of available P for crops.
1. Introduction The essentiality of phosphorus (P) as an important macronutrient element for plants is very well established due to its role in many physiological and biochemical processes (Soetan et al., 2007; Barreto et al., 2018). Plants generally uptake P from soil solution and P deficiency in plants caused negative effects on growth and development as P is considered the most limiting nutrient for proper growth of plants (Arruda et al., 2017). Therefore, an adequate P supply on regular intervals is necessary for better crop yields (Arshad et al., 2016). To fulfill the increased P demands, phosphate rocks are mainly utilized as a source of P production worldwide (Diatta et al., 2017). These P fertilizers are less soluble which makes them ineffective especially for short cycle crops (Diatta et al., 2017). Thus, P fertilizers are produced by the acidification of non-renewable P minerals such as apatite to solubilize P
∗
Corresponding author. E-mail address: [email protected] (M.F. Qayyum).
https://doi.org/10.1016/j.jenvman.2018.06.081 Received 21 April 2018; Received in revised form 2 June 2018; Accepted 26 June 2018 0301-4797/ © 2018 Elsevier Ltd. All rights reserved.
by using pure acids such as sulfuric acid which may increase the production costs of P fertilizers. Raw materials used to produce P fertilizers also contain several pollutants such as heavy metals which may increase these pollutants levels in the soil and finally in plants (Dang et al., 2016; Murtaza et al., 2015). On the other hand, raw materials of P fertilizers are not only low grade but declining worldwide which demands the alternate sources of P fertilizers to fulfill the requirements of plants. In addition, there is growing concern for managing P concentrations in the soil in order to decrease the surface run-off and contamination of the ground water (Sharpley, 2016). Sewage sludge (SS) is mainly produced during the treatment of wastewaters which is an important source of organic matter as well as a number of essential plant nutrients such as P (Eid et al., 2017; Wollmann et al., 2017). The production of SS is continuously increasing due to the increasing quantity of treated wastewaters and strict
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Table 1 Initial characterization of soil and disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB). pH
Soil DAS DASB PAS PASB MS MSB
8.75 6.67 8.45 6.86 8.25 7.01 8.5
EC (μS cm−1)
761 1200 1600 4200 5000 4000 5500
TOM (%)
1.25 22.45 25.5 23.08 25.4 43.02 40.15
Total metal concentration (mg kg−1 DW) Cu
Pb
Ni
Cd
100 110 145 170 120 125
10 13 20 22 15 18
15 16 35 50 55 63
2.6 3.4 5.5 6.2 5.6 6.5
Total N (%)
0.034 1.45 0.43 1.46 0.54 2.12 0.64
Phosphorus
Texture
Total P (g kg−1)
Inorganic P (g kg−1)
Organic P (g kg−1)
Olsen's P (mg kg−1)
13.33 13.03 13.38 12.44 12.40 13.87
12.89 12.77 13.21 12.28 12.25 13.80
0.44 0.27 0.17 0.15 0.15 0.07
25.0 7.76 8.25 3.56 2.97 3.41 3.32
Clay loam
TOM = Total organic matter; DW = dry weight.
different sites for collection and safe disposal of sewerage material. One site is at Qasim pur near Bahawalpur bypass chowk (capacity, 146 Cusecs), and the second one is at Suraj Miyani disposal center (capacity, 109 Cusecs). The SS was obtained from the both sites, mixed and termed as disposal areas sludge (DAS), The SS material was also collected from the drainage of populated areas of city which was termed as papulated area sludge (PAS). Similarly, SS was collected from the side of the main road termed as main road sludge (MS). The SS materials from all sites were collected, air dried and stored separately. For the preparation of biochars and their characterization, methods given in Qayyum et al. (2015) were adopted. Briefly, after air drying, the SS samples were pyrolyzed anaerobically at 450 °C in the vertical silo type reactor. After pyrolysis, biochar was left for some time to cool down and then grounded to pass through 2 mm sieve and finally stored for further use. The basic physicochemical characterization of soil, SS and biochars such as pH, electrical conductivity (EC), and volatile matter were performed following the recommended methodologies (McLaughlin, 2009). Different phosphorus fractions (total P, inorganic P, organic P, water-extractable P, and NaHCO3-extractable P), in the sludges as well as their biochars were determined followings the method of Olsen and Sommers (1982). For total P, 0.5 g sample were ash dried at 550 °C for 4 h, later extracted with 0.5 M H2SO4. For inorganic P, 0.5 g sample was directly extracted with 0.5 M H2SO4. Separate samples were extracted with water and NaHCO3 in the same way. Later, the P measurements were made according to Murphy and Riley (1962). The selected heavy metals (copper (Cu), lead (Pb), nickel (Ni), and cadmium (Cd)) in the SS and their biochars were determined after the digestion of samples in aqua regia followed by determination with atomic absorption spectrophotometer (Agilent FS 240). The initial properties of soil and treatments are reported in Table 1.
standards of effluent quality are being used to treat the wastewaters (Eid et al., 2017). The safe utilization of SS is always a serious worldwide challenge. The most common methods of SS-removal and utilization are landfilling, open incineration or agricultural applications as a source of plant nutrients or to increase soil properties (Kidd et al., 2007). Both landfilling and incineration of SS are discouraged owing to their ability to contaminate underground water and air pollution respectively. Thus, soil application of SS is continuously increasing due to its acceptable management as well as provision of essential plant nutrients and improving soil properties, thereby enhancing crop yields (Antoniadis et al., 2010; Bai et al., 2017). However, SS often contains toxic heavy metals and the concentrations of heavy metals varied with the types of SS (Samara et al., 2017; Xiong et al., 2018). The higher concentrations of heavy metals in SS may present the potential threats to crop plants, human health, and ecological system (Udayanga et al., 2018; Xiong et al., 2018). The heavy metals are toxic to plants and negatively affect the growth and yield (Rizwan et al., 2016, 2017). Thus, many countries have specified the heavy metal limits in SS for field application (Udayanga et al., 2018). Therefore, SS should be evaluated for their heavy metal concentrations before any field application. Sewage sludge is also a secondary source of P which is usually ignored at world level (Li et al., 2015). The P level in SS has been increasing due to the improvements in wastewater treatment technology (Li et al., 2015). Various organic and inorganic forms of P are present in SS due to variation in organic matter contents and wastewater treatment procedures (Li et al., 2015). The P in SS can be enriched through pyrolysis (Yue et al., 2017). Pyrolysis is closed burning of any kind of organic material that results in carbon rich product called biochar (Rizwan et al., 2016). Use of biochar as an amendment in soils has plentiful benefits such as increasing soil fertility, soil water holding capacity, and soil carbon sequestration but the response depends upon the type of feedstock used for biochar preparation and pyrolysis conditions (Abbas et al., 2017; Ali et al., 2017). Biochar produced from SS can decrease SS volume and its toxicity to plants (Song et al., 2014) and could improve soil properties (Yue et al., 2017). It was hypothesized that SS and its biochar might be a potential alternate source of P for plant growth and quality. Thus, the effects of four types of SS, based on collection areas, and their biochars were investigated on soil selected properties, P and K uptake and wheat growth and yield with and without P fertilizer.
2.2. Experimental detail Effect of SS and their biochars on P bioavailability to wheat was investigated in a pot experiment. For this purpose, a two-factorial complete randomized design was followed. The treatments comprised of, control, DAS, DASB (disposal area sludge biochar), PAS, PASB (papulated sludge biochar), MS, and MSB (main road sludge biochar). The second factor was application of phosphorus (0 and 50 mg P kg−1 soil as a single super phosphate. The treatments were applied at the rate of 1% w/w in each pot containing 10 kg air-dried soil. The treatments were mixed uniformly in the soil before sowing of seeds. Wheat (cv. Galaxy 2013) was sown as the test crop in each pot with three replicates of each treatment. Eight seeds were sown initially in each pot and finally 5 healthy seedlings were maintained for further growth. The experiment was conducted under ambient conditions with rain protection facility. Light duration was 10/14 and 13/11 day/night and mean relative humidity of 65% ± 5% and 51% ± 5% at the start and end of the
2. Materials and methods 2.1. Sludge collection, biochar preparation and characterization Sewage sludges were collected from different waste collecting areas in Multan, Pakistan (Location, 30.2°′″N, 71.45°′″E, Altitude 710 Feet). Water and sanitation agency (WASA) of Multan is operational on 608
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experiment respectively. After completion of crop cycle (about after 117 days of sowing), plants were harvested and dry weights of shoots and grains (70 °C until constant weight) and length of the shoots were measured. Roots were taken separately for determination of P and K in roots. 2.3. Soil analyses Soil samples from all pots were collected separately for their chemical analyses (EC, pH and Olsen's P). The soil EC and pH were determined in soil water suspensions of 1:5 ratios using EC meter and pH meter (BANTE 11WD). For determination of Olsen's P, 1.0 g soil was extracted with 5 mL of 0.5 M NaHCO3 after shaking on mechanical shaker (SHO-2D WiseShake). The suspensions were filtered and the P concentration was determined following the method of Ohno and Zibilske (1991). Briefly, color development was made using malachite green absorbance and readings were taken on spectrophotometer (BMS Canada) at 630 nm. 2.4. Plant analysis Plant samples were digested in di-acid mixtures for the determination of P and potassium (K) concentrations. Briefly, 0.5 g plant material was taken in digestion tube and 5 mL of nitric and perchloric acid mixture (2:1) was added. The materials were digested at 350 °C till colorless solution using microblock digestor. Finally, the appropriate volume of the solution was made by using distilled water. The P concentration in samples was measured after developing green color following method of Ohno and Zibilske (1991). Then readings were taken at spectrophotometer at 630 nm and flame photometer (Jenway PFP-7) was used for the determination of K. The metal concentration in the plant samples was determined with the help of atomic absorption spectrophotometer (Agilent FS 240).
Fig. 1. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on soil pH (a) and EC (b) with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
2.5. Statistical analysis All investigated parameters were statistically analyzed for two-way analysis of variance (ANOVA) using computer-based program STATISTIX 8.1. Where significant, the treatments were differentiated through Tukey-HSD test. The two-way analysis of investigated parameters is provided in Table 2.
EC remained as MSB > MS = DASB = PAS > PASB = control. The data regarding the effect of various treatments with or without P on Olsen's P concentration in soil is presented in Fig. 2. The results showed a significant interaction between treatments and P application for the Olsen's P in soil. Soil Olsen's P concentrations were higher in all treatments with P application than the same treatments without P application. Maximum P concentration was found in PASB followed by MS and MSB with P application. The DASB and PASB treatments without P application resulted higher Olsen's P than control with P application.
3. Results 3.1. Soil pH, EC and P concentration The interactive effect of various treatments and P application levels on soil pH and EC is presented in Fig. 1. There was a significant interaction effect between treatments and P levels on soil pH. The maximum value of pH was observed in MS treatment followed by the MSB and DAS. The P application did not cause any significant effect on soil pH. For soil EC, the interaction effect between soil EC and P application was non-significant. However, the treatments significantly affected the soil EC irrespective of P application. At both levels of P, the trend of soil
3.2. Plant growth The interactive effect of various treatments and P application on growth parameters is presented in Fig. 3. Except MS with P, all
Table 2 Two-way Analysis of Variance for different parameters.
P application Treatment P* treatment
Biomass
Grain yield
Plant height
P conc. shoot
P conc. root
K conc. shoot
K conc. root
Soil pH
Soil EC
Olsen's P in soil
127.24*** 57.79*** 3.01*
0.00n.s 54.13*** 3.94**
23.65*** 5.02** 3.21*
25.63*** 5.84*** 5.04***
139.00*** 8.95*** 9.66***
14.61** 6.61** 4.14**
22.81** 18.46** 4.84**
4.92* 15.84** 3.58***
0.24n.s 25.18*** 2.15n.s
983.08** 222.02** 12.25**
* = P ≤ 0.05. ** = P ≤ 0.01. *** = P ≤ 0.001. 609
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Fig. 2. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on Olsen's P in soil with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
treatments significantly increased the plant height as compared to control (Fig. 3a). Regarding total plant dry biomass, P application and biochar treatments resulted in significantly higher biomass values as compared to control, and sludges without P application (Fig. 3b). However, all sludges yielded higher biomass when compared with control treatment irrespective of P application and biochar. Similarly, the grain yield of wheat was also significantly influenced by the treatments (Fig. 3c). The P application did not cause any significant effect on all treatments including control. However, the application of sludges caused a significant increase in grain yield than control. Overall, P application, treatments and P × treatments showed a significant effect for plant height, biomass and grain yield (Table 2). 3.3. P and K concentration in plants The data regarding the P and K concentration in wheat shoot and roots is presented in Fig. 4. The P application increased the plant P uptake especially in control, DAS, DASB, PASB and MSB treatments. The maximum concentration of P was found in PASB treatment with P application. However, in all treatments, the P concentration was higher than control without P. The same trend was found for P concentration in roots. Regarding the concentration of K in wheat shoots, except DAS and DASB, none of the treatments caused any significant effect compared with the control treatment. All treatments except MS without P increased the K concentration in roots than control. Overall, P and K concentrations in shoots and roots showed significant effects among P application, treatments as well as P and treatments (Table 2).
Fig. 3. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on plant height, biomass, and grain yield with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
4. Discussion
(Table 1) which confirms the previous studies that biochar contains higher TOM especially stable organic carbon than feedstock depending upon the type of feedstock and preparation conditions (Rizwan et al., 2016). All SS and their biochars were also analyzed for total Cu, Pb, Ni and Cd concentrations and the results showed the variations in these metal concentrations in all amendments (Table 1). Variable results have been reported in literature regarding the concentrations of metal micronutrients in SS and their availability to plants (Samara et al., 2017; Sharma et al., 2018). The literature reported that the concentrations of heavy metals in the SS varies which might be due to several factors such as types of SS and soils as well as application rates (Samara et al., 2017; Sharma et al., 2018). The concentrations of toxic heavy metals such as
The SS used in our study were collected from different areas and labelled accordingly. The SS and biochars contained different concentrations of total organic matter (TOM), total N and different fractions of P concentrations (Table 1). The bioavailable P was much lower as compared to total P in all treatments used in the study. For this reason, application rates of SS should be higher as compared to commercially available fertilizers which contain most of the P as water soluble and plant available forms. Upon pyrolysis, the P concentration was increased in all sludges' biochars than their respective SS (Table 1). It is previously reported that nutrients are enriched in biochars than their respective feedstock (Rizwan et al., 2016; Igalavithana et al., 2017). Biochars contain higher TOM except MSB than respective SS 610
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Fig. 4. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on P and K concentrations in shoot and root with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
data (Samara et al., 2017). It was demonstrated that soil available P and other macronutrients increased before and after wheat harvest with the application of stabilized SS than control and the response depend upon the type of the soils, time, and rates of SS (Samara et al., 2017). In current study, Olsen's P varies with SS type and biochars (Table 1). The variations in bioavailable P concentrations with treatments might be due to variation in release of nutrients from different SS applied in the soil and the mobility of P with amendments. It was reported that P retention by soil colloids may decrease with SS application which might be due to the competition between organic ligands and phosphate on the soil surface as well as formation of soluble P complexes with humic substances in the soil (Bueno et al., 2011; Samara et al., 2017). However, this effect needs further detailed investigations in future studies. Our results also showed significant effects of SS and their biochars on plant growth attributes (Fig. 3). At no P application, the biomass and grain yield were increased with different SS or biochar treatments. Song et al. (2014) reported that biochar prepared from SS at 450 °C was suitable for the growth of garlic. Eid et al. (2017) reported that SS application increased the biomass of cucumber without showing any toxicities of heavy metals. Interestingly, at P application, the increases in biomass and grain yield were lower than SS. This might be due to the changes in soil properties with SS than P application as SS has the ability to positively affect the soil properties (Eid et al., 2017; Yue et al., 2017). Previously, it has been reported that SS can contribute nutrients to crop plants and increase the biomass and grain yield of cereals such as rice and wheat (Singh and Agrawal, 2008; Lakhdar et al., 2010; Latare et al., 2014). Similar to our results, Lemming et al. (2016) reported significant effects of SS-mixing in soil on maize growth and P uptake in a short term study. Wollmann et al. (2017) demonstrated that
Pb and Cd were below the limit of heavy metals in SS before reuse in soils for USA and European Union (Udayanga et al., 2018). The metal concentrations in biochars were slightly higher than respective SS (Table 1). It has been reported in the literature that biochar may decrease mobile forms of heavy metal in the soil (Rehman et al., 2017; Abbas et al., 2018). In addition, toxic metals such as Cd which regulate the use of SS were below the detection limit in wheat shoots. Thus, SS and biochars may be a suitable source of organic fertilizers for plant growth. Post-harvest analysis of the soil showed that the effect of treatments on soil pH, and EC depends upon the types of SS and their biochars (Fig. 1). Yue et al. (2017) demonstrated that biochar obtained from municipal SS (500 °C) decreased the soil pH while increased the soil EC and available P than control after harvesting the turf grass and reducing or enhancing trend in these parameters was higher with increasing doses of biochar applied in the alkaline soil (pH 8.7). It was demonstrated that miscanthus biochar slightly changed the pH of alkaline soil while considerably increased the pH of acidic soil (Luo et al., 2011). The application of stabilized SS increased the pH and EC of the soil before and after harvesting the wheat whereas the response varied with the type of soil (Samara et al., 2017). SS application increased the EC whereas decreased the pH of the soil than unamended soil (Sharma et al., 2018). Furthermore, the liming effects of biochars are usually observed in acidic soils (Jin et al., 2016; Rizwan et al., 2016). The decreased pH and EC of post-harvest soil with biochar application (Fig. 1) might be due to the nutrients released from biochars with time and soil type (Rizwan et al., 2016). Olsen's P concentrations depend upon the treatments applied to the soil (Fig. 2). These results are in accordance to the recently published 611
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References
fertilizers from SS might be a suitable alternate source of P than rock phosphate for enhancing plant growth and P contents but the response strongly depends upon SS preparation environment. In the present study, sewage sludges were selected from different areas while the results showed no major differences among SS for their positive effects on growth and yield as well as nutrients supply. However, their BCs differed in affecting soil properties and plant growth (Figs. 1 and 3). This might be due to the initial properties of biochars (Table 1) as well as modification of P and soil properties with biochars than SS (Figs. 1 and 2). The most important findings of present study show that these SS can be used as fertilizers either as sole application or after pyrolysis. Both sole application of SS and their respective biochars provided enough P for the plants to achieve biomass higher than conventional P-fertilizer (Figs. 3 and 4). The data of bioavailable P in soil shows that DAS and PAS did not cause any significant change in P concentration (Fig. 4). However, their biochars increased the Olsen's P in soil (Fig. 2). This might be because of pyrolysis conditions that have affected the nature of P compounds (Song et al., 2014). This shows that the SS and their biochars significantly contributed in terms of nutrient supply to wheat plants. It was reported that wheat has the ability to change P dynamics in the rhizosphere which is due to P uptake by plants and microbial activities in the soil (Arruda et al., 2017). According to Kahiluoto et al. (2015), the availability of P was higher in manure-compost than in SS. However, different treatments such as acidification increased P availability of SS in soils as well as to Italian ryegrass. They also reported that in the SS hygienized with Ca, P availability was reduced. In our study, the soil used was alkaline and calcareous in nature and this might be the possible reason of limited bioavailability of P in only SS treatments. Atienza–Martínez et al. (2014) recovered P from sewage sludge ash by pyrolysis and treating with different acids. Shiba and Ntuli (2017) extracted P from sewage sludge using sulfuric acid. The authors precipitated the leached P with different chemicals and observed the solubility tests. It was concluded that resulting precipitates can be used as P fertilizer. Our results demonstrated that P application significantly increased Olsen's P in post-harvest soil (Fig. 2) but plant growth, grain yield (Fig. 3) and shoot P concentrations (Fig. 4) were not significantly affected than SS and biochar treatments without P application. This showed that the inorganic P supply may enhance the risk of P surface runoff negatively affect the overall environmental quality.
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Phosphorus in manure and sewage sludge more recyclable than in soluble inorganic fertilizer. Environ. Sci. Technol. 49, 2115–2122. http://dx.doi.org/10.1021/es503387y. Kidd, P.S., Domínguez-Rodríguez, M.J., Díez, J., Monterroso, C., 2007. Bioavailability and plant accumulation of heavy metals and phosphorus in agricultural soils amended by long-term application of sewage sludge. Chemosphere 66, 1458–1467. http://dx.doi. org/10.1016/j.chemosphere.2006.09.007. Lakhdar, A., Iannelli, M.A., Debez, A., Massacci, A., Jedidi, N., Abdelly, C., 2010. Effect of municipal solid waste compost and sewage sludge use on wheat (Triticum durum): growth, heavy metal accumulation, and antioxidant activity. J. Sci. Food Agric. 90, 965–971. http://dx.doi.org/10.1002/jsfa.3904. Latare, A.M., Kumar, O., Singh, S.K., Gupta, A., 2014. Direct and residual effect of sewage sludge on yield, heavy metals content and soil fertility under rice-wheat system. Ecol. Eng. 69, 17–24. http://dx.doi.org/10.1016/j.ecoleng.2014.03.066. Lemming, C., Oberson, A., Hund, A., Jensen, L.S., Magid, J., 2016. Opportunity costs for maize associated with localised application of sewage sludge derived fertilisers, as indicated by early root and phosphorus uptake responses. Plant Soil 406, 201–217. http://dx.doi.org/10.1007/s11104-016-2865-6. Li, R., Zhang, Z., Li, Y., Teng, W., Wang, W., Yang, T., 2015. Transformation of apatite phosphorus and non-apatite inorganic phosphorus during incineration of sewage sludge. Chemosphere 141, 57–61. http://dx.doi.org/10.1016/j.chemosphere.2015. 05.094. Luo, Y., Durenkamp, M., De Nobili, M., Lin, Q., Brookes, P.C., 2011. Short term soil priming effects and the mineralization of biochar following its incorporation to soils of different pH. Soil Biol. Biochem. 43, 2304–2314. McLaughlin, H., 2009. All biochars are not created equal, and how to tell them apart. In: North American Biochar Conference. vol. 2. Boulder, CO, pp. 1–36 August 2009. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27, 31–36. http://dx.doi.org/10.1016/ S0003-2670(00)88444-5. Murtaza, G., Javed, W., Hussain, A., Wahid, A., Murtaza, B., Owens, G., 2015. Metal uptake via phosphate fertilizer and city sewage in cereal and legume crops in
5. Conclusion Sewage sludges and their biochars affected the soil pH and enhanced Olsen's P and EC of the soil which indicated that these treatments might be suitable for application in alkaline soils but the response varies with the type of biochars having maximum effect on these properties with PASB. Plant growth, P and K concentrations in plants can be improved with SS and biochar treatments without P application. Biochars from SS resulted in P enrichment in plants that can be used as an alternate source of P fertilizer simultaneously managing P entry into other environmental compartments by SS disposal. Both SS and their biochars can be a source of plant nutrients especially P than conventional P fertilizers but response varies with type of SS. Overall, some of the biochars prepared from SS could be the efficient alternate sources of P that are able to enhance the plant productivity and might be the suitable approach for organic farming systems. Further field scale studies with a variety of crops and seasons might be conducted to evaluate the effects of SS and their biochars on soil properties and plant growth in long-term seasonal experiments. Acknowledgements We greatly appreciate Higher Education Commission Pakistan for the research grant under National Research Program for Universities (NRPU project no. 3935). 612
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amended with sewage sludge-fly ash mixtures. Environ. Sci. Pollut. Res. http://dx. doi.org/10.1007/s11356-018-1475-7. Sharpley, A., 2016. Managing agricultural phosphorus to minimize water quality impacts. Sci. Agric. 73, 1–8. Shiba, N.C., Ntuli, F., 2017. Extraction and precipitation of phosphorus from sewage sludge. Waste Manag. 60, 191–200. Singh, R.P., Agrawal, M., 2008. Potential benefits and risks of land application of sewage sludge. Waste Manag. 28, 347–358. Soetan, K.O., Olaiya, C.O., Oyewole, O.E., 2007. The importance of mineral elements for humans, domestic animals and plants - a review, African Journal of Food Science. Acad. J. 4 (5), 200–222. Song, X.D., Xue, X.Y., Chen, D.Z., He, P.J., Dai, X.H., 2014. Application of biochar from sewage sludge to plant cultivation: influence of pyrolysis temperature and biochar-tosoil ratio on yield and heavy metal accumulation. Chemosphere 109, 213–220. Udayanga, W.C., Veksha, A., Giannis, A., Lisak, G., Chang, V.W.C., Lim, T.T., 2018. Fate and distribution of heavy metals during thermal processing of sewage sludge. Fuel 226, 721–744. Wollmann, I., Gauro, A., Müller, T., Möller, K., 2017. Phosphorus bioavailability of sewage sludge‐based recycled fertilizers. J. Plant Nutr. Soil Sci. http://dx.doi.org/10. 1002/jpln.201700111. Xiong, Q., Zhou, M., Liu, M., Jiang, S., Hou, H., 2018. The transformation behaviors of heavy metals and dewaterability of sewage sludge during the dual conditioning with Fe 2+- sodium persulfate oxidation and rice husk. Chemosphere 208, 93–100. Yue, Y., Cui, L., Lin, Q., Li, G., Zhao, X., 2017. Efficiency of sewage sludge biochar in improving urban soil properties and promoting grass growth. Chemosphere 173, 551–556.
Pakistan. Environ. Sci. Pollut. Res. http://dx.doi.org/10.1007/s11356-015-4073-y. Ohno, T., Zibilske, L.M., 1991. Determination of low concentrations of phosphorus in soil extracts using malachite green. Soil Sci. Soc. Am. J. 55, 892. http://dx.doi.org/10. 2136/sssaj1991.03615995005500030046x. Olsen, S.R., Sommers, L.E., 1982. Phosphorus. In: Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties. American Society of Agronomy, Soil Science Society of America, Madison, WI, pp. 403–430. http://dx.doi.org/10.2134/ agronmonogr9.2.2ed.c24. Qayyum, M.F., Abid, M., Danish, S., Saeed, M.K., Ali, M.A., 2015. Effects of various biochars on seed germination and carbon mineralization in an alkaline soil. Pakistan J. Agric. Sci. 51, 977–982. Rehman, M.Z., Khalid, H., Akmal, F., Ali, S., Rizwan, M., Qayyum, M.F., Iqbal, M., Khalid, M.U., Azhar, M., 2017. Effect of limestone, lignite and biochar applied alone and combined on cadmium uptake in wheat and rice under rotation in an effluent irrigated field. Environ. Pollut. 227, 560–568. Rizwan, M., Ali, S., Qayyum, M.F., Ibrahim, M., Zia-ur-Rehman, M., Abbas, T., Ok, Y.S., 2016. Mechanisms of biochar-mediated alleviation of toxicity of trace elements in plants: a critical review. Environ. Sci. Pollut. Res. 23, 2230–2248. Rizwan, M., Ali, S., Qayyum, M.F., Ok, Y.S., Zia-ur-Rehman, M., Abbas, Z., Hannan, F., 2017. Use of maize (Zea mays L.) for phytomanagement of Cd-contaminated soils: a critical review. Environ. Geochem. Health 39, 259–277. Samara, E., Matsi, T., Balidakis, A., 2017. Soil application of sewage sludge stabilized with steelmaking slag and its effect on soil properties and wheat growth. Waste Manag. 68, 378–387. Sharma, B., Kothari, R., Singh, R.P., 2018. Growth performance, metal accumulation and biochemical responses of Palak (Beta vulgaris L. var. Allgreen H-1) grown on soil
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
Efficiency of various sewage sludges and their biochars in improving selected soil properties and growth of wheat (Triticum aestivum)
T
Rabia Abdur Rehmana, Muhammad Rizwanb, Muhammad Farooq Qayyuma,∗, Shafaqat Alib, Muhammad Zia-ur-Rehmanc, Muhammad Zafar-ul-Hyea, Farhan Hafeezd, Muhammad Fasih Iqbala a
Department of Soil Science, Faculty of Agricultural Sciences & Technology, Bahauddin Zakariya University Multan, Pakistan Department of Environmental Sciences and Engineering, Government College University, Allama Iqbal Road, 38000 Faisalabad, Pakistan c Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Pakistan d Department of Environmental Sciences, COMSATS University Islamabad, Abbottabad Campus, Pakistan b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sewage sludge Biochar Wheat Phosphorus
Due to increasing demand of P fertilizers and gradual decrease in P resources, recyclable P is the focus of researchers in recent years. Sewage sludge (SS) is a municipal waste that contains appreciable amounts of P and probably other nutrients. In present study, the effects of various SS and their biochars (450 °C for 2 h) were investigated on soil properties and P uptake in wheat (Triticum aestivum) with and without P fertilizer. The biomass of plants and grain yield were significantly increased with application of SS and their biochars as compared to the control treatment either without or with P application. Moreover, there was significant interaction between treatments and P application for the concentration of K, and P in shoots and roots of wheat. Shoot P concentration was not significantly affected with SS than biochars whereas root P concentration was higher in SS treatments than respective biochars. Higher increase in Olsen's P concentration was observed in populated area sludge applied-soil as compared to disposal sludge and their biochars. Overall, it is observed that SS application increased the wheat yield and P concentrations in plants than control depending upon SS types whereas biochar application decreased the P concentration in roots. Grain yield and P concentration in shoots were not significantly affected for the treatment with P fertilizers than without P. Sewage sludge and their biochars might be a potential source of P but further research is needed to recommend the use of modified SSbiochars as source of available P for crops.
1. Introduction The essentiality of phosphorus (P) as an important macronutrient element for plants is very well established due to its role in many physiological and biochemical processes (Soetan et al., 2007; Barreto et al., 2018). Plants generally uptake P from soil solution and P deficiency in plants caused negative effects on growth and development as P is considered the most limiting nutrient for proper growth of plants (Arruda et al., 2017). Therefore, an adequate P supply on regular intervals is necessary for better crop yields (Arshad et al., 2016). To fulfill the increased P demands, phosphate rocks are mainly utilized as a source of P production worldwide (Diatta et al., 2017). These P fertilizers are less soluble which makes them ineffective especially for short cycle crops (Diatta et al., 2017). Thus, P fertilizers are produced by the acidification of non-renewable P minerals such as apatite to solubilize P
∗
Corresponding author. E-mail address: [email protected] (M.F. Qayyum).
https://doi.org/10.1016/j.jenvman.2018.06.081 Received 21 April 2018; Received in revised form 2 June 2018; Accepted 26 June 2018 0301-4797/ © 2018 Elsevier Ltd. All rights reserved.
by using pure acids such as sulfuric acid which may increase the production costs of P fertilizers. Raw materials used to produce P fertilizers also contain several pollutants such as heavy metals which may increase these pollutants levels in the soil and finally in plants (Dang et al., 2016; Murtaza et al., 2015). On the other hand, raw materials of P fertilizers are not only low grade but declining worldwide which demands the alternate sources of P fertilizers to fulfill the requirements of plants. In addition, there is growing concern for managing P concentrations in the soil in order to decrease the surface run-off and contamination of the ground water (Sharpley, 2016). Sewage sludge (SS) is mainly produced during the treatment of wastewaters which is an important source of organic matter as well as a number of essential plant nutrients such as P (Eid et al., 2017; Wollmann et al., 2017). The production of SS is continuously increasing due to the increasing quantity of treated wastewaters and strict
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Table 1 Initial characterization of soil and disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB). pH
Soil DAS DASB PAS PASB MS MSB
8.75 6.67 8.45 6.86 8.25 7.01 8.5
EC (μS cm−1)
761 1200 1600 4200 5000 4000 5500
TOM (%)
1.25 22.45 25.5 23.08 25.4 43.02 40.15
Total metal concentration (mg kg−1 DW) Cu
Pb
Ni
Cd
100 110 145 170 120 125
10 13 20 22 15 18
15 16 35 50 55 63
2.6 3.4 5.5 6.2 5.6 6.5
Total N (%)
0.034 1.45 0.43 1.46 0.54 2.12 0.64
Phosphorus
Texture
Total P (g kg−1)
Inorganic P (g kg−1)
Organic P (g kg−1)
Olsen's P (mg kg−1)
13.33 13.03 13.38 12.44 12.40 13.87
12.89 12.77 13.21 12.28 12.25 13.80
0.44 0.27 0.17 0.15 0.15 0.07
25.0 7.76 8.25 3.56 2.97 3.41 3.32
Clay loam
TOM = Total organic matter; DW = dry weight.
different sites for collection and safe disposal of sewerage material. One site is at Qasim pur near Bahawalpur bypass chowk (capacity, 146 Cusecs), and the second one is at Suraj Miyani disposal center (capacity, 109 Cusecs). The SS was obtained from the both sites, mixed and termed as disposal areas sludge (DAS), The SS material was also collected from the drainage of populated areas of city which was termed as papulated area sludge (PAS). Similarly, SS was collected from the side of the main road termed as main road sludge (MS). The SS materials from all sites were collected, air dried and stored separately. For the preparation of biochars and their characterization, methods given in Qayyum et al. (2015) were adopted. Briefly, after air drying, the SS samples were pyrolyzed anaerobically at 450 °C in the vertical silo type reactor. After pyrolysis, biochar was left for some time to cool down and then grounded to pass through 2 mm sieve and finally stored for further use. The basic physicochemical characterization of soil, SS and biochars such as pH, electrical conductivity (EC), and volatile matter were performed following the recommended methodologies (McLaughlin, 2009). Different phosphorus fractions (total P, inorganic P, organic P, water-extractable P, and NaHCO3-extractable P), in the sludges as well as their biochars were determined followings the method of Olsen and Sommers (1982). For total P, 0.5 g sample were ash dried at 550 °C for 4 h, later extracted with 0.5 M H2SO4. For inorganic P, 0.5 g sample was directly extracted with 0.5 M H2SO4. Separate samples were extracted with water and NaHCO3 in the same way. Later, the P measurements were made according to Murphy and Riley (1962). The selected heavy metals (copper (Cu), lead (Pb), nickel (Ni), and cadmium (Cd)) in the SS and their biochars were determined after the digestion of samples in aqua regia followed by determination with atomic absorption spectrophotometer (Agilent FS 240). The initial properties of soil and treatments are reported in Table 1.
standards of effluent quality are being used to treat the wastewaters (Eid et al., 2017). The safe utilization of SS is always a serious worldwide challenge. The most common methods of SS-removal and utilization are landfilling, open incineration or agricultural applications as a source of plant nutrients or to increase soil properties (Kidd et al., 2007). Both landfilling and incineration of SS are discouraged owing to their ability to contaminate underground water and air pollution respectively. Thus, soil application of SS is continuously increasing due to its acceptable management as well as provision of essential plant nutrients and improving soil properties, thereby enhancing crop yields (Antoniadis et al., 2010; Bai et al., 2017). However, SS often contains toxic heavy metals and the concentrations of heavy metals varied with the types of SS (Samara et al., 2017; Xiong et al., 2018). The higher concentrations of heavy metals in SS may present the potential threats to crop plants, human health, and ecological system (Udayanga et al., 2018; Xiong et al., 2018). The heavy metals are toxic to plants and negatively affect the growth and yield (Rizwan et al., 2016, 2017). Thus, many countries have specified the heavy metal limits in SS for field application (Udayanga et al., 2018). Therefore, SS should be evaluated for their heavy metal concentrations before any field application. Sewage sludge is also a secondary source of P which is usually ignored at world level (Li et al., 2015). The P level in SS has been increasing due to the improvements in wastewater treatment technology (Li et al., 2015). Various organic and inorganic forms of P are present in SS due to variation in organic matter contents and wastewater treatment procedures (Li et al., 2015). The P in SS can be enriched through pyrolysis (Yue et al., 2017). Pyrolysis is closed burning of any kind of organic material that results in carbon rich product called biochar (Rizwan et al., 2016). Use of biochar as an amendment in soils has plentiful benefits such as increasing soil fertility, soil water holding capacity, and soil carbon sequestration but the response depends upon the type of feedstock used for biochar preparation and pyrolysis conditions (Abbas et al., 2017; Ali et al., 2017). Biochar produced from SS can decrease SS volume and its toxicity to plants (Song et al., 2014) and could improve soil properties (Yue et al., 2017). It was hypothesized that SS and its biochar might be a potential alternate source of P for plant growth and quality. Thus, the effects of four types of SS, based on collection areas, and their biochars were investigated on soil selected properties, P and K uptake and wheat growth and yield with and without P fertilizer.
2.2. Experimental detail Effect of SS and their biochars on P bioavailability to wheat was investigated in a pot experiment. For this purpose, a two-factorial complete randomized design was followed. The treatments comprised of, control, DAS, DASB (disposal area sludge biochar), PAS, PASB (papulated sludge biochar), MS, and MSB (main road sludge biochar). The second factor was application of phosphorus (0 and 50 mg P kg−1 soil as a single super phosphate. The treatments were applied at the rate of 1% w/w in each pot containing 10 kg air-dried soil. The treatments were mixed uniformly in the soil before sowing of seeds. Wheat (cv. Galaxy 2013) was sown as the test crop in each pot with three replicates of each treatment. Eight seeds were sown initially in each pot and finally 5 healthy seedlings were maintained for further growth. The experiment was conducted under ambient conditions with rain protection facility. Light duration was 10/14 and 13/11 day/night and mean relative humidity of 65% ± 5% and 51% ± 5% at the start and end of the
2. Materials and methods 2.1. Sludge collection, biochar preparation and characterization Sewage sludges were collected from different waste collecting areas in Multan, Pakistan (Location, 30.2°′″N, 71.45°′″E, Altitude 710 Feet). Water and sanitation agency (WASA) of Multan is operational on 608
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experiment respectively. After completion of crop cycle (about after 117 days of sowing), plants were harvested and dry weights of shoots and grains (70 °C until constant weight) and length of the shoots were measured. Roots were taken separately for determination of P and K in roots. 2.3. Soil analyses Soil samples from all pots were collected separately for their chemical analyses (EC, pH and Olsen's P). The soil EC and pH were determined in soil water suspensions of 1:5 ratios using EC meter and pH meter (BANTE 11WD). For determination of Olsen's P, 1.0 g soil was extracted with 5 mL of 0.5 M NaHCO3 after shaking on mechanical shaker (SHO-2D WiseShake). The suspensions were filtered and the P concentration was determined following the method of Ohno and Zibilske (1991). Briefly, color development was made using malachite green absorbance and readings were taken on spectrophotometer (BMS Canada) at 630 nm. 2.4. Plant analysis Plant samples were digested in di-acid mixtures for the determination of P and potassium (K) concentrations. Briefly, 0.5 g plant material was taken in digestion tube and 5 mL of nitric and perchloric acid mixture (2:1) was added. The materials were digested at 350 °C till colorless solution using microblock digestor. Finally, the appropriate volume of the solution was made by using distilled water. The P concentration in samples was measured after developing green color following method of Ohno and Zibilske (1991). Then readings were taken at spectrophotometer at 630 nm and flame photometer (Jenway PFP-7) was used for the determination of K. The metal concentration in the plant samples was determined with the help of atomic absorption spectrophotometer (Agilent FS 240).
Fig. 1. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on soil pH (a) and EC (b) with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
2.5. Statistical analysis All investigated parameters were statistically analyzed for two-way analysis of variance (ANOVA) using computer-based program STATISTIX 8.1. Where significant, the treatments were differentiated through Tukey-HSD test. The two-way analysis of investigated parameters is provided in Table 2.
EC remained as MSB > MS = DASB = PAS > PASB = control. The data regarding the effect of various treatments with or without P on Olsen's P concentration in soil is presented in Fig. 2. The results showed a significant interaction between treatments and P application for the Olsen's P in soil. Soil Olsen's P concentrations were higher in all treatments with P application than the same treatments without P application. Maximum P concentration was found in PASB followed by MS and MSB with P application. The DASB and PASB treatments without P application resulted higher Olsen's P than control with P application.
3. Results 3.1. Soil pH, EC and P concentration The interactive effect of various treatments and P application levels on soil pH and EC is presented in Fig. 1. There was a significant interaction effect between treatments and P levels on soil pH. The maximum value of pH was observed in MS treatment followed by the MSB and DAS. The P application did not cause any significant effect on soil pH. For soil EC, the interaction effect between soil EC and P application was non-significant. However, the treatments significantly affected the soil EC irrespective of P application. At both levels of P, the trend of soil
3.2. Plant growth The interactive effect of various treatments and P application on growth parameters is presented in Fig. 3. Except MS with P, all
Table 2 Two-way Analysis of Variance for different parameters.
P application Treatment P* treatment
Biomass
Grain yield
Plant height
P conc. shoot
P conc. root
K conc. shoot
K conc. root
Soil pH
Soil EC
Olsen's P in soil
127.24*** 57.79*** 3.01*
0.00n.s 54.13*** 3.94**
23.65*** 5.02** 3.21*
25.63*** 5.84*** 5.04***
139.00*** 8.95*** 9.66***
14.61** 6.61** 4.14**
22.81** 18.46** 4.84**
4.92* 15.84** 3.58***
0.24n.s 25.18*** 2.15n.s
983.08** 222.02** 12.25**
* = P ≤ 0.05. ** = P ≤ 0.01. *** = P ≤ 0.001. 609
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Fig. 2. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on Olsen's P in soil with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
treatments significantly increased the plant height as compared to control (Fig. 3a). Regarding total plant dry biomass, P application and biochar treatments resulted in significantly higher biomass values as compared to control, and sludges without P application (Fig. 3b). However, all sludges yielded higher biomass when compared with control treatment irrespective of P application and biochar. Similarly, the grain yield of wheat was also significantly influenced by the treatments (Fig. 3c). The P application did not cause any significant effect on all treatments including control. However, the application of sludges caused a significant increase in grain yield than control. Overall, P application, treatments and P × treatments showed a significant effect for plant height, biomass and grain yield (Table 2). 3.3. P and K concentration in plants The data regarding the P and K concentration in wheat shoot and roots is presented in Fig. 4. The P application increased the plant P uptake especially in control, DAS, DASB, PASB and MSB treatments. The maximum concentration of P was found in PASB treatment with P application. However, in all treatments, the P concentration was higher than control without P. The same trend was found for P concentration in roots. Regarding the concentration of K in wheat shoots, except DAS and DASB, none of the treatments caused any significant effect compared with the control treatment. All treatments except MS without P increased the K concentration in roots than control. Overall, P and K concentrations in shoots and roots showed significant effects among P application, treatments as well as P and treatments (Table 2).
Fig. 3. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on plant height, biomass, and grain yield with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
4. Discussion
(Table 1) which confirms the previous studies that biochar contains higher TOM especially stable organic carbon than feedstock depending upon the type of feedstock and preparation conditions (Rizwan et al., 2016). All SS and their biochars were also analyzed for total Cu, Pb, Ni and Cd concentrations and the results showed the variations in these metal concentrations in all amendments (Table 1). Variable results have been reported in literature regarding the concentrations of metal micronutrients in SS and their availability to plants (Samara et al., 2017; Sharma et al., 2018). The literature reported that the concentrations of heavy metals in the SS varies which might be due to several factors such as types of SS and soils as well as application rates (Samara et al., 2017; Sharma et al., 2018). The concentrations of toxic heavy metals such as
The SS used in our study were collected from different areas and labelled accordingly. The SS and biochars contained different concentrations of total organic matter (TOM), total N and different fractions of P concentrations (Table 1). The bioavailable P was much lower as compared to total P in all treatments used in the study. For this reason, application rates of SS should be higher as compared to commercially available fertilizers which contain most of the P as water soluble and plant available forms. Upon pyrolysis, the P concentration was increased in all sludges' biochars than their respective SS (Table 1). It is previously reported that nutrients are enriched in biochars than their respective feedstock (Rizwan et al., 2016; Igalavithana et al., 2017). Biochars contain higher TOM except MSB than respective SS 610
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Fig. 4. Effect of control, disposal area sludge (DAS), disposal area sludge biochar (DASB), populated area sludge (PAS), populated area sludge biochar (PASB), mixed sludge (MS), and mixed sludge biochar (MSB) on P and K concentrations in shoot and root with and without phosphorus application. The bars represent means ± SE of three replicates. Different letters above bars represent significant differences among treatments at P ≤ 0.05 using two-way ANOVA followed by Tukey-HSD test.
data (Samara et al., 2017). It was demonstrated that soil available P and other macronutrients increased before and after wheat harvest with the application of stabilized SS than control and the response depend upon the type of the soils, time, and rates of SS (Samara et al., 2017). In current study, Olsen's P varies with SS type and biochars (Table 1). The variations in bioavailable P concentrations with treatments might be due to variation in release of nutrients from different SS applied in the soil and the mobility of P with amendments. It was reported that P retention by soil colloids may decrease with SS application which might be due to the competition between organic ligands and phosphate on the soil surface as well as formation of soluble P complexes with humic substances in the soil (Bueno et al., 2011; Samara et al., 2017). However, this effect needs further detailed investigations in future studies. Our results also showed significant effects of SS and their biochars on plant growth attributes (Fig. 3). At no P application, the biomass and grain yield were increased with different SS or biochar treatments. Song et al. (2014) reported that biochar prepared from SS at 450 °C was suitable for the growth of garlic. Eid et al. (2017) reported that SS application increased the biomass of cucumber without showing any toxicities of heavy metals. Interestingly, at P application, the increases in biomass and grain yield were lower than SS. This might be due to the changes in soil properties with SS than P application as SS has the ability to positively affect the soil properties (Eid et al., 2017; Yue et al., 2017). Previously, it has been reported that SS can contribute nutrients to crop plants and increase the biomass and grain yield of cereals such as rice and wheat (Singh and Agrawal, 2008; Lakhdar et al., 2010; Latare et al., 2014). Similar to our results, Lemming et al. (2016) reported significant effects of SS-mixing in soil on maize growth and P uptake in a short term study. Wollmann et al. (2017) demonstrated that
Pb and Cd were below the limit of heavy metals in SS before reuse in soils for USA and European Union (Udayanga et al., 2018). The metal concentrations in biochars were slightly higher than respective SS (Table 1). It has been reported in the literature that biochar may decrease mobile forms of heavy metal in the soil (Rehman et al., 2017; Abbas et al., 2018). In addition, toxic metals such as Cd which regulate the use of SS were below the detection limit in wheat shoots. Thus, SS and biochars may be a suitable source of organic fertilizers for plant growth. Post-harvest analysis of the soil showed that the effect of treatments on soil pH, and EC depends upon the types of SS and their biochars (Fig. 1). Yue et al. (2017) demonstrated that biochar obtained from municipal SS (500 °C) decreased the soil pH while increased the soil EC and available P than control after harvesting the turf grass and reducing or enhancing trend in these parameters was higher with increasing doses of biochar applied in the alkaline soil (pH 8.7). It was demonstrated that miscanthus biochar slightly changed the pH of alkaline soil while considerably increased the pH of acidic soil (Luo et al., 2011). The application of stabilized SS increased the pH and EC of the soil before and after harvesting the wheat whereas the response varied with the type of soil (Samara et al., 2017). SS application increased the EC whereas decreased the pH of the soil than unamended soil (Sharma et al., 2018). Furthermore, the liming effects of biochars are usually observed in acidic soils (Jin et al., 2016; Rizwan et al., 2016). The decreased pH and EC of post-harvest soil with biochar application (Fig. 1) might be due to the nutrients released from biochars with time and soil type (Rizwan et al., 2016). Olsen's P concentrations depend upon the treatments applied to the soil (Fig. 2). These results are in accordance to the recently published 611
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References
fertilizers from SS might be a suitable alternate source of P than rock phosphate for enhancing plant growth and P contents but the response strongly depends upon SS preparation environment. In the present study, sewage sludges were selected from different areas while the results showed no major differences among SS for their positive effects on growth and yield as well as nutrients supply. However, their BCs differed in affecting soil properties and plant growth (Figs. 1 and 3). This might be due to the initial properties of biochars (Table 1) as well as modification of P and soil properties with biochars than SS (Figs. 1 and 2). The most important findings of present study show that these SS can be used as fertilizers either as sole application or after pyrolysis. Both sole application of SS and their respective biochars provided enough P for the plants to achieve biomass higher than conventional P-fertilizer (Figs. 3 and 4). The data of bioavailable P in soil shows that DAS and PAS did not cause any significant change in P concentration (Fig. 4). However, their biochars increased the Olsen's P in soil (Fig. 2). This might be because of pyrolysis conditions that have affected the nature of P compounds (Song et al., 2014). This shows that the SS and their biochars significantly contributed in terms of nutrient supply to wheat plants. It was reported that wheat has the ability to change P dynamics in the rhizosphere which is due to P uptake by plants and microbial activities in the soil (Arruda et al., 2017). According to Kahiluoto et al. (2015), the availability of P was higher in manure-compost than in SS. However, different treatments such as acidification increased P availability of SS in soils as well as to Italian ryegrass. They also reported that in the SS hygienized with Ca, P availability was reduced. In our study, the soil used was alkaline and calcareous in nature and this might be the possible reason of limited bioavailability of P in only SS treatments. Atienza–Martínez et al. (2014) recovered P from sewage sludge ash by pyrolysis and treating with different acids. Shiba and Ntuli (2017) extracted P from sewage sludge using sulfuric acid. The authors precipitated the leached P with different chemicals and observed the solubility tests. It was concluded that resulting precipitates can be used as P fertilizer. Our results demonstrated that P application significantly increased Olsen's P in post-harvest soil (Fig. 2) but plant growth, grain yield (Fig. 3) and shoot P concentrations (Fig. 4) were not significantly affected than SS and biochar treatments without P application. This showed that the inorganic P supply may enhance the risk of P surface runoff negatively affect the overall environmental quality.
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