Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments
Introduction
The production of sewage sludge has gradually increased as the sewage treatment capacity has improved. Therefore, the problem of sewage sludge treatment and disposal must be urgently addressed (Robledo-Mahón et al., 2019). Sewage sludge is rich in inorganic nutrients and organic matter (OM), and it can be used as an organic fertilizer and soil amendment (Janowska et al., 2017). However, sewage sludge contains a high moisture content, and the application of improperly treated sewage sludge to soil may lead to the risk of the introduction of pathogens, heavy metals, organic pollutants, and other pollutants (Armstrong et al., 2018; Boruszko, 2017; Ignatowicz, 2017).
Composting is an efficient and cost-effective method for sewage sludge treatment; it can realize the removal of water, degradation of harmful substances, and passivation of heavy metals during sewage sludge composting. In addition, it can recover nutrients and energy (Ke et al., 2015). However, NH3 and N2O are usually produced and released during composting, which not only causes N loss but also causes environmental pollution (Maeda et al., 2018). Previous studies indicated that phosphate amendments, such as superphosphate, phosphogypsum, and calcium magnesium phosphate (CMP), can promote the degradation of OM, reduce N loss, and improve compost maturity and quality during pig manure composting (Li et al., 2018; Wu et al., 2019).
Since the heavy metal elements in sewage sludge are from sewage and always bioavailable and they cannot be degraded or evaporated during composting, the passivation method, which transfers heavy metals from the bioavailable phase to stable phases, was used to reduce the environmental risks of heavy metals. Phosphate amendments are known to be effective in the immobilization of heavy metals, including Pb, Cd, Zn, Cu, and Ni, and they are widely used in the remediation of heavy metal contamination in soil (Valipour et al., 2016). In addition, the use of phosphate to immobilize heavy metals in contaminated soil or water is comparatively economical and highly effective when suitable phosphate amendments are used (Seshadri et al., 2017). A previous study found that phosphate rock (PR) can enhance the efficiency of municipal solid waste composting and reduce the contents of water-soluble Zn, Pb, Cu, and Cd (Iqbal et al., 2010). Another study showed that PR can passivate Pb and Cd during sewage sludge vermicomposting (Wang et al., 2013). Our previous study showed that CMP and monopotassium phosphate (MKP) can passivate Cd, Zn, Cu, and Pb during sewage sludge and sawdust composting (Wang et al., 2019b). However, the comparison of the passivation effects as well as the passivation mechanisms of PR, CMP, and MKP during composting is still unclear.
Although previous studies have proven that the amendment of phosphate can promote N preservation and heavy metal passivation during the composting process, there is a lack of research on the transformation of phosphate amendments during the composting process. X-ray absorption near-edge structure (XANES) spectroscopy is an in situ and non-destructive spectroscopic technique that provides the greatest potential for directly characterizing inorganic P species at molecular levels, even when poorly ordered mineral phases are present (Luo et al., 2017). It has been used to evaluate P speciation in long-term organic fertilizer-amended soils (Schmieder et al., 2018; Yamamoto et al., 2018). It is expected to provide spectroscopic evidence for the effects of phosphate amendments and new insights into the change in P speciation during sewage sludge composting.
In this study, PR, CMP, and MKP were selected as the target phosphate amendments to improve the composting efficiency as well as passivate heavy metals. The objectives of this study were to 1) illustrate the performance of target phosphate amendments for heavy metal passivation and nutrient enhancement, 2) illustrate the possible mechanism of passivation during composting and the changes in P speciation, 3) investigate the effects of the target phosphate amendments on the physicochemical properties of the composting process, and 4) confirm the safety of the applied compost as a soil amendment.
Section snippets
Composting materials
Dewatered sewage sludge was collected from a municipal wastewater treatment plant in Wuhan, China. Spent mushroom substrate obtained from a mushroom farm in Wuhan was used as an organic bulking agent. Perlite was used as an inorganic bulking agent, and it was purchased from Xinyang, China (Yusheng Perlite Co., Ltd.). PR, CMP, and MKP were purchased from a fertilizer shop in Suzhou, China. The physical and chemical characteristics of the raw materials are displayed in Table 1.
Composting process
The sewage sludge,
Changes in the Cd and Pb concentrations
The distribution of different fractions of Cd and Pb in compost is shown in Fig. 1. Heavy metals in the exchangeable and reducible fractions are generally considered mobile and bioavailable, and exchangeable fractions possess the highest mobility and bioavailability among the four extraction fractions (Zhou et al., 2018).
Cd is one of the most mobile heavy metals in soil, and it is always the restrictive factor for the land application of sewage sludge (Hanc et al., 2009). According to Fig. 1A,
Conclusions
Three phosphate amendments were added to the sewage sludge composting process to obtain a higher quality compost. The addition of PR and MKP had a good passivation effect on Cd and Pb during sewage sludge composting. In addition, the XRD pattern showed that phosphate amendments promoted the formation of phosphate precipitation, and the XANES spectra showed that phosphate amendments changed the speciation of P. Although the addition of these phosphate amendments had little effect on the
CRediT authorship contribution statement
Guodi Zheng: Methodology, Writing - review & editing. Xiankai Wang: Data curation, Writing - original draft. Tongbin Chen: Writing - original draft, Methodology, Supervision. Jun Yang: Data curation, Writing - review & editing. Junxing Yang: Data curation, Writing - review & editing. Junwan Liu: Formal analysis, Data curation, Writing - original draft. Xiaoxiao Shi: Data curation, Writing - original draft.
Declaration of competing interest
We declare no conflicts of interest.
Acknowledgements
This work was supported by the National Key Research and Development Program of China (2018YFD0800601) and the National Natural Science Foundation of China (41371455). We thank the staff at beamline 4B7A of the Beijing Synchrotron Radiation Facility for the collection of P K-edge XANES data. We also thank Dr. Lei Luo at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences for the help during the XANES analysis.
References (39)
- et al.
Lead and copper immobilization in a shooting range soil using soybean stover- and pine needle-derived biochars: chemical, microbial and spectroscopic assessments
J. Hazard Mater.
(2016) - et al.
Degradation of triclosan and triclocarban and formation of transformation products in activated sludge using benchtop bioreactors
Environ. Res.
(2018) Research on the influence of anaerobic stabilization of various dairy sewage sludge on biodegradation of polycyclic aromatic hydrocarbons PAHs with the use of effective microorganisms
Environ. Res.
(2017)- et al.
Total concentrations and speciation of heavy metals in municipal sludge from Changsha, Zhuzhou and Xiangtan in middle-south region of China
J. Hazard Mater.
(2008) - et al.
Protein and carbohydrate drive microbial responses in diverse ways during different animal manures composting
Bioresour. Technol.
(2019) - et al.
Assessment contributions of physicochemical properties and bacterial community to mitigate the bioavailability of heavy metals during composting based on structural equation models
Bioresour. Technol.
(2019) - et al.
Changes in cadmium mobility during composting and after soil application
Waste Manag.
(2009) The impact of sewage sludge treatment on the content of selected heavy metals and their fractions
Environ. Res.
(2017)- et al.
Effect of enrichment on chemical properties of MSW compost
Bioresour. Technol.
(2010) - et al.
Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts
Environ. Res.
(2017)
Performance of phosphogypsum and calcium magnesium phosphate fertilizer for nitrogen conservation in pig manure composting
Bioresour. Technol.
Phosphorus speciation in sewage sludge and the sludge-derived biochar by a combination of experimental methods and theoretical simulation
Water Res.
Nutrient transformations during composting of pig manure with bentonite
Bioresour. Technol.
Biochars induced modification of dissolved organic matter (DOM) in soil and its impact on mobility and bioaccumulation of arsenic and cadmium
J. Hazard Mater.
Effects of biochar on nitrogen transformation and heavy metals in sludge composting
Bioresour. Technol.
Speciation of Cu and Zn during composting of pig manure amended with rock phosphate
Waste Manag.
Response of the denitrifier community and its relationship with multiple N2O emission peaks after mature compost addition into dairy manure compost with forced aeration
Chemosphere
Sewage sludge composting under semi-permeable film at full-scale: evaluation of odour emissions and relationships between microbiological activities and physico-chemical variables
Environ. Res.
New advancement perspectives of chloride additives on enhanced heavy metals removal and phosphorus fixation during thermal processing of sewage sludge
J. Clean. Prod.
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