Behavior of heavy metals in municipal sludge during dewatering: The role of conditioners and extracellular polymeric substances

• Published in: Journal of environmental management 2023-09, Vol.342, p.118287-118287, Article 118287
• Main Authors: Guo, Zhiying, Ma, Liping, Dai, Quxiu, Liu, Yanhong, Zhang, Degang, Ao, Ran
• Format: Article
• Language: English
• Subjects: Extracellular Polymeric Substance Matrix; Heavy metal fraction; Metals, Heavy; Protein; Risk assessment; Secondary structure; Sewage - chemistry; Waste Disposal, Fluid - methods; Water - chemistry; Zea mays; β-Sheet
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2023.118287

Heavy metals, the main harmful substances in the sludge, are easily enriched, have adverse effects on the treatment and disposal of the sludge. In this study, two conditioners (modified corn-core powder, MCCP, and sludge-based biochar, SBB) were separately added and jointly added into municipal sludge to enhance sludge dewaterability. Meanwhile, diverse organics, such as extracellular polymeric substances (EPS), were released under pretreatment. The different organics had different effects on each heavy metal fraction and changed the toxicity and bioavailability of the treated sludge. The exchangeable fraction (F4) and carbonate fraction (F5) of heavy metal were nontoxic and nonbioavailable. When MCCP/SBB was used to pretreat the sludge, the ratio of metal-F4 and -F5 decreased, indicating that MCCP/SBB reduced the biological availability and ecological toxicity of the heavy metals in the sludge. These results were consistent with the calculation of the modified potential ecological risk index (MRI). To understand the detailed function of organics in the sludge network, the relationship between EPS, the secondary structure of the protein, and heavy metals was analyzed. The analyses revealed that the increasing proportion of β-sheet in soluble EPS (S-EPS) generated more active sites in the sludge system, which enhanced the chelate or complex function among organics and heavy metals, thus reducing the migration risks. •Modified corn-core powder (MCCP) could fix metals to form oxidizable fraction.•Sludge-based biochar (SBB) fixed heavy metals with MCCP, synergistically.•Modified potential ecological risk index of metals decreased after adding MCCP/SBB.•Protein had a significant effect on the fixation of heavy metals.•β-Sheet could bring sites into sludge to enhance the fixation of heavy metals.