Mechanistic insights into chemical conditioning on transformation of dissolved organic matter and plant biostimulants production during sludge aerobic composting

• Published in: Water research (Oxford) Vol. 255; p. 121446
• Main Authors: Zhang, Yu, Yang, Boyuan, Peng, Siwei, Zhang, Ziwei, Cai, Siying, Yu, Junxia, Wang, Dongsheng, Zhang, Weijun
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.05.2024
• Subjects: Composting; Humification; Poly aluminum chloride; Poly ferric sulfate; Sludge treatment; Humification; Composting; Poly aluminum chloride; Sludge treatment; Poly ferric sulfate
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2024.121446

•PAC conditioning inhibited composting microbiomes with a decreased enzymatic reaction.•PFS conditioning increased the content of humification intermediate-indole.•PFS conditioning increased humic acid and indoleacetic acid content in the compost.•PFS conditioning changed the dominant humification occurrence stage during composting.•PAC conditioning declined compost quality, while PFS dosage increased compost quality. Inorganic coagulants (aluminum and iron salt) are widely used to improve sludge dewaterability, resulting in numerous residues in dewatered sludge. Composting refers to the controlled microbial process that converts organic wastes into fertilizer, and coagulant residues in dewatered sludge can affect subsequent compost efficiency and resource recycling, which remains unclear. This work investigated the effects of two typical metal salt coagulants (poly aluminum chloride [PAC] and poly ferric sulfate [PFS]) conditioning on sludge compost. Our results revealed that PAC conditioning inhibited composting with decreased peak temperature, microbial richness, enzymatic reaction intensities, and compost quality, associated with decreased pH and microbial toxicity of aluminum. Nevertheless, PFS conditioning selectively enriched Pseudoxanthomonas sp. and resulted in more fertile compost with increased peak temperature, enzymatic reaction intensities, and humification degree. Spectroscopy and mass difference analyses indicated that PFS conditioning enhanced reaction intensities of labile biopolymers at the thermophilic stage, mainly comprising hydrolyzation (H2O), dehydrogenation (-H2, -H4), oxidation (+O1H2), and other reactions (i.e., +CH2, C2H4O1, C2H6O1). Unlike the common composting process primarily conducts humification at the cooling stage, PFS conditioning changed the main occurrence stage to the thermophilic stage. Non-targeted metabolomics revealed that indole (a humification intermediate) is responsible for the increased humification degree and indoleacetic acid content in the PFS-conditioned compost, which then promoted compost quality. Plant growth experiments further confirmed that the dissolved organic matter (DOM) in PFS-conditioned compost produced the maximum plant biomass. This study provided molecular-level evidence that PFS conditioning can promote humification and compost fertility during sludge composting, enabling chemical conditioning optimization for sustainable management of sludge. [Display omitted]