Performance and mechanism of enhanced phosphorus release and volatile fatty acid production from Fe-P sludge via co-fermenting with agricultural wastes

Anaerobic fermentation is an efficient method to extract phosphorus from excess sludge, thereby facilitating its recovery and mitigating the phosphorus resource shortage. However, the prevalent metal-bound phosphorus species within sludge was difficult to release into the fermentation liquor. To address this, this study evaluated the enhanced phosphorus release performance from sludge containing iron-phosphorus compounds (Fe-P) via co-fermenting it with agriculture wastes. Specifically, protein-rich feather (Feather Group) and polysaccharide-rich tea residue (Tea Group) was respectively dosed into batch-scale fermentation jar. Results showed that the Feather Group exhibited significantly higher levels of released soluble phosphorus (2.1 folds) and volatile fatty acids (41.4 folds) compared to the Control Group, with concentrations reaching up to 280 mg/L and 9366 mg chemical oxygen demand /L, respectively. The activities of α-glucosidase, neutral protease and acetate kinase in the Feather group were increased by 11.1 %, 92.3 % and 37.6 %, respectively, compared with the Control group. Methanogen abundance decreased while hydrolytic acid-producing bacteria and iron-reducing bacteria increased significantly after supplying agricultural wastes. Metagenomic analysis demonstrated a significant increase in genes related to acetic acid synthesis. Mechanism elucidation suggested that increased iron-reducing bacteria abundance promoted Fe 3+ reduction into Fe 2+, thus enhancing phosphorus release from Fe-P compounds. This work may provide valuable information for developing effective strategy to extract phosphorus resource from complex environmental wastes.