Effect of complexing agents on phosphorus release from chemical-enhanced phosphorus removal sludge during anaerobic fermentation

Phosphorus (P) release from sludge containing phosphate precipitates (FePs or AlPs) as well as the anaerobic performance with the addition of complexing agents (citric, tartaric and EDTA) during ambient anaerobic fermentation process were investigated. Results showed that citrate addition was the most effective method to enhance P release from inorganic phosphate by chelation and promote volatile fatty acids (VFAs) production simultaneously during anaerobic fermentation. Equimolar citrate addition with chemical precipitates was the optimal dosage. Microbial analysis revealed that EDTA has the strongest inhibitory effect on microbial activity and community structure, while citrate was more effective in enhancing important acidifying microorganisms than tartrate and EDTA. Therefore, citrate addition can be regarded as an alternative and promising method to recover P and carbon source from sludge containing chemical precipitates. These important discoveries will help to enrich P recovery path from sludge produced in the chemical-enhanced P removal treatment processes.