Enhancing phosphorus recovery from efficient acidogenic fermentation of waste activated sludge with acidic cation exchange resin pretreatment: Insights from occurrence states and transformation.

Achieving phosphorus (P) recovery during treatment and disposal of waste activated sludge (WAS) by anaerobic-based processes has received increasing attention. To solve the problem of low phosphorus release efficiency, anaerobic fermentation (AF) combined with acidic cation exchange resin (ACER) pretreatment was first proposed in this study. Results showed that the isoelectric point pretreatment with ACER increased the recoverable phosphorus content by 2.3 times compared to that without ACER pretreatment. Phosphorus transformation was systematically analyzed from a whole-process perspective, and the results visually revealed that the release of phosphorus during the conventional AF process (without ACER pretreatment) was limited by insufficient phosphorus release from extracellular polymeric substances (EPS) and mineral precipitation, as well as the reprecipitation of soluble phosphorus with metals. ACER enabled effective dissolution of mineral phosphorus by acidifying WAS. On the other hand, ACER adsorbed metals to promote EPS disintegration and hydrolysis, thereby enhancing the release of EPS-bound P, which also reduced the reprecipitation of soluble phosphorus during AF. Furthermore, ACER pretreatment increased volatile fatty acids production by >2-fold with enhanced sludge hydrolysis. This finding has important implications for both non-renewable phosphorus recovery and sludge resource recovery.