Role of extracellular polymeric substances in enhancement of phosphorus release from waste activated sludge by rhamnolipid addition

This study investigated the role of extracellular polymeric substances (EPSs) in enhanced performance of phosphorus (P) release from waste activated sludge (WAS) by adding rhamnolipid (RL). Results showed that compared to WAS without pretreatment, the released PO₄^3--P increased with RL addition from 0 to 0.2g/gTSS (total suspended solid), and increased by 208% under the optimal condition (0.1gRL/gTSS and 72-h fermentation time). The cumulative PO₄^3--P was better fitted with pseudo-first-order kinetic model. Moreover, the contents of metal ions increased in liquid but decreased in EPSs linearly with RL addition increasing, and WAS solubilizations were positively correlated with the released metal ions. The enhanced total dissolved P mainly came from cells and others (69.39%, 2.27-fold higher than that from EPSs), and PO₄^3--P was the main species in both liquid and loosely bound EPSs, but organic P should be non-negligible in tightly bound EPSs.