Insights into the simultaneous nitrification, denitrification and phosphorus removal process for in situ sludge reduction and potential phosphorus recovery.

A simultaneous nitrification-denitrification and phosphorus removal (SNDPR) system operated in an alternating anaerobic/aerobic/anoxic (A/O/A) mode was revisited from new perspectives of sludge reduction and potential phosphorus recovery. Reliable and robust removal performance was obtained even under winter temperatures, with average removal efficiency of COD, TP, NH4+-N and TIN being 89.68%, 93.60%, 92.15% and 79.01% at steady state, respectively. Inoculated sludge got enhanced in biomass density, settleability, and bioactivity. And relatively stable amounts of extracellular polymeric substances (EPS) with a stable protein/ polysaccharide (PN/PS) ratio were observed over operation. Meanwhile, a low observed sludge yield (Yobs) of 0.083 g MLSS/g COD (0.082 g MLVSS/g COD) was obtained. A maximum anaerobic phosphorus release up to 43.54 mg/L was found, thus providing phosphorus-rich and low-turbidity stream for further phosphorus recovery. Overall, the SNDPR system deserved attention for in situ sludge reduction and potential phosphorus recovery, beyond reliable and stable wastewater treatment.