Ionic response of algal-bacterial granular sludge system during biological phosphorus removal from wastewater

Abstract

Biological phosphorus removal (BPR) from wastewater can be generally realized through alternative non-aeration and aeration operation to create anaerobic and aerobic conditions respectively for P release and uptake/accumulation by polyphosphate accumulating organisms (PAOs), with P removal finally achieved by controlled discharge of P-rich sludge. In this study, the response of algal-bacterial aerobic granular sludge (AB-AGS) during BPR to main ions including Ac− (acetate), Cl−, SO42−, NH4+, K+, Mg2+, Ca2+ and Na+ in wastewater was investigated with conventional bacterial AGS (B-AGS) as control and acetate as the sole carbon source. Results show that BPR process mainly involved the changes of Ac−, K+, Mg2+, and Ca2+ rather than Cl−, SO42−, NH4+ and Na+. The mole ratio of ΔP/ΔAc kept almost unchanged during the non-aeration (P release) phase in both B-AGS and AB-AGS systems (ΔPB-AGS/ΔAcB-AGS > ΔPAB-AGS/ΔAcAB-AGS), and it was negatively influenced by the light in AB-AGS systems, in which 62% of acetate was not utilized for P release at the high illuminance of 81 k lux. During the entire non-aeration/aeration period, both ΔK/ΔP and ΔMg/ΔP remained constant, while ΔKAB-AGS/ΔPAB-AGS > ΔKB-AGS/ΔPB-AGS and ΔMgAB-AGS/ΔPAB-AGS ≈ ΔMgB-AGS/ΔPB-AGS. The presence of algae seemed not beneficial for PAOs to remove P, while more K+ and P uptake by algae in AB-AGS suggest its great potential for manufacturing biofertilizer.