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

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, SO, NH, K, Mg, Ca 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, Mg, and Ca rather than Cl, SO, NH 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 (ΔP/ΔAc > ΔP/ΔAc), 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 ΔK/ΔP > ΔK/ΔP and ΔMg/ΔP ≈ ΔMg/ΔP. 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.