Enhanced biological phosphorus removal in the retrofitting from an anoxic selector to an anaerobic selector in a full-scale activated sludge process in Singapore

摘要

This paper presents the investigation results of retrofitting an anoxic selector to an anaerobicnselector through stepwise reduction of air supply in a full-scale activated sludge process with anfocus on enhanced biological phosphorus removal (EBPR). The process experienced gradual shiftnfrom a Ludzack-Ettinger (LE) to an anaerobic-anoxic-oxic (A2O) process and subsequently, annanaerobic-oxic (A/O) process. The major findings are: (i) the average influent-based PO32n4 -Pnrelease in the anaerobic selector compartment was 16.3mg P l 21 and that in the secondarynclarifier was 1.7mg P l 21. 75% of the SCOD and 93% of the acetic acid in the primary effluentnwere taken up in the anaerobic selector compartment, respectively; (ii) PO32n4 -P uptakencontributed by both aerobic and denitrifying phosphorus accumulating organisms (DPAOs)noccurred mainly in the first and second aerobic lanes together with simultaneous nitrification andndenitrification (SND) while there was not much contribution from the last aerobic lane; (iii) Thenaverage PO32n4 -P concentration of the final effluent was 2.4mg P l 21 corresponding to a removalnefficiency of 85%; (iv) the SVI was satisfactory after retrofitting; and (v) the increase of NHtn4 -N innthe final effluent from the commencement to the completion of the retrofitting resulted in annapproximate 40–50% reduction in oxygen demand and a significant aeration energy saving wasnachieved.