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

Abstract

This paper presents the investigation results of retrofitting an anoxic selector to an anaerobic selector through stepwise reduction of air supply in a full-scale activated sludge process with a focus on enhanced biological phosphorus removal (EBPR). The process experienced gradual shift from a Ludzack-Ettinger (LE) to an anaerobic-anoxic-oxic (A(2)O) process and subsequently, an anaerobic-oxic (A/O) process. The major findings are: (i) the average influent-based PO(4) (3-)-P release in the anaerobic selector compartment was 16.3 mg P l(-1) and that in the secondary clarifier was 1.7 mg P l(-1). 75% of the SCOD and 93% of the acetic acid in the primary effluent were taken up in the anaerobic selector compartment, respectively; (ii) PO(4) (3-)-P uptake contributed by both aerobic and denitrifying phosphorus accumulating organisms (DPAOs) occurred mainly in the first and second aerobic lanes together with simultaneous nitrification and denitrification (SND) while there was not much contribution from the last aerobic lane; (iii) The average PO(4) (3-)-P concentration of the final effluent was 2.4 mg P l(-1) corresponding to a removal efficiency of 85%; (iv) the SVI was satisfactory after retrofitting; and (v) the increase of NH(4) (+)-N in the final effluent from the commencement to the completion of the retrofitting resulted in an approximate 40-50% reduction in oxygen demand and a significant aeration energy saving was achieved.

Experimental Methods in Wastewater Treatment

“…Usually, most of the tests are executed around 20 °C, but it can be as low as 5 ºC (to assess the biomass activity under winter/cold climate conditions) or as high as 30 -35 °C for tropical conditions or industrial applications (Cao et al, 2009;Ong et al, 2014), and even up to 55 °C for thermophilic conditions (Lopez-Vazquez et al, 2014). Tests are rarely performed below 5 °C because in practice the temperature of municipal wastewater is seldom colder and is usually around 7 -12 °C.…”

“…While extensive research has been advocated to assess the temperature dependencies of EBPR cultures, suggesting that temperatures lower than 20 °C enhance the growth of PAOs whereas higher temperatures favour the development of GAOs (Brdjanovic et al, , 1998bLopez-Vazquez et al, 2009a), certain observations have indicated that stable EBPR systems can operate at temperatures higher than 25 °C (Cao et al, 2009). Though case-specific combinations between wastewater composition, operating and environmental conditions will play a major role, the long-term operation and acclimatization of EBPR cultures to those particular conditions can also lead to the development and enrichment of PAO cultures (or similar organisms sharing the PAOs' phenotype) capable of performing stable EBPR at a higher temperature.…”

Use of an aerobic selector to overcome filamentous bulking in an activated sludge wastewater treatment plant

“…[9,12] The anaerobic selectors generally showed good performances in controlling filamentous bacteria when treating both municipal and industrial wastewaters, namely when bulking occurred following Type 0041 overgrowth. [10] Other authors refer the advantages of using selectors to enhance phosphorous removal under anaerobic conditions [14][15][16] or even in the optimization of the general depuration process, [17] including the energy saving of aeration consumption by allowing the lowering of dissolved oxygen (DO) in the tanks. [10] The main objective of this research was the use of an aerobic selector to improve the performance of an urban wastewater treatment plant (WWTP), located in North of Portugal, receiving domestic wastewater with irregular industrial discharges and, consequently, suffering from severe problems of bulking.…”