Analysis of phosphorus removal and anaerobic selector performance in a full-scale activated sludge process in Singapore

Abstract

This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed.

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

“…The bulk of the propanoic acid and isobutyric acid also reduced in the anaerobic selector, which was similar to what was observed in Jurong WRP (Cao et al 2006). Given the data for PO 32 4 -P release and acetic acid uptake, the ratio of PO 32 4 -P release to acetic acid uptake in the anaerobic selector was 0.69 mol P (mol C) 21 , which was .…”

“…4 -P release, 3.9 mg PO 32 4 -P (g COD MLSS .h) 21 ; acetic acid uptake, 5.6 mg CH 3 COOH (g COD MLSS .h) 21 and SCOD uptake, 30.1 mg COD (g COD MLSS .h) 21 . The average PO 32 4 -P release to SCOD uptake ratio was 0.13 mg PO 32 4 -P (mg COD) 21 , which was lower than the reported range of 0.23-0.73 mg PO 32 4 -P (mg COD) 21 for municipal sewage treatment (Smolders et al 1994), but higher than 0.08 mg PO 32 4 -P (mg COD) 21 obtained for Jurong WRP (Cao et al 2006), and indicated that approximately 7.7 mg SCOD was taken up per mg of PO 32 4 -P release in the anaerobic selector. No regular correlations between PO 32 4 -P release and SCOD of the primary effluent and that between PO 32 4 -P release and SCOD uptake in the anaerobic selector were found.…”

“…All samples were kept in an environment at a temperature ,48C. For the analytical details, see Cao et al (2006).…”

“…It was reported that, compared to the conventional activated sludge process, savings in aeration energy of up to 30% might be achieved through anaerobic stabilization (ANS) as a result of COD uptake in an anaerobic environment (Wable & Randall 1994;Reusser 2005). The full-scale application of the anaerobic selector technology in Singapore was initially pioneered in Jurong WRP for verifying the effects of anaerobic selector on improvement to sludge settleability, suppression of foaming and aeration energy saving (Cao et al 2006). Aiming at energy saving (due to the oxygen demand reduction through the phasing out of nitrification and anaerobic stabilization), the anoxic selector of Kim Chuan WRP was retrofitted into an anaerobic selector.…”

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.…”