title: Performance analysis of anoxic selector in upgrading activated sludge process in tropical climate.
abstract: The paper describes and analyses the performance of anoxic selectors in upgrading activated sludge process in a municipal wastewater treatment plant under tropical climate, where poor sludge settleability is a problem due to elevated temperature. Site monitoring and laboratory experiment were conducted to study the denitrification, sludge settleability, kinetics, mass balance, pH and alkalinity variation in the system. The sludge settleability measured in Sludge Volume Index (SVI) was observed to improve with the increasing degree of denitrification in the anoxic selector. Under well-developed stable state, an average SVI value of 136 ml/g was achieved, which was significantly lower than the value of 250 ml/g before the application of anoxic selector. The specific reaction rates for denitrification and nitrification at 30 degrees C were 0.06 mg NO3-N/mg MLSS day and 0.08 mg NH4-N/mg MLSS day, respectively. The overall efficiencies of nitrification and denitrification were 86 percent and 55.4 percent, respectively, with an alkalinity recovery ratio of 15.4 percent. 32 percent of total COD removed was used up as electron donor in the denitrification process. However, due to absence of the internal Mixed Liquor Recirculation (MLR), a higher degree of denitrification occurred in the secondary sedimentation tank than in the anoxic zone. Issues for further studies are also discussed.
authors.affiliation: The Centre for Advanced Water Technology (CAWT), the Singapore Utilities International Ltd (SUI), Innovation Centre (NTU), Block 2, Unit 237, 18 Nanyang Drive, Singapore. yscao@cawt.sui.org.sg
authors.forename: Y S
authors.initials: YS
authors.lastname: Cao
authors.forename: K H
authors.initials: KH
authors.lastname: Teo
authors.forename: W A
authors.initials: WA
authors.lastname: Yuen
authors.forename: W Y
authors.initials: WY
authors.lastname: Long
authors.forename: B
authors.initials: B
authors.lastname: Seah
mesh_terms: D000641:Ammonia / Q000032:analysis; D001420:Bacteria, Aerobic / Q000378:metabolism; D019149:Bioreactors; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009566:Nitrates / Q000032:analysis / Q000302:isolation & purification; D012722:Sewage / Q000737:chemistry*; D014329:Tropical Climate; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D009566:Nitrates; D012722:Sewage; D000641:Ammonia