title: Effect of recycle-to-influent ratio on activities of nitrifiers and denitrifiers in a combined UASB-activated sludge reactor system.
abstract: A laboratory study using a combined upflow anaerobic sludge bed (UASB)-activated sludge (AS) reactor system was undertaken to explore the effect of recycle-to-influent ratio (R(e)=1, 2, and 3) on the activities of nitrifiers and denitrifiers. Suspended-solids pre-settled piggery wastewater was used as the substrate-feed wastewater. At the R(e) of 1-3, the combined reactor system achieved efficient removal of COD (96-97%), TKN (100%) and total nitrogen TN (54-77%). Methanogenesis occurred with nearly-complete denitrification in the UASB reactor, whereas complete nitrification took place in the AS reactor. A higher R(e) (i.e., accompanied with a shorter solids retention time) resulted in a larger amount of high-activity denitrifiers and thereby achieved a higher TN removal efficiency. Compact granules and a high biomass concentration in the UASB reactor were observed. At the R(e) of 1-3, the maximum specific reaction rate of nitrifiers (0.45-0.49 NH(4)(+)-NmgVSS(-1)d(-1)) and the specific nitrification rates of mixed culture (0.18-0.22mg NH(4)(+)-NmgVSS(-1)d(-1)) in the AS reactor varied slightly; whereas the maximum specific reaction rate of denitrifiers (0.18-0.27mg NO(x)(-)-NmgVSS(-1)d(-1)) and the specific denitrification and COD removal rates of mixed culture (0.025-0.050mg NO(x)(-)-NmgVSS(-1)d(-1); 0.24-0.31mgCODmgVSS(-1)d(-1)) in the UASB reactor increased with increasing R(e). The primary finding of the study is that the combined UASB-AS reactor system should be operated at a higher R(e) to maintain high-activity denitrifiers to remove organic materials and nitrogen from piggery wastewater.
authors.affiliation: Department of Environmental Engineering, Kun Shan University, Tainan County 710, Taiwan, ROC.
authors.forename: Ju-Sheng
authors.initials: JS
authors.lastname: Huang
authors.forename: Hsin-Hsien
authors.initials: HH
authors.lastname: Chou
authors.forename: Chih-Ming
authors.initials: CM
authors.lastname: Chen
authors.forename: Chun-Mao
authors.initials: CM
authors.lastname: Chiang
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors; D007220:Industrial Waste; D009566:Nitrates / Q000378:metabolism*; D012722:Sewage / Q000382:microbiology*; D013552:Swine; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D007220:Industrial Waste; D009566:Nitrates; D012722:Sewage