title: Nitrogen reduction in wastewater treatment using different anox-circulation flow rates and ethanol as a carbon source.
abstract: We studied the optimization of nitrogen reduction from municipal wastewater in a laboratory-scale modified Ludzack-Ettinger activated sludge wastewater treatment plant (WWTP). The unit consisted of primary denitrification, secondary nitrification, a sludge clarifier and a post-denitrification unit. The process simulates the Kuopio WWTP, which provided the influent utilized. We describe the effect of varying anox-circulation schemes on the nitrogen removal efficiency. We further compare the denitrification efficiencies of ethanol and methanol applied in the post-denitrification unit, and compare the properties and costs of these chemicals as carbon sources. Maximum efficiency of total nitrogen removal (70.8%) was obtained with 256% anox-circulation. The process was, however, not very sensitive, as a wide range of 150-400% of anox-circulations gave good results for nitrogen reduction. The unit achieved high BOD, and COD reductions of wastewater also when nitrogen reduction was moderate. The addition of 40 mg/L/day of ethanol to the post-denitrification tank meant that the nitrate-levels of effluent could be controlled to below 10 mg/L of nitrate nitrogen. Methanol and ethanol were equally effective for denitrification. The use of ethanol instead of methanol could reduce treatment costs by 30% to 0.02 E/m3 of treated wastewater according to 2008 market prices.
authors.affiliation: Department of Environmental Science, University of Eastern Finland, Finland. hannu.poutiainen@uef.fi
authors.forename: H
authors.initials: H
authors.lastname: Poutiainen
authors.forename: S
authors.initials: S
authors.lastname: Laitinen
authors.forename: S
authors.initials: S
authors.lastname: Pradhan
authors.forename: M
authors.initials: M
authors.lastname: Pessi
authors.forename: H
authors.initials: H
authors.lastname: Heinonen-Tanski
mesh_terms: D001420:Bacteria, Aerobic / Q000502:physiology*; D001673:Biodegradation, Environmental; D002244:Carbon / Q000737:chemistry; D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D000431:Ethanol / Q000378:metabolism*; D008954:Models, Biological; D009584:Nitrogen / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D012212:Rheology / Q000295:instrumentation*; D012722:Sewage / Q000382:microbiology*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification / Q000378:metabolism*; D018508:Water Purification / Q000295:instrumentation*
chemical_list: D012722:Sewage; D014874:Water Pollutants, Chemical; D000431:Ethanol; D002244:Carbon; D009584:Nitrogen