title: Electroflotation clarifier to enhance nitrogen removal in a two-stage alternating aeration bioreactor.
abstract: Stringent water treatment criteria and rapidly growing pollutant loads provoke the demand for retrofitting wastewater treatment plants towards a higher capacity. In this study, we assess a two stage alternating aeration (AA) bioreactor equipped with electroflotation (EF) clarifier, for nitrogen removal within a short hydraulic retention time (HRT). The EF under steady solids loading required a minimum unit height and gas: solids ratio of 0.006 for efficient clarification. The separated sludge blanket was further thickened with retaining stability when the cyclic solids loading was smaller than 1.0 kg m(-2). In the continuous operation of the bioreactor, the returned activated sludge concentration increased to more than 18,000 mg L(-1), while the effluent suspended solids concentration was lowered below 5 mg L(-1). Under influent chemical oxygen demand (COD)/total inorganic nitrogen (TIN) concentration of 300/30 mg L(-1), the TIN removal efficiency was near 70% with cycle time ratios of 0.17 and 0.27. Under higher influent COD concentration of 500mg L(-1), TIN removal efficiency was found to be 73.4% at a carbon:nitrogen (C:N) ratio of 10 and even higher (80.4%) at a C:N ratio of 16.6. The increased mixed liquor suspended solids concentrations (> 6000 mg L(-1)) under the high COD loading were efficiently maintained by using the EF clarifier. The results of this study demonstrate that an EF clarifier with a HRT of less than 1 h can support reliable nitrogen removal in the AA process that has a HRT of 6 h, even under increasing influent loadings.
authors: Linde-Robinson Laboratories, California Institute of Technology, Pasadena, CA, USA.
authors: Kangwoo
authors: K
authors: Cho
authors: Department of Urban Engineering, The University of Tokyo, Bunkyo, Tokyo, Japan.
authors: Chong Min
authors: CM
authors: Chung
authors: R&D Center, POSCO E&C, Younsugu, Incheon, Republic of Korea.
authors: Yun Jung
authors: YJ
authors: Kim
authors: Linde-Robinson Laboratories, California Institute of Technology, Pasadena, CA, USA.
authors: Michael R
authors: MR
authors: Hoffmann
authors: Department of Civil and Environmental Engineering, Seoul National University, Gwanak-gu, Seoul, Republic of Korea.
authors: Tai Hak
authors: TH
authors: Chung
mesh_terms: D019149:Bioreactors / Q000382:microbiology; D055664:Electrochemical Techniques / Q000295:instrumentation*; D004867:Equipment Design; D009584:Nitrogen / Q000302:isolation & purification*; D012722:Sewage / Q000032:analysis* / Q000382:microbiology; D018508:Water Purification / Q000295:instrumentation*
chemical_list: D012722:Sewage; D009584:Nitrogen