title: High-rate activated sludge system for carbon management--Evaluation of crucial process mechanisms and design parameters.
abstract: The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redirection of organics from wastewater to energy generating processes in an efficient manner. A HRAS pilot plant was operated under controlled conditions resulting in concentrating the influent particulate, colloidal, and soluble COD to a waste solids stream with minimal energy input by maximizing sludge production, bacterial storage, and bioflocculation. The impact of important process parameters such as solids retention time (SRT), hydraulic residence time (HRT) and dissolved oxygen (DO) levels on the performance of a HRAS system was demonstrated in a pilot study. The results showed that maximum removal efficiencies of soluble COD were reached at a DO > 0.3 mg O2/L, SRT > 0.5 days and HRT > 15 min which indicates that minimizing the oxidation of the soluble COD in the high-rate activated sludge process is difficult. The study of DO, SRT and HRT exhibited high degree of impact on the colloidal and particulate COD removal. Thus, more attention should be focused on controlling the removal of these COD fractions. Colloidal COD removal plateaued at a DO > 0.7 mg O2/L, SRT > 1.5 days and HRT > 30 min, similar to particulate COD removal. Concurrent increase in extracellular polymers (EPS) production in the reactor and the association of particulate and colloidal material into sludge flocs (bioflocculation) indicated carbon capture by biomass. The SRT impacted the overall mass and energy balance of the high-rate process indicating that at low SRT conditions, lower COD mineralization or loss of COD content occurred. In addition, the lower SRT conditions resulted in higher sludge yields and higher COD content in the WAS.
authors.affiliation: Brown and Caldwell, 2301 Lucien Way, Suite 250, Maitland, FL, USA. Electronic address: jjimenez@brwncald.com.
authors.forename: Jose
authors.initials: J
authors.lastname: Jimenez
authors.affiliation: Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Miller
authors.affiliation: Hampton Road Sanitation District, 1436 Air Rail Avenue, Virginia Beach, VA, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Bott
authors.affiliation: DC Water, 5000 Overlook Avenue, Washington, DC, USA.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Murthy
authors.affiliation: DC Water, 5000 Overlook Avenue, Washington, DC, USA.
authors.forename: Haydee
authors.initials: H
authors.lastname: De Clippeleir
authors.affiliation: ARA Consult, Unterbergerstraße, 6020 Innsbruck, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Wett
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D019149:Bioreactors; D002244:Carbon / Q000378:metabolism*; D003080:Cold Temperature; D010100:Oxygen / Q000032:analysis*; D010865:Pilot Projects; D012722:Sewage / Q000032:analysis*; D013997:Time Factors; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D012722:Sewage; D002244:Carbon; D010100:Oxygen
keywords: A-stage; Activated sludge; Bioflocculation; Biosorption; Energy; High-rate treatment