Abstract
A pilot-scale study was conducted to evaluate a traditional contact stabilization activated sludge system (CSASC) and a modified CSAS (CSASM) treating domestic wastewater. The CSASC system was comprised of a contact reactor (CR), a stabilization reactor (SR) and a secondary settler (SS); the CSASM included a second CR, a second SS (CR2 and SS2), and a modified SR (SRM) divided into four zones: an attached-suspended growth zone which allowed the system to reach an average sludge retention time close to 36 d and favored the occurrence of nitrification; an anoxic zone for denitrification occurrence; an aerated suspended growth zone with a high presence of organic carbon; and an additional aerated suspended growth zone with a high ammonia concentrations environment. The CSASC’s removal efficiencies of chemical oxygen demand (COD) and total ammonia nitrogen (TAN) were respectively 94±4 % and 53±12%; whereas CSASM’s efficiencies were 88±7% for COD and 92±7% for TAN. Concentrations of TAN and NO3 --N in the CSASC’s final effluent were 14.3±5.2 and 5.0±2.9 mg×L-1; and 4.8±4.4 and 9.1±5.8 mg×L-1 in the CSASM’s final effluent. Results demonstrated that the proposed configuration obtained higher nitrogen removal efficiencies than traditional CSAS.</p>
Highlights
Municipal wastewater contains a variety of organic compounds of carbon and nitrogen
The process begins in the Contact Reactor (CR), where influent wastewater is mixed with recirculation sludge from the Stabilization Reactor (SR) to conform the mixed liquor (ML)
Recent works in Contact Stabilization Activated Sludge system (CSAS) have proposed system modifications to improve phosphorus removal [11], but no research has been carried out for a nitrogen removal optimization. Considering this background, this study evaluated a CSASC system and a CSASM in order to evaluate nitrogen removal efficiencies
Summary
Municipal wastewater contains a variety of organic compounds of carbon and nitrogen. Conventional wastewater treatment plants aim to reduce concentrations of such compounds in final effluent through secondary and tertiary treatment processes. Contact Stabilization Activated Sludge system (CSAS) is a variation of the conventional activated sludge system (Figure 1a), where two aerated tanks and a secondary settler are used to remove carbonaceous material concentrations incoming with influent wastewater. The process begins in the Contact Reactor (CR), where influent wastewater is mixed with recirculation sludge from the Stabilization Reactor (SR) to conform the mixed liquor (ML). After a short hydraulic retention time (HRT) in the CR, the ML is conduced to the Secondary Settler (SS), where separation of clarified effluent and sludge occurs. Separated sludge is recirculated to SR to start the process again after a HRT of 2–8 h. The process’ conceptual base is to optimize adsorption of carbonaceous material over the floc structure during CR’s HRT, which ranges between 0.5-1.5 h, whereas SR is conceived with a longer HRT to metabolize in there substrates previously adhered to floc structure [1]-[3]
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