Abstract
The high-rate activated sludge (HRAS) process is being studied for the removal and recovery of organics with short solids retention time (SRT) from wastewater, facilitating energy recovery by the subsequent anaerobic digestion process. In the present study, the feasibility of a novel high-rate contact stabilization (HRCS) process coupled with a membrane bioreactor (MBR) was investigated as a HRAS technique to harvest organics compared to a high-loaded MBR (HL-MBR) process treating the same sewage. Results showed that higher chemical oxygen demand (COD) removal efficiency and better bioflocculation performance were obtained using HRCS-MBR compared with HL-MBR with SRTs from 0.5 to 1.8 days. The increased bound extracellular polymeric substances content in the contactor was responsible for the improved biosorption and bioflocculation performance in the HRCS-MBR configuration. At an optimal SRT of 1.2 days, incoming organics of 47.5% and 40.5% were harvested in concentrate for HRCS-MBR and HL-MBR. These harvested organics from the concentrate per liter from HRCS-MBR and HL-MBR produced 4.28 × 10−3 and 3.72 × 10−3 kWh of electricity, respectively. The clear advantage of fouling control for HRCS-MBR was determined because of significantly lower concentrations of colloidal materials and soluble microbial products in the concentrate compared with HL-MBR. Therefore, HRCS-MBR holds promise for organics recovery and sustainable wastewater treatment.
Highlights
Municipal wastewater is typically treated with the conventional activated sludge (CAS) process.This biological process consumes a considerable amount of energy for aeration, at 0.3–0.6 kWh/m3 of wastewater [1], and produces a significant amount of carbon dioxide (CO2 )
For membrane bioreactor (MBR), the differences in CODtot removal efficiency for similar influent was determined via CODdiss removal efficiencies because particulate and colloidal organic matter that contributed most to the CODtot could be completely retained by the membrane
The results indicate that more influent chemical oxygen demand (COD) was oxidized, whereas less COD was to the significant differences of all COD fractions in the concentrate between the two MBRs at the diverted to the concentrate and membrane effluent at longer solids retention time (SRT) in both MBRs
Summary
Municipal wastewater is typically treated with the conventional activated sludge (CAS) process. This biological process consumes a considerable amount of energy for aeration, at 0.3–0.6 kWh/m3 of wastewater [1], and produces a significant amount of carbon dioxide (CO2 ). 1.9 kW [2,3] This energy can be partially recovered via the anaerobic digestion of surplus sludge to produce biogas for onsite heat and electric energy generation. Through this method, the organic carbon in wastewater is harvested and recovered instead of being oxidized and energy self-sufficiency or energy-neutral wastewater treatment can be fully realized in practice. The first step is to maximize organic carbon harvesting and minimize respiration losses to CO2 from municipal wastewater, enabling maximum energy recovery
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