Enhanced Membrane Coagulation Reactor(E-MCR) For Maximizing Sewage Resource Recovery

This study aims to maximize resource recovery from sewageby anaerobic digestionin a more sustainable way.To improve the cost-effectiveness and limit the energy consumption of the technology, the potential ofsewage pre-concentration to achieve the requirement for anaerobic digestion was identified. Accordingly, Enhanced Membrane Coagulation Reactor(E-MCR) was designed and set up in this study to pre-concentrate raw sewage from a wastewater treatment plantaiming for larger-scaled application.The feasibility of E-MCR was evaluated based on the results offiltration performance, retention performance, concentration performance as well as an integrated scaling-up performance.In the optimization study of enhanced coagulation process, the combination of Powdered Activated Carbon(PAC) and Polyaluminium Chloride(PACl) was found to be the best solutionto improve the organic matter retention, sewage solid-liquid separability and filtration properties. According to the combined membrane filtration model fitting, the enhanced coagulation process can induce effective inhibition of membrane pore blocking and improvement of permeability of the cake layer.Withthe hollow fiber membrane module, the lab-scale microfiltration E-MCR achieved permeate COD less than 30 mg/L under long-term optimized operationconditions with a PACl dosage of 30 mg/L and a PAC dosage of 20 mg/L along with periodical air backflushing under air backflushing pressure of 150 kPa and backflushing ratio of 1min20s:16min40s. The COD concentration of the concentrate with a SRT of 1d reached 8000~10000 mg/L, which amounted for over90% of the total influent COD. Theperformance of the pilot-scale ultrafiltration E-MCR was similar to the lab-scale microfiltration E-MCR. The concentrate with a SRT of 2.5 d in the pilot-scale reactor had a COD concentration above 17000 mg/L under the air backflushing pressure of 100 kPa and backflushing ratio of 30s:5min30s at the same dosage of PACl and PAC. The recoverable COD proportion reached 90% as well.Regarding for the product quality, the COD concentration and the Biochemical Methane Potential(BMP) of the concentrate turned out to be at the same level as or even better than blackwater.The added coagulants and adsorbents did not inhibit anaerobic microbessignificantly. Meanwhile, the activity of aerobic microbes was low according to the SOUR test, implying that the mineralization of organic matters can be ignored. Furthermore, the structure of the cake layer and particle clusters in the concentrate turned out be very porous, which supported the fact that enhanced coagulation process led to less fouling compared to the direct sewage membrane filtration. The total and polysaccharide LB-EPS concentrations in E-MCR were higher than applied full-scale MBRs, which explains the poor performance of aeration in fouling control in this study and the need of another improved fouling control method, such as air backflushing.According to the concentrations of TN, TP and NH4+-N in the permeate, the produced water could achieve some low-quality wastewater reuse requirements, as the relative high NH4+-N concentration limits the application of high-quality water reclamation. Further study on the reduction of NH4+-N concentration in permeate is anticipated.The concentrate of the pilot-scale E-MCR was used for long-term CSTR reactor to study the CH4 production performance. Scenarios with 20 d and 30 d of HRT were found to have good performancein biogas production. For example, the CH4 production rate could be 3.19 m3CH4/m3 concentrate, and the CH4 conversion rate could reach 61.3%, which is slightly better than blackwater. The enhanced coagulation process had no obvious adverse impact on the long-term CH4 production of sewage concentrate.Accordingly, E-MCR is generally calculated to achieve net energy production rather than consumption compared to conventional activated sludge process.