Development of novel pumpless anaerobic membrane bioreactor for energy-negative treatment of high-strength wastewater

Abstract

permeate flux, operating pressure, gas production rate, void volume ratio, and hydraulic retention time. For operating 2 cycles of permeate production in one day, the operating factors have been determined by the theoretical calculation and experimental data (Flux: 15 LMH, Operating pressure: 3 bar, Gas production rate: 12.5 mL/min, Void volume ratio: 0.1, HRT: 2 days) To verify the operation of p-AnMBR, a simulated operation of p-AnMBR has been done by using a mixture of gas (CH$_4$: 60%, CO$_2$: 40%), by comparing theoretical value and experimental value. The experimental time for pressure build-up was 4.1 h, which was similar to the theoretical value of 3.9 h. For the ratio of gas usage, 50 % of gas was used for pressure maintenance in the reactor, and 20 % was dissolved in the sludge for a total of 2.6 L. The CH$_4$ percentage in gas was enhanced to 28 %, compared with the value at normal pressure. The permeate production has been done for 2 cycles, corresponding with the theoretical flow rate and demanded time for 1 cycle. However, due to the occurrence of membrane fouling, only 75% of permeate volume has been produced, increasing up to 2 bar of transmembrane pressure (TMP) before the permeate production. In conclusion, the pressurized anaerobic membrane bioreactor was developed, and theoretical calculation optimized each operating factor. By simulated operation of p-AnMBR, each operating factor has been compared with the theoretically calculated values, which was showing good agreements. However, as the membrane fouling was severe, more definite strategies for mitigating the membrane fouling should be developed. Also, further researches for fouling propensity, mechanism, and method for recovery of supersaturated biogas is needed.

The anaerobic membrane bioreactor (AnMBR) is a technology that is integrated with an anaerobic digestion process and membrane process, which can convert organic pollutants in wastewater into biogas as renewable energy, and by the usage of the membrane, hydraulic retention time (HRT) and sludge retention time (SRT) can be decoupled allowing the independent control. From these advantages, it is possible to reduce the total energy consumption by about 50% compared to the conventional wastewater treatment plant (WWTP). However, due to the occurrence of membrane fouling, which is the blockage of the membrane pore, more pressure is demanded on the pump for permeate production with the constant flux, and backwashing is required to reduce membrane fouling. This accounts for a significant amount of the total energy consumption in the AnMBR system, accounting for about 43% of the total energy consumption. In this study, the energy-negative pressurized-anaerobic membrane bioreactor (p-AnMBR) has been developed by utilizing auto-generative pressure from biogas production and produced permeate flow and backwashed membrane without the usage of the pump. The operation of p-AnMBR consists of four stages: the inflow stage of wastewater, the pressure build-up stage by the anaerobic digestion process, the permeate production stage, and lastly, the backwashing stage. The operation method for the p-AnMBR is developed by classifying a total of five operating factors which have been derived from fixed factors, such as the total volume of the reactor and the effective filtration area or else