Two Phase Anaerobic Digestion in Membrane Separated Bio-Reactor

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Membrane separated bio-reactor was found to be an appropriate technology for single-phase anaerobic digestion rather than for two-phase anaerobic digestion. In the first year of the program, membrane separated anaerobic digestion was studied in laboratory scale experiments. Glass bottles (3L) were prepared as reactors, which were heated and mixed with magnetic stirrers and hot plates. Membrane modules (75mm diameter) with ultrua-filtration membrane were connected to the reactors therefore separating permeate from the mixed liquor by suction. Sewage sludge from an actual wastewatter treatment plant was used as a substrate and was fed to the reactors everyday. In the second year of the program the volume of the reactors was increased to 5L with the purpose of measuring mass balance in the reactors. The diameter of the membrane module was also increased to 150mm. In the last year of the program, plastic reactors were used instead and mechanical mixing was introduced. Hollow-fiber membrane … More module was used for the separation. The operation had been very good and stable during a long period. The results and conclusions obtained in the last year of the research were as follows.(1) CODcr concentration of the permeate was less than 200mg/l when the production rate of methane gas was reasonably high.(2) MLSS concentration in the reactor was increased up to 40,000mg/l with the increase of the substrate loading rate.(3) About 60% MLSS in the reactor had been organic matter during the operation and no accumulation of inorganics in the rector was observed.(4) The self-degradation rate of MLSS was very low.(5) Volatile fatty acid concentration becomes the highest level in 4-5h after the feeding of sludge and then gradually decrease.(6) Hydrolysis rate of solids in the reactor was very low.(7) Both microfiltration membrane and ultrafiltration membrane can produce treated water at almost similar quality level. High molecular weight organics were removed in the both system.(8) It took several weeks for the recovery of the operation even by the reduction of the loading rate when methane production was damaged.An equilibrium condition can be obtained in the reactor balancing the growth of bacteria and the selfdegradation by preventing the wash-out of bacteria completely with the membrane separation. Input organics can almost completely go to gas phase besides organics in the permeate (less than 1% of total input). Inorganics, which occupies more than 30% of sludge will be dissolved completely. Ash treatment could be non-necessary process by introducing membrane-separated anaerobic digestion. Less