Reaction Kinetics of Membrane Separation Anaerobic Digestion

Membrane separation anaerobic digestion is a process that consists of a complete mixing digester and membrane separation units that separates mixed liqueur to permeate and concentrate. The former one is discharged and the later is returned to the digester. The combined process is a kind of immobilized bioreactor that holds all of biomass and undigested solid. Treated permeate contains COD of less than 500 mg/L.There is not any organic solid accumulation nor inorganic solid that is liquefied and passes through membrane. Experiments were conducted by semi-batch reactors of which volume was 20L at 35ﾟC to determine reaction kinetics of real sewage sludge digestion. After feeding substrate, small amount of permeate was withdrawn through membrane at proper interval. VFA concentration of each sample was measured by gas chromatogram. Reaction velocity of VFA was estimated by using pure VFA solution as substrate. Employing those parameters obtained, a reaction model of the process was produced. Disintegration of VFA was estimated to follow first order reaction. Hydrolysis of organic solid in sewage sludge was also first order reaction on the condition that velocity of acidification was not a limiting factor. When first order reaction of biomass autolysis was introduced, change of VFA concentration in the permeate fitted well to the reaction model. Disintegrated biomass seemed to be used as substrate by the proposed model and observed stable concentration ratio of inorganic substance. To confirm this fact, digested sludge was stabilized by high temperature and was fed to the digesters. Gas production was observed, but amount of it was smaller than that of flesh sludge. The experiment indicated a new process of complete disintegration of sewage sludge.