Research On PH Control Dynamics For Anaerobic Digestion Of The Organic Fraction Of Municipal Solid Waste

Anaerobic digestion has been proven a popular technology for treatment of the organic fraction of municipal solid waste (MSW) which could generate renewable energy in the form of methane. However, because the process of anaerobic digestion is a very complicated biologic process, it is very important to enhance the stability of biogas production. As a main controls parameter of the anaerobic digestion, the value and stability of pH have notable influence on the biogas production. Therefore, the simulation and effective control of the optimal value of pH are very crucial in anaerobic digestion.The pH―methane yield process optimization model for anaerobic digestion of organic fraction of MSW has been formulated based on mass balances of substrates, products and microbial components, and physico-chemical equilibrium relationships among ionized/unionized species. The computer calculation process was compiled by the language of Matlab6.5. Using the method of inputting the basic technical parameters, the model can predict the concentrations of anaerobic bacterium, the concentration of soluble carbohydrate, total volatile organic acids, ammonia nitrogen and the methane yield in different value of pH. In addition, the optimal value of pH and the maximal methane yield can be evaluated.Two comparative experiments in mesophilic(35℃) and pyrophilous(55℃) temperature were conducted to validate the validity of model under different temperature. The experiments demonstrated that the methane production of anaerobic system under the optimal pH was steadier than the same condition under uncontrolled pH, and the cumulative methane production had an average increment about 20%. The results showed that the model had notable effect on the anaerobic process stability and the increase of methane production in mesophilic and pyrophilous temperature.The validity of the model under different concentration of total solid (TS) was validated by two comparative experiments. The results demonstrated that the biogas yield of anaerobic process was steadier and the methane production was increased after controlling the pH under the optimal value. However, the optimal value of pH under different concentration of TS was basically approximate. And it can be explained that the TS had less influence on the optimal value of pH than temperature in anaerobic system.