Effect of pH value on VFA concentration and composition during anaerobic fermentation of kitchen waste

Under mesophilic conditions(35℃),batch experiments were carried out to determine the effect of pH value on volatile fatty acid(VFA) concentration and composition during anaerobic acidogenesis of kitchen wastes.The pH value was uncontrolled in one reactor and controlled at 5.0,6.0,7.0 in other reactors.The results showed that the greatest degree of hydrolysis and acidogenesis was obtained and more organic acid was produced when the pH value was controlled at 6.0.When the pH value was controlled at 6.0,the maximum VFA concentration and yields of 40.89g/L and 0.328gVFA/gVS was obtained in the 68th hour,and was 8 times of that when the pH value was not controlled.The product composition in the acid reactor strongly depended on the pH value.The pH value of the uncontrolled reactor dropped from 6.6 to 3.8 quickly within 24 hours.Ethanol was the main product,accounted for 59.8% of total end products.So the typical ethanol-type fermentation occurred when the pH value was not controlled.It was butyric acid-type fermentation when the pH value was controlled at 5.0,6.0 and 7.0.Acetic acid was main product at pH 5.0,butyric acid was dominant at pH 6.0,proportion of acetic acid and butyric acid was similar to each other at pH 7.0.The optimum pH value of hydrolysis and acidogenesis of kitchen wastes was 6.0.