EFFECTS OF ORGANIC ACID CONCENTRATIONS AND PH ON METHANE FERMENTATION OF WASTE BIOMASS

Abstract

 Effects of lactic acid, as an example of organic acids which affects pH and methane fermentation performance, on methane fermentation of waste biomass are evaluated. In batch experiments, when the initial lactic acid concentration was 17.2 gCOD/L, pH dropped from 7.4 to below 6 and methane fermentation was inhibited. When the initial lactic acid concentration was 11.5 gCOD/L, pH dropped to around 6.3, but the inhibitory effect was suppressed with equivalent alkali addition for pH recovery, and the ratio of methane production amount to lactic acid input was about 0.8 on COD base. The calculation of pH based on acid-base equilibrium for sludge from methane fermentation plants treating different substrates was able to reproduce pH change by acid titration. These results confirm that pH under high organic acid concentrations can be predicted by analyses of sludge characteristics. Prediction of pH decrease can be used to evaluate the effect of temporal high loading on methane fermentation performance.