Acidogenesis of gelatin-rich wastewater in an upflow anaerobic reactor: influence of pH and temperature

The influence of temperature and pH on the acidification of a synthetic gelatin based wastewater was investigated using an upflow anaerobic reactor. Gelatin degradation efficiency and rate, degree of acidification, and formation rate of volatile fatty acids and alcohols all slightly increased with temperature. Temperature affected the acidogenesis of gelatin according to the Arrhenius equation with an activation energy of 1.83 kcal/mol. Compared with temperature, pH had a more significant effect on the acidogenesis. Gelatin degradation efficiency substantially increased with pH, from 60.0% at pH 4.0 to 97.5% at pH 7.0. The degree of acidification increased from 32.0% at pH 4.0 to 71.6% at pH 6.5, but dropped to 66.8% when pH increased to 7.0. The optimum pH for the overall acidogenic activity was found to be 6.0, close to 5.9, the optimum pH calculated using a semiempirical model. Operation at pH of 4.0–5.0 favored the production of propionate, hydrogen, whereas the operation at pH 6.0–7.0 encouraged the production of acetate, butyrate, and i-butyrate. The region between pH 5.0 and 6.0 was the transition zone.