Effect of alkali metal cation on the anaerobic hydrolysis and acidogenesis of vegetable waste

Five batch testing scenarios were designed to evaluate the effects of alkali metal cations on anaerobic hydrolysis and acidogenesis. These scenarios were A (c=0 g l^-1), B (c_Na+=25 g l^-1), C (c_Na+=50 g l^-1), D (C_K+=25 g l^-1), and E (c_K+=50 g l^-1, pH 7.0). A solution pH of 7.0 or above favored protein hydrolysis, higher proteinase activity and higher ammonia production. However, such a pH suppressed carbohydrate hydrolysis, as indicated by low α-amylase activity. Cation interference at pH 5.0-6.0 seemed not to affect carbohydrate hydrolysis, as showed by the unimpaired α-amylase activity at 50 g l^-1 K⁺. Acidogenesis was more sensitive to alkali metal cations, so acid production and the drop in pH were lowest in a 25-50 g l^-1 Na⁺, acidic environment (pH 4.0-6.0). It was insensitive to cations when the pH was maintained at 7.0-8.0. When the pH was uncontrolled and decreased freely to acidic values, 25 g l^-1 of cation inhibited the action of the microbes, which rapidly acclimated, as presented by the slow transformation of soluble polymers to soluble metabolites. However, acidogenetic microbes could not easily recover from inhibition by 50 g l^-1 of cation. When the pH was maintained at over 7.0, the microbes were not inhibited by cation (50 g l^-1) as indicated by the more active acidogenesis. The metabolic pathways to lactate, acetate and alcohols were not fully coupled. © Selper Ltd., 2006.