Effects of ammonia on acidogenesis of protein-rich organic wastes

This study investigated the influence of ammonia on mesophilic acidogenesis of protein-rich organic waste, examined at initial ammonia concentration of 0-16 g-N L-1 at a neutral pH. VFA was dominant products from protein's acidogenesis, accounting for 80-90%, compared to lactic acid and alcohols. Among all VFA products, acetic and butyric acid accounted for 30-50% and 25-40% of VFA carbon, respectively, followed by propionic acid (10-15%), iso-valeric acid (10-15%), caproic acid (5-10%), and iso-butyric acid (3-6%). The protein's acidogenesis efficiency was found to be slightly reduced by ammonia less than 8 g-N L-1, while 16 g-N L-1 ammonia had a much stronger inhibition to acidogenesis, indicated by accumulation of lactic acid and formic acid. The formation of acidogenic metabolites like VFA (C-1 to C-6) was suppressed by ammonia. However, the metabolic pathways to producing various acidogenic metabolites were inhibited differently by ammonia, resulting in different schemes of products distribution. The formation of butyric acid was suppressed a lot as long as more than 2 g-N L-I of ammonia was added. The formations of acetic and propionic acid gradually declined with increasing ammonia across 0-8 g-N L-1, but dropped sharply at 16 g-N L-1 ammonia. The formation of iso-valeric acid declined gradually with increasing ammonia across 0-16 g-N L-1. The index of acetate kinase activity could demonstrate the inhibition of ammonia sensitively in mixed-cultivated fermentation.