Sulfidogenic volatile fatty acid degradation in a baffled reactor

The effect of staging the sludge bed on volatile fatty acid degradation by sulfidogenic reactors was evaluated in a baffled reactor. In a 5.4 l baffled reactor, containing three equal compartments, a volatile fatty acid (VFA) mixture (acetate:propionate:butyrate ratio 1:2:2 on COD basis; pH 8) was treated under mesophilic (30°C) and sulfidogenic (COD:SO₄^2- ratio: 0.5) conditions for 38 days. At a specific sludge loading rate of 0.50 g COD.gVSS^-1.d^-1, a COD and sulfate removal of 85% and 30%, respectively, was obtained. In the baffled reactor, staging of the sulfidogenic VFA degradation occurred. Propionate and butyrate were mainly degraded in the first compartment. Their degradation was incomplete, resulting in elevated acetate concentrations in compartment I. In the second and third compartment of the baffled reactor, a net degradation of acetate took place. Acetate was the sole substrate present in compartment III and residual acetate concentrations of about 200 mg/l were present in the effluent at a specific sludge loading of 0.50 g COD.gVSS^-1.d^-1. Sludges with different maximum specific VFA and acetate degrading activities developed in the first and second compartment. These maximal specific activities were almost equal for sludge present in compartment II and III.