Assessment of initial inert soluble cod in yeast industry wastewater under anaerobic conditions

In this paper, both direct and indirect methods have been applied to determine the initial inert soluble COD (SI) of yeast wastewater under anaerobic biological conditions. Indirect determination process consists of running two parallel batch reactors, one with the tested wastewater and the other with glucose. The two parallel batch reactors start with the same initial COD of 6500 mg/L (S-m) and continue long enough to deplete the degradable substrate entirely. The degradation rate of glucose is much faster than that of the wastewater under the same conditions with COD reducing rates of 80% and 40%, respectively, in about 15 days. The final soluble COD of glucose comes to a stable level of about 340 mg/L after 30 days, and that of the wastewater is 65 days of about 1240 mg/L, the S, fraction is 840 mg/L. The ratio of the initial inert soluble COD to the initial soluble COD (S-I/S-T0) is 0.13. Direct experimental procedure involves running two reactors fed with unfiltered wastewater and filtered wastewater, respectively, which lasts 70 days. The COD degradation curves of the two reactors are similar. The COD values reduce linearly during the first 15 days, and then the decomposing rates become much slower and reach steady-state with COD of 400 mg/L on the 30(th) day. It shows that the residual COD cannot be removed, even with extended operation time, and the S-I/S-T0 is 0.10. To strong industrial wastewater, direct method overcomes the interference of residual soluble inert microbial products (S-p), and the results are closer to the real value.