Biodegradation characteristics of organic pollutants contained in tannery wastewater

In the batch experiments inoculated with activated sludge from tannery wastewater treatment plant, biodegradation characteristics and kinetics of three tanning agents, naphthalene- 2-sulfonic sodium, tannic acid and bayberry tannin, were studied under aerobic and anaerobic conditions. And the aerobic/anaerobic biodegradation laws of real tannery wastewater with respect to COD change were also investigated using the same batch experiments. The results showed aerobic degradation was superior to anaerobic degradation for tanning agent removal and mineralization. The removal rates of naphthalene- 2-sulfonic sodium, tannic acid and bayberry tannin by aerobic biodegradation were >90%, >90% and 50%- 75%, respectively whereas 10%- 40%, >95% and 20%- 30%, respectively by anaerobic degradation. In terms of COD removal about tannic acid biodegradation, the removal rates under aerobic and anaerobic conditions were >75% and <75%, respectively. The first-order kinetic constants during aerobic biodegradation of tannic acid and bayberry tannin were slightly influenced by initial concentrations while initial concentration had a significant effect on the first-order kinetics rate in the case of naphthalene- 2-sulfonic sodium aerobic-biodegradation because naphthalene- 2-sulfonic sodium with initial concentration ≥70 mg·L^-1 was toxic to microorganism leading to a significant decline of kinetic constants. Biodegradation of real tannery wastewater under aerobic and anaerobic conditions represented obvious stage characteristics and the COD concentration had a good linear correlation with reaction time in the phases of fast degradation and slow degradation. The aerobic maximum specific degradation rate was 11.6 times higher of anaerobic degradation.