Effect of chloride and condensable tannin in anaerobic degradation of tannery wastewaters

Toxic effect due to chloride and condensable tannin on anaerobic digestion of vegetable tanning wastewater was investigated at different hydraulic retention times viz 24, 48 and 60 hr respectively. The toxicity to anaerobic contact filter was observed at a chloride concentration of 4500 mg/l and tannin concentration of 790 mg/l respectively under synergistic condition. In the case of constant influent tannin concentration of 600 mg/l, the toxicity due to chloride on anaerobic contact filter was observed at 5500 mg/l. The COD removal percent ranged from 50% to 79% at 48 hr and 67% to 91% at 60 hr HRT respectively. In the case of constant influent chloride concentration of 4000 mg/l and at an increasing influent COD concentration, the toxicity due to tannin on anaerobic contact filter was observed at 1180 mg/l. The COD removal percent ranged from 64% to 89% at 48 hr and 78% to 96% at 60 hr HRT respectively. The results showed that at least 60 hr HRT would be desirable to have good COD removal percent.