Treatment of tannery wastewater using hybrid upflow anaerobic sludge blanket reactor

In India, and in the State of Tamilnadu, tanning is a small-scale industry. During the tanning process, a huge volume of wastewater is generated and in most cases it pollutes the environment. In the present study, an attempt has been made to treat the tannery wastewater by using hybrid upflow anaerobic sludge blanket (hybrid UASB) reactors that offer the advantages of both fixed film and upflow sludge blanket treatment over a period of 370 d, at two different hydraulic retention times (HRT) viz., 60 and 70 h. The average concentration of COD and tannin in the influent tannery wastewater used was 14 000 mg/L and 1987 mg/L, respectively. The reactor performed to its maximum at an organic loading rate (OLR) of 2.74 kg COD m(-3) d(-1) and 3.14 kg COD m(-3) d(-1) at a HRT of 70 and 60 h, respectively. Increase in OLR beyond 2.74 kg COD m(-3) d(-1) and 3.14 kg COD m(-3) d(-1) caused a gradual decrease in COD removal efficiency. The degradation of inhibitor substance such as tannin during the anaerobic digestion was investigated and it was in the range of 65-91% at a HRT of 70 h and 63-89% at a HRT of 60 h. The performance of the reactor with reference to COD, TS removal, and biogas production were also evaluated.