Studies on the Effect of Bacterial Tannase Supplementation to Biodegradation of Tannins in Tannery Wastewater

Tannins present in the vegetable tanning process wastewater (VTW) affect the aerobic microbes and reduce the treatment efficiency in the tannery effluent treatment plants. Studies were performed with the supplementation of crude tannase enzyme to improve the efficiency of aerobic treatment of composite wastewater from raw to vegetable tanning process (CWRVT). Screening, isolation, optimization of growth conditions, and sequencing of the bacterial isolate Bacillus nitratireducens were studied. Aerobic reactors were operated in continuous mode for a period of 210 days, with and without tannase supplementation. The reactors with and without tannase supplementation showed 84%–88% and 44%–47% tannin removal, respectively, for a maximum organic loading rate (OLR) of 30.5 g COD/L d with a tannin concentration of 1000 mg/L. Confirmation of tannin degradation was done with the help of electrospray ionization–mass spectrometry (ESI-MS) and pyrogallol analysis. The kinetic parameters were derived based on Contois model considering tannin as a substrate. For the treatment of 1 m3 of CWRVT, the supplementation of tannase enzyme will add an additional cost of Rs.30.58/- toward the cost of chemicals in the overall operation and maintenance cost of the treatment process. This study suggests that supplementation of tannase enzyme in existing treatment plants will enhance the efficiency of tannin removal.