Pyridine influence on a sequential anaerobic-anoxic-aerobic FMBR system for phenol, thiocyanate and ammonia removal.

A synthetic wastewater containing various pyridine concentrations (25-250 mg/L) was treated in a sequential anaerobic(B1)-anoxic(B2)-aerobic(B3) fed batch moving bed reactor (FMBR) system. Pyridine was associated with phenol (1500 mg/L), SCN- (800 mg/L), chemical oxygen demand (COD) (5400-5430 mg/L) and NH4+-N (500 mg/L) at hydraulic retention time (HRT) of 6 (B1: 3 days; B2 and B3: 1.5 days each) days. In B1, pyridine removal was 10-12% from influent concentration of 25-100 mg/L and beyond that, it was zero. Removal of phenol (53-39%) and COD (33-22%) occurred in B1, but pyridine above 50 mg/L inhibited both. In B2, 68-90% of pyridine removal occurred along with phenol (>98%), COD (>67%), SCN- (>85%) removal and denitrification. In B2, with an increase in pyridine loading removal rate of phenol, COD and nitrate increased, whereas SCN- removal decreased beyond pyridine loading of 0.031g/L day. In B3, nitrification decreased with high generation of free ammonia. Pyridine degradation in B1, B2 and B3 follows the Stover-Kincannon model with a maximum substrate removal rate of 111.1, 333.3 and 23.81 g/L day, respectively. Thiocyanate removal in B2 and ammonia removal in B3 follows the Bhatia inhibition model with a maximum substrate removal rate of 0.641 and 0.528/day, respectively. The overall efficiency of the FMBR system remained unaffected up to 250 mg pyridine/L at 6 days HRT.