Pulp and paper mill effluent treatment by hybrid anaerobic upflow fixed-bed bioreactor combined with slow sand filter

In the present work, pollutant removal study of Century Pulp and Paper Mill effluent was done. A hybrid unit of upflow fixed-bed anaerobic bioreactor (UFBAB) along with slow sand filter (SSF) was compared with single unit UFBAB for pollutant removal at different hydraulic retention time (HRT). The hybrid system showed better removal efficiency which can be attributed to SSF. It was observed that SSF provides a polishing effect to the effluent treated by UFBAB. The biodegradation rate in both filters was observed to be increased in first six weeks of experiment, prior to the acclimatization of microbial communities. The relative removal efficiency of biological oxygen demand and chemical oxygen demand was found to between 0.90 and 0.99, respectively, at 24h HRT, demonstrating very high removal efficiency of the hybrid system. The relative removal efficiency of total dissolved solids and total suspended solids was around 1 at 16h HRT indicating 100% efficient and within the limits as prescribed by Central Pollution Control Board India (CPCB) for treated effluent discharge in surface water bodies. Best removal efficiency was observed in case of sulfate at low HRT of 8h. Relative removal efficiency for phenols was found to be greater than 1 at 12h HRT. SSF was found to be a suitable substrate for polishing of treated effluent of pulp and paper mill wastewater, demonstrating promising relative efficiency.