Optimization of Upflow Fixed Bed Bio-Denitrification Reactors in Water Treatment

In this research, optimization of biological denitrification upflow fixed bed reactors was studied.A rectangular shape bench scale reactor filed with PVC corrugated plate was used. Our result showed that a minimum of 93 percent nitrate removal for a range of reactor detention time from 0.5 to 48 hours were achieved while the influent nitrate concentration was 100 mg/L. It means, nitrate removal/efficiency is independent of these parameters.Increasing of hydraulic detention time had more effect on effluent residual COD and nitrite concentration (denitrifiction product).It was found for detention time of more than one hour, nitrite concentration was about less than one ppm.Decreasing of hydraulic detention time to less than 0.5 hour caused a significant increase in effluent nitrite concentration. Our results also indicated that with increasing C/N ratio nitrate removal percentage increased and nitrite residual and also COD concentration decreased in effluent.Optimum C/N ratio (for hydraulic detention time equal to one hour and influent nitrate concentration equal to 100 mg/L) were found to be equal to 1.6. Considering this ratio, residual nitrate and COD concentration were determined. 3.7, 7.3, 0.09, mg/L respectively.This study also showed that with increasing nitrate concentration in influent, effluent nitrate concentration increased but nitrate removal efficiency almost remain constant. This was not observed for effluent nitrite. Effluent nitrite concentration is strongly under influence of influent nitrate concentration. This problem can be solved by reactor detention time modification. In summary, modification of operational condition of denitrification reactor has a significant effect on nitrate removal rate.