Effect of C/N ratio on denitrification of high-strength nitrate wastewater in anoxic granular sludge sequencing batch reactors

Denitrification of high strength nitrate wastewater was investigated in granular sludge sequencing batch reactors (SBRs) with the objective of optimizing electron donor requirement, in terms of acetate-carbon to nitrate-nitrogen (C/N) ratio. Three SBRs of each 6 L working volume were inoculated with activated sludge and operated in parallel at C/N ratios of 1.5, 2 and 3. Formation of denitrifying granular sludge was observed in all the three SBRs. Complete and stable denitrification of feed containing nitrate up to 5420 mg L−1 NO3-N was achieved in 24 h cycle period for all three C/N ratios studied. However, time for complete denitrification and maximum amount of nitrite accumulation, increased with an increase in C/N ratio. Thus, C/N ratio of 1.5 was found to be optimum for denitrification of high-strength nitrate wastewaters, with acetate as the carbon source. The studies indicate that denitrification in SBRs using granular biomass and acetate as carbon source was highly efficient for denitrification of high strength nitrates.