Denitrification of high-nitrate, high-salinity wastewater

Denitrification of a wastewater containing 36,000 mg/L NO3− (8,200 mg/L NO3–N) with ionic strength of 3.0 has been achieved using activated sludge in bench-scale sequencing batch reactors. An activated sludge culture was acclimated to denitrify the wastewater at pH 9, by step-wise increase in wastewater nitrate concentration from 2,700 mg/L NO3–N to 5,400 mg/L NO3–N and finally to 8,200 mg/L NO3–N. Simultaneously, wastewater ionic strength was increased from 0.8 to 2.7 and to 3.0 (5, 16, and 18% total dissolved solids (TDSI). Although complete denitrification occurred, the maximum specific nitrate reduction rate decreased from 50 to 19 mg NO3–N/g MLSS/h as wastewater nitrate and TDS concentration increased. Also, accumulation of nitrite increased and the maximum nitrite reduction rate decreased. A similar attempt to acclimate activated sludge to denitrify the high-TDS, high-nitrate wastewater at pH 7.5 was unsuccessful.