Use of Sequencing Batch Reactor for Biological Denitrification of High Nitrate-Containing Water

The efficiency of a sequencing batch reactor in denitrification of drinking water with relatively high nitrate concentrations (40–250 mg/L as N) was evaluated. Ethanol at a COD/N of 2.00 was found sufficient to reduce nitrate concentrations to acceptable levels (<10 mg/L as N). Within the first 6 min of reaction, nitrite accumulation in the range of 0.03–3.5 mg/L as N was observed increasing with the increase of initial nitrate concentrations. In the first hour, nitrate removal was significantly high in the range of 85.7–91.5%. Anoxic reaction times of 3, 5, and 7 h were required for nitrate concentrations of 40–160, 200, and 250 mg/L (as N) to achieve acceptable levels of nitrate and nitrite. Alkalinity of the denitrified water increased on average by 3.53 mg as CaCO3 for each milligram of nitrate reduced and pH increased from 7.3 to the range of 8 to 9. Idle times between the operation cycles, in the range of 1–14 h, had an insignificant effect on denitrification. Residual COD concentrations in the rang...