A study on a simultaneous biological nitrification-denitrification of an aqueous solution simulating a refinery wastewater

Abstract

A bench-scale bioreactor with a five-liter working volume was used to carry out a simultaneous biological nitrification-denitrification (SBND) of an aqueous solution simulating refinery wastewater. The bioreactor was also used to perform a similar scheme of experiments on real refinery wastewater (RRW). Despite the higher salinity of the RRW, the obtained results of the two cases demonstrated a fair trend agreement, but a lower nitrogen removal efficiency for the RRW. Anaerobic bacteria (Phenobacter) was successfully adapted to perform nitrification (aerobic) and denitrification (anaerobic) processes. Dissolved oxygen (DO), pH, chemical oxygen demand (COD), total dissolved salts (TDS), and nitrate (NO3 −) ions were periodically measured (each 1 hour) to determine the time for the nitrification and denitrification. The time for nitrification was around 4 hours and the time for denitrification was approximately 3 hours (75% of the nitrification time). The minimum and maximum values of the pH, COD, TDS, and NO3 − ions at the start and the end of the nitrification-denitrification processes were 7.3-8.5, 318-585, 779.88-7710, and 2.4-56 respectively for the aqueous solution, while their range was 7.3-8.3, 310-660, 4736.9-8086, and 5.6-78 respectively for the RRW. The nitrogen removal efficiencies of the aqueous solution and the RRW were 95% and 87% respectively. The results prove the successful adaptation of an aerobic bacteria (Phenobacter) for nitrifying and denitrifying a refinery wastewater and reducing the investment and operational costs of the wastewater treatment plant.