Reclamation of wastewater from a steel-making plant using an airlift submerged biofilm reactor

A bench-scale airlift submerged biofilm reactor was developed to test the possibility of nitrification of the final effluent discharged from a wastewater treatment process of a steel-making plant with an aim of reusing it as irrigation water. Despite the fluctuation of ammonia concentration in the wastewater (55-90 mg NH₃-N dm^-3), the ammonia was completely converted to nitrate in the hydraulic retention time of 8 h. When decreasing the hydraulic retention time further down to 4 h, the nitrification efficiency decreased to 67.9%. However, the nitrification efficiency could be significantly enhanced by increasing the airflow rate due to an increase in both of the oxygen transfer rate and liquid circulation rate. At the aeration rate of 4 dm³ min^-1 and the hydraulic retention time of 4 h, the nitrification efficiency was as high as 92.6% and the nitrification rate was 34.6 mg NH₃-N dm^-3 bed h^-1.