A Feasibility Study of Ammonia Recovery from Coking Wastewater by Coupled Operation of a Membrane Contactor and Membrane Distillation

More than 80% of ammonia (NH(3)) in the steel manufacturing process wastewater is contributed from the coking wastewater, which is usually treated by biological processes. However, the NH(3) in the coking wastewater is typically too high for biological treatment due to its inhibitory concentration. Therefore, a two-stage process including a hollow fiber membrane contactor (HFMC) and a modified membrane distillation (MD) system was developed and applied to reduce and recover NH(3) from coking wastewater. The objectives of this paper are to evaluate different membrane materials, receiving solutions, and operation parameters for the system, remove NH(3) from the coking wastewater to less than 300 mg N/L, which is amenable to the biological process, and recover ammonia solution for reuse. As a result, the polytetrafluoroethylene (PTFE) HFMC using sulfuric acid as a receiving solution can achieve a maximum NH(3)-N transmembrane flux of 1.67 g N/m(2)·h at pH of 11.5 and reduce NH(3) in the coking wastewater to less than 300 mg N/L. The NH(3) in the converted ammonium sulfate ((NH(4))(2)SO(4)) was then recovered by the modified MD using ice water as the receiving solution to produce ≥3% of ammonia solution for reuse.