Biological treatment of a coal gasification process wastewater

An 8 month experimental study was performed to assess biological treatability characteristics of Hygas coal gasification process pilot plant wastewater comprised of cyclone and quench condensates. The study evaluated treatability characteristics of ammonia stripped and unstripped wastewater at full strength and at 1:1 dilution. It was determined that minimum pre-treatment required for biological oxidation consisted of reducing wastewater alkalinity, and decreasing raw ammonia concentration by dilution or by stripping. Kinetic studies with stripped Hygas wastewater showed the waste could be processed at mean cell residence times varying from 10 to 40 days with hydraulic residence times of 2–3 days; the bacteriological yield coefficient was 0.10 (COD basis), and the decay coefficient was 0.01 day −1. Hygas wastewater seemed to inhibit bacteriological growth because mean cell residence times less than 10 days do not appear feasible and because apparently higher yield coefficients were observed with diluted wastewater. However, this factor should not effect removal efficiencies for organic contaminants at recommended processing conditions.