Treatment of wastewaters from manufactured gas plants

Concentrated wastewaters from a gasworks were treated by the addition of formaldehyde which condensed the phenol at an optimal temperature of 60C. The complex was settled after adjustment of the pH to 10.5 with a lime solution. The pH was then raised to 10.5-11.2 and ammonia removed by air stripping. The effluent from this process was then diluted 5 times and treated with activated sludge. Electrocoagulation and electrochemical oxidation or chemical oxidation with sodium hypochlorite, followed. The whole process reduced the COD from 84,000 to 112-150 mg per litre.