Treatment of effluent from man-made fibre plants with ammonia and calcined soda

Conclusions

1. Complete replacement of soda by ammonia for neutralisation of effluent is undesirable because the precipitate formed is very wet and difficult to dehydrate.

2. To cut down the amount of calcined soda used, its partial replacement by ammonia may be recommended. The effluent should be neutralised with ammonia to pH 4–5, then with soda to pH 8.3–9.3. Since a considerable amount of zinc remains in solution, further treatment of the effluent with sulphide may be required.

3. The ammonium sulphate formed must be removed from the effluent by the biochemical method, which ensures that the concentration of ammonium salts in the treated water is not more than the maximum permissible value (5 mg/litre).