The treatment of paint‐stripping wastewaters which contain phenol and chromium

The wastewaters from paint stripping and surface treatment operations on aircraft contain a range of materials including phenolic compounds and chromium. The wastewaters are generated erratically and only during part of the paint stripping, repainting cycle. A Fenton's reagent system employing 100–200 mg.L‐1 of ferrous iron and hydrogen peroxide at a weight ratio of hydrogen peroxide to phenol of 2.5–3.0 to 1, has been shown to oxidise phenols and reduce any hexavalent chromium to trivalent chromium. Subsequent lime treatment removed the organic residues, chromium and phosphate into the sludge and produced a supernatant suitable for discharge to sewers and subsequent biological treatment. The laboratory results have been confirmed by pilot plant scale studies.