Treatment of the effluent comprising =6C aliphatic aldehyde cpds. and their halogenated derivatives, =4C chlorinated hydrocarbons and/or carboxylic acids and their salts in which the pH of the effluent is raised to 9-12 addn. of alkaline soln, at 45-75 degrees C, comprises further adjusting the pH to 0.5-6 and then incorporating free adhesive or a substance capable of releasing chlorine. The process is partic. applied to effluent from the mfr. of 1,2-dichloroethane, by oxychlorinated of ethylene. The known alkali treatment to decompose the choral and other cpds. results in an aq. effluent of high COD. The above improvement is simple, economic and enables a reduction of the COD-level by 50-80% compared to without the chlorine treatment.
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