DEVELOPMENT OF A WASTE-WATER TREATMENT PROCESS - REDUCTIVE DEHALOGENATION OF CHLORINATED HYDROCARBONS BY METALS

A low-energy dechlorination technique has been applied to the detoxifi cation of chlorinated hydrocarbons (CHCs) in aqueous solution. This al ternative to biological or physico-chemical decomposition methods achi eves reduction by means of metal particles or copper-activated metal p articles (Mg, Fe, Al, Zn). The paper presents data from two pilot stud ies, covering fundamental process design aspects. Experimental investi gations of pilot study 1 were conducted in a laboratory-scale fixed be d reactor. In weak acidic or neutral medium (pH-range 4-7) proper proc ess application resulted in very rapid removal of hexachlorocyclohexan e concentration (gamma-BHC, lindane) from model wastewaters with up to 99.3% efficiency. During the course of reaction the main products for med are chloride and benzene, the by-product being small amounts of ch lorobenzene. After employing different metals in the dechlorination re action zinc proved to be the optimum reducing agent since it achieved the best space-time yield. Pilot study 2 dealt with a couple of screen ing reactions of various CHCs with zinc as the reducing agent, which w ere performed in the batch mode. Even volatile CHCs (chloroform, 1,1,1 -trichloroethane) could be completely dechlorinated by forming the cor responding hydrocarbons (methane; ethane and ethene respectively). Pse udo-first order rate constants (k, s(-1)) were determined to assess su bstrate reactivity with respect to possible process applications. Proc ess design aspects, advantages and limitations are discussed.