Process for the purification of contaminated water

Claim 1

A process for the purification of aqueous acid effluent from a dyehouse and containing dissolved solids without substantially building up the total dissolved solids content in the effluent, said effluent being effluent of pH less than 6.5 from a dying process and which is contaminated with at least one dye, heavy metal ions and surface active agents, but substantially free from fibres, which process comprises the steps of (i) subjecting the acid effluent to upflow ion-exchange to remove surface active agents present; (ii) thereafter passing the treated effluent to an electrolysis bath containing iron electrode which introduces sufficient ferrous ions from the iron electrode into the treated effluent to form a ferrous hydroxide flocculate by passing an electric current between said iron electrode through the effluent thereby the iron electrode is consumed during the electrolysis; (iii) removing said formed ferrous hydroxide flocculate and adhering heavy metal hyroxides and dyes from the effluent at a pH of 6 to 7.; (iv) adjusting the pH of said effluent to within the range 7 to 9 and causing oxidation of any ferrous ions remaining to ferric ions by means of at least one oxidizing agent selected from air, any oxidizing agent present in the effluent and added oxidizing agents to precipitate the ferrous hydroxide as ferric hydroxide; and (v) removing the precipitated ferric hydroxide with adhering heavy metal hydroxides to leave a treated effluent; (vi) subjecting the treated effluent to an examination for acceptable color and determination of the heavy metal content; (vii) recycling any treated effluent which is of unnacceptable color or which has an unacceptably high heavy metal content to the electrolysis step (ii), and repeating steps (ii) to (vi), thereby increasing the total content of ferrous ions introduced from the iron electrode into the effluent, the actual content of ferrous ions being dependent on the content of heavy metal ions in the effluent; (viii) adjusting the pH of the treated effluent from step (vi) which has an acceptable color and an acceptably low heavy metal content to a pH below 6.5 and (ix) recycling the treated effluent from step (viii) back to the dyehose.