Waste water purifying procedure

DETAILED DESCRIPTION I claim: 1.
A waste water purifying process for treatment of waste water containing chlorinated phenols in a biofilter having a layer containing bark of wood, said process comprising the steps of forming a bacterial population in said bark layer, said population comprising one or several of the bactery strains deposited in the University of Helsinki Institute of General Microbiology under the deposition codes YM 134-202 and YM 241-268 and which have been formed by packing into biofilters crushed coniferous tree bark and bacteriferous water, ooze, mud or bark residues taken from a water body polluted by chlorinated and unchlorinated phenols and by aromatic carboxylic acids and by thereafter feeding into the biofilters water containing said substances, whereby the bactery strains are characterized by an ability to tolerate the presence of chlorinated phenols and to use compounds selected from said chlorinated and unchlorinated phenols and aromatic carboxylic acids as their sources of carbon and energy, and then conducting the waste water to be treated through the biofilter, whereby the purification is effected by means of the bactery population working in the presence of chlorinated phenols contained in the waste water.
2.
The process according to claim 1, wherein in the biofilter, a bactery population is formed which contains a strain belonging to the deposited bactery strains YM 241-268 and growing in thichlorophenol and a strain belonging to said deposited bactery strains and growing in tetrachlorophenol, whereby the bacterial population is characterized by an ability to decompose said chlorinated phenols present in a waste water.
3.
The process of claim 1 wherein the waste water is a bleaching effluent from a cellulose sulfate mill which includes chlorination and alkali steps.
4.
The process according to claim 3, wherein the waste water contains about 50% bleaching effluent from the chlorination step and about 50% bleaching effluent from the alkali step.
5.
The process according to claim 1, wherein the waste water to be purified is circulated in such manner that the water flows through the biofilter several times