BIODEGRADABILITY CHARACTERIZATION OF MIXTURES OF CHEMICAL CONTAMINANTS IN WASTE-WATER - THE UTILITY OF BIOTESTS

A practical scheme for assessment of the functional biodegradability o f industrial effluents in terms of degradable and persistent toxicity is suggested, and the general problems of biodegradability characteriz ation of complex mixtures is discussed. Persistent toxicity is assesse d after a long-term stabilization (aging) of the effluent brought abou t by incubating an effluent sample with at least an equal volume of te st medium (nutrient enriched surface water or mineral medium) containi ng a natural consortium of microorganisms. Degradable toxicity is the toxicity of the fresh effluent less its persistent toxicity. The two c ategories of toxicity should be managed differently. While for example dilution in the receiving water can be an effective means of mitigati ng degradable toxicity, dilution is in principle an insufficient contr ol instrument for persistent toxicity. A degradability study with an u nbleached sulphite pulp mill effluent, highly toxic to algae, is prese nted as a case history to illustrate the suggested biodegradability as sessment scheme and the results' interpretation. Copyright (C) 1996 IA WQ.