THE EFFICIENCY OF DIFFERENT PHENOL-DEGRADING BACTERIA AND ACTIVATED SLUDGES IN DETOXIFICATION OF PHENOLIC LEACHATES

Phenolic composition, toxicity and biodegradability of three different phenolic leachates/samples was studied. Samples A and C were the leac hates from the oil-shale industry spent shale dumps at Kohtla-Jarve, E stonia. Sample B was a laboratory-prepared synthetic mixture of 7 phen olic compounds mimicking the phenolic composition of the leachate A. T oxicity of these 3 samples was analyzed using two photobacterial test (BioTox(TM) and Microtox(TM)), Daphnia test (DAPHTOXKIT F(TM) pulex) a nd rotifiers' test (ROTOXKIT F(TM)). All the LC50 values were in the r ange of 1-10%, leachate A being the most toxic. The growth and detoxif ying potential (toxicity of the growth medium was measured using photo bacterial tests) of 3 different phenol-utilizing bacteria and acclimat ed activated sludges was studied in shake-flask cultures. 30% leachate A (altogether 0.6 mM total phenolic compounds) was too toxic to rhodo cocci and they did not grow. Cell number of Kurthia sp. and Pseudomona s sp. in 30% leachate A increased by 2 orders of magnitude but despite of the growth of bacteria the toxicity of the leachate did not decrea se even by 7 weeks of cultivation However, if the activated sludge was used instead of pure bacterial cultures the toxicity of the 30% leach ate A was eliminated already after 3 days of incubation. 30% samples B and C were detoxified by activated sludge even more rapidly, within 2 days. As the biodegradable part of samples A and B should be identica l, the detoxification of leachate A compared to that of sample B was m ost probably inhibited by inorganic (e.g., sulphuric) compounds presen t in the leachate A. Also, the presence of toxic recalcitrant organic compounds in the leachate A (missed by chemical analysis) that were no t readily biodegradable even by activated sludge consortium should not be excluded. (C) 1998 Elsevier Science Ltd. All rights reserved.