BIODEGRADABILITY SIMULATION STUDIES IN SEMICONTINUOUS ACTIVATED-SLUDGE REACTORS WITH LOW (MU-G L RANGE) AND STANDARD (PPM RANGE) CHEMICAL CONCENTRATIONS/

The official OECD/EEC activated-sludge biodegradability simulation tes t has been criticised for providing a poor simulation of the biodegrad ability behaviour of industrial chemicals in municipal sewage treatmen t plants due to the high dosed concentration of test substance of appr ox. 20-40 mg/L necessitated by measuring compound removal by DOG-analy sis. Realistic concentrations of industrial chemicals are more commonl y in the mu g/L range. With increasing concentration both the kinetic regime of degradation and the adaptation behaviour can be expected to change. Results from a comparative study in semicontinuous reactors wi th high (20 mg DOC/L) and low (10 mu g test substance/L) inlet concent rations of aniline, 4-chloroaniline, and pentachlorophenol, conducted by means of C-14-tracer technique, revealed large differences in biode gradation behaviour between the two concentration levels and led to th e following tentative general conclusions: 1) the percentage of test c ompound removed by unadapted sludge tends to be higher with test compo und dosed at trace concentrations than at standard (high) concentratio ns (20 mg/DOC/L); 2) by contrast, in successfully adapted systems, the removal percentage (and the ''extent of adaptation'') may be largest with high concentrations; 3) the use of real sewage instead of peptone synthetic sewage better safeguards against sludge deterioration, in p articular at low sludge retention times, and tends to increase the ada ptation potential of the sludge; 4) the use of synthetic sewage in com bination with regular reinoculation of the reactor (in this study by r eplacing 10% of the sludge with freshly collected sludge once a week) may be a feasible alternative to using real sewage. Copyright (C) 1996 Elsevier Science Ltd