Bakterielle Biotestverfahren zur Bestimmung der Toxizität von Abfällen

For a risk assessment of wastes, fast and sensitive screening methods are required to detect possible toxic effects. In this study, different leachability methods (DIN 38414, part 4; EPA 1310; EPA 1320) were used to prepare aqueous leachates from different wastes; these leachates were rested in different bacterial toxicity test systems for possible toxic effects. As bacterial toxicity tests, the luminescent bacteria test and the growth inhibition test with activated sludge bacteria were used. The test systems showed a good agreement of the results from the different leaching methods, thereby indicating the reliability of the test systems used. The luminescent bacteria inhibition test showed a higher sensitivity than the growth inhibition test which is in good accordance with literature data. We conclude that both test systems are well suited to assess the toxic potential of aqueous waste leachates.     

Evaluation and further development of the activated sludge respiration inhibition test

The activated sludge respiration inhibition test is an important bacterial test system for the determination of bacterial toxicity of chemical compounds. The exposure period recommended by OECD 209 and ISO 8192 protocols is 30 and 180 min. A modified version of the test was developed which allowed a prolonged incubation period of 27 h to enhance the possibilities of the test system. The test system with the prolonged incubation time was evaluated by the recommended reference compound 3.5-dichlorophenol and showed an EC50 of 6.3 mgl(-1) with a coefficient of variation of 12.7%. Furthermore, the use of an open test system was evaluated showing a comparable toxicity but a higher coefficient of variation than the closed test system. A storage of activated sludge for several days accompanied by a daily feed with OECD nutrient solution should be avoided, for it can cause a decreased sensitivity of the inoculum. Different statistical fit procedures were tested indicating that Weibull fit procedures were superior for extended data sets covering a wide range of concentrations whereas Gamma and Probit fits were appropriate for smaller data sets mainly restricted to the linear part of the dose response curve.     

The use of Microtox to assess toxicity removal of industrial effluents from the industrial district of Camaçari (BA, Brazil)

The treatment efficiency, as toxicity removal, of complex effluents from the Industrial District of Cama?ari (BA, Brazil), after biological treatment with activated sludge was evaluated using Microtox. Samples of the equalised effluent (EE) were collected prior to treatment together with samples of the treated effluent (TE), which remained 24 h in the treatment plant. Rehydrated colonies of Vibrio fischeri were exposed to sequential dilutions of EE and TE to assess luminosity interference. Values for EC50 were calculated, together with the respective toxicity units. In all, twenty assays of each effluent type were carried out and the mean toxicity removal was 92.71%, while the chemical oxygen demand (COD) presented mean reduction of 83.04%. There was a variability of an order of magnitude between the Microtox results for the two types of effluents. The mean EC50 values were 2.12 for EE and 47.78% for TE. In spite of its weakness in some conditions, the Microtox system demonstrated to work adequately in assessing effluent toxicity removal in this treatment plant and therefore can be used for further toxicity removal programs.     

Evaluation of a respirometric test method to determine the heterotrophic yield coefficient of activated sludge bacteria

The heterotrophic yield coefficient of activated sludge bacteria is an important parameter in the field of wastewater degradation kinetics and the determination of degradation kinetics of defined chemicals. With the help of easily biodegradable organic compounds like glucose and acetate the respiration kinetics of degrading activated sludge bacteria was studied. The results of the respiration analysis were transformed to examine the degradation and respiration kinetics of municipal wastewaters at different food to microorganism ratios (F/M ratios). It was proved that the heterotrophic yield coefficient of aerobically degrading activated sludge bacteria could reliably be determined and that the heterotrophic yield coefficient was independent of the F/M ratio over a wide range.     

An integrated test strategy for the assessment of anaerobic biodegradability of wastewaters

The anaerobic biodegradability of wastewaters from different chemical plants was determined by an integrated test strategy consisting of an anaerobic toxicity test, a static anaerobic biodegradation test and a continuously operated fixed bed reactor test. This integrated procedure offered a useful tool for screening wastewaters for anaerobic biodegradability. Four different wastewaters were tested for anaerobic toxicity and biodegradability. One wastewater was used in subsequent testing in a fixed bed reactor which aimed to illustrate a potential design of an anaerobic treatment plant.     

Kinetics of ammonium removal with suspended and immobilized nitrifying bacteria in different reactor systems

The degradation of ammonium by free and immobilized bacteria in different reactor systems was investigated. It was found that the start-up of a nitrifying system is enhanced if a reservoir of immobilized bacteria is present. It was also found that in a single stage system with suspended nitrifying bacteria a stable ammonium removal > 95 % could be established up to an influent ammonium concentration of 1000 mg/1 and a volumetric loading rate (VLR) of 2.3 kg NH₄⁺ m⁻³ d⁻¹. The oxygen uptake rate (OUR) due to nitrification processes was greatly enhanced with increasing volumetric loading rates. Using nitrifying bacteria immobilized on Siran material it was demonstrated that the ammonium degradation rate was directly proportional to the initial ammonium concentration.