Assessing microbial communities for a metabolic profile similar to activated sludge.

To search for reliable testing inocula alternatives to activated sludge cultures, several model microbial consortia were compared with activated sludge populations for their functional diversity. The evaluation of the metabolic potential of these mixed inocula was performed using the Biolog EcoPlates and GN and GP MicroPlates (Biolog, Inc., Hayward, California). The community-level physiological profiles (CLPPs) obtained for model communities and activated sludge samples were analyzed by principal component analysis and hierarchic clustering methods, to evaluate the ability of Biolog plates to distinguish among the different microbial communities. The effect of different inocula preparation methodologies on the community structure was also studied. The CLPPs obtained with EcoPlates and GN MicroPlates showed that EcoPlates are suitable to screen communities with a metabolic profile similar to activated sludge. New, well-defined, standardized, and safe inocula presenting the same metabolic community profile as activated sludge were selected and can be tested as surrogate cultures in activated-sludge-based bioassays.

Ecotoxicological evaluation of cork-boiling wastewaters.

Toxicity tests with Vibrio fischeri, Daphnia magna, and Lemna minor were used to evaluate acute and chronic toxicity of cork-boiling wastewaters and correlation analysis was performed with physicochemical parameters. Acute toxicity values (EC(50)) ranged from 2.3% to 24.2% in the Microtox test and from 4.4% to 29.5% in the Daphnia test. According to these values, 78% of the samples were classified as acutely toxic to the most sensitive species (V. fischeri). Significant correlation was obtained between EC(50) and chemical oxygen demand, biochemical oxygen demand after 5 days, total organic carbon, tannin and lignin and total solids. No significant correlation was found between the two acute tests. The D. magna chronic test showed significant differences between all tested concentrations and the control, with an EC(50) of 0.32%. An EC(50) value of 26.0% was calculated for L. minor. For the analysis of cork-boiling wastewater toxicity and routine biomonitoring, the use of the Microtox test is suggested, to afford greater environmental protection.

Biodegradability testing using standardized microbial communities as inoculum.

Reference materials are important tools for maintaining high-quality assurance standards, including for biological materials. A significant number of environmental international standards, including biodegradability and toxicity, involve utilization of activated sludge (AS) inocula. The absence of inoculum standardization in these tests is a potential source of error influencing the results. In this study three defined microbial consortia, two commercial inocula and a designed bacterial inoculum, were evaluated as an AS alternative seed for the Zahn-Wellens test, using diethylene glycol as the reference chemical. The results showed that to achieve diethylene glycol biodegradation with these inocula, a number of 10(5) colony-forming units per milliliter of effective degrader microorganisms had to be present. Moreover, the addition of AS supernatant to the test mixtures improved inocula performance (the biodegradability curves), bringing them closer to those obtained with AS inocula. Among the three defined consortia, the designed inoculum replicates bested the AS behavior in the range of concentrations tested, with degradation completed in 12-14 days. Comparisons of the community substrate utilization profiles corroborated these results, showing that the designed inoculum profile was the most similar to the AS profile. The biodegradability and metabolism results provided support for the assertion that the designed inoculum can be used in the Zahn-Wellens test and as a base to develop reference inocula for other biodegradability and toxicity tests.

Alternative inocula as activated sludge surrogate culture for a toxicity test.

The use of activated sludge to assess the potential toxicity and environmental impact of chemicals and wastewaters suffers from several drawbacks related to the heterogeneity, absence of standardization, and health risk associated with this mixed-sewage population. To search for reliable testing inoculum alternatives, the performance of two commercial inocula (BI-CHEM and BIOLEN M112), a garden-soil inoculum and a pure culture of Pseudomonas sp., was compared with an activated sludge inoculum (AS) in the inhibition respiration test ISO 8192-1986 (E). The respiration rates of microbial inocula were assayed for the reference compound 3,5-dichlorophenol. The acute toxicity values (IC(50)) ranged from 6.7 mg/L (Pseudomonas sp.) to 22.7 mg/L (garden soil), overlapping the expected values for activated sludge microorganisms despite the bacterial diversity. The assayed microbial inocula also showed higher reproducibility than AS and an overall similarity of catabolic profiles obtained with Biolog EcoPlates was observed between AS and some mixed inocula. These results point to the potential ability of such inocula as surrogate cultures in relevant activated sludge-based bioassays. New, well-defined, standardized, and safe tools will then be available for monitoring the ecological impact of hazardous substances and effluents, thus providing environmental protection.

Effect of olive mill wastewaters on the oxygen consumption by activated sludge microorganisms: an acute toxicity test method.

The test for inhibition of oxygen consumption by activated sludge (ISO 8192-1986 (E)) was evaluated as a tool for assessing, the acute toxicity of olive mill wastewaters (OMW). According to the ISO test, information generated by this method may be helpful in estimating the effect of a test material on bacterial communities in the aquatic environment, especially in aerobic biological treatment systems. However, the lack of standardized bioassay methodology for effluents imposed that the test conditions were modified and adapted. The experiments were conducted in the presence or absence of an easily biodegradable carbon source (glucose) with different contact times (20 min and 24 h). The results obtained showed a remarkable stimulatory effect of this effluent to the activated sludge microorganisms. In fact, the oxygen uptake rate values increase with increasing effluent concentrations and contact times up to 0.98 microl O(2) h(-1) mg(-1) dry weight for a 100% OMW sample, 24 h contact time, with blanks exhibiting an oxygen uptake rate of ca. 1/10 of this value (0.07-0.10). It seems that the application of the ISO test as an acute toxicity test for effluents should be reconsidered, with convenient adaptation for its utilization as a method of estimating the effect on bacterial communities present in aerobic biological treatment systems.

Landfarming in a PAH-contaminated soil.

The present work describes a coke oven soil treatability study by land-farming, conducted on-site in a field scale facility covering 100 m2. The soil contamination was mainly due to high concentrations of polynuclear aromatic hydrocarbons (PAHs) up to 1,140 mg/Kg dry weight (sigma EPA). Along the treatment process the soil was characterised at the chemical, microbiological and ecotoxicological levels. After 3 months a reduction of 63% in total PAHs concentration was observed, being detected a more pronounced reduction for PAHs with 2, 3 and 4 rings (79%). Concomitantly, a change in the composition of the microbial population was observed with a significant increase in the PAHs degrading and total heterotrophic colonies. Concerning the ecotoxicity and genotoxicity data no effect was detected in the treated soil samples eluates.