Chemical and toxicological assessment of a full-scale biosolid compost.

The impact of a full-scale biosolid composting plant on the fate of a broad range of priority organic pollutants was investigated. Chemical analysis was performed at different steps of the process during two seasons. Simultaneously, the toxicological quality was assessed using estrogen α-, dioxin-, and pregnane X-receptor reporter cell lines. Mass-balance calculation highlighted the removal of easily degradable pollutants during composting. The important variations observed for each compound and for the two seasons might be explained by pollutant-fate dependency on process parameters like temperature. The final compost displayed low pregnane X activity but high estrogenic activity. The dioxin-like activity stayed constant through the process. The chemical and toxicological results highlight the importance of combining both approaches to accurately assess the compost quality. Such compilation of data on full-scale processes may be also very helpful for the environmental risk assessment of new organic waste disposal practices.

Behaviour of pathogenic and indicator bacteria during urban wastewater treatment and sludge composting, as revealed by quantitative PCR.

Two enteric pathogens, Salmonella spp. and Campylobacter jejuni, and two bacteria commonly used as indicators, Escherichia coli and Clostridium perfringens, were monitored using quantitative real-time PCR during municipal wastewater treatment and sludge composting. The results were compared with those obtained using standard culture methods. A reduction of all bacteria was observed during wastewater treatment and during the thermophilic phase of composting. However, the bacterial groups studied behaved differently during the process, and the main differences were observed during biological treatment in activated sludge basins. In particular, Salmonella spp. and C. jejuni survived better during activated sludge treatment than E. coli. C. jejuni was the most resistant to wastewater treatment among the four bacterial groups. Overall, differences in survival were observed for all bacteria studied, when submitted to the same environmental pressure. This holds both for differences between indicators and pathogenic bacteria and between pathogenic bacteria. These results show the difficulty in defining reliable indicators.