With new EEC regulations, alternative treatment and disposal techniques of the excess sludge produced by Activated Sludge (AS) wastewater treatment plants have to be performed. In order to reduce the excess sludge produced, experiments have been carried out with a Membrane BioReactor (MBR) to study the maintenance and cryptic growth phenomena of Pseudomonas fluorescens culture taken as a model when grown on a limiting substrate complex medium similar to a synthetic urban wastewater. Experiments with various imposed wasting rates showed that viability and sludge production yield decreased when sludge age increased. Same variations were observed on the cell content ratio protein/polysaccharide by analysis of the cell lysis products released after discontinuous thermal treatment. Biomass growth on these cell lysis products was achieved to characterize cryptic growth and its impact on sludge production yield. Finally, a continuous sludge thermal treatment system was operating with MBR to amplify sludge breakage and consequently biomass growth on the lysis products. With the promising results obtained, this work gives a new outlook on the AS process and leads to the development of processes with control and reduction of sludge production.
This research found evidence of an association between occupational exposure to bioaerosols in composting plants and health outcome occurrence in exposed workers. An occupational exposure assessment in six composting plants was performed to better characterize personal exposure levels and evaluate associated health risk in workers. Sampling results showed large ranges of concentrations of dust, bacteria, molds, and endotoxin in ambient air and in personal samples, both when driving a front-end loader and when cleaning, monitoring, and performing maintenance tasks. Mean personal exposure levels were high at 100 to more than 10 000 times higher than outdoor background levels and fully consistent with occurrence of inflammatory and allergic respiratory outcomes among workers. Engineering control, personal protection, and education and training programs for employees, health, and safety officials, and occupational physicians are being developed and implemented. Water Environ. Res., 81, 866 (2009).
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