Bulking and Foaming in France: The 1999–2001 Survey

To assess bulking in French wastewater treatment plants we developed a three-topic approach, including analysis of i) technical assistance annual reports, ii) a questionnaire, and iii) microscopic sample observations. A seasonal effect was very apparent on the average SVI (mL/g). Three situations appear to promote bulking according to statistical analysis and operators' comments: i) low-organic loading or rapid variation in organic loading, ii) raw sewage dilution or hydraulic loading variation, iii) rapid high-organic loading. Phosphorus removal by metallic salt addition leads to an average SVI reduction of 40 mL/g. Two situations in the sludge treatment process, which call for improvement, are: - The maintaining a high MLSS concentration in the aeration tank due to the limitation of sludge evacuation, - When storing sludge for several days or weeks in sludge thickening tank, thereby favoring the formation of septic compounds, which are subsequently reintroduced in the influent. Our study highlights Type 0092 as the most frequent filamentous microorganism observed followed by Microthrix parvicella. Thiothrix spp. ranks third.