A combined approach for a better understanding of wastewater treatment plants operation: statistical analysis of monitoring database and sludge physico-chemical characterization.

Biological wastewater treatment plants (WWTP) are complex systems to assess. Many parameters are recorded daily in WWTP to monitor and control the treatment process, providing huge amounts of registered data. A combined approach of extracting information from the WWTP databases by statistical methods and from the sludge physico-chemical characterization was used here for a better understanding of the WWTP operation. The monitored parameters were analysed by multivariate statistical methods: Principal Components Analysis and multiple partial linear regression. The WWTP operational conditions determine the sludge characteristics. The bacterial activity of the sludge in terms of extra-cellular polymeric substances (EPS) production was assessed using size exclusion chromatography and the internal structure of sludge flocs was observed by confocal laser scanning microscopy. The diagnosis of three paper mill WWTP enabled the identification of an important EPS production, the presence of the nitrification process and the presence of PO(4)(3-) nutrient in WWTP-A. These three main characteristics of WWTP-A were related with a systematically good sludge settling. In WWTP-B and C with bad settling, the bacterial activity was weak.

Exopolymeric production by bacterial strains isolated from activated sludge of paper industry.

The bacteria originated from the paper mill sludge were identified, isolated and cultured. Enterobacter (E) and Klebsiella (K) represented 70% of the culturable aerobic flora. Kinetics of EPS production in isolated culture and in arbitrary 1:1 mixture was investigated by high-pressure size exclusion chromatography (HPSEC). In isolated culture, Enterobacter produced regularly and gradually during 24 h of culture, while Klebsiella produced the total amount of EPS already after 4 h without any changes later. The chromatographic profiles of the EPS production of the 1:1 mixture after 4, 8 and 24 h of culture could be fitted as a linear combination of the profiles of exopolymers produced by pure Enterobacter and Klebsiella strains. After 24 h of culture, Enterobacter was predominant in term of population (82%) and produced about 77% EPS amount, in spite of competition phenomena observed during culture.