On-line monitoring of the dynamics of trihalomethane concentrations in a warm public swimming pool using an unsupervised membrane inlet mass spectrometry system with off-site real-time surveillance.

To study the long-term dynamics of trihalomethanes (THMs) in a warm (31-33 degrees C) public swimming pool, we built a robust membrane inlet mass spectrometer that could perform unsupervised, on-site monitoring of the concentration of these compounds with off-site, real-time surveillance. The instrument was installed in a technical room below the pool and operated continuously for more than a year practically only interrupted for filament replacements every 6-8 weeks. One to two days after a filament replacement, the instrument stabilized and kept its calibration until shortly before the next filament burnout. The on-line monitoring of THMs revealed a daily rhythm in the concentrations of chloroform and bromodichloromethane. They increased during the pool's closing hours and decreased during opening hours with the minimum concentration being approximately half of the maximum. Over the 1 year monitoring period, the variation in the maximum registered daily concentration was 30-100 microg/L for chloroform. The variation of bromodichloromethane was 5-10 microg/L, except during bursts of 1-2 days duration, where the concentration of bromodichloromethane could reach 100 microg/L. The burst in bromodichloromethane concentration was directly correlated with salt addition (sodium chloride) to the pool water for use in the pool's electrolytic in-line chlorination system. A correlation between THM removal from the pool water and the operation of a strong water jet system was also found.

Variations in microcolony strength of probe-defined bacteria in activated sludge flocs.

The strength of activated sludge flocs is important for the flocculation, settling and dewatering properties of activated sludge and thus the performance of wastewater treatment plants. Little is known about how different bacteria affect the floc properties, so in this study it was investigated whether the strength and other characteristics of large microcolonies within activated sludge flocs from a full-scale nutrient removal plant varied significantly between different phylogenetic groups of bacteria. The investigation was carried out by using a shear method for deflocculation of activated sludge flocs, combined with different chemical manipulations under defined conditions. The identification and quantification of the microcolony-forming bacteria were conducted with group-specific gene probes and fluorescence in situ hybridization. The focus was on the microcolonies and not on the entire sludge flocs. In general, the results showed large difference in the strength and colloid-chemical properties of the different probe-defined microcolonies. By applying extensive shear to the system, less than 12% of the microcolony biovolume of the Beta-, Gamma- and Deltaproteobacteria and Actinobacteria could be disrupted, thus forming strong microcolonies. Alphaproteobacteria and Firmicutes formed weaker microcolonies (42-61% could be disrupted by shear). For most groups, several intermolecular forces determined the strength of the microcolonies: hydrophobic interactions, cross-linking by multivalent cations and perhaps entanglements of extracellular polymeric substances. However, the dominant force varied between the various phylogenetic groups. The large difference between the different phylogenetic groups indicated that only a few species were present within each group, rather than many different bacterial species within each phylogenetic group had similar floc properties.