Presence of biofilms on ultrafiltration membrane surfaces increases the quality of permeate produced during ultra-low pressure gravity-driven membrane filtration.

This study evaluates the effect of the presence of biofilms on membrane surfaces on the quality of permeate produced during Gravity-driven membrane ultrafiltration. GDM ultrafiltration is applied to the decentralized production of drinking water. A second objective was to evaluate to what extent permeate quality is enhanced by pre-treating feed-water (using a packed bed biofilm reactor or a slow sand filter). The influence of the ageing of the biofilm on the permeate quality was evaluated and compared to the effect of virgin membranes. Permeate quality was evaluated in terms of Assimilable Organic Carbon (AOC) content and dissolved organic carbon fractions (e.g. biopolymers). Our results indicate that virgin ultrafiltration membrane remove a small fraction of the AOC and biopolymers (rejection <10%). The presence of a young and thin biofilm on the surface of the ultrafiltration membranes increases the permeate quality due to the degradation of AOC (>80%). However, over long-term the hydrolysis of the organic matter that accumulated on membrane surfaces increases the AOC content of the permeate, thus deteriorating the permeate quality. Pre-treatment of the feed-water help to control the biofilm accumulation and thus to limit the deterioration of the permeate quality. Permeate flux stabilised at average values of 7.5-8.9 L m(-2) h(-1). But the presence of pre-treatment helped to increase permeate flux (+12 and 19%, with the packed bed biofilm reactor and with the slow sand filter, respectively). Overall our study demonstrates that tolerating the presence of biofilm on membrane surface has a beneficial effect on the quality of permeate even if its quantity is decreased.

Routine bacterial analysis with automated flow cytometry.

The impact of multi-well plate automation on bacterial flow cytometric analyses was investigated. Cell concentrations in up to 96 samples can be measured accurately, as long as a reproducible staining protocol and a total measurement time of below 80 min is used. Fluorescence distribution in the samples may, however, display some variability.

Weathering-associated bacteria from the Damma glacier forefield: physiological capabilities and impact on granite dissolution.

Several bacterial strains isolated from granitic rock material in front of the Damma glacier (Central Swiss Alps) were shown (i) to grow in the presence of granite powder and a glucose-NH(4)Cl minimal medium without additional macro- or micronutrients and (ii) to produce weathering-associated agents. In particular, four bacterial isolates (one isolate each of Arthrobacter sp., Janthinobacterium sp., Leifsonia sp., and Polaromonas sp.) were weathering associated. In comparison to what was observed in abiotic experiments, the presence of these strains caused a significant increase of granite dissolution (as measured by the release of Fe, Ca, K, Mg, and Mn). These most promising weathering-associated bacterial species exhibited four main features rendering them more efficient in mineral dissolution than the other investigated isolates: (i) a major part of their bacterial cells was attached to the granite surfaces and not suspended in solution, (ii) they secreted the largest amounts of oxalic acid, (iii) they lowered the pH of the solution, and (iv) they formed significant amounts of HCN. As far as we know, this is the first report showing that the combined action of oxalic acid and HCN appears to be associated with enhanced elemental release from granite, in particular of Fe. This suggests that extensive microbial colonization of the granite surfaces could play a crucial role in the initial soil formation in previously glaciated mountain areas.