Interaction of Different Groups of Micro-Organisms in Biological Phosphate Removal

Observations under continuous flow conditions in a bench-scale activated sludge unit and in full-scale nutrient removal activated sludge plants indicated that, despite relatively high numbers of Aoinetobaoter oalooaoetious, no enhanced biological phosphate removal was achieved. Total bacteriological analyses of the mixed liquor of these plants indicated that in all cases Aeromonas spp. were present in low numbers, particularly Aeromonas punotata. This bacterium is described as being able to produce acetate as one of its major fermentation end products. Phosphate uptake batch experiments using pure cultures showed that Aeromonas punotata enhances the phosphate uptake capability of Aoinetobaoter calooaoetious by converting carbohydrates present in the sewage to a substrate required for phosphate removal. It was shown that the anaerobic zone in a phosphate removing activated sludge plant is a fermentation reactor, where suitable substrates are generated rather than stress conditions imposed on the bacteria, a condition which was previously believed to be essential for enhanced phosphate uptake.