Simultaneous enhanced biological phosphate uptake and biological denitrification under anoxic conditions were investigated in a modified lab-scale nutrient removal activated sludge system (DEPHANOX). The aim of the experiments was to find whether it can be technologically convenient to use the capability of poly-P bacteria of taking up phosphate under anoxic condition by utilizing nitrate as electron acceptor. An experimental comparison of removal efficiencies with a more conventional treatment flow scheme (JHB), using low influent TKN/COD ratio, was also carried out. Phosphate uptake in anoxic condition was compared to that in oxic environment in batch tests. PHB anoxic and oxic degradation was evaluated by respirometric tests. Results of the long-term operation of continuous-flow lab-scale system as well as results of batch tests showed that the anoxic phosphate uptake with simultaneous denitrification after a previous anaerobic substrate uptake could significantly reduce the extent of competition for organic substrate between poly-P bacteria and denitrifiers. A side-stream nitrification in fixed-film reactor reduced the losses of organic carbon by oxidation and stabilized the slow-growing population of nitrifiers in the system.
A comparative kinetic study was carried out on the anaerobic digestion of olive mill wastewater (OMW) and OMW that was previously fermented with Geotrichum candidum, Azotobacter chroococcum and Aspergillus terreus. The reactors used were continuously fed and contained sepiolite as support for the mediating bacteria. A kinetic model for multicomponent substrate removal by anaerobic digestion has been used. The model is based on the linear removal concept which is a special case of the broader Monod equation. The second-order kinetic constant, k 2s , was found to be in¯uenced by the pretreatment carried out, and was 4.2, 4.0 and 2.5 times higher for Aspergillus, Azotobacter and Geotrichum-pretreated OMWs than that obtained in the anaerobic digestion of untreated OMW. This was signi®cant at 95% con®dence level. This behaviour is believed to be due to the lower levels of phenolic compounds and biotoxicity present in the pretreated OMWs. In fact, the kinetic constant increased when the phenolic compound content and biotoxicity of the pretreated OMWs decreased. In addition, the macroenergetic parameters of the anaerobic digestion of OMW, i.e. the speci®c rate of substrate uptake for cell maintenance, m, and the yield coef®cient for the biomass, Y, decreased by a factor of 2.4, 3.6 and 5.1 and increased by a factor of 1.9, 2.2 and 2.4 respectively, for the OMWs previously treated with Geotrichum candidum, Azotobacter chroococcum and Aspergillus terreus in relation to the observed values for the untreated OMW.
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