Issue 1 [March]( Issue on Wastewater Treatment ) An experimental and mathematical simulation of biological processes in a sewerage systemGavalakis Ε., Mamais D., Marinos C. and Andreadakis A., Pages:75-81 DOI: https://doi.org/10.30955/gnj.000399Paper Topic: General Issue: Issue 1Get Full Paper AbstractSewer systems may often operate as bioreactors causing considerable wastewater quality changes and in some cases reducing the pollution load conveyed to the treatment plant. Conceptually, transformation of organic matter takes place both in the bulk water (by suspended micro-organisms) and by the sewer biofilm, under aerobic and anaerobic conditions. The most important processes are the hydrolysis of hydrolysable substrate to readily biodegradable substrate and the uptake of the latter for the growth of the biomass (in the form of biofilm and suspended in the liquid) and for maintenance purposes. Depending on whether the critical parameter is the hydrolysis rate or the growth rate of biomass there is a significant increase (former) or decrease (latter) of readily biodegradable substrate. The scope of the work presented herein was to study the processes governing the fate of readily biodegradable substrates in sewer systems in an attempt to verify the mathematical model of a sewerage system developed by Gavalakis et al. (2003) [5]. The specific objectives were to evaluate the effect of (1) biofilm growth, (2) suspended biomass and (3) dissolved oxygen (DO) concentration on readily biodegradable substrate removal. The experimental results obtained showed that high soluble substrate uptake rates can be observed in sewer systems indicating that sewer systems can act as biological reactors where substantial changes in sewage quality characteristics can occur. Especially for soluble substrates like acetate these changes that take place in the sewer may significantly affect enhanced biological phosphorus removal and denitrification in the wastewater treatment. The experimental data on soluble substrate removal in sewers showed that the previously developed mathematical model describes in a satisfactory way the kinetics of acetate removal. Acetate removal rates due to biofilm growth did not appear to be influenced by biofilm mass or biofilm thickness. Acetate removal as described by the model appeared to follow a linear correlation between pipe surface to liquid volume (A/V) ratio and soluble COD removal was obtained. In addition acetate uptake rate appeared to increase significantly with increasing DO concentration. The kinetics describing the effect of DO on substrate removal appeared to follow a half order reaction rate throughout the range of DO concentrations studied. Influence of the Presence of Long Chain Fatty Acids (Lcfas) in the Sewage on the Growth of M. Parvicella in Activated Sludge Wastewater Treatment Plants Mamais D., Nikitopoulos G., Andronikou E., Gavalakis E., Andreadakis A., Noutsopoulos K., Giotakis C. and Tsimarakis G., Pages:82-88 DOI: https://doi.org/10.30955/gnj.000400Paper Topic: General Issue: Issue 1Get Full Paper AbstractFoaming and bulking problems in activated sludge treatment plants are associated to the presence of a variety of filamentous bacteria. However, it has been observed that M. parvicella is the most frequent filamentous microorganism causing sludge bulking and foaming, especially in treatment plants involving nutrients removal. High sludge retention time, low DO, low temperature, presence of anoxic, anaerobic, and intermittently aerated zones, are the most commonly cited conditions associated with its growth. Substrate composition is another significant factor, as it has been found that slowly degradable organic material may favour the growth of M. parvicella. If has also been suggested that M. parvicella may preferably store long chain fatty acids (LCFAs) under anaerobic conditions and subsequently use it for growth. The paper presents the results of an investigation conducted at the wastewater treatment plant of Ioannina, aiming to establish a cause-effect relationship between the presence of LCFAs and the abundance of M. parvicella. This investigation is a part of a wider study sponsored by the Greek Secretariat for Research, under the PENED programme. The duration of the investigation covers 8 months, from January 2004 to August 2004. During this period samples were taken from the sewage collection network and wastewater treatment plant of Ioannina and analysed for, among other parameters, LCFAs and total fatty acids while samples of the mixed liquor and the foam in the biological reactors were microscopically analysed in order to determine the presence and amount of various types of filamentous bacteria. Two main conclusions were drawn. The first is related to the effect of temperature on the growth of M. parvicella, indicating that the growth of this specific filamentous bacterium is favoured by low temperatures (generally below 20 oC), while higher temperatures cause the practical elimination of M. parvicella, irrespectively of other factors. This conclusion verifies previous studies in pilot units and full scale plants. The second conclusion is that during winter periods there seems to be a positive correlation, between the presence of fatty acids and more specifically LCFAs and the amount of M. parvicella. 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