engleski

Influence of side-stream pressure aeration system on the biological wastewater treatment

Membrane bioreactors (MBRs) combining activated sludge processes with membrane filtration are becoming a promising technology for wastewater treatment. In spite of many advantages offered by MBRs, more than half of the total energy expenditure accounts for aeration in MBRs. Conventional diffused aeration systems have been widely adopted for providing oxygen into wastewater treatment process. As mixed liquor suspended solids (MLSS) increase, the oxygen transfer efficiency (OTE) decreases. The decrease on the OTE is more noticeable at an MLSS higher than 15 g/L, even reaching a limit at an MLSS of approximately 20 g/L (Germain et al. 2007) where ambient oxygen cannot longer be transferred into the mixed liquor solution when using conventional diffused aeration systems. That is, those technologies bring about not only higher aeration costs, but also influence the maximum achievable MLSS in the MBR with a direct impact on the footprint requirements of the system. In this context, there is a need for innovation on more efficient oxygen transfer systems both to reduce the energy for aeration, as well as to allow the design of more compact and movable MBRs, for operating MBRs at high MLSS beyond conventional MLSS concentrations. Among aeration systems, pressure aeration (PA) technology is used to improve the oxygen solubility by increasing total air pressure in bioreactors, enhancing the oxygen transfer rate and biochemical reaction rates. The main objective of this research is to assess the effects of high pressure used in a novel type of PA system on biological wastewater treatment processes by comparing conventional diffused aeration with PA. Specifically, experiments were conducted in each batch reactor aerated with fine bubble diffusers and the PA system, respectively, to evaluate the oxygen transfer capabilities (OTC) of the PA system compared to the OTC of a conventional aeration system in sludge at MLSS ranging from 4 to 40 g/L. Results reveal that an optimum MLSS concentration of 20 g/L is suggested to maximize the treatment capacity while minimizing the system’s footprint when operating MBRs aerated with fine bubble diffusers. On the other hand, the oxygen transfer on the evaluated PA system did not appear to be as affected as the fine bubble diffusers by the high MLSS concentrations. This study also provides a better understanding of both the effects of the PA technologies on the diversity in microbial communities, as well as the potential impacts of the PA systems on solid/liquid separation processes (membrane fouling).

SDOX, MBR, aeration system, OTE

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