Abstract
We studied new micro-perforated diffuser concepts for the aeration process in wastewater treatment plants and evaluated their aeration efficiency. These are micro-perforated plate diffusers with orifice diameters of 30 µm, 50 µm and 70 µm and a micro-perforated tube diffuser with an orifice diameter of 50 µm. The oxygen transfer of the diffuser concepts is tested in clean water, and it is compared with commercial aerators from the literature. The micro-perforated tube diffuser and micro-perforated plate diffusers outperform the commercial membrane diffusers by up to 44% and 20%, respectively, with regard to the oxygen transfer efficiency. The most relevant reason for the improved oxygen transfer is the fine bubble aeration with bubble sizes as small as 1.8 mm. Furthermore, the more homogenous cross-sectional bubble distribution of the micro-perforated tube diffuser has a beneficial effect on the gas mass transfer due to less bubble coalescence. However, the pressure drop of micro-perforated diffusers seems to be the limiting factor for their standard aeration efficiencies due to the size and the number of orifices. Nevertheless, this study shows the potential for better aeration efficiency through the studied conceptual micro-perforated diffusers.
Highlights
Gas dispersion in liquids is crucial for a large number of multiphase reactions in chemical and biochemical processes
The biological wastewater treatment is accountable for the majority of the energy consumption [1]
Aeration is responsible for more than 50% of the overall electric energy consumption of a treatment plant operating with activated sludge [2]
Summary
Gas dispersion in liquids is crucial for a large number of multiphase reactions in chemical and biochemical processes. One example is the gas dispersion in wastewater treatment, where high amounts of air are dispersed into large tanks for activated sludge aeration or ozonation for contamination removal. The aeration promotes suspension of the activated sludge and mixing for improved contacting of microorganisms with organic matter. This is the most energy-intensive process step in the activated sludge wastewater treatment. The gas–liquid oxygen mass transfer, as well as the turbulent mixing, is highly affected by the bubble size, the bubble residence time, the gas hold-up, the gas–liquid surface area and the liquid properties [3,4,5]
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