Utilization of pure oxygen from water-electrolysis combined with micro- and nanobubble aeration technologies in wastewater treatment
Prof. Dr.-Ing. M. Engelhart
Technical University Darmstadt, Faculty of Civil and Environmental Engineering, Institute IWAR, Chair of Wastewater Technology
Technical University Darmstadt, Faculty of Civil and Environmental Engineering, Institute IWAR, Chair of Wastewater Technology
With the proposal of the so called “Hydrogen Strategy” by the European commission industry and society is being faced with a need for high amounts of green hydrogen. As a consequence, electrolysis capacity is expected to increase rapidly over the next years to feed the hydrogen demand. As a coproduct of water-electrolysis pure oxygen is being produced. To improve the economics of water-electrolysis researchers are looking into potential use cases of the electrolysis oxygen including applications in wastewater treatment and specifically in the aeration of activated sludge processes.
Pure oxygen needs to be utilized it in a most efficient way. State of the art fine bubble aeration systems typically reach oxygen transfer efficiencies (kg O2 dissolved per kg O2 aerated) only in the range of 20-25 % (depending on the depth of submergence of the diffusers, airflow rate and diffuser density). Novel aeration technology concepts that advance into micro- and nanobubble range, see Figure 1 for scale comparison, promise significantly higher oxygen transfer efficiencies because of higher gas-liquid-interface and thus may be suitable to combine with pure oxygen aeration.
Pure oxygen needs to be utilized it in a most efficient way. State of the art fine bubble aeration systems typically reach oxygen transfer efficiencies (kg O2 dissolved per kg O2 aerated) only in the range of 20-25 % (depending on the depth of submergence of the diffusers, airflow rate and diffuser density). Novel aeration technology concepts that advance into micro- and nanobubble range, see Figure 1 for scale comparison, promise significantly higher oxygen transfer efficiencies because of higher gas-liquid-interface and thus may be suitable to combine with pure oxygen aeration.
Implementation of micro- and nanobubble aeration still lacks fundamental knowledge on oxygen transfer, because basic research has been restricted to lab-scale so far. Therefore, different to other known studies, this project aims to experimentally evaluate micro- and nanobubbles for their fundamental bubble dynamics in water and oxygen mass transfer in a technical scale on a water test tank with 3.5 – 4.0 m water depth Additionally, blends of air and pure oxygen as feed gas, as well as behavior in clean water and wastewater surrogates will be studied. The results will be used to discuss the suitability of these very small bubbles combined with pure oxygen or oxygen-enriched feed air for efficient aeration in wastewater treatment processes as well as guiding directions for upcoming further research in this field.
Therefore, the project aims to address three main topics:
1. Oxygen mass transfer will be systematically evaluated using micro- and nanobubbles on a technical scale at a relevant water depth of 3.5 – 4 m. Bubble generators will be fundamentally studied for their methodology and boundary conditions. Generated bubbles shall be measured for their size distribution to allow for a thorough understanding of the oxygen transfer mechanism and bubble dynamics.
2. In order to assess effects of oxygen blending on gas mass transfer, oxygen-air-mixtures of 20 – 100% O2 will be investigated. This is to simulate the blending of PO from electrolysis in the aeration.
3. For clarification of effects of impurities on bubble coalescence in the micro- and nanobubble range and resulting consequences, wastewater surrogates including surfactants, high salinity and both will be tested.