Sang Yeob Kim earns PhD for research on wastewater treatment with a new type of oxygen delivery system

My research is about the treatment of wastewater. This is, for example, the water used for washing dishes and showering. The wastewater is often sent to a sewage treatment plant through a pipe to be treated.

Biological wastewater treatment, that is, treating wastewater using microorganisms, is an effective way of breaking down and eliminating organic waste often found in waste products produced in the food and drink, chemical, oil and gas industries. A typical biological wastewater treatment system uses bacteria and other microbes to clean contaminated water so that it passes predetermined standards. When consuming the pollutants found in the wastewater, the bacteria begins to create particles which stick together in larger clumps. This process allows the organic matter to be separated from the wastewater solution, producing a sludge which can be easily disposed of as solid waste.

For the microorganisms to be able to treat the wastewater, they need oxygen.  Usually, this is delivered to the wastewater through a fine bubble diffuser that releases air. Such systems are quite inefficient in delivering oxygen – less than 10% of the supplied oxygen is available to the organisms in the end. I studied whether a new type of oxygen supply system could transfer oxygen more efficiently. Better oxygen transfer saves on costs and enables wastewater to be treated quicker, which is particularly helpful for wastewater treatment in emergency situations resulting from natural or man-made disasters.

The most memorable moment was when my PhD defence date was confirmed and when the first paper was published, in February 2019. This came after some challenges: my work was not always going well, and I had to ask my advisor for another chance.

The most challenging part of my PhD studies was to maintain the Supersaturated Biological Wastewater Treatment experimental device in a stable state. It was important to my work that the injected oxygen should be completely dissolved in the liquid solution – there should be no leaks. For the oxygen transfer efficiency to be accurately calculated, the pressure in the supersaturated dissolved oxygen pressurized chamber must be kept constant. But the unit leaked frequently until it was repaired. Looking back, if I could advise myself at the start of my PhD, I would say: prepare for the research proposal before arriving, which will help you in a later stage.

I would like to continue with my research. I am currently working at Sejong University located in Seoul, South Korea as a senior researcher – this is somewhat difficult but truly exciting. As I finished my PhD, I saw a lot of shortcomings in my experimental work, and I want to do further research related to my PhD work. Since I studied for a PhD outside of my home country, South Korea, I would like to live and work in South Korea. However, if new good opportunities arise outside of South Korea, I am open for this. In the next few years, I hope to work in a research institute or a university.

Applications of Supersaturated Oxygenation to Biological Wastewater Treatment with High Biomass Content

The operation of membrane bioreactors (MBRs) at high mixed liquor suspended solids (MLSS) concentrations (higher than 15 g/L) may enhance the loading rate treatment capacity, while minimizing even further the MBR system’s footprint. However, oxygen transfer in wastewater treatment is significantly influenced by the MLSS concentrations. Particularly, conventional diffused aeration systems (fine and coarse bubble diffusers) exhibit a poor oxygen transfer in wastewater treatment applications; particularly, when operating at MLSS concentrations higher than 15 g/L. The oxygen transfer performance of the supersaturated dissolved oxygen (SDOX) system was evaluated in activated sludge with MLSS concentrations from 4 to 40 g/L as a promising technology for uncapping such limitation. The operational conditions exerted by the SDOX technology did not affect the concentration of active biomass. Moreover, the biological performance of the MBR was not affected by the introduction of the SDOX technology. In addition, the microbial community was relatively stable although some variations at the family and genus level were evident during each of the study phases. Indeed, the membrane filtration performance was affected by the SDOX technology. A combination of several factors (certainly including particle size distribution of sludge) resulted in the serious membrane fouling imposed by the high-pressure and shear effects. However, this could be influenced due to the scale of the laboratory-based research. More research would be needed to confirm those findings.