In this study, an ensemble machine learning model was developed to predict the recovery rate of water quality in a water treatment plant after a disturbance. XGBoost, one of the most popular ensemble machine learning models, was used as the main framework of the model. Water quality and operational data observed in a pilot plant were used to train and test the model. Disturbance was determined when the observed turbidity was higher than the given turbidity criteria. Therefore, the recovery rate of water quality at a time t was defined during the falling limb of the turbidity recovery period. It was considered as a relative ratio of the differences between the peak and observed turbidities at time t to the difference between the peak turbidity and turbidity criteria. The root mean square error–observation standard deviation ratio of the XGBoost model improved from 0.730 to 0.373 by pretreatment, removing the observation for the rising limb of the disturbance from the training data. Moreover, Shapley value analysis, a novel explainable artificial intelligence method, was used to provide a reasonable interpretation of the model’s performance.

We developed a lab-scale aerobic–methane oxidation bioreactor (MOB)–anoxic system, combining a MOB and the aerobic–anoxic denitrification process, and evaluated its potential for advanced nitrogen treatment in wastewater treatment plants (WWTPs). The MOB used biogas generated from a WWTP and secondary-treated wastewater to support mixed methanotroph cultures, which mediated the simultaneous direct denitrification by methanotrophs and methanol production necessary for denitrifying bacteria in the anoxic chamber for denitrification. Compared to the aerobic–anoxic process, the aerobic–MOB–anoxic system with an influent concentration of 4.8 L·day⁻¹ showed a marked increase in the reduction efficiency for total nitrogen (41.9% vs. 85.9%) and PO₄⁻³-P (41.1% vs. 69.5%). However, the integrated actions of high nitrogen and phosphorus consumption are required for methanotroph growth, as well as the production and supply of methanol as a carbon source for denitrification and methane monooxygenase-mediated oxidation of NH₃ into N₂O by methanotrophs. After three months of continuous operation using actual wastewater, the total nitrogen removal rate was 76.3%, equivalent to the rate observed in a tertiary-advanced WWTP, while the total phosphorus removal rate reached 83.7%.

Micro-porous cellulose filters were fabricated from paper mulberry pulp, which has been used for thousands of years with Korean history. ‘Han-ji’ is the name of a traditional paper used widely in Korea in construction, textile, craftworks and many household items but before now it has not been used for filtration purpose. Seeking for the utilization of this abundant natural material, this study aims to develop a fabrication process for the traditional paper to be used as a filter for dust filtration, and evaluate the performance by lab-scale experiments. To create pores in the paper, cellulose pulp was pretreated using several methods such as TEMPO oxidation and enzyme hydrolysis, or freeze dried with an alcoholic freezing medium, t-butyl alcohol, instead of water. The filters were characterized and their dust removal performance was tested at a lab scale while also monitoring pressure loss. Chemical oxidation and enzymatic pretreatment were helpful in fabricating a homogeneous filter but would not remove fine-dust particles because of its loose, enlarged pores. The best removal efficiency was observed with filters that were not pretreated but in which water had been exchanged with t-butyl alcohol before freeze-drying. The filter attained a dust removal efficiency higher than 99% over the entire experimental period, with a pressure loss of less than 230 Pa, at a 6.67 (cm³/s)/cm² air-to-cloth ratio.

The development of cost-effective methods, which generate minimal chemical wastewater, for methanol production is an important research goal. In this study, treated wastewater (TWW) was utilized as a culture solution for methanol production by mixed methanotroph species as an alternative to media prepared from commercial or chemical agents, e.g., nitrate mineral salts medium. Furthermore, a realistic alternative for producing methanol in wastewater treatment plants using biogas from anaerobic digestion was proposed. By culturing mixed methanotroph species with nitrate and phosphate-supplemented TWW in municipal wastewater treatment plants, this study demonstrates, for the first time, the application of biogas generated from the sludge digester of municipal wastewater treatment plants. NaCl alone inhibited methanol dehydrogenase and the addition of 40 mM formate as an electron donor increased methanol production to 6.35 mM. These results confirmed that this practical energy production method could enable cost-effective methanol production. As such, methanol produced in wastewater treatment plants can be used as an eco-friendly energy and carbon source for biological denitrification, which can be an alternative to reducing the expenses required for the waste water treatment process.

Objectives : This paper summarizes effective waste management and disposal methods for plastic and medical wastes during the prolonged COVID-19 pandemic.Methods : We reviewed the literatures reporting and identifying the current status and characteristics of wastes related to COVID-19, and the management and treatment guidelines for those wastes. We also investigated various technologies for waste treatment and disposal, and assessed the current status and future direction of the technologies in Korea.Results and Discussion : In the first half of 2020 in Korea, the amount of plastic waste produced had increased by 15.6% year-on-year, and medical waste production also increased significantly from 0.6 ton in January 2020 to 2,928 ton in August 2021. All of the infectious wastes are currently being incinerated in Korea, but there are concerns on air pollutant emissions and insufficient treatment facilities. Municipal solid waste also suffers from a lack of landfill capacity and low price competitiveness in the recycling industry.Conclusions : Policy and system need to be improved to reduce the infectious waste generation from the sources, and treatment and disposal technologies for produced wastes also need to be developed. Furthermore, hospitals and health care facilities should establish their own waste reducing systems which may include chemical treatment and sterilization units.

Domestic wastewater treatment facilities(WTF) in Korea consume a lot of energy and generate greenhouse gases in the process of treating contaminated sewage. In response to climate change and the government's carbon neutrality, measures for energy reduction in WTF is an important issue along with water quality management, and simultaneously, diversification of renewable energy based on treatment facilities is essential. The energy independence and renewable energy utilization by facility capacity were analyzed based on sewage statistics (2019) and operation data of the National Sewage Information System. The amount of energy consumed by WTF was analyzed to be 83.6 million TOE, and the renewable energy produced was 10.8 million TOE. In consequence of analysis, the energy independence of domestic WTF in Korea was 12.9%. Among renewable energy, the contribution of biogas was the highest at 83.6%, but the current status of energy independence is somewhat insufficient to energy independence plan of WTF, requiring support for alternatives and policies to produce and secure additional renewable energy. In order to increase and diversify the use of renewable energy, the integrated digestion biogas of organic waste resources, the use of cooling and heating energy based on sewage heat, and the development of salinity gradient power generation were reviewed. Based on this, it was intended to contribute to the preparation of measures to achieve carbon neutrality in sewage treatment facilities.