Microplastics (MPs), which result from the breakdown of plastic waste, have become ubiquitous in various environmental compartments. The “plastisphere”, referring to the unique bacterial communities inhabiting plastic debris, includes pathogens and antibiotic resistance genes. Wastewater treatment plants (WWTPs) are hotspots for plastisphere formation, but significant releases of MPs still occur. This study investigates the microbial communities on polystyrene (PS) MPs through in situ deployment across primary, secondary, and tertiary WWTP stages. Biofilms formed on the PS MPs exhibited greater bacterial diversity than background waters. Certain genera acted as pioneers in the biofilms, attracting and facilitating the accumulation of other microbes from background waters. The biofilms formed on the MPs became more resistant to treatment processes compared to freely floating bacteria. This study sheds light on the evolution of microbial communities on MPs within WWTPs and their roles as carriers of microbes in effluents, with implications for environmental and public health. Understanding these dynamics is crucial for effective control over MPs and microbial pollution in WWTPs.

The object of this research is to analyze the water quality improvement of Lake Paldang by implementing Integrated Lake Basin Management (ILBM). To establish ILBM, the basin environment database was built as well as water environment management support system for monitoring present conditions, and predicting changes in basin environment. The major contaminants in Lake Paldang Basin are from domestic pollution, agricultural land, and livestock. Scenarios for reducing contaminants were targeting the increase percentage of sewered population, agricultural and livestock contaminants reduction to analyze the water quality improvement effects. This study applied the SWAT model to Lake Paldang Basin using the basin environment database to improve the water quality of Lake Paldang in Korea. The results of calibration and validation of flow rate, Suspended Solids (SS), Total Nitrogen (TN) and Total Phosphorus (TP) showed that the measurement values and simulation values turned out to be similar, and that it is possible to apply the SWAT model to Lake Paldang Basin. The reduction efficiency of SS by scenario was 11-45%, TN 8-37%, and TP 7-35% and this shows that water quality was significantly improved prior to application. Therefore, to improve the water quality of Lake Paldang, it is recommended to implement the ILBM which is considered to play an important role in making water quality management policy in Korea.

The abundant growth in cyanobacterial blooms poses severe ecological threats with a high risk to aquatic organisms and global public health. Control of cyanobacterial blooms involves spraying cyanobacteria removal materials, including coagulants. However, little is known about the fate of the coagulated-cyanobacteria-laden water. Here, we examined long-term changes in water quality following treatment with various coagulants and minerals for cyanobacterial removal when the coagulated cyanobacterial cells were not removed from the water. An experiment in a controlled water system tested the effects of six different compounds, one conventional coagulant, two natural inorganic coagulants, and three minerals. All tested coagulants and minerals exhibited >75% of cyanobacterial removal efficiency. However, compared to the control, higher concentrations of nitrogen were observed from some samples treated during the experimental period. After 20 months, the final total phosphorus concentration of the raw water increased 20-fold compared to the initial concentration to 11.82 mg/L, indicating significant nutrient release over time. Moreover, we observed that the decomposition of sedimented cyanobacterial cells caused the release of intracellular contents into the supernatant, increasing phosphorous concentration over time. Therefore, cyanobacterial cells should be removed from water after treatment to prevent eutrophication and maintain water quality.

An electrochemical floatation system (EFS)-based sewage-treatment process that applied a dimensionally stable anode (DSA) was developed to secure treated sewage water from sewage-treatment plants for reuse. The DSA was fabricated at a temperature of 673–923 K by dispersing a low quantity of activated carbon on a titanium plate coated with mixed metal oxides (Pt, Re, Pd, Re, and Ir) to a thickness of 5 μm. The average size of the bubbles generated through the DSA of the EFS was 20–40 μm, thus confirming microbubble generation. An efficiency assessment of a titanium-based DSA confirmed metal oxide activity through the removal of Escherichia coli (100%) and total organic carbon (TOC; 48.83%) at a reaction time shorter than 10 min and a low current density (19.6 A/m²). During the long-term operation of the EFS with the separation membrane process, the average removal efficiency was 94.7%, 90.0%, 96.1%, 90.9%, and 98.0% for suspended solids, biochemical oxygen demand, TOC, total nitrogen, and total phosphorous, respectively. Coliforms were not detected. Overall, our EFS coupled with the separation membrane process produced high-quality recycled water that could be used for various purposes according to the water-quality standards for different applications.

Replication of natural mixing through artificial water circulation techniques, such as convectional water circulation systems (CWCS), can break thermal stratification in stagnant water and suppress algal blooms. Here, the field performance of a novel CWCS was evaluated in a eutrophic reservoir (Shingal reservoir, South Korea) for three seasons between September 2016 and September 2018. The CWCS was deployed in a corner of stagnated water in the reservoir. The changes in water temperature and dissolved oxygen (DO) concentrations at different water depths were examined at the deployment site and two control sites within the stagnant area during the 2016 and 2017 seasons. In 2018, the performance of the CWCS in replicating natural mixing was assessed by monitoring water temperature changes at different depths at the CWCS unit deployment site and a comparison site with natural water flow. The differences in water temperature and DO concentrations between the epilimnion and the hypolimnion were significantly smaller at the deployment site than at the control sites, demonstrating the effectiveness of the CWCS in vertical and horizontal mixing as well as in oxygen transfer. The findings of the field study revealed that the CWCS effectively induced natural-like mixing without disturbing the hypolimnion.