COVID-19 case prediction via wastewater surveillance in a low-prevalence urban community: a modeling approach.

Estimating and predicting the epidemic size from wastewater surveillance results remains challenging for the practical implementation of wastewater-based epidemiology (WBE). In this study, by employing a highly sensitive detection method, we documented the time series of SARS-CoV-2 RNA occurrence in the wastewater influent from an urban community with a 360,000 population in Japan, from August 2020 to February 2021. The detection frequency of the viral RNA increased during the outbreak events of COVID-19 and the highest viral RNA concentration was recorded at the beginning of January 2021, amid the most serious outbreak event during the study period. We found that: (1) direct back-calculation still suffers from great uncertainty dominated by inconsistent detection and the varying gap between the observed wastewater viral load and the estimated patient viral load, and (2) the detection frequency correlated well with reported cases and the prediction of the latter can be carried out via data-driven modeling methods. Our results indicate that wastewater virus occurrence can contribute to epidemic surveillance in ways more than back-calculation, which may spawn future wastewater surveillance implementations.

Impact of nitrogen compound variability of sewage treated water on N2O production in riverbeds.

Nitrous oxide (N2O), a strong greenhouse and ozone depleting gas, is known to be generated in the river environment. However, the impact of sewage treated water on the production mechanism has not been clarified. In this study, N2O production in the upper reach of a river was evaluated by field survey and activity test. The results demonstrated that the N2O production activity of the river pebbles increased with the inflow of the sewage treated water, which was supported by field survey results, such as the dissolved N2O concentrations and water quality. The emission factors of N2O were determined to be 0.02-0.05% in nitrification and 0.01-0.025% in denitrification. Our study shows that combining a field survey and an activity test improves the reliability of the results and leads to the appropriate quantitative evaluation. From a perspective of controlling the N2O emissions from the sewage treatment plant, N2O generation inside the plant is critical. However, appropriate nitrogen removal in the treatment plant is connected to the reduction of N2O generation in the river environment.

Assessment of nitrous oxide production in eutrophicated rivers with inflow of treated wastewater based on investigation and statistical analysis.

Accurate estimation and control of greenhouse gas emissions have been recognized as imperative in recent years. Therefore, frequent investigations under uniform environmental conditions are required to better understand this concept. Thus, six sampling sites with characteristic concentrations of nitrogen and other water quality parameters were selected to investigate the behavior of water quality parameters throughout the year and to statistically examine the correlations among the parameters. Dissolved nitrous oxide (D-N2O) showed the highest positive correlation coefficient with NO2-N among nitrogen species. The results of the principal component analysis suggested that river water quality could be broadly classified based on photosynthesis and contamination from treated wastewater. Photosynthesis caused an increase in pH, with concomitant decrease in D-N2O concentration. Using the results of multiple regression analysis, D-N2O was accurately estimated based on nitrogen concentration, pH, and concentration of organic matter in various situations. The results of a detailed survey suggested that D-N2O was produced in the river from nitrogen sources released from the wastewater treatment plant. The main roles of the wastewater treatment plant for D-N2O behavior in the river were the supply of the nitrogen source that was the precursor of D-N2O, the supply of the nutrients that induced the photosynthesis, and the direct supply of D-N2O at a low water temperature. The models based on multiple regression analysis could efficiently predict the D-N2O concentration produced in rivers at sites downstream of the wastewater treatment plant, except for the direct supply of D-N2O as an effluent at low water temperature.

Early warning of COVID-19 via wastewater-based epidemiology: potential and bottlenecks.

An effective early warning tool is of great administrative and social significance to the containment and control of an epidemic. Facing the unprecedented global public health crisis caused by COVID-19, wastewater-based epidemiology (WBE) has been given high expectations as a promising surveillance complement to clinical testing which had been plagued by limited capacity and turnaround time. In particular, recent studies have highlighted the role WBE may play in being a part of the early warning system. In this study, we briefly discussed the basics of the concept, the benefits and critical points of such an application, the challenges faced by the scientific community, the progress made so far, and what awaits to be addressed by future studies to make the concept work. We identified that the shedding dynamics of infected individuals, especially in the form of a mathematical shedding model, and the back-calculation of the number of active shedders from observed viral load are the major bottlenecks of WBE application in the COVID-19 pandemic that deserve more attention, and the sampling strategy (location, timing, and interval) needs to be optimized to fit the purpose and scope of the WBE project.

Contribution of dissolved N2O in total N2O emission from sewage treatment plant.

The characteristics of nitrous oxide, N2O, from a sewage treatment plant, which conducts nitrogen removal, and the river that receives its effluent water, were investigated by intensive daily surveys in summer and winter. N2O production in the sewage treatment plant was promoted in winter when nitrite accumulated in the reaction tank. The dissolved N2O concentration in the effluent water was also high in winter, which caused the dissolved N2O concentration to increase in the river downstream. In contrast, the N2O production inside the plant and the dissolved N2O emission through the effluent water, the dissolved N2O discharge, was controlled in summer when the nitrogen removal was more complete and there was no-nitrite accumulation. The dissolved N2O in the effluent water was rapidly lost after leaving the plant by as much as 26% in summer and 59% in winter. Additionally, the amount of the dissolved N2O discharge in winter was almost equal to that of the indirect N2O emission. When the nitrogen removal proceeded successfully, the amount of dissolved N2O discharge was small. In contrast, when the nitrogen removal was insufficient, the dissolved N2O discharge became an important N2O source.