Wastewater-base epidemiology may be a promising approach to capturing the dynamics of the spread of diseases as well as emerging mutants in a catchment. Herein, we describe the key components of the wastewater-based epidemiology of viral infectious diseases, including the optimization of the methodology of the detection and quantification of viral genomes and the development of a back-calculation model to estimate the number of infected individuals. Early warning based on the influent viral concentration in a wastewater treatment plant may be feasible when it takes longer than one week to tally the number of patients of the target infectious disease by the currently used sentinel surveillance under the infectious diseases control law. The variables of a back-calculation model are categorized into two types: common variables irrespective of the type of infectious disease and variables specific to the infectious disease including shedding profiles of viruses. Greater effort is required to develop a robust back-calculation model against variability and uncertainty due to environmental, geological, and personal differences.

Nutrient load reduction has been conducted in many semi-enclosed coastal seas in Japan for restoration from eutrophication. The nutrient concentrations in these seas have significantly decreased; however, the expected reductions were not seen in the organic matter indices (e.g., chemical oxygen demand (COD) ) . The causes of these phenomena were analyzed and the following was found. (1) The decrease in total nitrogen (TN) concentration caused a reduction in organic nitrogen, but no or lesser reductions in total organic carbon (TOC) and COD. This phenomenon is caused by the increase in C:N ratio in the organic matter in the sea. (2) The increase in C:N ratio caused by the nitrogen deficit is also seen in seaweeds (macroalgae) . (3) This plant characteristic suggests that nutrient availability controls the quality (e.g., C:N ratio) of autochthonous organic matter in estuaries and coastal seas. (4) The relationships between COD and TOC have changed spatially and temporally. (5) Nutrient reduction has changed not the quantity but the quality of the organic matter.

We propose a method of estimating the overall behavior of filtration using the fouling index obtained from limited membrane filtration data. The blocking index and plugging constant required for estimating filtration behavior were determined from the fouling mechanism index (FMI) with the aid of the blocking filtration law. The calculated data of the variation over time of the flux decline using the blocking index, plugging constant, and membrane properties were in reasonable agreement with experimental data. It was confirmed that this method can be widely applied to estimate membrane filtration behavior regardless of filtration conditions, such as sample concentration and the type of membrane, and fouling mechanisms, such as membrane pore blocking and cake formation. The calculated data of filtration behavior obtained from the membrane properties and FMI are useful because they can be used to determine the timing of membrane cleaning and membrane replacement.

Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo instrument, YODA Profiler, in Lake Kitaura to investigate the formation of oxygen-deficient water. The results of observations showed that oxygen-deficient water widely appeared at a depth of deeper than 4 m, and the dissolved oxygen (DO) concentration in deep areas was particularly low. Furthermore, it was suggested that high phosphorus (PO₄-P) concentrations were eluted from sediments in areas of oxygen-deficient water. The DO concentration at 10 cm above the lake bottom tended to be lower than that at 50 cm above the lake bottom. The oxygen-deficient water in Lake Kitaura is greatly affected by the water depth, which implies that the ratio of the area of oxygen-deficient water can be inferred by lake bathymetry and observed DO profiles. The area of oxygen-deficient water reached 55.9% at 50 cm above the bottom and 63.2% at 10 cm above the bottom of the total area of Lake Kitaura.

Fish mortality was investigated in a shallow, constantly stored-water-type regulating pond located in a cold region in mid-March 2018 after ice had melted. In general, fish mortality occurs when water temperatures increase; however, in this case, it occured under freezing conditions. In this study, we attempted to understand the actual water quality by referring to the results of water quality surveys conducted throughout the year and the factors leading to the accident. The studied pond is eutrophic with treated wastewater. Phytoplankton proliferated during the non-freezing season by consuming nutrients in the treated wastewater, and organic matter derived from the phytoplankton accumulated as bottom mud. In early March 2018, the dissolved oxygen (DO) concentration in the bottom layer was almost 0 mg L^-1, while it was also under 1.2 mg L^-1 in the upper layer. Concurrently, NH₄-N leached out from the reduced bottom mud, and its concentration in the bottom layer increased to 25.4 mg L^-1. The pH of the bottom layer increased to 8.96, and the free ammonia concentration was estimated to be about 3.0 mg L^-1. These results indicate that the low DO and elevated NH₄-N concentrations under freezing conditions directly caused this fish mortality incident.