The public sewage (PS) and night soil mixed with johkasou sludge (JO) have similar chemical compositions; however, the concentrations of organic matter and nitrogen compounds were different. We investigated the microbial community of the rotating biological contactor (RBC) units treating PS and JO, in which the RBC was submerged in the mixed liquor of activated sludge. Here, we observed that the microbial community compositions at the phylum and class levels were similar between the PS-RBC and JO-RBC, whereas the relative abundances of several phyla (Euryarchaeota, Acidobacteria, Chloroflexi, Firmicutes, Patescibacteria, and Betaproteobacteria) significantly differed between them. The microbial community composition of RBC (an attached growth process) was similar to that of the activated sludge (a suspended growth process). The microbial community of activated sludge likely affected that of RBC. The relative abundance of total denitrifying bacteria in the PS-RBC was twice as much as that in JO-RBC, while nitrifying bacterial phylotypes had a similar relative abundance. The predominant denitrifying genera were different between the PS-RBC and JO-RBC, as well as in the cross-sectional layers of the PS-RBC, suggesting the functional diversity of denitrifying bacterial genera inhabiting the RBC.

We assessed the photosynthetic efficiency of the lab-cultured large benthic foraminifers (LBFs), Calcarina gaudichaudii and Baculogypsina sphaerulata, by means of a pulse-amplitude-modulated (PAM) fluorometer for representative photosynthetic activity; and identified an optimal light intensity and water temperature for the lab-scale cultivation. It is known that in the actual environment, the convex side of LBFs exhibit higher photosynthetic efficiency [Y(II)] than concave one. However, our experimental results from the lab setting showed that Y(II) values apparently did not differ on the basis of their having convex and concave sides. This was due to the condition between the position of the LBFs within the glass vial and light irradiation. The LBFs were exposed to eleven different light conditions for a period of 72 h. The LBFs exhibited relatively higher Y(II) at 40−120 and 240 lum/ft², compared with that at 1150−1800 lum/ft². Using a light intensity of 80 lum/ft² and water temperature of 20°C to inhibit epiphyte infestation due to the growth of suspended microalgae released by the LBF hosts, LBFs were able to be cultured for 120 d under laboratory conditions, while B. sphaerulata could be cultured for 57 d under the on-site conditions in a previous study.

In this study, the environmental monitoring of Anzali international wetland (based on water surface temperature (WST), chlorophyll-a (Chl-a) and transparency (secchi disk depth (SDD)) parameters) using Landsat images in the period 1985–2018 has been studied. Based on the results of zoning maps, in 2018 and 2013, WST fluctuations are higher, with the lowest water temperature observed in 2007. Based on Chl-a, the trend for this parameter is increasing from 1985 to 2018. Also, from 1985 to 2018, we saw a decrease in transparency (SDD), which could indicate an increase in opacity and concentration of suspended and organic particles in the wetland, which was consistent with the results of chlorophyll-a. Graph examination of wetland showed more changes belonged to the central and eastern parts of the wetland. The results of this study indicate that in the Anzali international wetland, comparing the values of the parameters studied, there are not good conditions for water quality and the need for a solution and management policies to improve the condition of this unique ecosystem is necessary more than ever.

In full-scale sewage treatment plants, long-term and high-frequency monitoring is required to mitigate nitrous oxide (N₂O) emissions. In this study, the profile of the dissolved N₂O concentration in a full-scale oxidation ditch reactor was investigated to determine the variation of the N₂O emission factor. It was found that the concentration of dissolved N₂O depended on microbial activity, which is affected by water temperature, dissolved oxygen concentration, and the dimensional relationship between the rotator and the inflow point. In the reactor, higher transcription levels of amoA mRNA and lower transcription levels of clade II type nosZ mRNA may be associated with N₂O production. The emission factor for removed dissolved inorganic nitrogen presented a mean value of 0.86% and a median of 0.19%. When N₂O production was promoted, gasification from the water surface was the most significant emission source, accounting for 52% of the total N₂O emitted, on average. The N₂O emission factor was often lower than 0.01% during stable operation; however, this factor was subject to sudden increases caused by nitrite accumulation.

To identify the factors controlling the distribution of dissolved organic carbon (DOC) in the northern Ariake Sea (Japan), we measured DOC, salinity and chlorophyll a (Chl. a) along transect lines from the largest river discharging into the Ariake Sea (the Chikugo River) to the opposite shore. The DOC concentration was significantly correlated with salinity, although no correlation was found between the Chl. a concentration and DOC. Thus, river inflow is the primary source of DOC. However, the expected concentration of riverine DOC, represented by the y-intercept of the regression curve between salinity and DOC, was much higher than the DOC concentration of the Chikugo River, suggesting the presence of additional DOC sources to the Ariake Sea. We conducted particulate organic matter (POM) decomposition experiments and observed DOC production after incubation. Thus, microbial POM decomposition may be a source of excess DOC. This study is the first to show that river inflow and microbial decomposition of POM affect the DOC distribution in the northern Ariake Sea.

To assess the effect of temperature on the electric power generation of a microbial fuel cell (MFC), a series of experiments was conducted across a 5–55°C temperature range. We found that the currents generated were not proportional to the temperature, with the currents at 15 and 45°C higher than those at other temperatures. In order to determine the reason for this, a mathematical model, using a diffusion layer in an MFC, was developed, and analysis of this model suggested that the MFC temperature characteristics were caused by aerobic and anaerobic reactions being lower at 15 and 45°C. Our calculations indicated that the consumption of organic compounds predominantly occurred at specific temperatures and that diffusion of the compounds affected the current. These calculations made it possible to estimate the influence of aerobic and anaerobic reactions on power generation in the MFC within a prescribed temperature range. This work suggests that, using this model, competitive reactions in electrogenic bacteria could be controlled by setting the correct temperature.

Amid the ongoing battle against COVID-19, the scientific community has high hope in wastewater-based epidemiology (WBE). It was not only proposed as a complement to capacity-plagued clinical testing, but also an early warning tool that may enable timely intervention measures. In this study, we developed a wastewater SARS-CoV-2 RNA load model based on the fecal shedding profile of infected individuals. The epidemic data of COVID-19 in the Tokyo metropolitan area were used to perform a simulation to analyze the capability of WBE in providing early warning. The simulation result suggests that under the current settings, WBE is not a feasible approach as the detection limit is too high to provide a warning signal in the early stage of the epidemic. However, it also indicates that if the methodology can be reasonably improved by new experimental practices, optimized sampling strategy, and refined model, the concentration of viral RNA in Tokyo wastewater would exceed the detection limit as early as in April 2020, when Tokyo was being hit by the first wave of COVID-19 outbreak. This early detection may have great social benefit if the detection can be used to facilitate the decision-making process and form epidemic emergency response.