The objective of this study was to deepen the understanding on the fouling of reverse osmosis (RO) membranes by alginate and the role of calcium ions (Ca²⁺) in the integrated membrane system for the reclamation of municipal wastewater. When feed water was not pretreated with the microfiltration (MF) membrane, the fouling of the RO membrane was accelerated with an increase in Ca²⁺ concentration. This result is explained by the ability of Ca²⁺ to bind to alginate and the corresponding formation of calcium alginate gel, which has a higher water resistance than sodium alginate. It was also found that the ratio of β-D-mannuronate (M) to α-L-guluronate (G) of alginate is distributed, and GG and MG blocks with a higher affinity with Ca²⁺ than MM blocks were preferentially deposited on the RO membrane surface. On the other hand, when feed water was pretreated with the MF membrane, the fouling propensity of the RO membrane was significantly alleviated because the multimer of GG and MG blocks was effectively removed by the pretreatment. Additionally, contrary to the case where MF pretreatment was not performed, less fouling of the RO membrane occurred for higher Ca²⁺ concentrations because of the more effective formation of large alginate multimers.

The relationship between seawater nutrient concentrations and ecosystem production was studied by in situ growth experiments, which have been conducted along the nutrient concentration gradient from the eutrophic Osaka Bay head to the oligotrophic adjoining Harima Sea. Bivalves (asari clam Ruditapes philippinarum) were cultured in suspended cargo, and sessile organisms were collected on a suspended plate at each station. The distribution of the primary production was also calculated within the study area. The wet weight of the molluscous part and the condition index of asari clam are strongly correlated with the annual mean total nitrogen (TN) . The primary production (PP) is significantly correlated with TN in the area of TN > 0.2 mg L^-1. In contrast, PP is small and of a pelagic nature in the area of TN ≦ 0.2 mg L^-1. The annual mean TN is strongly correlated with TP, and TN = 0.2 mg L^-1 is equivalent to TP = 0.029 mg L^-1.

A local association, “Wagagawa no seiryu wo mamoru kai” (The Association for Protection of Clean Water of the Waga River) , was established by diverse stakeholders to protect the “clean” Waga River in 1972. As a major activity, the association has been monitoring the water quality (pH and concentrations of Cu, Zn, Cd, Pb, and As) of discharges from closed mines and downstream river sites, and reporting the results in their annual newsletter. To understand how information should be disclosed, it is worth noting that all the monitoring results, including the exceedance of mine discharge standards of the above-mentioned metals, have been made public and discussed in the newsletters. The analysis of the text of the annual newsletters published in 1972-2019 showed long-term primary changes in topics, that is, from (1) initial concern about general environmental pollution to (2) water quality monitoring and measures for preventing environmental pollution by closed mines to (3) the protection of natural environments including aquatic organisms. Our results would contribute to further analysis and discussion of the activities of this association to consider purpose-driven flexible environmental management in abandoned and closed mines in Japan.

Sewer stormwater overflow, one of the causes of water pollution in Higashi-Yokobori River–Dotonbori River that flow through central Osaka, has been stored in a rainwater storage pipe called “Heisei no Taiko Gesui” since April 2015, but the number of coliform bacteria in both rivers did not decrease significantly. If the pipe is working, the number of coliform bacteria at a downstream point should depend on the number at the upstream point, flowing time, and water temperature. Thus, the decay rates of coliform bacteria were determined experimentally, and the predicted numbers of coliform bacteria at the downstream point were compared with the expected values obtained by the Monte Carlo method. The predicted values tended to be underestimated because the obtained decay rates did not reflect the effects of sunlight and other factors. However, the differences between the expected and predicted values after completion become close regardless of the weather, indicating that the pipe is functioning. It was considered that the number of coliform bacteria has not declined in both rivers because the increased load from the upstream cancelled the reduction effect of the pipe.