The removal of chemical substances during wastewater treatment plays a key role in environmental risk assessments. In this study, the usefulness of the activated sludge die-away test (OECD Test Guideline [TG] 314B) was evaluated in terms of its accuracy for predicting the removal of cationic surfactants in wastewater treatment using an ester-amide-type dialkylamine salt (EA) . The results show that the estimated removal rate through aerobic biological treatment (37.1%) in activated sludge, calculated from a first-order elimination rate constant, was lower than measured removal rates in actual water treatment systems (wastewater treatment plant [WWTP]: ≥ 99.9%; on-site domestic wastewater treatment plant: ≥ 99.7%) . The lower estimation was probably caused by the tendency that chemical substances with high K_oc values were transferred from the aqueous fraction to the suspended solid (SS) fraction to activated sludge. Thus, the EA concentration in effluent from the WWTP was calculated from the EA concentration of the SS fraction and the SS concentration in effluent; the estimated removal rate (99.7-99.9%) was equivalent to the measured removal rate. Therefore, when using OECD TG 314B to estimate the removal of chemical substances with a high K_oc value, removal via adsorption to activated sludge should be considered.

We investigated the efficiency of an advanced water treatment to remove formaldehyde (FA) and chloroform (CF) precursors. The formation potential of haloacetic acid (HAA) from CF precursors was also evaluated. The results of a jar test showed that FA and CF precursors, except for acetonedicarboxylic acid (ADC) , were not removed by raising the dosage of a coagulant. On the other hand, the results of the test at the experimental plant showed that FA and CF precursors were removed, and the formation potential of FA, CF and HAA, were reduced by ozonation and granular activated-carbon treatment. We found that ADC and 1,3,5-trihydroxybenzene were not only the precursors of CF, but also the precursors of dichloroacetic acid and/or trichloroacetic acid.

We conducted ecological risk assessment of copper in coastal areas of Japan. For risk assessment, we used a method in the initial environmental risk assessment conducted by the Ministry of the Environment, Japan, and several methods considering bioavailability, used for setting water quality criteria in Europe and the United States. The hazard quotient (HQ) method was used for risk characterization. Risk assessment was conducted using 1,622 copper concentration values from the Japanese coastal areas over the past 31 years that we were able to collect. As a result, the area with HQ exceeding 1 was 70.2% of the total in the screening level evaluation; considering bioavailability, it was 3.6 to 4.0%, and the risk characterization result changed depending on the hazard assessment method. Also, considering bioavailability, it was clear that there is a difference in the risk characterization result because water quality varies depending on the location even within the same bay. These results suggest that it is important to obtain toxicological data of species inhabiting Japan and copper concentrations in Japanese coastal areas and to examine what kind of evaluation method should be used for risk assessment.

This study was aimed at investigating the influence of a sewage treatment plant's seasonal operation on the water quality and nutrient transport of a tidal river. Cross-sectional observations were carried out in the Honjoe River, which flows into Ariake Bay in Japan. Field surveys and experiments focusing on the transport of ammonium nitrogen (NH₄⁺-N) in the tidal river were performed. As a result, suspended solid (SS) sediment formation close to the river, including in the vegetation areas, was accelerated and exhibited the potential local accumulation of NH₄⁺-N with SS. In addition, some experiments revealed an empirical equation for the removal rate of NH₄⁺-N. According to the equation, the NH₄⁺-N sedimentation rates tended to be low when the salinity and initial SS were high. Furthermore, the removal rate of NH₄⁺-N calculated using the empirical equation agreed qualitatively with the field results.

The purpose of this study is to investigate the formation of seaweed bed substrata using different sizes of Ferromanganese slag and Ferromanganese slag block in the sea area and by comparing them with the surrounding natural seaweed bed. We were unable to confirm any changes in pH or manganese concentration in seawater as a result of using FMS and FMSB. Small seaweed such as Hypnea grew five months after the material was set up. After 17 months, Sargassum horneri, Myagropsis myagroides, Undaria pinnatifida, and Ecklonia kurome grew on FMS, whereas S. horneri, Sargassum piluliferum, and Ecklonia kurome grew on FMSB. The vegetation transition progressed from undergrowth seaweed to large seaweed. About one year after the installation of the FMS and FMSB substrata, there was no significant difference in the number of seaweed species that grew on FMS and FMSB and the nearby natural seaweed bed. However, there was a small difference in the seaweed biomass between the FMS (30-75 mm) and the surrounding natural seaweed bed. We found that when using smaller material, FMS (30-75 mm) has higher seaweed biomass except in November 2017. By installing FMS and FMSB seaweed beds, we were able to confirm that the gathering fish are similar to those that gather around the nearby natural seaweed bed, but we were unable to confirm the relationship between seaweed biomass, material size, and fish density.