The environmental effects of combined sewer overflows (CSOs) in Toyama, Japan were evaluated using toxicity tests and chemical analyses. Chronic and sub-chronic tests with three freshwater organisms (Danio rerio, Ceriodaphnia dubia, and Raphidocelis subcapitata) were applied to seven samples collected during three rainfall events from October to December 2016. Five samples from CSOs including the first flush and the following overflows of CSOs, and two samples from river water (upstream and downstream) were collected. The chronic toxicity unit (TUc), total organic carbon (TOC), and coliform count were higher in the first flush than in other samples. In the three samples collected at the third sampling event, toxic effects were only observed on daphnia. Thus, toxic influence was the strongest on crustaceans and toxicity identification evaluation (TIE) procedures using daphnia were applied to the three samples. To further examine the effect of heavy metals on samples’ toxicity to daphnia, this study also clarified the change of toxic effect during the overflow event, and compared the Hazard Quotients (HQ) of heavy metals with TUc in samples collected at the third sampling event. The possible causes of toxicity and the contribution of heavy metals are discussed.

Estimation of dissolved organic carbon (DOC) runoff load in forested watersheds is important for the assessment of the global carbon cycle as well as for the local water quality control. A few process-based models previously proposed exhibited difficulties with the availability of input data and applicability to short time-scale rainfall-runoff processes in the Asian monsoon area. With the four years’ data from two nested study areas in Yamanashi, Japan, this study developed a new numerical model that consists of two processes for determining DOC loads. For the hydrologic process, a semi-distributed hydrological model (modified TOPMODEL) was installed. For the soil process, a wet-dry cycle was successfully simulated by an advection-diffusion and dissolution formulation. Finally, cumulative DOC loads were also successfully estimated during baseflow and stormflow periods separately, showing reasonable matching between the simulations and the observations for both study sites. Considering the storm periods, from 27% to 47% of high flows contributed to 50% of the total DOC load at the two monitoring areas, respectively. In essence, the proposed model was expected to identify and evaluate the importance of DOC production potentially linked with internal processes within forested river systems.

Here, we explored the Intermittent Contact Oxidation Process (ICOP) for the degradation of lipids for in-sewer applications. The ICOP is an attached growth process that utilizes biologically active sponge media fixed within a vessel to treat wastewater. In this study, ICOP was explored for its capacity to degrade lipids with an emphasis on the effect of media exposure to headspace-gas. Three laboratory-scale air-tight pipe reactors were fabricated and operated with margarine, calcium oleate, and 5% methyl oleate in hexadecane as the carbon sources, respectively. The degradation rates found for with intermittent water flow ranged 1.3 − 9.2 kgCOD/(m³ · day) at 20 ± 1°C expressed per volume of sponge media. Lipid degradation was observed during prolonged periods without water flow. Further, results indicated that increasing oxygen concentration positively affected degradation rate of lipids. The obtained findings provide understanding for the application of ICOP in collection systems.