Yugo Takabe

Effects of hydraulic retention time on cultivation of indigenous microalgae as a renewable energy source using secondary effluent

Secondary effluent from wastewater treatment plants is suitable media for cultivating microalgae as a renewable energy source, and hydraulic retention time (HRT) control in culture is important to conduct well-planned outdoor indigenous microalgae cultivation with secondary effluent. This study revealed cultivation characteristics under various HRT by continuous 6-month experiments. In addition, effects of HRT on cultivation were determined by a mathematical model that described indigenous microalgae growth. Cultivated biomass mainly consisted of Chlorophyceae and its detritus regardless of HRT, and 5.93-14.8g/m(2)/day of biomass yield was obtained. The cultivated biomass had a stable higher heating value of 16kJ/g. Sensitivity analysis of the model suggests that HRT control had great effects on biomass yield, and 2-3days of HRT were recommended to obtain maximum biomass yield under certain weather conditions (temperature: approximately 12-25°C and solar radiation: approximately 8-19MJ/m(2)/day).

Applicability of Corbicula as a bioindicator for monitoring organochlorine pesticides in fresh and brackish waters

The applicability of Corbicula as a bioindicator for monitoring organochlorine pesticides (OCPs) in fresh and brackish waters is presented here. Differences in isomer compositions and OCP bioaccumulation levels were analyzed in western Japan and the Pearl River Delta (PRD) in China. Isomer compositions of DDTs, chlordanes, and HCHs were significantly different between the two areas because of their different historical uses and property of the chemicals. This is represented by the (DDE + DDD)/DDT ratio in Corbicula, ranging 4.9–39 in western Japan and 1.1–2.4 in the PRD. However, isomer compositions in Corbicula reflected those in water, and the different patterns in Corbicula likely reflected the usage history. Concentrations of dissolved oxygen, suspended solids, and volatile suspended solids in water, and the difference in species did not influence OCP bioaccumulative levels in Corbicula when conducting biomonitoring. These levels are likely similar to those in Mytilus galloprovincialis. Therefore, Corbicula could be an appropriate bioindicator for monitoring OCPs in fresh and brackish waters.

Bioaccumulation and primary risk assessment of persistent organic pollutants with various bivalves

Field surveys on persistent organic pollutant (POP) bioaccumulation were conducted with oysters, clams and scallops whose consumption amount accounted for large shares in the total consumption of shellfish in Japan. There was no numerical difference in bioaccumulation characteristics between oysters, clams, scallops, Corbicula and Mytilus galloprovincialis. Therefore, it was clear that the bioaccumulation characteristics in oysters, clams and scallops, which are important for food, could be ascertained by using the monitoring results with Corbicula and M. galloprovincialis which are easily sampled in various water areas in the world. Non-cancer risk (hazard quotient, HQ) and cancer risk (excess cancer risk, ΔR) via shellfish ranged from 10⁻⁸ to 10⁻⁴ and from 10⁻¹¹ to 10⁻⁷, respectively, at sampling points, which showed the risks of POP exposure via shellfish to be low enough. However, concerning the intake of other food, the importance of dieldrin monitoring should be suggested in Japan. Based on these results, the effectiveness of primary risk assessment could be suggested for screening chemicals whose preferential monitoring is needed.