Experiments to determine the efficacy of radioactive irradiation in inactivating Cryptosporidium parvum oocysts were conducted. The infectivity decreased exponentially as radiation dose increased. The gamma ray and electron beam doses resulting in a 2 log₁₀ reduction in infectivity for mice were 94 Gy and 92 Gy, respectively. Although gamma rays had been reported to be twice as potent as beta rays in inactivating E. coli, no marked differences were found between gamma ray and an electron beam in terms of efficacy in inactivating C. parvum oocysts. The required dose increase to yield a 2 log₁₀ reduction in infectivity was only 5% for every 10°C decrease in water temperature and 2% for a 10-fold increase in intensity. The gamma ray and electron beam doses required for a 2 log₁₀ reduction in viability, as evaluated by in vitro excystation experiments, were 13 kGy and 12 kGy, respectively. The large differences in the radioactive doses required to reduce infectivity versus those required to reduce excystation suggest that exposed oocysts are still viable following a low dose of radiation, but not infective. The potential to recover infectivity was also investigated. There was no recovery in infectivity following fluorescent-light irradiation or storage in darkness. Moreover, the degree of inactivation can be estimated if radiation dose delivered to oocysts is known.

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Abnormal growth of phytoplanktons (water bloom) in eutrophic lakes impedes water utilization. In a eutrophic lake, pH increases with the carbon dioxide assimilation of the algae. Phosphorus should be released from suspended solids (SS) when pH increases. Therefore, the pH rise may promote eutrophication. The release of phosphorus from SS has not attracted attention until now. However, it is an important problem. In this study, we investigated the release of phosphorus from SS. The possibility that algae utilize the particulate phosphorus was examined by algal culture experiments. The relationship between pH and the amount of phosphorus released from SS was examined by the phosphorus release experiments. The major results obtained in this study are as follows: (1) The amount of phosphorus released from SS depends on the strength of the alkali, and the release is fast. (2) It is thought that the release of phosphorus from SS promotes algal growth in eutrophic lakes (lakes where the pH increased with the carbon dioxide assimilation of the algae).

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Variations in dissolved silicate (DSi) concentration and ratio to dissolved inorganic nitrogen (DSi:DIN ratio) were investigated in the Yahagi River, Aichi Prefecture, Japan over a three-year period (from June 2000 to June 2003). During the observation period, DSi concentration and DSi:DIN ratio at the downstream station ranged from 75 to 254 μM (average: 162 μM) and from 0.74 to 4.3 (average: 2.3), respectively. Regarding the DSi:DIN ratio, there is a possibility of Si depletion in the Yahagi River and Mikawa Bay during the low flow period. DSi:DIN ratio in the main stream was reduced by high DIN loading from the lower tributaries, and its effect was stronger when the main stream flow was low. From November to May, the low water exchange rate of the dam water leads to diatom blooms and results in the reduction in DSi:DIN ratio in the river water. Therefore, it is suggested that the increased nitrogen loading due to land development and lower river flow induced by water resources development, such as dam construction, brought about not only a decrease in the DSi supply to the coastal sea but also a reduction in DSi:DIN ratio.

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Electrokinetic (EK) remediation is a technology for removing pollutants from clayey soil on the basis of electrokinetic phenomena. Zero valence iron (Fe⁽⁰⁾) has recently attracted attention as a new sorption and reaction medium for removing Trichloroethylene (TCE) from wastewater. The purpose of this study is to demonstrate the combined use of EK remediation and permeable reactive barrier (PRB) technology to remediate soil contaminated by TCE and p-chlorophenol (PCP). The dechlorination by iron of TCE in a solution was performed at various pHs. Chloride ions generated by the dechlorination of TCE with iron powder were found in the solution. An EK remediation system with an iron reaction wall cannot only move organochlorine compounds in soil but also convert these to other compounds by dechlorination. PCP level was decreased more by the use of an EK remediation system with an iron reaction wall than by the use of an EK remediation system without. Therefore, the combination of the use of an iron reaction wall with EK remediation facilitates the removal of pollutants from the clayey soil contaminated with organochlorine compounds such as TCE and PCP.

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In this paper, we present the results of a feasibility study of swine wastewater treatment by a full-scale plant comprising an upflow anaerobic sludge blanket (UASB) reactor and a trickling filter. The UASB reactor had a volume of 6.6m³, a hydraulic retention time range of 1.2∼1.7 days and at water temperature range of 10-30°C. The trickling filter had a useful volume of 16.2m³, in which 77 sheets of unwoven fabric (2m wide, 3.5m long, 3mm thick; made of polyester) were suspended. The plant was fed with swine wastewater pumped from swine barns. The average BOD removal performance of the UASB reactor was 50% (SD 17%) throughout the experimental period of 3 years. The effluent BOD of the trickling filter was about 60 mg·l^-1 when the BOD loading rate was less than 0.2kg BOD₅·m^-3·d^-1. Fifty percent total nitrogen was removed by the trickling filter, probably by simultaneous nitrification and denitrification by biofilm developed on the unwoven fabric medium. The removal of hydrogen sulfide in biogas of the UASB reactor can be successfully achieved with a packing column reactor using the trickling filter effluent as absorbing liquid. A gas-engine-type cogeneration machine was successfully operated using the purified biogas.

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A method for the on-site estimation of lead contamination in soil by anodic stripping voltammetry using a mercury film microelectrode was developed. The optimized pretreatments were as follows: 1 g of soil sample was initially dried using a hot plate for 30 min with stirring; the sample was then extracted of lead with 33ml of a 1 mol·l^-1 hydrochloric acid solution at 70°C for 15 min; the extract was finally filtered through a disk type glass fiber filter and a membrane filter. The lead extracted was electrodeposited on the microelectrode at -1.3V vs. Ag/AgCl for 2 min and the deposits were then stripped at a rate of 50 mV·s^-1 to 0.15V vs. Ag/AgCl. By the application of a heated hydrochloric acid solution as an extracting solvent, the extraction time was greatly reduced compared with that of the official method based on soil contamination countermeasures law. The downsizing of the extraction was achieved using this method. The downsizing allowed the use of a portable mini-shaking machine and enabled the on-site extraction of lead from soil. The proposed method could be sufficiently applied to the on-site soil survey of lead contamination from bullets at a shooting range.

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