Wooden timber from scrapped housing is not sufficiently recycled. Since timber made from Japanese cedar has been used in Towada, Aomori Prefecture for housing construction, we investigated the mulching method of Japanese cedar wooden chips made from scrapped housing timber. The main recycled chip diameter was comprised of two classes: 4.76 to 10 mm and 10 to 19 mm. They contained negligible amounts of heavy metals. By using 10 cm thick mulching chips, the growth of weeds was controlled due to a shading effect. It also contributed to making soil temperature and moisture stable, which are preferable for tree plantations at parks, orchards, and roadsides. Therefore, we concluded that Japanese cedar wooden chips are available for mulching when they were applied with a 10 cm mulching chips.

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This study focuses on effluent COD concentration from wastewater treatment in regards to the reduction of pathogenic bacteria and trace substances in public waters. The main types of secondary wastewater treatment were conventional activated sludge processes. Recently, however, advance wastewater treatment processes have been developed aimed at the removal of nitrogen and phosphorus, and the effluent quality of these processes was analyzed in this study. Treatment processes for water reclamation that make effluent to meet the target water quality for reuse purposes were selected and also optimum design parameters for these processes were proposed. It was found that the treatment cost to water reclamation was greatly affected by the effluent COD of the secondary treatment. It is important to maintain low COD concentration in the secondary treated effluent. Therefore, it is considered that adequate cost benefits would be obtained by achieving target COD quality through shifting from a conventional activated sludge process to an advanced treatment process.

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