Small-Scale Domestic Wastewater Treatment Technology in Japan, and the Possibility of Technological Transfer

In Japan, the coverage rate of domestic wastewater treatment among the population was 82.4% at the end of FY 2006, but the coverage rate of domestic wastewater treatment in areas with a population of 50,000 or less remains low (about 65%). In addition, because a smallscale treatment system requiring low construction and maintenance costs is sought because of municipalities’ financial difficulties, past technologies are being reexamined. Based on the background mentioned previously, small-scale domestic wastewater treatment technologies were organized in search for technologies that can be transferred, and the ideal way for the future was proposed. Introduction There is a trend in domestic wastewater treatment in which large city areas are accommodated more readily than medium and small city areas, or rural communities. Because the population density is less compared with large city areas in areas with smaller populations, a small-scale dispersed treatment system is sought. The conventional activated sludge process that is widely popular for domestic wastewater treatment in large cities is a stable treatment system, but the process is sometimes not suitable for a small-scale treatment system, so other systems are being selected. The issue of domestic wastewater treatment has been shifting from large-scale intensive systems for large cities, to small-scale systems necessary for small city areas, and rural communities. In addition, “locally suitable technology” that is adaptable to local social and economic conditions is sought in developing countries, but it is difficult to transfer the general Japanese technological system without modification. With these things as a background, this paper gives an overview of Japan’s domestic wastewater treatment and small-scale treatment technology, and discusses cases of technological systems that are highly likely to be transferred. In addition, this paper will introduce cases of the technological development situation in China, where lifestyles have changed drastically due to economic development, and there is great demand for a small-scale treatment system. Lastly, this paper will sort out the future of technological transfers with regard to small-scale domestic wastewater treatment systems. The Situation and Problems of Domestic Wastewater Treatment in Japan Figure 1 indicates the flow of domestic wastewater treatment in Japan. Domestic wastewater are roughly classified into human waste discharged from toilets (night soil), and wastewater discharged from kitchens and bathrooms (gray water). Domestic wastewater are mainly treated through wastewater facilities, rural community sewerage, and the in site treatment system (Johkaso). When vault toilets are used instead of flush toilets, human waste is stored there. In this case, stored night soil is transported to night soil treatment facilities several times a year, and Gray water Domestic wastewater Night soil Sludge Gray water Treated water