A Study Of Wastewater Treatment Characteristic Of Japanese Johkasou Using Transparency As The Main Evaluation Index

From the mid-20thcentury to the1970s, Japan has been in rapid economic development.With the rise of income, people in Japan prefer to lead a more healthy and comfortable life.Sewage systems are used for wastewater treatment in urban areas, while for those who live inrural area, a household wastewater treatment facility called Johkasou is widely used.Johkasou, invented by Japanese, has many advantages for treating domestic wastewater.For example, many different kinds of domestic wastewater can be treated, and processedwater can easily be reused for various purposes. Transparency is used as the main evaluationindex for water quality. But, due to structural and/or maintenance problems by residents,some Johkasou, for instance, about15%of Gappei-Johkasou in one prefecture, can not meetthe quality expectation for the index of transparency above20cm. This research aims atanalyzing the index influencing the transparency, and finding out how to increase the effluentperformance of Johkasou.Based on the two above-mentioned objectives, first, we should find out and test waterquality indexes which may affect the transparency, such as suspended solids, VSS, turbidity,TOC, DO, DBOD, SBOD, microorganisms, some metal ions, dissolved organic matters, etc.,and then evaluate the performance of Johkasou, and offer the solution for the improvement ofeffluent, such as adding filtration, coagulant, or increasing the HRT.By analyzing indexes affecting the transparency, we can conclude that turbidity, DBODand particle number size range around0.5-1.0m have negative correlation with transparency.VSS/SS is over84%, and organic matter comprises most of the SS. The first tank and aerationtank of Johkasou have the most purifying capacity, and the impact resistant ability is low. Byconducting the decomposition experiment, organic matters which can decompose glucoseexist in all tanks of Johkasou, and the bio-activity of aeration tank is the highest. By usingSEM, some fiber like material can be one of the cause of low transparency.From the economic perspective, the physical methods are better to increase thetransparency of Johkasou. Adding filter in the tanks of Johkasou can improve the effluent.Filters with pore size of2.7m have the most effective result of removing turbidity andparticle number.By conducting coagulation experiment for Johkasou water samples, the sameconcentration of FeCl3-6H2O has a better treatment effect than Al2(SO4)3-14~18H2O. Also,the optimum dosage for FeCl3-6H2O is80mg/l.