A TEMPERATURE HYSTERESIS EFFECT IN ON-SITE DOMESTIC WASTEWATER TREATMENT FACILITIES

Abstract

 In Japan, on-site household wastewater treatment facilities consisting anaerobic and aerobic tanks are called Johkasou. The water temperature is well known as one of the important parameters for wastewater treatment. However, no correlation between temperature and effluent water quality of Johkasou in the period of temperature increase has been reported. In this study, influence of the current and the previous water temperature on treatment performance of Johkasou was investigated. The dissolved oxygen concentration in the aerobic tank and the residual chlorine concentration in the disinfection tank had high correlations with current water temperature, whereas the biochemical oxygen demand and total nitrogen concentration of treated water, among other items, were influenced by moving average of the previous water temperature. The numbers of months used for the moving average calculation that showed the highest correlations were four to five months. This temperature hysteresis effect was found in not only the quality of Johkasou-treated water but also the amount of scum in the anaerobic filter tank. These results suggest that the sludge accumulated in the anaerobic filter tank decomposed and solubilized over a period of 4-6 months, then influenced the Johkasou performance.