Abstract
Decentralized domestic wastewater treatment systems are generally used in rural areas for preventing pollution of local water environment. Treated waters of decentralized systems potentially contain fecal contaminants and the degree of contamination can vary seasonally. To identify the seasonal characteristics of fecal indicators in the area of decentralized system, seasonal monitoring on the characteristics of fecal indicators (total coliforms, Escherichia coli, and F-specific coliphages) was performed along an open channel receiving johkasou effluents over 3-year period. Fecal indicators were detected higher than environmental quality standard throughout the season, particularly for total coliforms, and the concentrations of Escherichia coli downstream seemed to be higher than upstream in winter. The low water quality was recorded during cold-low flow season and the effluent of johkasou was an important factor reflecting water environment quality. In contrast with most physicochemical parameters, significant seasonal differences of total coliforms and Escherichia coli were not observed both in water and sediment. The principal component analysis results show that four dominant factors related to chemical contaminants, environmental conditions, byproducts, and fecal contaminants were responsible for the water quality data structure and significant seasonal differences were observed for chemical contaminants, environmental conditions, and byproducts, accounting for 59 % of the total variance in the data set. Seasonal maintenance of discharged water quality and controlling downstream network capacities are necessary to reduce the potential impact of johkasou effluents into local water environment.
