Abstract: "Three-Grille-Mode" septic tank is a common approach used in renovating latrines in the rural areas in Jiangsu,accounting for about 50% of the total sanitary latrines in the area.Its treatment efficiency directly affects quality of the rural water environment.A total of 168 normally running "Three-Grille-Mode" latrines in 9 cities(counties) of Jiangsu were selected as objects of the research.In the period from June to August,2006,water samples were collected at the inlet and outlet of the latrines 3 times consecutively with an interval of 5 days.Analysis of the samples showed that "Three-Grille-Mode" septic tanks could reduce COD_Cr by 48.51%,TN by 6.83% and TP by 23.92%,and the efficiency varied with the influent concentration,and followed a decreasing order of South Jiangsu>Central Jiangsu>North Jiangsu.Generaly its treatment efficiency was lower than the biogas-digester′s.The treated water flowing out of the septic tanks fails to meet the criteria of the national standard for wastewater discharge and its discharge will significantly affect the environment.

Key words: "Three-Grille-Mode", septic tank, treatment efficiency, evaluation, Jiangsu