| Summary: | 碩士 === 嘉南藥理科技大學 === 環境工程與科學系暨研究所 === 97 === In order to improve the problem facing to domestic sewage in rural community, Environmental Protection Administration Executive Yuan, R.O.C. (Taiwan) offered Da-jia community in Jen-Te Township, Tainan County, a subsidy to set up a subsurface wastewater infiltration system (SWIS) in 2004. It is a natural treatment system for collecting wastewater and operating on-site treatment to meet the requirement of national Effluent Standard; and the ground of the SWIS can also function as a park for residents to spend their spare time. This research had been conducted from April, 2006 to April, 2007 to record and monitor the flow rate of influent and effluent, water quality, ecology and utilization of the SWIS. The treatment performance of the system for improving water quality of domestic sewage was investigated to assess the feasibility of the SWIS as an ecological engineering on-site treatment technology in rural community.
The site of the SWIS in Da-jia community occupies approximately 1650 m2 and is composed of numerous units, including pumping sump, flow metering flume, anaerobic tank (settling tank), soil filter and the eco-pond for discharging treated wastewater. Among them, soil filter, the main unit to purify the pollutants, is an underground tank with surface area of about 1248 m2, and is filled with soil and rice hull as the filtering media. Backfilled soil was filled above the filter for vegetation planting. The soil filter was divided into three beds, which were designated as A, B, C bed and were designed for rotational operation, in which only one filter compartment was operated for wastewater treatment at the same time. The wastewater flowed into metering flume from the pumping sump, and then flowed through anaerobic tank and soil filter by gravity. After the treatment, the treated wastewater entered the eco-pond for reuse in farm-land irrigation and effluent discharge.
The results indicate that the SWIS could not operate under high hydraulic loading due to the inherently high hydraulic resistance, which was induced by the small particle of the soil media used. The C bed reached a highest hydraulic lading up to 0.17 m3/m2/d (m/d), while the other two beds operated only under 0.04 m3/m2/d (m/d). The SWIS exhibited substantial removal of the pollutants such as BOD5、COD、PO4 and total coliforms. The resulting average removal efficiencies of BOD5, COD, PO4 , and total coliform were 77~82%, 44~55%, 79~93%, 76~87%, respectively. After treatment, the BOD5 concentration of the treated effluent consistently satisfied the national Effluent Standard (<30 mg/L). Totally 31 of the 32 samples of the treated wastewater conformed to the Effluent Standard of COD (<100 mg/L). Although the soil filter showed the significant removal efficiency of total coliforms, 28 of the 33 samples of the treated wastewater did not meet the Effluent Standard of total coliforms (<2000 CFU/mL). The SWIS had lower removal of TSS, turbidity, TN, and TP, resulting in removal efficiencies of 4~29%, 15~26%, 17~37%, and 15~33%, respectively. Since the TSS concentration was not high in the influent wastewater, 30 of 33 samples of the treated wastewater still conformed to the Effluent Standard of TTS (< 30 mg/L).
After treatment and purification, the treated sewage offered water to irrigate terrestrial plants in the system. Besides, the farmers nearby were willing to use the treated sewage for irrigation of their farmlands. To the middle of 2009, the SWIS in Da-jia have worked for five years, and its treatment efficiency and the water quality of the treated wastewater are still very stable.
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