Domestic wastewater treatment in Indonesia, mostly treat by using septic tanks. The use of septic tanks preferred by the public because of the design, construction, and maintenance are easy and more economical for the system of domestic wastewater disposal. Effluent from the septic tank still contains BOD about 100 mg /l, COD about 250 mg/l and TSS about 100 mg /l. This effluent is still dangerous to public health and is not fulfill wastewater effluent standards yet. If there is open space available, extended treatment of septic tank effluent can be done by field infiltration. This open space must suitable for infiltration without contaminating the ground water or well water. In urban areas with ground water level is high such as Surabaya, water infiltrate into the ground causing the problem. Problems that arise are due to pollution of ground water and surface water contaminated by effluent from the septic tank. Because of these problems, it would require an alternative treatment of septic tank effluent. Appropriate technology would be a simple, economical, easy in operation and maintenance. One of wastewater processing that can be applied to the septic tank effluent is a constructed wetland system.

Previous research carried out by using Cyperus papyrus plant with sand media in batch experiments showed satisfactory results. In this study, experiments conducted by using Cyperus papyrus plant with sand media with continuous flow in a horizontal subsurface flow wetland method. Wastewater flows with varying flow 90 ml /min and 180 ml /min. The objective of this research is to determine the ability of a horizontal subsurface flow wetland for treating septic tank effluent. The parameters analyzed were BOD and TSS. The results show the relation of organic loading rate with BOD removal efficiency. The highest organic loading rate of 0.051 kg BOD/m2.d on first day observations has BOD removal efficiency of 73.63% and the lowest organic loading rate of 0.029 kg BOD/m2.d with an efficiency of 70.82%. This shows that BOD removal efficiency is affected by organic loading rate. If BOD loading rate increase, it will decrease BOD removal efficiency. Organic loading rate recommended for domestic wastewater is 0.037-0.4 kg BOD5 /m2.d. Although in this study the organic loading rate exceeds the above recommendations, but efficiency is still good, above 70%.

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