Intermittent sand filtration for wastewater treatment in rural areas of the Middle East - a pilot study

This paper concentrates on Intermittent Sand Filtration (ISF) as a polishing stage for effluent from a facultative pond. During the three-year research program, the system operated with an influent flow-rate of 500-1,000 L/day and an average BOD concentration of 200-400 mg BOD/L, with the corresponding hydraulic and BOD loadings of 110-200 L/m2/day and 20-40 gBOD/m2/day, respectively. Flow to the ISF was applied intermittently with a different number of doses in each run. In addition, the effects of the frequency and the duration of rest periods (no feeding) were studied. Removal of 90-95% of BOD and 75-90% of COD and TSS was achieved consistently throughout the study period. Elevated levels of nitrification were observed with 95-100% removal of NH3. The ISF performed best when fed with 5-10 doses/day. Reducing the daily number of doses to 3/day at the same hydraulic loading rate resulted in a 20-30% reduction in removal efficiency. The 2-4 week rest period had no effect on the biological activity in the subsequent run. However, rest periods of more than 30 days were found to negatively affect removal efficiency.