Denitrification of GroundWater Using Sand Filter

Abstract

Groundwater is the sole source of potable water inGazastrip. Nitrate concentrations are increasing, in sonic cases rapidly, at rates of up to 10 mg/L per year and generating health hazards especially for babies (Less than six months) and pregnant women. The quality of the water extracted from the aquifer varies by area and time, but in general, does not satisfy the WHO guideline values for drinking water quality with regard of the concentrations of nitrates. Most municipal wells have nitrate in excess levels of the 50 mg/l. The main sources of nitrates are fertilizers and domestic sewage effluent. The quantities of sewage that infiltrate to the water table on an annual basis through cesspits and septic tanks are significant, about 12 million cubic meters per year. This research is devoted for the contribution in the improvement of water quality in Gaza Costal Aquifer using sand filters to remove nitrate from drinking water. Biological removal of nitrate from drinking water was studied in a slow sand filter with using different medium had different particle size. Sand, gravel pack, and granite gravel were used with adding ethanol as source of carbon to enhancing the potential of denitrification. The flow rate, nitrate concentration and pH were studied there impact on nitrate removal through the sand filter. The denitrification process need start-up period to allow the bacteria to attach to the support particles before it can be able to start removing nitrate. As a result of this research the slow sand filter was able to provide NO3 removal up to 95% (110 mg NO3/liter). The NO3 removal efficiency dropped when the surface loading rate increased. The efficiency of nitrate removal is more than 90% (60 to 80 g/ m2.day), 55% (40 to 60 g/ m2.day), when flow rate velocity 1.2 m/day for reactor with diameters = 50mm and 75mm with gravel media, while 95% (140 to 200g/ m2.day) for diameter = 75mm for gravel pack media at the same velocity. The optimum flow rate for each medium depends on its surface area. The material which has more surface area can be able to remove nitrate more than others at the same flow rate. pH will be affected with the same factors affecting the denitrification process, so when the flow rate velocity was below 0.36 m/day, the pH will be more than 9 and when the surface loading rate was below 30 g NO3/ m2.day, the pH was more than 9.