Optimal Use of Nanofiltration for Nitrate Removal from Gaza Strip Municipal Wells

Abstract

Groundwater is one of the most precious natural resources in the Gaza Strip as it is the only source of drinking water for the majority of the population. 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 in terms of the 50 mg/L as NO3. The nitrate sources in the groundwater of Gaza Strip are wastewater, septic tank, sewage sludge animal manure and N-fertilizer. The aim of this study is to optimize the use of Nanofltraiton for removal of nitrate in Gaza Strip as case study. One commercial membrane (NF90) was used in this study. The stirred dead end flow model was used in addition, two types of water was used: Aqueous solution and real water. The performance of the tested membrane was measured in terms of flux rate and nitrate rejection under different operation conditions: nitrate concentration was varied between 50-400mg/L, applied pressure (6-12) bar and TDS concentration (500-3570) mg/l. The results showed that, in aqueous solution, increasing operating pressure posed positive effects on both nitrate rejection and flux rate performance of nanofiltration. However, increasing the feed nitrate concentration reduced the rejection and flux performance. The percentage of nitrate removal was in the range of 21.67% and 66.68% and the flux rate range between 5.39 and 14.88- L/m2.hr. These values depend on operation conditions such as nitrate concentration and operation pressure. In real water, the percentage of nitrate removal was influenced by TDS value in general, but to be more specific, it was found that the concentration of sulphat has a great effect on nitrate removal, as the sulphat concentration increased the nitrate removal decreased. In addition, the flux rate influenced by TDS concentration and specific chloride concentration. NF90 was observed to be an effective membrane for nitrate removal of Gaza Strip at higher permeate flux and lower applied pressure, especially in North Gaza Strip were low TDS and Sulphat concentration were observed. In other Gaza Strip places TDS and sulphat need to be removed before using nanofiltration. The optimum operating pressure was tested by number of wells. The results indicated that NF90 is better than RO in nitrate removal and energy cost in terms of lower pressure.