Enhancement of the Efficiency of Infiltration Basins for Effluent Recharge

Abstract

The Agricultural sector in the Gaza Strip on an average consumes around 75-80 MCM of water annually. All amounts of water used for this purpose come from groundwater wells. Wastewater reuse is envisaged primarily as a means to support the agricultural sector in Gaza Strip as addressed by Palestinian Water Authority (PWA). The artificial recharge (AR) of treated wastewater to groundwater can be achieved by means of spreading basins the commonly used methods for infiltration purposes to unconfined aquifers. The problem of the AR is the reduction of infiltration capacity in the infiltration basins resulting from using partially treated wastewater due to accumulation of suspended solids (SS) and the organic load, and the poor maintenance. The goal of this research is enhancement of the efficiency of Infiltration Basins for effluent recharge. Field experiments was performed in order to achieve the required objectives such as the quality of the soil under the infiltration basin, and quality of the effluent water to the basin. Also modeling for the unsaturated zone using the Green-Ampt model (1911) was performed in order to predict the existing and enhanced infiltration rate. The field and lab tests results showed that the soil strata in the infiltration basin IB1 consists of Sand which is non-plastic and has good permeability characteristics, Clayey Sand: which is the wide spreading layer at the top of the basin, and of low to medium plasticity, and of low permeability, and Sandy Silty Clay which is of medium plasticity, and of low permeability. The results showed that the infiltration rate is affected by the soil properties; sandy soils have the highest infiltration rates and clayey soils have the lowest infiltration rates. Also the results showed that the infiltration rate is affected by the quality of the effluent water, operation cycles and maintenance for the top surface. According to the results which have been supported by model; removing the upper 2.0 meters of soil layer at IB1 and replacing it with new sand martial with high permeability introduced an efficient solution for enhancement the infiltration rate. Also penetrating the lower soil layers with 60 piles and filling the piles with gravel fine media with high permeability, will increase the infiltration rate for the whole basin according to the study. Performing 35 cycles of wetting and drying during the year with 2 days of wetting in summer and winter and 7 days of drying in summer and 12 days of drying in winter, will help to reach the optimal infiltration rate. Soil plowing after each drying cycle for the basin is required to maintain good infiltration rate and prevent accumulation of the organic matter (OM) in the top soil layer.