REUSE OF WASTEWATER IN AGRICULTURE-ECONOMIC ASSESSMENT OF TREATMENT AND SUPPLY ALTERNATIVES AS AFFECTING AQUIFER POLLUTION

摘要

Treated wastewater in Israel is the unlimited and a reasonable alternative for water supply to agriculture as the high-quality fresh water supply is gradually transferred to urban uses. Still, the domestic and industrial effluents carry pollutants including micro and macro organic and inorganic matter which potentially pose hazards to health, the environment, crops and soils, and may deteriorate aquifer quality. Nevertheless, for irrigation in Israel, using treated wastewater is the best means to facilitate agricultural production under conditions of water scarcity, since it uses a water resource that is available in large quantities and that already requires treatment, in order to prevent environmental damage. Salinity level is higher in effluents than in influents, while regular treatment processes do not get rid of salinity, unless combining relatively expensive desalination processes. In this paper the focus is on salinity/chlorides as representing groundwater pollution. Hydrological model is used to predict the flow of chlorides through the unsaturated zone of the subsoil and into the groundwater below. We assumed that there is a threshold value for chloride concentration in the water supply for domestic consumption, and considered that when the concentration of chlorides in the supplied water reaches this threshold, desalination of groundwater should be initiated. When irrigation is with treated wastewater, desalination processes are initiated earlier than under conditions of irrigation without effluent, and this increases the water supply costs. The damage to groundwater by effluent irrigation is assessed in terms of increased costs that arise from processes including water pumping and transporting, wastewater treatment and earlier initiation of desalinization. We compared several scenarios regarding salinity threshold levels and irrigation combinations with and without wastewater. This was applied to a specific case study in the Coastal aquifer of Israel composed of 8 hydraulic cells. The resulting salinity levels decrease with stricter restrictions and increase with wastewater irrigation. Water supply costs increase with stricter restrictions while with wastewater irrigation, desalination costs increase but total costs decrease.