Salt Reduction in Municipal Sewage Allocated for Reuse: The Outcome of a New Policy in Israel

Weber B., and Juanico M. (2004).
Salt Reduction in Municipal Sewage Allocated for Reuse: The Outcome of a New Policy in Israel.
Water Sci. Technol. 50(2):17–22.

ABSTRACT

The problem:
Israel has practiced agricultural irrigation with treated wastewater for decades and is presently reusing about 70% of its sewage. Sewage is more saline than the supplied freshwater and the salts are recycled together with the water. Salts (mainly Cl, Na and B) have negative effects on crops, soil and groundwater. The buildup of salts in soils and aquifers has already been detected in some areas of the country. There are no inexpensive ways to remove the salts once they enter sewage, and the prevention of sewage salt enrichment is one of the most immediately available solutions. Main industrial contributors to sewage salinity are the water softening process, meat 'koshering', textile dyeing plants and food processing. Detergents largely contribute Boron and Sodium.

The initiatives to solve the problem:
The discharge of certain kinds of brines to municipal sewers is now prohibited by national law, and a scheme to discharge these brines to the sea has been implemented with nine discharge points along the coast. Some discharge points are outfalls from big factories while others are for cistern trucks coming from smaller factories or from those located far from the coast. The concentration of salts in industrial effluents, which is presently limited by municipal bylaws and by the business licensing law, will be limited by a stronger national water law in the near future. The Ministry of the Environment has encouraged the substitution of Na by K or Ca in industrial processes and the substitution of softening technology by reverse osmosis or anti-scaling technologies, and of water-based air conditioning by air-based systems. A new unique regulation limiting the Boron and Sodium content in detergents has been implemented.

The outcome of the initiatives:
Israeli industry has undergone a radical change in recent years. Many factories have adopted K or Ca for softening and neutralization, while others have shifted to reverse osmosis or other technologies. All hospitals have changed the softening technology. More than 120 factories discharged brines to sea in 2001 and this number continues to increase as enforcement is implemented. The amount of brines discharged to the sea has increased from 580,000 m3 in 1999 to more than 700,000 m3 in 2002, corresponding to 22,000 T and 32,000 T of salts respectively. These amounts of salts are thus definitively taken out of the reuse cycle, year after year. The concentration of Cl and Na in the sewage reaching treatment plants is declining. The addition of Cl to sewage has dropped from 120 mg/l to 70 mg/l. The average Boron concentration in sewage has dropped from 0.6 mg/l to 0.3 mg/l and should reach 0.2 mg/l by 2008.
Prevention of the increase in salt content in sewage for irrigation is a feasible practice.

KEYWORDS
salinization, sewage, water reuse, irrigation, Chloride, Sodium, Fluoride, Boron