Israel continues to be a world leader in the successful exploitation of treated wastewater, and over the past decade it nearly doubled the area in which this water can be used for crop irrigation, according to a comprehensive survey conducted by the state Water Authority.
Although the survey noted an improvement in the quality of the treated water as a result of the increased use of desalinated water, much of the treated water is not yet of a quality suitable for use on all crops.
The survey, which was carried out by employees of the Israel Nature and Parks Authority on behalf of the Water Authority’s water quality division, was a comprehensive, nationwide study of 1,400 households, industrial and agricultural producers of wastewater. The survey is carried out every other year; the most recent figures are from 2012.
According to the most recent survey, untreated wastewater is no longer released into the Mediterranean Sea from Israel. Israel produces 500 million cubic meters of wastewater every year, more than 90 percent of which reaches the various treatment plants.
In the territory administered by the Palestinian Authority, in the West Bank – which was included in the survey – the situation is very different. Only one-quarter of the wastewater produced by Palestinian communities in the West Bank is connected to a sewage collection system, and only one-tenth reaches treatment plants.
Of all the wastewater from all of the areas that reaches the treatment plants, 85.6 percent is reused – a worldwide high. Some of this water comes from the Dan Region Wastewater Treatment Plant, or Shafdan, which treats wastewater to a particularly high standard. Most of the treated wastewater is used for crop irrigation, with a smaller amount used for gardens and industry.
The total area of land under cultivation that is approved for irrigation with treated wastewater is 1.3 million dunams (325,000 acres), nearly double the approved acreage a decade ago. Some 50 million cubic meters of treated wastewater are discharged into the environment; one-fifth of that amount is released into the Yarkon River, keeping the river flowing year-round.
While the use of treated wastewater significantly reduces water use from natural sources, it comes at an environmental price, since the treated waster contains relatively high concentrations of salts, which affect certain crops as well as the soil and groundwater. This, in addition to a high concentration of sodium, which affects soil percolation rates and is associated with certain plant diseases.
According to the latest survey, the majority of the treated wastewater still cannot be used without restrictions on all crops. Low to moderate levels of sodium were found in more than half of the wastewater storage reservoirs that were tested, but a clear decrease in salinity levels was found as a result of the growing use of desalinated water in the national water supply system. As a result, the amount of salt in wastewater declined by nearly nine percent in two years.
It should be noted that a few Israeli experts argue that treated wastewater should be desalinated before being used for irrigation, in order to prevent the damage caused by salinity.
A few months ago the results of a study on the effects of irrigation on banana crops conducted by a team from Galilee Technology Center, led by Avner Silber, were published. The researchers concluded that irrigation with desalinated water led to increased crop yield and obviated the need to add additional water in order to reduce soil salinity.