Articles & Case Studies

Improving water availability in Israel

Posted: Wednesday 28th March 2012

Be’er Sheva, one of Israel’s largest cities with a population of approximately 200,000, is located in the country’s Negev Desert in the southern portion of the country. Seven consecutive years of drought, coupled with increased demand from a growing population, have led to the overexploitation of the water supply in the country and the Middle East region. While five percent of the world’s population resides in the Middle East and North Africa, the region has less than one percent of the world’s available water supply. As a result, the people of Israel and other nearby countries have long sought innovative ways to use every available drop of water.

Farmers build own effluent reuse system for crop irrigation

The reuse of wastewater effluent has become a common strategy in the region for a variety of applications, in particular agricultural irrigation. But for the farmers of the Negev Settlements, a cooperative union of 34 settlements outside of Be’er Sheva, the quality of reclaimed water from a local wastewater treatment plant was not suitable for “unlimited irrigation” purposes. According to Zeev Gottlieb, managing director of MODOtec Advanced Systems, a water and wastewater solutions company, “These farmers had no suitable source of water to irrigate their crops, so they decided to take matters into their own hands. In order to provide the tertiary filtration necessary for unlimited irrigation, the farmers pooled their resources and paid for the construction of an effluent reuse system next to the wastewater treatment plant. Effluent from the plant was treated by the reuse system and then pumped to the fields.”

The farmers selected MODOtec as the solution supplier for the project. After investigating several filtration alternatives, the company chose the TETRA® DeepBed™ filtration system from Severn Trent Services. The filtration system’s treatment capacity is 60,000 m3/day, with 90 percent of the effluent used for agricultural irrigation and 10 percent for irrigation of Be’er Sheva’s municipal parks. In addition to the new filtration technology, a UV system is used downstream for disinfection.

The TETRA DeepBed Filter at Be’er Sheva consists of six cells, each 17.07m in length and 2.9m wide, providing a total area of 300 m2. The filtration system uses 900 tons of TETRA quartz sand media and 2,500 TETRA SNAP T® Blocks, a wastewater filter underdrain design. The underdrain system is required to support filter media and to separate the filter media from the bottom of the filter. In addition to providing support for the filter media, the underdrain system serves two primary purposes: to allow filtered water to pass through to the collection system and to start the distribution of backwash water and backwash air across the filter.

Unique filter block design

The floor of the TETRA DeepBed filters deliver high process flexibility and superior distribution of both backwash air and water, either separately or concurrently. The system’s underdrain design uses a positive backwash air distribution system with an air header and laterals which allows the water to follow the air. The wastewater underdrain blocks are plastic-jacketed and concrete-filled, preventing gravel from entering the underdrain system while allowing filtrate to pass to the filter discharge location. The filter floor has no nozzles or small orifices that can lead to blockage by biofouling and as such is ideally suited for use in a wastewater environment.

The plant operates as a single filter consisting of a number of cells into which the influent flow is distributed. The flow passes through the media and suspended solids are removed. Filtered effluent is discharged through a clear well which retains a reservoir of water for cell backwashing. The size of the media used enables solids to penetrate deep into the bed. This use of depth rather than surface filtration gives the filters greater solids-holding capacity and, thus, longer run times between backwashes. The filter is "regenerated" by taking one cell offline at a time and employing an air and water backwash to clean the media. The dirty backwash water generated (typically one to three percent of forward flow for design solids loadings) is returned to the treatment works. While a cell is offline for backwashing, the influent flow is redistributed to the other cells, and operation of the filter continues with minimal impact on the quality of the effluent.

Reducing operating costs by taking filters offline

One of the benefits of the TETRA system is that it is able reduce operating costs by adapting to changes in loading conditions. Individual filters can be taken offline and brought back into service as needed according to fluctuations in influent flow and solids loadings. If the filter is left idle for more than seven days, the filter is backwashed and drained before being taken offline and an extended backwash is performed before bringing the filter back online.

The new filtration plant was commissioned in April 2011, and its performance in the first few months of operation has been exceptional. Effluent turbidity measures an average of 0.7 NTU and the effluent TSS concentration averages 2.5 ppm. Utilizing the TETRA system, neither coagulant, flocculent nor media chlorination has been required during backwash.

“The farmers of the Negev are very happy with the performance of the new filtration technology,” said Gottlieb. “Ten thousand acres of desert have literally been turned into beautiful, green, productive farmland.”

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