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Projects
| Wastewater Collection, Treatment and Reuse System for the Greater Tel Aviv Metropolitan Area |
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| Client: |
Dan Region Association of Towns (Sewage) |
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| Country: |
Israel |
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| Project Information: |
Wastewater flows in the year 2000 reached a total annual volume of some 160 MCM. Total urban service area - 200 sq.km with 800 industrial enterprises generating large quantities of industrial wastes of widely varying qualities.
The scheme is designed to serve two main purposes:
• Collection of wastewaters from the region and their conveyance for treatment by processes which will enable the resulting product water to be delivered to the arid regions of the country for unrestricted irrigation use and thus provide a considerable additional non-conventional water resource to supplement the country's scarce water resources.
• Discontinuation of the discharge of sewage to the Mediterranean and elimination of marine pollution from this source of the sea and beach area, a major recreation and tourist attraction.
The scheme is being implemented in two principal stages, the first of which has been in operation since 1977; the first modules of the second stage plant have been in operation since 1987. The second modules are under construction (1995).
The first stage treatment plant is based on biologicalchemical processes, while the second stage plan applies biological-mechanical processes. Both treatment plants produce a very high quality effluent from the chemical as well as sanitary points of view, allowing the reclaimed water to be used for unrestricted irrigation of all crops.
MAIN PROJECT COMPONENTS
The Collector System
• Main collector network comprising main collectors of up to 72-inch dia., an 84-inch trunk sewer and two parallel 50-inch dia pressure lines.
• The Reading pumping station, with an installed capacity of 26,000 HP and a discharge of 33,000 cu.m/hour at a 15-m head.
• The Bassa pumping station, with a discharge of 35,000 cu.m/hour at a 50-m head.
The First Stage Treatment Plant
Wastewater delivered to the plant undergoes biological treatment in two parallel series of facultative recirculated oxidation ponds, extending over an area of 120 ha, (in operation since 1977), without incurring any undesirable environment effects, such as noxious odors. The secondary effluent from the ponds is then treated in a twophased chemical process consisting in the first phase of high lime and magnesium precipitation in sludge blanket reactor-clarifiers where the pH is raised to 11.5 and pollutants, such as algae, organic matter - both colloidal and soluble - phosphorus and nitrogen compounds, heavy metals, toxic substances, bacteria and viruses, are eliminated. From there the effluents are delivered to the second phase installations of the chemical plant consisting of polishing ponds occupying some 80 ha where they remain for about 15 days, for ammonia stripping and pH reduction.
For final treatment, the effluents are pumped into spreading basins in the sand dunes of Rishon Le Ziyon for soil-aquifer treatment and percolation to, and recharge of, the local groundwater aquifer. The recharge operations, also initiated in 1977, have been carefully monitored, to measure effluent movement through the unsaturated zone and within the aquifer itself. The recharged water, mixed with the naturally recharged water of the aquifer, is then withdrawn from the aquifer through a battery of wells drilled in the surrounding area and delivered by pipeline to the Yarkon-Negev Water Supply System. The first stage plant produces on average 20 MCM/year of reclaimed effluents and will eventually produce about 30 MCM/year. When, after operation of the first stage for same years, it was found that nitrification take place in SAT (Soil-Aquifer Treatment) the lime treatment was eliminated. The oxidation ponds now serve as equalization basins for the biological treatment plant.
The Second Stage Treatment Plant
This stage is based on the activated sludge process with extended aeration also followed by recharge to the aquifer. The treatment includes a nitrificationdetrification process for nitrate stripping and phosphate elimination by a biochemical process. Two biological reactors of 55,000 cu.m each form the core of the plant. Each reactor consists of a system of convoluted, deep, wide channels through which the effluent flows. Aeration is achieved by means of 36 horizontal aerators of the "Mammoth Rotor" type. This process, one of the most advanced at this date, allows the simultaneous removal of nitrogen and phosphorus compounds together with organic matter in one single reactor.
Sludge separation from the effluent is obtained by the use of 55-m dia secondary sedimentation tanks, each reactor being connected to a system of five sedimentation tanks. The sludge is disposed of by means of a 16-inch dia, 5-km long sea outfall. Plant effluents are discharged to spreading basins, extending over an area of 75 ha of the Yavne sand dunes for aquifer recharge. Here, too, batteries of wells have been drilled in the area surrounding the spreading basins for pumpage of the recharged effluents to t h e Yarkon-Negev Water Supply System.
According to the results of tests over a period of two years, performed in a pilot plant on the effluents prior to recharge, the following removal rates were obtained: BOD filtered of 98 percent; suspended solids - 95 to 96 percent; nitrogen - 73 percent; phosphorous - 74 percent. Detention of the effluents in the aquifer for a period of several months results in an effluent of high quality.
Reuse System
The effluent is withdrawn through some 90 recovery wells surrounding the spreading basins and delivered via a 55-72-inch dia main over a distance of about 90 km to the arid southern region for irrigation. This main is used solely for conveyance of the reclaimed wastewaters and is properly isolated from the domestic water supply systems.
Total supplies for irrigation from the two treatment plants are expected to reach 165 MCM/year by the year 2005. |
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