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Sewage Treatment Plant for the City of Medinet Zayed
Medinet Zayed is a fast-growing city within the Abu Dhabi Emirate of the United Arab Emirates.
Abu Dhabi Municipality decided to provide sewage treatment facilities as part of the development plan for the city to cater for daily sewage of 5000m3/day in Medinet Zayed complete with a collection network. The treated effluent is of a quality suitable for irrigation use which conforms to Abu Dhabi’s highly acknowledged standards of improving environmental protection. Specifications were drawn up by Abu Dhabi Municipality and consultants KEO / Metcalf and Eddy to the latest international standards with due recognition for the emirates concern for environmental protection.
Metito secured the multi-million-dollar project against tough competitive bidding and subsequently completed the project to the entire satisfaction of the authorities.
Scope of Work
This included the complete design, engineering, manufacture, supply, inspection and testing, site storage, installation, commissioning, performance test, and training of personnel.
Plant General Information
The sewage treatment facilities are extensive and mainly comprise the following units:
Two pumping stations are provided to pump the city sewage to the treatment plant. These stations are located at a distance between five and seven kilometers from the plant. Each lift station is provided with two sewage grinders each having a capacity to handle sewage flow rates up to 500m3/hr. Three pumps supply the sewage to the treatment site. The pump capacities range from 300 m3/hr to 460 m3/hr. The station equipment is installed 11 m below ground with appropriate ventilation and odor control equipment.
The aerated water passes through circular clarifiers 20m in diameter. The clarified water flows into a peripheral launder over an adjustable weir plate. The clarifiers are equipped with a gear-driven central cage and rake mechanism. Sludge is raked into a central cone at the bottom of the clarifier. The system has been designed 10 provide continuous sludge bleeding, sludge re-circulation and excess sludge discharge.
The clarified water is treated in the gravity filters so as to further improve the quality of the water. The filters are provided with traveling bridge backwash equipment. The equipment is mounted on a frame structure that moves along the filter by a mechanism powered by a reversing motor. The backwash equipment comprising of a moving stainless-steel hood and a submersible pump are mounted onto this bridge. Hydraulically sized orifices are provided to uniformly collect the backwash water.
The clarifier sludge and plant drain flows are collected in a 140m3 sludge holding tank. A Metering station measures and monitors the was e and re-circulation sludge flows. Aspirating aerators are provided in the sludge holding tank.
The thickened sludge is pumped to the sludge drying beds by means of progressive cavity type or pumps having a design pumping capacity of 170 m3/hr. Underflow from the sludge drying beds and decanted water from the sludge holding tank are returned to the inlet for further recovery.
Complete chlorinating equipment is housed in a separate building. Two wall-mounted vacuums operated, solution feed, sonic flow type gas chlorinators are supplied to provide the chlorine solution to the chlorine contact tank and filters. An automatic switchover facility ensures the continuous supply of chlorine and the gas feed flow is automatically controlled.
Other equipment installed includes on-line chlorine analyzer, chlorine leak detection and monitoring.
The treated water from the chlorine contact tank is stored in an effluent storage tank. Effluent pumps deliver water both for process use and supply to irrigation reservoirs. A hydropneumatic tank provided on the process water line assures minimum supply pressure. The hydropneumatic tank is 20m3 ASME stamped carbon steel pressure vessel. The associated compressors, control and monitoring devices for automatic operation of the irrigation system are also supplied.
The irrigation reservoir receives the treated water from the sewage treatment plant for storage and subsequent distribution. The reservoir is provided with inlet control valves and four sets of pumps supply water to the irrigation system. The water passes through a further hydropneumatic tank to maintain a minimum pressure in the system.
Electrical equipment includes MCC’s, cabling, wiring, earthing, plant and street lighting, protection, etc. Four diesel generator sets are supplied for emergency electric supply. The generator sets prime rating varies from 87 kW to 1024 kW and is provided with both Auto/Manual Transfer switch (ATS/MTS) in line with the latest Water and Electricity Department requirements.
A central control panel monitors and controls the operation of the entire plant. A Mimic panel provides easy to understand graphic display or the various components of the plant and the status of each equipment is shown on the Mimic through illuminated LED’s.
In addition, the plant is equipped with a telemetry and SCADA system. The whole system monitors the Medinet Zayed Sewage Treatment plant and also all other pumping stations within the city and sewerage systems in the western region of Abu Dhabi. The entire water treatment package for the defined scope of work was commissioned in November 1998.
Since that time the plant has been in continuous and trouble-free operation. This has enabled the Authorities to achieve their objectives including the ability to increasingly turn the desert green.