Plant General Information
The sewage treatment facilities are extensive and mainly comprise the following units:
Plant Technical Characteristics
Sewage Pumping Stations
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 500 m³/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.
Sewage Treatment Plant
This includes the following units:
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Raw Sewage Metering Station
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Aeration Tanks
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Clarifiers
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Traveling Bridge Gravity Filters
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Sludge Handling
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Gas Chlorinating Equipment
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Effluent Pumping Station
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Irrigation Pumping Station
Aeration Tanks
The incoming raw sewage is metered and then enters four aeration tanks in two streams. A total of sixteen surface aerators (30 kW each) are installed to aerate the raw sewage.
Clarifiers
The aerated water passes through two circular clarifiers 20 m 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 to provide continuous sludge bleeding, sludge re-circulation and excess sludge discharge.
Traveling Bridge Gravity Filters
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 which 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 on this bridge. Hydraulically sized orifices are provided to uniformly collect the backwash water.
Sludge Handling
The clarifier sludge and plant drain flows are collected in a 140 cubic meter sludge holding tank. A metering station measures and monitors the waste and re-circulation sludge flows. Aspirating aerators are provided in the sludge holding tank.
Thickened sludge is pumped to the sludge drying beds by means of progressive cavity type pumps having a design pumping capacity of 170 m³/hr. Underflow from the sludge drying beds and decanted water from the sludge holding tank is returned to the inlet for further recovery.
Gas Chlorinating Equipment
Complete chlorinating equipment is housed in a separate building. Two wall-mounted, vacuum-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.
Effluent Pumping Station
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 the irrigation reservoir. A hydropneumatic tank provided on the process water line assures minimum supply pressure. The hydropneumatic tank is a 20 m³ ASME stamped carbon steel pressure vessel. The associated compressors, controls and monitoring devices for automatic operation of the irrigation system are also supplied.
Irrigation Pumping Station
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 so as to maintain a minimum pressure in the system.