Covering more than 150 acres and serving an area of 725 square miles, the Blue Plains Advanced Wastewater Treatment Plant (AWTP) in Washington DC is the largest advanced wastewater treatment plant in the world. A quick check of its performance statistics reveal that Blue Plains has a design capacity to treat up to 370 million gallons every day, meeting the needs of the Metro-DC area’s wastewater and collection treatment needs. The treated effluent is discharged into the Potomac River resulting in the plant having to meet some of the most stringent nitrogen standards in the world. DC Water has a $3.8 billion, 10 year capital investment program in place for all its capital projects, and one part of this has been the construction of the Enhanced Nitrogen Removal Facility (ENRF). Central to the operation of this facility are submersible wastewater pumps, an area where the expertise of KSB USA has been of major significance particularly in the supply of pumps and the design of the pumping wells.
The latest ENRF process expansion of Blue Plains has been designed to reduce nitrogen levels to the limit of technology prior to being discharged into the Potomac River, a tributary of the Chesapeake Bay. The goal of the project was to meet or exceed the new EPA requirement to reduce effluent nitrogen production to 4 million pounds per year. Nitrogen is an odorless, tasteless, colorless non-metallic chemical element that occurs naturally in the earth and in atmosphere. It is a vital component of life for many organisms, but too much nitrogen can be harmful. In waterways, having too much nitrogen can deplete the oxygen that fish and other aquatic life need to thrive. Nitrogen removal at Blue Plains is a two-stage process that involves nitrifying secondary effluent within the existing 12 Nitrification/Denitrification reactors and essentially complete denitrification occurs in the newly constructed ENRF tanks.
Pump station requirements
A key element of the new ENRF process was the addition of a new high-capacity pump station. The design specifications mandated 24/7 operation, with a planned life span of at least 20 years. The selected pumps had to be robust and have a high degree of reliability. Azir Khan, KSB‘s project engineer takes up the story. “We had to demonstrate to DC Water that we had pumps with a proven track record. To this end we were able to point to similar facilities in other parts of the world where the recommended pumps had given trouble-free operation for many years. The pumps that we recommended are our Amacan P Submersible propeller pumps and Amarex KRT pumps. These are the largest submersible propeller pumps produced by any manufacturer.” Not only was KSB able to demonstrate the effectiveness of these pumps, they were the only company that could factory-test pumps in accordance with operating conditions. It was a very stringent set of criteria that KSB had to pass in order to be accepted by DC Water. The pumps were optimized specifically for the project, using motors that were identified as being the most suitable and the hydraulics exactly matched the requirements of the project. “The Amacan and Amarex pumps run at their optimum performance point at the peak flow, which is highly important both for the project and the longevity of the pumps,” continues Azir Khan.
KSB Amacan and Amarex KRT pumps are true work horses for the wastewater treatment and water supply sectors, and are to be found operating in many applications around the world where the most challenging water industry applications have to be satisfied. At Blue Plains AWTP seven Amacan pumps are located at various locations in the denitrification return sludge gallery sumps and are used for pumping drainage, wash down and potentially sludge and chemicals if a pipe breaks. Four submersible Amarex KRT pumps are located at two dewatering pump stations in the denitrification return sludge gallery and are used for liquor pumping groundwater, pump/floor wash down drainage and wet weather run-off duties. In the Alternate Carbon Building, two submersible Amarex KRT pumps are used for sump pumping eye wash station drainage, laboratory sink drainage, pump/floor wash down drainage and potentially carbon chemicals if a pipe or pump leaks. Portable submersible Amarex units have also been supplied and can be moved to various locations in the denitrification reactors and post-aeration tanks, their purpose being to handle mixed liquor. Their primary function is to dewater the denitrification reactors and post-aeration tanks if they are taken out of service. The Amacan P series submersible motor denitrification pumps supplied to DC Water are typically used around the world for industrial and agricultural water supply, stormwater and flood prevention stations and the water and wastewater treatment industries. It is a close-coupled, wet-installed single entry axial propeller pump where the propeller is located in a tubular casing immersed in the water. To satisfy the requirements of this project, the pitch angle of the propellers was adjusted and the motors were specially wound. Each of the five pumps has a maximum flow capacity of up to 179 mgd and a maximum head of 12m and together they deliver a total of 895 mgd. Low vibration hydraulics and a vortex-free flow due to the inlet ribs and wide bellmouth ensure that the pump is hydraulically optimized. Operating efficiency is provided by the slim motor that minimizes discharge tube flow losses. The Amacan is a safe, reliable and energy-efficient solution for a wide range of pumping jobs in industrial and municipal wastewater processes. In order to provide maximum versatility/flexibility for applications, KSB offers this pump in a wide range of materials. A range of specially adapted hydraulic systems with high operational reliability, due to wide free passages, make for optimum economic transport of all types of liquids. The Amarex KRT submersible pumps are used for raw sewage pumping and on treatment plants. Unlike the water supply pumps, the pumps used in the handing of untreated and treated effluent have to operate all day long, which places them under a considerable workload.
Working with KSB
KSB went to great lengths to demonstrate the capabilities of its pump technologies and understanding of the project including that pumps of a similar capacity were in use at facilities worldwide. Having specified these high capacity pumps for this unique application, DC Water also realized additional benefits from working with KSB which included alternative configurations. Optimizing the configuration resulted in considerable power savings, as much as $200,000, in operating costs that could be achieved every year. Furthermore, KSB had the engineering resources to assist design engineers in optimizing the design of the pump station. By reducing the number of pumps, the overall pump station footprint could also be reduced. Less excavation, less concrete, less rebar and fewer control panels all contributed to lower operating, capital and construction costs. Furthermore, extensive hydraulic calculations were performed to develop a pump curve required at various speeds. “We were pre-selected for the project following a competitive procurement process,” reports Azir Kahn. “KSB has been able to equip Blue Plains with the most appropriate pumping technology designed to ensure reliable and long working life, and enable our customer to benefits of reduced capital construction costs and lower yearly operating expenses.”