Bello Wastewater Treatment Plant (BWTP), Medellin, Colombia
Bello Wastewater Treatment Plant (BWTP) is being constructed as part of the second phase of the Medellin River Sanitation Program.
The programme aims to meet the required water-quality target set by the Aburra Valley Metropolitan Area, to bring down dissolved oxygen levels to an average 5mg per litre.
The construction works for the new treatment plant, located in the northern end of the Aburra Valley, started in November 2012, and are scheduled for completion in 2015.
The project is being implemented with an investment of about €260m ($347m) by Aguas Nacionales S.A. ESP, a subsidiary of Empresas Publicas de Medellin. The project is expected to generate approximately 1,200 direct and indirect jobs.
Medellin River Sanitation Program details
The Medellin River Sanitation Program is being executed by Empresas Públicas de Medellín (EPM).
The first phase of this larger project involved the construction of the San Fernando Wastewater Treatment Plant in the southern end of the Aburra Valley, with an investment of $130m financed by the Inter-American Development Bank (IDB).
The bank further provided a loan of $450m for the current project in February 2009.
The loan is for a period of 25 years, with a six-year grace period, at an interest rate based on LIBOR.
Details of Colombia's wastewater treatment plant
The new plant will treat 80% of the wastewater from the Aburra Valley and 95% of the overall treated wastewater dumped in the Medellin River.
The project also involves the construction of the North Interceptor with a length of 7.7km and inside diameter ranging between 1.8m and 2.4m.
The new wastewater treatment plant will receive about 120t a day of industrial, commercial and residential organic waste. The plant will be designed for a treatment capacity of five m³ per second. The project site will cover an area of 40ha.
The wastewater treatment plant will comprise of infrastructure for biological treatment by activated sludge and fine bubble aeration, sludge digestion and energy recovery, odour control and ancillary infrastructure.
Bello Wastewater Treatment Plant processes
The wastewater treatment plant will first incorporate a pretreatment process to remove solids from the water. The facility will comprise of a protection grate and a gate to initially remove large solids. It will be followed by the use of six thick grates and six thin grates to remove other solids.
The water will be conveyed to eight rectangular and aerated grit chambers and then to the primary settlement tanks, made up of four lines of tanks with four tanks arranged in parallel. The hydraulic retention time during the primary treatment will be one hour.
The water will then undergo a secondary treatment using biological treatment by activated sludge. In this stage the water from the primary tanks will flow to the aerated tanks designed with a cascade system.
The water in the aerated tanks will come into contact with activated sludge and the organic matter transformed by the bacteria into water, carbon dioxide, energy and other microorganisms. The oxygen required for the aeration process will be supplied using centrifugal blowers.
The flow will then proceed towards eight secondary settlers, where a sludge sweeper will concentrate the sludge in a small chute. A part of the sludge from the secondary settler will be recirculated to the aeration tanks to maintain high concentrations of bacteria in the biological reactors. The sludge that is not re-circulated goes for treatment.
The treatment of sludge from the plant will be carried out using six anaerobic digesters, while the odour treatment will be done using chemical scrubbing.
Contracts awarded for Colombia's BWTP
The design, build, operation and maintenance contract for the wastewater treatment plant was awarded to Aguas de Aburra HHA, a consortium comprising of Acciona, Hyundai Engineering and Construction, and Hyundai Engineering. Poyry has been contracted to provide assistance during the tendering and construction phase of the project.
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