Doha North Sewage Treatment Works (DNSTW), Qatar
Doha North Sewage Treatment Works (DNSTW) is a huge sewage treatment project that is being undertaken by the Public Works Authority of Qatar (Ashghal).
The project site is located about 22km north-west of Doha. Construction works for the project commenced in February 2008.
The project is being carried out in four phases and is expected to be completed by 2012. It is targeted to serve a population of 900,000 citizens by 2020, treating 439,000 cubic metres of wastewater on a daily basis.
Treated wastewater from the project site will be utilised for irrigation and other non potable purposes while the sludge from the treatment plant will be used as soil conditioner in the neighbouring agricultural fields and as a source of green energy.
The project will primarily serve the city of Doha and its neighbouring suburbs, comprising of Umm Salal, Gharafa, Semiesma and Lusail.
DNSTW construction phases
Phase one of the project involves the design, construction and operation of the plant for ten years.
Phase two involves the construction of a PS70 pumping station located at Al Kheesa, pumping mains and other ancillary works. PS70 will have a capacity to process 900,000 cubic metres per day.
Phase three of the project will comprise of constructing the main complex of the sewage and sewerage lines by micro tunnelling. The complex will be micro tunnelled at depths ranging from 25m to 34m. Concrete pipes measuring 2.4m in diameter and 32km in length will be laid.
A pipeline measuring 45km in length and 1.6m in diameter will also be laid from the pumping station to the wastewater treatment plant.
Phase four of the project will witness the construction of the sewage pumping station for treated sewer effluent (TSE 3). The contract also includes construction of the connecting pipelines and mains.
Water treatment process details
Wastewater at the plant will be treated in three stages. The first stage involves fine screening using step screens and grit removal using vortex degritters.
The secondary treatment will involve biological treatment using an anaerobic-anoxic-aerobic (AAA) method for the removal of organic material and nitrogen from the wastewater. The treatment process in this stage will also include clarification / sedimentation through the use of settling tanks.
The tertiary treatment will comprise of granular media filtration using dual media filters, ultrafiltration using an advanced membrane and disinfection using ultra-violet (UV) technologies.
Sludge recovered from the plant following the secondary treatment process will undergo digestion, thickening, dewatering and wet sludge treatment. The treatment of sludge will be done using aerobic digesters, centrifuges and thermal sludge dryers.
The wastewater treatment plant will further be equipped with odour control facilities.
Doha North Sewage Treatment Works contractors
Kepel Seghers was awarded with the design, build and operate contract for the first phase of the project in September 2007. The contract is worth QR3.6bn ($1.5bn).
Phase two of the project has been contracted to Vinci Construction Grands Projets, Entrepose Contracting and QDVC. This contract is valued at QR1.78bn ($489m).
Ultra Construction and Engineering is responsible for carrying out the third phase of construction. The contract is worth QR1.3bn ($352m).
Marubeni Corporation is responsible for the last phase of the project under a QR1.3bn ($352m) contract. The company further subcontracted Qatar Building Company (QBC) to carry out the construction works for the last phase.
Key players involved with Qatar's DNSTW
Rotork is supplying its IQ Pro intelligent electric valve actuation technology to assist in the operations of the wastewater treatment plant. Mechanical and electrical installation works at the project site are being carried out by AMEM.
Formwork for the construction of various facilities at the project site is being provided by Doka.
The Norit XIGA UV membranes and Norit standardised UV skids to be used by the treatment plant are being provided by Norit X-Flow.
Two automatic bag packing and palletising systems, which will be used for conveying the treated sludge, will be supplied by Webster Griffin, who is acting as a subcontractor to TSL Engineering. The contract is worth $800,000.
The aerobic digester and SAS balancing tank are being built by the ITC Group. Construction management services for the project are being provided by Stanley Consultants.
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