STP & DGS Conveyance System
Construction of a Sewage Treatment Plant and a Deep Gravity Sewer Conveyance System in Muharraq.
Project Overview
GPZ was appointed as the main civils contractor under the EPC contractor Samsung Engineering Co. Ltd for the construction of a new Sewage Treatment Plant (STP) and a Deep Gravity Sewer (DGS) Conveyance System in Muharraq. The project site covers an area of approximately 157,000m2 on reclaimed land and comprises a 100,000 m3/day wastewater treatment plant, a sludge incinerator, and 16km of deep gravity sewer and wastewater collection networks between Busaiteen and Hidd to convey flows to the site for treatment.
As part of the Bahrain 2030 National Masterplan for Sanitary Engineering Services, the multi-million dollar project was conceived to provide essential infrastructure and reduce the burden on Bahrain’s ageing network. The project under Bahrain’s Ministry of Works was overseen by Muharraq STP Co BSC (a company consisting of the EPC Contractor Samsung Engineering, United Utilities and Invest AD) as part of a 27 year build, own, operate and transfer (BOOT) scheme. This is the first scheme of its kind in the country, representing a significant inward investment to help facilitate Bahrain’s development and growth. The plant is designed to have a lifespan of 25 years and has a provision for future expansion to treat 160,000m3 a day.
The work carried out for the Sewage Treatment Plant and Deep Gravity Sewer shafts have been to the highest quality standards, under stringently controlled Health & Safety procedures, and have fulfilled all the Environmental Authorities’ requirements. Over 10 million safe man-hours were recorded without a lost-time incident on the project.
The project won the Middle East Water/PPP Deal of the Year in 2011 that was awarded by Project Finance Magazine, and two MEED Quality Awards for Projects: 2015 GCC Winner in the “Sustainable Projects of the Year” category and 2016 National Winner in the “Power & Water Project of the Year” category.
Sewage Treatment Plant (STP):
The STP is designed to collect and treat wastewater to a high standard using established technology in pre-treatment, filtration and disinfection, so that the Treated Sewage Effluent is suitable for re-use in industrial applications, irrigation and landscaping.Treated sludge from the Plant is used as fertilisers in the agricultural sector. The STP has an option to discharge the treated effluent to the sea through a sea outfall.
GPZ’s scope of works included construction of the Terminal Lifting Station (TLS), 6 SBR Basins measuring 60mx30mx11m high, secant piling works, a Liquid Sludge Tank, a Sludge Incinerator Plant, Disk Filter, UV Tank, Discharge Channel, UV Control Room,Polymer Dissolving Unit, boundary walls, underground piping, duct banks, cable trench works, asphalt works and other associated civil and building works. As the STP has been constructed on reclaimed land, one of the challenges faced was the dewatering of the TLS shaft that has a depth of 23m below ground level.
Deep Gravity Sewer (DGS):
The Deep Gravity Sewer, which is 1.8m in diameter and has a maximum depth below ground level of 16m, feeds into theTerminal Lifting Station (TLS) that was constructed at the head of the new Sewage Treatment Plant. The network connections intercept 24 existing pump stations and divert the flows to the DGS pipeline prior to reaching the new Sewage Treatment Plant. A 20m deep Intermediate Lifting Station (ILS) approximately halfway along the pipeline route serves to lift the flow of effluent, further preventing the sewer exceeding a depth of 16m below ground level.
The scope of works for the DGS included the Intermediate Lifting Station (ILS) and 51 shafts of various diameters measuring up to 9 meters and with depths ranging from 6m to 23m (at the TLS). A trenchless construction technology referred to as “micro-tunneling,” was used for the first time in Bahrain for the sewer construction. This technique eliminated surface disruption and in particular avoided the need for what would have been significant traffic roadworks.
The shafts were constructed to facilitate and receive the micro-tunneling heavy equipment and pipes that would be ‘jacked’ into position for the sewer network. Each shaft includes exit and entry ‘eyes’ and were constructed with 42-54 secant piles around their perimeter, depending upon diameter, using approximately 810m3 of concrete per shaft, to support them from soil pressure and water infiltration. After the pipeline had been installed the shafts were used as the sites for access manholes around which the backfilling of shafts was completed.
Principal Quantities:
- Excavation: 278,400 m3
- Structural Concrete: 122,500 m3
- Reinforcement: 14,100 tonnes
- Masonry: 1,500 m2
