Halcrow is currently involved in delivering the largest Membrane BioReactor (MBR) sewage treatment plant in the world.
Halcrow has been continuously involved in the development of the Sharjah Main Drainage Scheme since 1969 when the proposed development plan for Sharjah was submitted. The first main drainage contract was let in 1974. These substantial contracts included the construction of the first phase of the sewage treatment works which was commissioned in 1978. The continuing growth in the population of Sharjah has led to a need to provide additional treatment capacity at the existing wastewater treatment plant. The existing plant has been previously expanded under Phases 1-6 and will now be additionally expanded by Phase 7, to provide an additional 75 000 m3/day capacity to the existing 156 000 m3/day capacity.
In the 1970’s the whole of Sharjah relied on the use of septic tanks. Sharjah Municipality began to develop a sewerage network and the Phase 1 treatment plant, which at the time was located in the desert at the edge of the city, was commissioned in 1978.
The incredible growth rate of Sharjah throughout the 1970’s led to the need for phase 2 of the treatment works in 1983. This unprecedented growth continued over the following 26 years and resulted in five more phases being commissioned through the period.
Today the treatment plant which started on the edge of the city has now been swallowed up by the urban development, and is wedged between the famous Sharjah Cricket Stadium and the large local fruit market. Currently the works can treat flow up to 206,000m³/day to the required effluent quality. The sludge from the works is treated, collected and then either transferred to a composting plant, or disposed of in landfill.
Due to the water scarcity in the region, Sharjah Municipality have been leading the way in water re-use. The treated sewage effluent (TSE) is used for irrigation of the municipal parks and gardens, being of a suitable high quality not to cause any odour or public health problems.
Recent master planning work demonstrated that the existing treatment works will reach full capacity by 2010, and as a consequence the Sharjah Municipality commissioned Halcrow to design the Phase 8 plant to provide sufficient treatment capacity until 2020.
The Technical Solution
The robustness of the flow predictions was critical to a successful solution. Various information sources were cross referenced including local government databases, statistical books published by the Economic Development Department, land use development plans and water company master plans to come up with four different methods of predicting population growth rates. Due to the fact that any further extensions would be difficult because of lack of available land adjacent to the existing STW, it was decided to use the highest growth rates.
To meet the site constraints, and high effluent quality requirements, an MBR plant was selected for Phase 8. As well as producing a reliable effluent quality, an MBR would provide more treatment capacity per m2 than conventional process technology.
As the treatment works is located in the middle of a residential and light industrial area, odour control was a concern to the client and a significant amount of design time was dedicated to this which was complicated by the high ambient temperatures and the high sewage loading from septic tanks.
The phased expansion of the effluent distribution systems over the years has resulted in a complex, manually operated distribution system. The new system required integrating with the existing one to allow the higher quality effluent from the new Phase 8 extension to be sent down the existing effluent pipelines to where it was needed in Sharjah.
To achieve this, a new pumping main was designed which allowed the four existing effluent pump stations to discharge into a central irrigation pipeline with automatic wasting of surplus flows through pressure sustaining valves to a new sea outfall.
The combination of multiple pump stations, pressure sustaining valves, old pumping mains, a 2200mm diameter outfall and flows up to 4050 l/s, required very careful design to minimise the risk of surge problems. Extensive modelling was carried out by specialist surge teams in the UK, and mitigation measures incorporated into the design.
Scope of Works
- Sewage treatment works process design
- Structural, geotechnical and electro-mechanical works
- Inlet Works
- Aeration tanks and return activated sludge facilities
- Final settlement tanks
- Rapid gravity sand filtration and chlorination
- UV disinfection
- Effluent distribution and disposal
- Distributed control system
- Mechanical, electrical, instrumentation & control equipment
Key to Success
The size and specialised nature of the project and the limited availability of suitable engineering resources in the Middle East region demanded a large multi disciplinary international team. The key to the successful delivery of this project was the effective communication systems and efficient working methods were developed in order to deliver the project within a very demanding timescale.
Ensuring there was the correct mix of people working on the project was crucial. It was essential to get the right team structure, lines of communication, defined roles and responsibilities. Working with an international team carries with it, many challenges but this project has demonstrated that the opportunities for knowledge transfer can greatly outweigh any of the “lost in translation” issues. The mix of people and cultures created a vibrant and dynamic working environment as well as delivering significant client benefits.