Seawater Desalination: A Concrete Solution to Fresh Water in Algeria

By Tim Wilkey

• Algiers' Hamma Seawater Desalination Plant benefits from concrete structural support and process piping design expertise of USA-based engineering firm Stanley Consultants.

Overview of Hamma Seawater Desalination Project (top) and its location (lower left) [Map Source: Metoc plc]

Algeria’s new Hamma Seawater Desalination plant will help this North African country meet its potable water demands for many years. The seawater reverse-osmosis (SWRO) desalination plant is in the capital city of Algiers along the Mediterranean Sea near the Port of Algiers. With a population that’s grown to 3.5 million and in a country with only 3% arable land, water is a necessity for this semiarid seaside city.

Officially opened in February 2008, the 200,000 m³/day (53 mgd) plant is one of the largest public private partnerships (PPP) in Africa, and the largest desalination plant on the African continent. Once in full production, it’s expected to supply almost a quarter of Algiers’ potable water needs. This will offer relief for the country’s residents, plagued with potable water shortages for years and currently without a 24-hour water supply.

The $275 million build-own-operate project was a multi-party effort with the Overseas Private Investment Corp. (OPIC), General Electric and the Algerian Energy Co. (AEC) -- with GE and AEC forming the PPP. Construction was a joint effort between GE/Hamma Water Desalination (HWD) and Orascom Construction Industries (OCI). GE will take final ownership at construction's end and operate the plant under a 25-year agreement with HWD to provide water for purchase for a portion of Algeria’s potable water needs. The plant’s process design was developed by GE and utilizes the firm’s RO process equipment with an energy recovery system from San Leandro, California-based Energy Recovery Inc., and related support systems.

Stanley Consultants, a global consulting engineering firm, provided construction level detail for OCI. Fitting all the required process structures and equipment into the limited space of the plant site was challenging even though the RO process takes up 25% less land area on average than competing desalination platforms such as multi-stage flash (MSF) distillation. The firm was able to assist with optimization of the available space so all of the process units could be successfully placed.

Main gate and looking westSeawater intake lift pumps Main process pipe gallery The Iowa-based consultant also provided structural design for the large concrete water treatment process units and site design for support systems including clarifiers, dual media filters, product tank, outfall basin and all other concrete structures -- for which Algeria's geologically active nature required special consideration. These included site soil problems such as high chloride and sulfate content, and building on unconsolidated fill material. Therefore, stone columns were used throughout for all concrete structures and pipe supports. Marine grade concrete was used in all structures that come in contact with soil.

Additional site design included support systems such as the administration building; workshop and warehouse building; guardhouse building; process and chemical pumping and piping systems; electrical high voltage area, substation, and electrical distribution; and high mast site lighting. Design also was provided for required site utilities such as roadways; fire protection for the HV transformers, potable water, and service water distribution; service and instrument air distribution; process drain and stormwater collection; site security; site communications; and perimeter fencing.

For process piping design, Micro-Station V8 by Bentley-Plantspace Design Series Modeling 3D software was used. The software has the ability to precisely place pipes and pipe elements in the model, develop a bill of materials when the isometric piping drawings were generated, and perform precise interference checks with other pipe systems and structures. Another feature of the 3D model is that it can directly translate into several stress analysis programs.

Bank of RO modulesRemineralizer vessels

The plant is equipped with a clean-in-place (CIP) system commonly found in RO plants. This standalone system is piped into the plant process piping to clean the RO membranes when an individual RO train is out of service. Sodium hypochlorite solution is generated onsite from a brine solution and used for disinfection purposes. The solution is added to the stabilized permeate prior to storage, and also used to assist in cleaning of the intake line.

The plant uses the Mediterranean Sea as a raw water source and is located near the seaport facilities. The RO process will require relatively clean water, so the raw water is collected several hundred meters offshore and brought into the plant via two large transmission pipes.

The raw seawater has to go through several process steps before reaching the RO process equipment. It's screened at the intake structure to remove floatable and larger material. The screened seawater is lifted up to the clarifiers where chemicals are added to promote flocculation and coagulation of colloidal solids and to aid in settling of the material. The resulting water, now clarified, is then directed to dual media filters where finer material is removed by using a fine aggregate and anthracite media. The filtered water is collected in a clear well and sent through cartridge filters where any remaining particulate material larger than 0.1 micron (µm) is removed.

The filtered water then proceeds to the RO trains where it passes through the high pressure membranes. Because the majority of the total dissolved solids (TDS) have been removed, the resulting permeate -- water that's passed through the membrane -- will have a relatively low pH and will require stabilization and remineralization before it can be considered potable water and suitable for public use. The "reject" or "concentrate" water that would not pass through the RO membrane has a high TDS concentration. The concentrate is returned to the Mediterranean several hundred meters from shore via another large diameter discharge pipe.

Energy recovery systemProduct pumps

The stabilization of permeate includes pH adjustment by caustic chemicals and/or carbon dioxide, and remineralization with lime. The treated water is now considered potable and is disinfected and placed in the product water tank to await distribution. Three large pumps then push the water out to the city’s fresh water storage system for distribution to the city. Hamma was required to discharge into two different pressure zones, so additional piping was required at the product tank to accommodate this special requirement.

By using the Mediterranean Sea as an abundant source of raw water, desalination provided by the Hamma Seawater Desalination plant will reduce the city of Algiers future hardships caused by the lack of potable water. WWi

Author's Note: With over 20 years of experience in water and wastewater operations and design, Tim Wilkey is a project manager and environmental engineer with Stanley Consultants, which is based in Muscatine, Iowa, USA. The company has offices in 17 U.S. cities, Jamaica, Puerto Rico, Iraq, Jordan, Kuwait, Qatar, Saudi Arabia, the UAE and India. Contact: www.stanleyconsultants.com

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