Hamma Seawater Desalination Project Providing Fresh Water to Algeria
The new Hamma Seawater Desalination plant will help Algeria meet its potable water demands.
by Tim Wilkey
The new Hamma Seawater Desalination plant will help Algeria meet its potable water demands. The seawater reverse-osmosis (RO) desalination plant is located in the capital city of Algiers along the Mediterranean Sea near the Port of Algiers.
The 200,000 cubic meters per 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, the plant is expected to supply almost a quarter of Algiers' population with potable water. The production of potable water will provide relief for the country's residents, who have been plagued with potable water shortages for years, and currently do not have a 24-hour water supply.
The $275 million build-own-operate project was a multi-party effort with the Overseas Private Investment Corporation (OPIC), General Electric (GE), and the Algerian Energy Company (AEC) with GE and AEC forming the PPP.
Construction of the plant was a joint effort between GE/Hamma Water Desalination (HWD) and Orascom Construction Industries (OCI). GE will take final ownership at the end of construction, and will 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 uses the firm's RO process equipment with an energy recovery system, and related support systems. Stanley Consultants, a consulting engineering firm with offices worldwide, provided construction level detailing for Orascom. Fitting all of the required process structures and equipment into the limited space of the plant site was challenging. The firm was able to assist with the optimization of the available space so that all of the process units could be successfully placed.
Stanley Consultants 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.
The geologically active nature of Algeria necessitated giving special consideration to the design of all concrete structures. Site soil problems included high salinity and building on unconsolidated fill material. Therefore, stone columns were used throughout the site for all of the 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; guard house building; process and chemical pumping and piping systems; electrical high voltage area, substation, and electrical distribution; and site lighting. Design was also provided for required site utilities such as roadways; fire protection for the HV transformers, potable water, and service water distribution; process drain and storm water collection; site security; site communications; and perimeter fencing.
For process piping design, 3D modeling software was used. It was used because of the software's ability to precisely place pipes and pipe elements in the model, develop a bill of materials when the isometric piping drawing was generated, and to perform precise interference checks with other pipe systems and structures. In addition, one feature of the 3D model is that it will directly translate into stress analysis programs.
The plant is equipped with a “clean-in-place” system commonly found in RO plants. This stand alone system is piped into the plant process piping to clean the RO membranes in the RO skids. Sodium hypo-chlorite solution is generated onsite for disinfection purposes. The solution is added to the stabilized permeate prior to storage, and also used to assist in the cleaning of the intake line.
The plant uses the Mediterranean Sea as a raw water source. The RO process requires relatively clean water. Because the plant is located near seaport facilities, the raw water is collected several hundred meters off shore and brought into the plant via two large transmission pipes.
The raw seawater then goes through several steps. It enters the sea water intake where it is screened to remove floatable and larger material. The water is then lifted up to the clarifiers where coagulation chemicals are added to aid in the settling of colloidal material. The resulting water, now clarified, is then directed to dual media filters where finer material is removed. The filtered water is then sent through cartridge filters where any remaining particulate material more than 0.1 micron is removed.
The filtered water then proceeds to the RO trains where it passes through high pressure membranes. The permeate has a relatively low pH and will require stabilization before it can be used by the public. The reject water has a high total dissolved solids concentration and is returned to the Mediterranean several hundred meters from shore via another large diameter discharge pipe.
The permeate goes through a remineralization process for stabilization, is disinfected, and then 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.
Since the plant was completed, it has consistently met and exceeded WHO 2003 water quality parameters at the design production volume of 200,000 m3d. The target levels for key water quality indicators are, a hardness of 50-64 ppm as CaCo3, a pH 8.0 to 8.5, a Langlier Index = 0 to +0.4, and an alkalinity of 65 ppm CaCo3.
With the Mediterranean Sea as an abundant source of raw water, and the Hamma plant to provide desalination, the city of Algeria can finally be free from the hardships caused by the lack of potable water. —m
About the Author:
Tim Wilkey is a project manager and environmental engineer with Stanley Consultants. He has over 20 years of experience in the water/wastewater field.