WEC projects designs and constructs a desalination and wastewater treatment plant for GAC bauxite mine

For a new bauxite mine and bauxite export facility at the Port of Kamsar in Guinea, WEC Projects designed and constructed a desalination and wastewater treatment plant. The two projects will generate potable, process, and fire water, as well as treat effluent from the port camp and activities. Despite facing some unique and challenging obstacles, both projects were completed successfully.

The Guinea Alumina Corporation (GAC) bauxite mine, worth US$1.4 billion, is a greenfield project in Guinea's northwest area. Between the cities of Boké and Sangaredi, the mining firm holds a 690-square-kilometer bauxite concession with deposits estimated to be approximately 400 million tonnes. The bauxite, which is needed to make aluminium, is mined and carried by rail to the Port of Kamsar, where it is loaded onto barges for transhipment to freight ships farther out to sea.

One of the mine's problems was providing potable water for 1,000 permanent mining camp personnel, as well as water for processing, general utilities, dust suppression, and fire control. Borehole water has a high degree of salt due to the mine's proximity to the country's shore. The mine used to provide fresh water via tanker, which resulted in high transportation and logistics expenses. Portable toilets were employed as a temporary remedy since the mining site lacked appropriate sewage treatment facilities. However, there was a need for a long-term solution to provide a steady supply of clean water and sewage treatment. For its operations, the mine also keeps two million gallons of fuel on site, posing a fire hazard. A dependable water supply was necessary to mitigate the risk.

The desalination plant has a unique modular and containerized design that made shipping and installation to the distant location much easier. Clarification, medium filtration, ultrafiltration, seawater reverse osmosis, chemical dosing, and remineralization are among the system's numerous processing steps. Because the facility processes saltwater at high pressures, an energy recovery system was added to turn the pressure into electricity, lowering the system's total energy needs and expenses.

The desalination plant's water supply was a big problem. A neighbouring estuary provides the seawater. The mine's engineers, on the other hand, had not anticipated the difficulty of the estuary's extremely fluctuating tidal circumstances, which had a negative impact on the water quality. The pumps drew in enormous volumes of sludge and suspended particles during the months new and full moon phases because of the very low tides.

The facility was not meant to manage such large solids loads from the start, necessitating the construction of a novel lamella clarifier, or inclined plate settler, to remove particles from the plant's DMF and ultrafiltration systems upstream.

The filters safeguard the sensitive reverse osmosis membranes that are utilised in the desalination process. The working lifespan of the filters was greatly extended by decreasing the solids load, resulting in significant operational savings for the mine.

WEC's basic modular Model B Biological Nutrient Removal (BNR) plant serves as the foundation for the wastewater treatment facility's bespoke design, which includes integrated activated sludge and clarifying facilities capable of handling flows up to 300 m3 per day. Its design makes it simple to carry and deploy on location.

“The major challenge we faced with this project was the last-minute changes to the plant design which were required to cope with the unforeseen high solids content of the estuary seawater. This was easily overcome due to the customisable nature of its design. We have extensive experience with projects throughout Africa, so we are used to dealing with often unpredictable conditions,” said Wayne Taljaard, the Managing Director of WEC Projects.