Water everywhere, and now a drop to drink

Facing a scenario where the demand for water exceeded supply, Veolia was commissioned to install a new desalination plant in Lamberts Bay to supply the 50 000 residents of the greater Cederberg municipality with 1.7 Ml of high-quality potable water per day.

The new Lamberts Bay plant utilises reverse osmosis (RO) membrane desalination to separate salt from seawater, achieving a 42% recovery rate of clean, drinkable water. Seawater desalination was the preferred method of increasing the municipality's water supply, due to excessive iron and manganese content in potential borehole sites as well as its sustainable, perennial functionality.

To minimise the high energy demands of reverse osmosis, the plant is fitted with an innovative energy recovery system which recycles excess pressure energy back into the system mechanics. The system is a result of Veolia's continuous research into technology and process improvement aimed at minimising plant energy consumption of the plants.

Veolia will maintain the plant via routine service requirements and its Hydrex chemical range for correcting water quality and eliminating scale within the infrastructure.

The Lambert's Bay desalination process consists of the following stages:

Pre-treatment and preparation

Prior to RO, abstracted seawater from boreholes is shock dosed with sodium hypochlorite to prevent biological growth. Ferric Chloride is also dosed to coagulate suspended matter and organic species. 95% of the particles are removed through two filtration layers of silica and anthracite in the Dual Media Filter (DMF) tanks.

Seawater RO

Water is pumped at high pressure through two RO membrane "trains", which removes the saline content of the seawater. The resulting brine solution is returned to the sea via a specifically-designed brine outfall system, extending 150m into the sea, which minimises the impact of the discharged brine on the surrounding marine ecosystem.

Up to potable standard

Water produced by RO is sterile and unhealthy to drink in this form, requiring the addition of carbon dioxide to produce carbonic species before it is fed into a limestone filter. Finally, soda ash is added to bring the water to SANS 241 2006 Class 1 specifications dictating ideal mineral content and pH.

Backwash effluent treatment

The DMF filters are backwashed regularly to remove the build-up of organic matter. The resulting effluent is fed into a buffer sump. A coagulant and flocculant is added to bind suspended particles, which are then separated from the effluent through a lamella clarifier to upgrade the quality of the effluent before disposal, as per the EIA, before being discharged into the sea with the brine. The remaining "sludge" then enters a drying bed before disposal.

Plant Management System

The plant's equipment is controlled and monitored by a Supervisory Control and Data Acquisition (SCADA) computer system, alerting operators to any maintenance requirements. A testing lab, situated adjacent to the operator room, enables comparative measurements of pH, turbidity (presence of suspended particles) and chlorination levels with required values in the SCADA system.

The Lamberts Bay installation brings to seven the number of seawater desalination plants constructed by Veolia along the Cape coastline since 2009.

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