As water scarcity continues to be one of the largest challenges facing societies today, desalination remains one of the more reliable methods of providing safe and clean water. The global desalination sectors continue to grow rapidly and the impetus for reducing the adverse environmental impacts of brine (wastewater) discharge grows concurrently.
One of the major environmental related issues with seawater desalination is the generation of brine (associated wastewater high in salt concentrations) and brine discharge. For several desalination plants across the globe, the most practical and economical brine disposal method is discharging it into the sea at the water treatment plant’s outfall. This results in the largest environmental impact of most desalination plants on the environment occurring at the outfall to the respective seas/ocean. Furthermore, there are several harmful environmental effects (water temperature, salinity, dissolved oxygen content, pH and alkalinity fluxes) caused by this direct discharge of brine. This discharged brine (concentrate wastewater) has many physical, chemical and biological properties, which can badly affect any environment if not treated, recycled or disposed of sustainably. Brine solutions can sometimes consist of highly concentrated salts and any unreacted pretreatment chemicals used in the water treatment process. Brine can also bring with it some heavy metals resulting from corrosion of pipelines and walls of materials within the treatment works.
Although modern brine outfall designs have significantly limited such environmental impacts, they are costly. Recovering valuable components and chemical derivatives from brine has the potential to resolve both environmental and economic concerns. There is definitely an environmental problem with brine management, but there are solutions for dealing with brine and wastewater generated from the desalination production processes. One such proposal is the on-site generation of sodium hypochlorite (NaOCl), on-site at the water treatment (desalination) Plant.
On-Site Generation of Sodium Hypochlorite from desalination facilities has been in commercial use for over 45 years. This technology sheds some light on the business opportunities associated with brine waste streams by using the brine solution for on-site generation of sodium hypochlorite. However, the technology has not been as widely utilised in water treatment plants due to the operating costs compared to that of bulk chlorine products.
Sodium hypochlorite is a useful and valuable water disinfection product. It is used as a bleaching and disinfecting agent and is commonly found in household bleach products. It is widely used as an active compound in the disinfection process. Sodium hypochlorite can be used for chlorination to prevent bacterial growth within the desalination facility. The substitution of chlorine with on-site produced sodium hypochlorite can improve the desalination processes environmentally. There is a dual benefit of on-site generation of sodium hypochlorite reducing the volumes as well as the concentrations of brine generated. Because this technology can eliminate dependency upon outside suppliers and the high costs of purchased imported commercial products, it can be applied in a broad spectrum of industrial facilities requiring biological growth control across various water systems. This proposed technology of on-site generation of sodium hypochlorite solutions from seawater is to economically and safely produce a powerful biocide and disinfecting agent for use in industrial plants. Therefore, the process will not only generate the sodium hypochlorite, but can also protect the environment from unsustainable brine discharge.
There are several large water treatment plants and commercial swimming pools worldwide utilising on-site sodium hypochlorite generation systems from desalination water treatment plants. In addition, Occupational Health, Safety and Environmental issues have caused water utilities and engineers to specify the technology in place of chlorine gas and commercial grade sodium hypochlorite. Furthermore, generating sodium hypochlorite on-site can be a viable, cost-effective and safe alternatives to commercial grade liquid or gaseous chlorine used in disinfection. Taking safety issues into account, it is still a viable alternative for water utilities.
Future research and pilot-scale demonstrations need to bring this technology to commercial feasibility in the Caribbean.
Head of Civil & Environmental Engineering
Centre for Water, Communities and Resilience (CWCR)
University of the West of England (UWE Bristol)