A combined approach for the management of desalination reject brine and capture of CO₂

Water desalination plants produce huge amounts of reject brine, which are usually sent back to the sea, where they could, in the long run, result in detrimental effects on the aquatic life as well as the quality of the seawater in the area. In this study, a new approach for the management of desalination reject brine and capture of CO₂, where ammoniated brine is reacted with carbon dioxide, has been investigated. The effects of reaction temperature, reaction time, and excess ammonia were assessed. Carbon dioxide was used either as a pure gas or a mixture of 10% CO₂ in methane. The experimental results indicated that the optimum reaction temperature was about 20 °C and the optimum NH₃/NaCl ratio was 2 for synthetic brine solutions and 3 for actual reject brine. The proposed process proved to be effective in reducing the CO₂ concentration in a CO₂-CH₄ gas mixture by more than 90%. The solubility of sodium bicarbonate was found to play a key role in the removal of sodium. The results indicated that the new approach can reduce the salinity of reject brine and, at the same time, contribute to the reduction CO₂ emissions.