Comparative study of brine management technologies for desalination plants

In recent years, reverse osmosis (RO) has grown as an alternative to traditional potable water sources. A major disadvantage of the RO process is the huge amount of brine and its negative impact as a result of its high salinity. This brine is usually discharged to inland water bodies or to the sea and constitutes a threat to ecosystems and species, such as Posidonia oceanica in the Mediterranean Sea; thus, further research is needed for introducing environmentally friendly and economically viable management options for RO brines. This paper gives an overview of recent research as well as different technologies available at several scales to overcome the environmental problems and evaluate profitability related to discharge of RO concentrates. The treatment options have been classified into four different groups according to their final purpose: 1) technologies for reducing and eliminating brine disposal, 2) technologies for commercial salt recovery, 3) brine adaptation for industrial uses and 4) metal recovery. Solar evaporation, two-stage reverse osmosis, electrodialysis, integrated processes and brine adaptation for the chlor-alkali industry are some of the topics that this paper deals with. In the conclusion section, all of the technologies are compared emphasizing all their advantages and drawbacks, feasibility and development stage in order to provide a decision tool to select the best technology for each situation. © 2014 Elsevier B.V. All rights reserved.

Table 5 summarizes the most important characteristics of the technologies described in this article. The study reveals that zero discharge of desalination brine is a goal involving very high treatment costs, which means it can be applied only in very specific cases. Nonetheless, technologies are currently under development for reducing effluent volume, which will help achieve this goal. In general, the emerging technologies are promising for the reduction of effluent volume, although most have been developed on a laboratory scale and it is difficult to determine their applicability on an industrial scale. Furthermore, the research has been addressed mainly to the treatment of brackish inland waters at considerably lower volumes than commonly found in seawater desalination plants, so the results cannot be extrapolated directly to these plants. In-depth research is therefore needed in the field of seawater desalination plant waste. Evaporation ponds are a method worth bearing in mind for small amounts of effluent in arid or semi-arid places because they are simple and operating costs are low. However, they are ineffective in damp climates because the evaporation rate is very low, or for processing large quantities because they require vast amounts of land. WAIV technology reduces land requirements compared to evaporation ponds, but its availability has been demonstrated only on a pre-commercial scale. Neither are the ponds feasible for large amounts of brine. Phytodesalination is simple and makes it possible to produce forage and reuse brine simply by irrigating the soil. However, it is still in the experimental stage and can lead to soil and aquifer salinity. Concentrators and crystallizers are a technology developed on an industrial scale but the energy expense Table 3 Cost of desalination and salt production in UF–NF–RO–MSF-crystallization system per 1 m3 of UF permeate [75]. Unit cost UF NF RO MSF Crystallization Total $0.07/m $0.18/m3 $0.63/m3 $1.00/m3 $8.00/t Cost per 1 m3 of UF permeate $0.070/m3 $0.126/m3 $0.287/m3 $0.158/m3 $0.137/m3 $0.778/m3 Fig. 20. Flow sheet of the integrated membrane system for the recovery of dissolved salts in seawater NF retentate [76].