Water Resources Professional Project Reports
Document Type
Report
Publication Date
Spring 2023
Abstract
There is a growing interest in treating brackish groundwater to supplement freshwater resources for inland communities in arid climates. Water recovery by desalination of brackish groundwater is challenging due to mineral scaling from ions which form carbonate and sulfate minerals, dissolved silica which forms silicates, iron, manganese, and other constituents along with the difficulties and cost of disposing of large volumes of brine from the desalination process. The MRED process consists of a pretreatment process to increase water recovery and decrease waste production from brackish groundwater. The MRED process uses a unique sequence of unit processes consisting of: (1) Air stripping for removal of dissolved CO₂, (2) high pH selective precipitation of magnesium hydroxide Mg(OH)₂ via membrane filtration, (3) ion exchange (IX) to remove calcium, and (4) nanofiltration (NF) to remove sulfate. Following MRED pretreatment, water is fed to a desalination unit, which is able to achieve increased feed water recovery due to the low scaling potential of the feed water. The IX resin is regenerated using the salt concentrate from the RO process, which eliminates the need to purchase salt. The IX concentrate containing calcium is combined with the high sulfate concentrate from the NF process to precipitate high purity gypsum (CaSO₄⋅2H₂O). The only waste from desalination is the concentrated NaCl brine that is not used to regenerate the IX resin and some water wasted throughout the process in order to balance flows. The advantages of this process are: (1) Recovering high purity commodity minerals for subsequent sale, (2) Increased recovery of feed water due to reduced scaling potential, and (3) Substantial reduction in mass and volume of desalination wastes leading to savings in waste management and disposal costs. This project describes the results of a pilot testing project to demonstrate the performance of MRED process and confirm that the advantages claimed for the process can be achieved.
Language (ISO)
English
Keywords
brackish groundwater, supplement freshwater, desalination, MRED
Recommended Citation
Professional Project report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resource Program, UNM.
