Evaluation of technologies for a desalination operation and disposal in the Tularosa Basin, New Mexico

According to the United Nations Environment Programme, one-third of the world's population lives in a situation of water stress. In the case of New Mexico, about 90% of the 1.8 million inhabitants depend on ground brackish water as their only source of potable water in many areas of the state. This report presents a technically-supported, economically-feasible and environmentally friendly proposal to desalinate brackish water to supply potable water to inland, isolated communities in southwest New Mexico. Several existing technologies were reviewed to identify opportunities for optimization by combining them to provide potable water and reduce the waste stream. Alternatives were studied and experimentation was conducted for some of them. The alternatives proposed were the use of natural coagulants for pretreatment, various solar collectors' arrangements for energy supply, reverse osmosis (RO), low temperature multi-effect distillation (LT-MED), multi-stage flash distillation (MSF), solar distillation (SD), and electrodialysis for desalination process; Spirulina cultivation and SD for waste treatment, and deep well injection (DWI) for waste disposal. Some alternatives were eliminated because they are either technologically or economically not feasible for this case and present high environmental impact. Three plant configurations were analyzed. Option A involves using the linear Fresnel systems (LFS) to produce steam for the first effect of a nine-effect evaporation plant. The number of effects was determined to achieve the optimal relation between equipment investment costs and steam production cost. This plant operates 8 h per day with solar energy and the rest of the 24 hour operating time is provided with fossil fuels. The waste produced will be further evaporated with SD to minimize its flow and the concentrated brine will be injected into a deep well. Option B has the same elements as option A, except that it does not consider the SD, but direct brine injection into a deep well. Option C considers the use of SD as the only process for distillation with DWI as the waste disposal method. The selection criteria for the best configuration were optimal use of solar energy resources, minimization of fossil fuel consumption and waste stream generation and disposal. Operation requirements and economic analysis were considered to select a proposal easy to implement and operate in rural isolated communities. For the following reasons option A is the best configuration to cover the necessity of potable water in New Mexico: (A) the plant is easy to construct and operate. In addition, it can handle different ranges of brackish water flow. (B) The 76% water recovery of the system almost matches the recovery achieved in a RO plant (80%), with the advantage that maintenance costs are reduced and treatment flowrates cannot be matched by the RO plant. (C) Use of the LFS reduces the emission of combustion gases to the atmosphere by 33%. This manifests as a positive point in a LCA evaluation. (D) The minimum environmental impact of the process facilitates the public involvement plan (PIP) because it gives the plant an environmentally responsible image in terms of avoiding greenhouse gases emissions. (E) The return on investment (ROI) is 10.2% at a price of $5.00/m3 of desalinated water, which is superior to the estimated minimum attractive rate of return (MARR) used for LT-MED plants as 9.5% annually.