• Comprehensive Manual for a Sweeping Gas Membrane Distillation Prototype and Design of a Field Scale Solar Nanofiltration Membrane Desalination Facility

      Arnold, Robert G.; Serwon, Daniel Morrow; Farrell, James; Reyes, Sierra, Maria (The University of Arizona., 2016)
      Approximately 35% of the population of the Navajo Nation does not have direct access to the electric grid and public water supply. Tribal members haul their potable and livestock water from public water systems that are located great distances from their homes. The Navajo Nation Solar Desalination Research Pilot Demonstration Project is designed to provide residents affordable livestock water. The same technology can later be adopted to provide potable water. The project has deployed an off-grid, prototype water purification unit at a demonstration site north of Leupp, AZ utilizing membrane distillation (MD) technology. A second prototype for the same purposes utilizing nanofiltration (NF) membrane technology has been designed, built, and operated at The University of Arizona. Through experimentation I confirmed information provided the manufacturer of the NF membrane, calculated the production rate to be 636 gallons per day, and calculated the cost of desalinated water to be $0.003 per gallon. Both systems use solar energy to desalinate brackish ground water and the second prototype will later be deployed at the same site for side-by-side comparison. A critical part of the project is the development of technology transfer methods that will help the community take ownership of the project. To accomplish this goal I have written a comprehensive manual that will be given to the Navajo Department of Water Resources. The demonstration site will act as an applied research site for investigation, demonstration, and training related to sustainable water and energy systems designed to address the needs of remote, rural communities in arid and semi-arid regions. The aim is to inform a regional plan for Southwestern Navajo Nation Chapters to address chronic water and energy shortages, demonstrate renewable energy application for water treatment of brackish ground water, evaluate trade-offs in energy and water supplies, and foster community development. The research and demonstration site has been developed by an interdisciplinary and collaborative effort between the Bureau of Reclamation, Apex Applied Technology, Inc., and The University of Arizona.
    • Off-Grid Solar-Powered Nanofiltration Pilot Study Relevant to The Navajo Nation

      Karanikola, Vasiliki; Brizo, Ailyn Torres; Hickenbottom, Kerri; Achilli, Andrea (The University of Arizona., 2022)
      Rural communities that are not connected to the electric or water grid often face challenges with access to affordable and safe potable water. Photovoltaic-powered membrane processes are being explored as an option to meet this need for cost-effective, safe drinking water in rural communities. In particular, the lower power requirements and palatable product water make nanofiltration an attractive option. The suitability of nanofiltration depends on many factors such as water quality, operating conditions, and maintenance. Commercially produced nanofiltration membranes are generally assumed to be operated near-continuously, but the nature of the solar power means that photovoltaic water filtration systems are operated intermittently, which may increase fouling and increase likelihood of microbial growth.Water quality analyses was conducted on at 17 sites on the Navajo Nation to determine the need for water treatment and the suitability of nanofiltration. Exceedances of water quality standards for arsenic and/or uranium were found at five sites and exceedances for total dissolved solids were found at 12 water sources, indicating the need for water treatment. Intermittent operation was tested on a pilot-scale nanofiltration prototype for two months with a salt solution with a total dissolved solids concentration of 1350 mg/L containing Mg2+, SO42+, Cl-, and Ca2+. There was little to no change in performance over the two months. Operation with a solution including ferric sulfate caused membrane fouling within 3 days. The system was also tested with a solution containing humic acid alone and a solution containing humic acid and Mg2+, SO42+, Cl-, and Ca2+ with a TDS of 1350 mg/L. The addition of salts decreased flux by about 30% when pH was maintained above 7.5 and about 12% when pH was not controlled. Finally, the membrane fouled by ferric iron was subjected to an autopsy. The results suggest the foulant layer consists primarily of amorphous, colloidal iron.