Ensuring a Safe, Sustainable Future Water Supply--Case Study


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Ensuring a Safe, Sustainable Future Water Supply--Case Study

  1. 1. Ensuring a Safe, Sustainable Future Water Supply Case Study Teresa Long May 3, 2011
  2. 2. Introduction By the year 2060, water usage in Texas will exceed the available water supply due to rapidly increasing population growth.Existing sources of water supply are inadequate to sustain future demands for farming, ranching, recreation, and the environment.An additional 8.5 million acrefeet per year of new water supplieswill be needed. Ensuringa sustainable water supply in a semiarid climate is challenging and exacerbated by unpredictable factors such as climate change associated with global warming. How will stakeholders meet future demand? Methodology New technologies must be identified and developed to supply increased demand. This study focuses on several innovative technologies in various stages of planning and implementation by the Texas Water Development Board. This study also briefly examines technologies emerging in other countries that will help ensure a safe, sustainable future water supply. Meeting Future Demand Ensuring a safe, sustainable water supply to meet the demand required for the projected population for the year 2060 will entail development and implementation of many options. Strategic water management practices which advocate usingexisting sourceswisely, capturing and storing water, and reusing wastewatermust be implemented and followed. Innovative
  3. 3. technologies must be identified and developed. After suffering the most severe drought in the history of Texas (1954-1956), the Texas Water Development Board (TWDB) was founded in 1957. According to the TWDB, plans to meet the projected demand of 8.5 million acre-feet per year of new water supplies necessary to keep up with expected population growth for 2060 include: 60 % --Conventional water sources 24%-- Conservation 16 % --Desalination, brackish groundwater desalination, reuse and reclamation, rainwater harvesting, and aquifer storage and recovery A single source will not be adequate to supply demand. We must develop a diverse combination of technologieswhich includes desalination, brackish groundwater desalination, rainwater harvesting, aquifer storage and recovery (ASR), reuse, and emerging technologies. Desalination Desalination is the process of removing dissolved salts from saline water to produce freshwater. Texas has an infinite, drought proof-supply of seawater along its 370 miles of coastline. Although Texas does not currently have a seawater desalination plant, optimization of existing technology has decreased the cost associated with desalination, making it a costeffective alternative source of water. Twoprocesses are currently used, the thermal process and the membrane process. The thermal process involves heating saline water to the boiling point, then condensing and collecting the water vapor. Membrane processes such as reverse osmosis and electrodialysis separate salts from
  4. 4. water using a permeable membrane.Both processes generate toxic by-products (salts and brine) which must be disposed of, adding to the cost of producing freshwater from saline water. Brackish Groundwater Desalination Seawater typically contains greater than 35,000 milligrams per liter of Total Dissolved Solids (TDS). The higher the concentration of TDS, the more pressure required to push the water through membranes, which increases the cost of production. Brackish groundwater contains a significantly lower concentration of TDS,making it less costly to process than desalination of seawater. Almost every aquifer in Texas contains brackish groundwater. Approximately 2.78 billion acre-feet are available for desalination.Currently, 38 brackish groundwater desalination plants, many of which are small-scale facilities and pilot plants, are operational. While past studies estimated volumes, they failed to assess groundwater quality. In 2009 a program was funded and implemented todevelop better tools to assess parameters, characterize and map brackish groundwater aquifers, and develop flow models to determine aquifer productivity. Rainwater Harvesting Rainwater harvesting is the forgotten practice of capturing, storing, and using rainwater. One inch of rainfall that falls on a 2,000 square foot roof yields 1,000 gallons of harvestable water. Average household systems can collect as much as 32,000 gallons per year even in a semi-arid region. Rainwater collected is suitable for use in landscape irrigation, household use, and may be suitable for drinking with minimum treatment. Large-scale systems are being developed by municipalities.
  5. 5. Aquifer Storage and Recovery During periods of heavy rain, appropriated surface water can be collected for subsequent retrieval and injected, via well used for both injection and recovery, into a geologic formation capable of underground storage (Class V aquifer).Stored water can be retrieved in dry or drought years to help meet demand.Today, more than 75 ASR wells are operational in the United States, compared to only three in 1968.Texas is lagging behind other states with only 67 Class V aquifers in use today. Feasibility studies using different water supply sources, in addition to different types of aquifers, show the technology is viable but many regulatory and legal barriers remain. Reuse Reuse and reclamation of wastewater is drought-proof and a key component in ensuring future water supply. Texas is expected to nearly double its reuse capacity by 2060.Domestic or municipal wastewater can be reclaimed and treated to a quality suitable for either direct or indirect reuse. In direct reuse, effluent is piped directly from wastewater treatment plant to point of use. Indirect reuse is when effluent re-enters a river, stream, or aquifer and is retrieved for subsequent use at a different point in the system.Reclaimed water is commonly used for industrial and power plant cooling water. Reusing treated wastewater effluent from wastewater treatment plantsafter further treatment at an integrated membrane facility in close proximity to industrial users, can supply industrial users with water suitable for use as process and boiler water. Reuse of this water releases the surface water for currently used for industry to meet other needs.
  6. 6. Emerging Technologies The atmosphere contains 0.001% of the Earth’s total water reservoir volume of 350 million cubic miles. Water-from-air technology converts the humidity in the atmosphere to liquid water using refrigeration methods that cool the air below its “dew point” Site-specific designs for tropical coastal sites with access to deep, cool ocean waters that are used as a coolant produce freshwater from saline water without pumping salts back into the ocean. Solar powered desalination units and solar powered atmospheric generation units are currently under development. These processes do not require fossil fuel to operate, and do not produce toxic by-products that require disposal. Units can be either small-scale or large-scale. Conclusion Identifying and developing new technologies, along with a strategic water management plan that includes using existing sources wisely, is absolutely essential in ensuring a safe, sustainable water supply. Humankind cannot continue to squander our most precious resource.Future generations will ultimately suffer if our misuse continues unchecked. There is no substitute for water.
  7. 7. Cited References Texas Water Development Board [homepage on the Internet]. (TX): n.d. [cited 2011 Apr. 4]. Available from: http://www.twdb.state.tx.us. Air Water Well [homepage on the Internet]. n.d. [cited 2011 Apr. 3]. Available from: http://www.airwaterwell.com/. Warair [homepage on the Internet]. n.d. [cited 2011 Apr. 3]. Available from: http://www.watair.com. DeSalWave[homepage on the Internet]. n.d. [cited 201 Apr. 4]. Available from: http://www.desalwave.com/. Texas Water Development Board (USA) Ship Channel Wastewater Reclamation and Reuse Feasibility Study Final Report. Austin (TX): 2005 Oct.