By West Marrin, Ph.D.
Conventional seawater desalination, wastewater recycling, geoengineering, and transcontinental water importation are a few of the solutions that have been proposed to address the shortage of available freshwater. While useful for a limited timeframe or in certain locations, these technologies have drawbacks related to energy requirements, environmental effects and long-term sustainability.
Contributors to atmospheric carbon dioxide are recommending the “sequestering” of carbon in the oceans or underground in saline aquifers that frequently involves capturing greenhouse gases and relocating them to environments that are not in direct contact with the atmosphere. Ocean sequestration can have devastating effects on marine chemistry and biodiversity, whereas underground sequestration can pollute potable groundwater aquifers.
Technologies such as cloud seeding have long been hyped as a potential means of increasing local rainfall and, although potential side effects are often minimal, their reliability is still in question. Fertilizing the oceans with soluble iron and creating tropical tree plantations have been proposed to limit the rise in atmospheric carbon dioxide levels, but their effects on soil productivity, ecosystem stability and critical water quality parameters are unknown. Those who recommend geoengineering techniques often believe that the immediate consequences of climate change are more of a concern than are the potential longer-term negative effects.
The reuse of wastewater can produce potable water, although treatment to drinking water standards is both energy- and water-intensive. Constructed wetlands, or living machines (wetland-like systems), and various types of treatment lagoons that utilize aquatic plants or microalgae to remove pollutants from wastewater streams are significantly more efficient than are conventional treatment facilities. Conventional or and centralized treatment facilities utilize chemicals and electrical energy to clean wastewater, while wetlands and lagoons primarily utilize plants and microorganisms. Although constructed wetlands cannot produce potable water, they can produce water suitable for irrigation, cooling, and other household purposes.
Water reuse and conventional seawater desalination may eventually become expensive necessities for providing potable water to drought-stricken regions; however, exploring more energy-efficient alternatives that produce fewer wastes may be prudent in the interim.
Figure 1. Seawater desalanization is a non sustainable solution
Alternative Energy Sources.
Conventional energy sources (e.g., fossil fuels, nuclear, hydroelectric) are major users and/or polluters of water, but a number of supposedly “green” energy sources are nearly as water inefficient. Hydrogen gas is often touted as a substitute fuel, but most hydrogen gas is produced by reacting steam with natural gas, a process that is both water consumptive and polluting.
Bioethanol is even more water unfriendly as a result of its dependence on cultivating starchy plants that have the same irrigation demands as food crops and that pollute waters with pesticides, fertilizers and processing wastes. Moreover, the global production of bioethanol has been linked to regional food shortages. Alternatively, the combined actions aquatic algae and bacteria can produce hydrogen gas in a complex process that generates a renewable fuel.
Bulk Water Imports.
A common response to drought is moving water from where it is to where it is not. Much of the U.S. Southwest was developed (or overdeveloped) using this tactic, and now the hunt is on for water from more distant sources. Beyond the enormous energy demands of transporting water through pipelines or canals and the staggering costs of building the required infrastructure, importing entire water supplies is neither sustainable nor secure.
Similarly energy inefficient and unsustainable is the proposed shipping of bulk water (via large tankers) between continents or towing of icebergs from Polar Regions. Questions remain as to whether shipping a more limited volume of bottled drinking water is even energy efficient.