Applicability of Hydrophobic Sand to Combat Water Scarcity and Possible Chemical Risk
Freshwater scarcity is known as a sever constraint in in the Middle East, especially in the Gulf Region. The cities in the Gulf Region including in the United Arab Emirates (UAE) depend mainly on seawater desalination due to existing arid climate and poor groundwater resources. Some cities in the UAE faced water demand escalation about 15% annually from 2004 to 2010 despite of seawater desalination direct cost of 1 dollar per meter cube. Thus, calling all measures of water conservation techniques to reducing indoor and outdoor water demands is inevitable. Hydrophobic sand (HS) can be a solution to reduce outdoor water consumption for landscaping and agricultural activities as it can reduce water seepage and increase the contact time between irrigation water and plants’ roots. The HS is Normal Sand (NS) coated by a thin layer of hydrophobic organic silica compound called trimethylsilanol. However, concerns were raised about the leaching of harmful organic coating chemicals into the soil and groundwater. For some plants, requiring a certain range of permeability suggests a mixture of NS and HS. Assessing the potential risks of leaching additives including organic trimethylsilanol is one of the objectives of this research. The permeability of mixtures of HS with abundant NS was examined to assess validity and cost effectiveness of such technique when a certain permeability is required. Several leaching tests were conducted with monitoring the release of selected elements and nutrients. The soil classification were examined and constant head permeability tests were conducted for different configurations and mixtures of NS and HS layers. The leached elements and nutrients were within the allowable limits set by the typical standards and very small concentrations of organic silica were leached. This indicates that HS does probably not constitute an environmental hazard. Mixing different portions of NS and HS revealed unforeseen increase in the permeability and suggest invalidity of controlled sand mixture for a targeted permeability. Instead, a layer of NS should be placed over a bottom layer of HS to trap water for a relatively long period and improve roots’ contact with irrigation water.
Keywords- Hydrophobic, Sustainable, Irrigation, Leaching, Permeability