Hydrophobic sand to combat water scarcity – Properties and possible chemical risk.

Abstract: The city of Dubai, which lies in the Middle East is, as many other cities in the area, suffering from shortage of fresh water resources. This issue is handled by desalination of sea water, which is a rather expensive procedure. Recently, the city tends to promote using hydrophobic sand in order to reduce irrigation water quantity and watering durations. Economically, this procedure has fewer costs than water desalination but concerns were raised regarding whether the chemical compounds, used in the treatment process of normal sand, impose any contamination risks for soil and groundwater. Due to the fact that normal sand has high permeability comparing to other types of soil, such as silt and clay, the rates of water seepage in normal sand is considerably high which results high water consumption in agriculture. One of the objectives of this thesis is to identify the most effective design for utilizing hydrophobic sand and normal sand layers to obtain the most suitable permeability rates for plantation purposes. Another objective is to discuss the probability of organic chemicals and heavy metals seepage when using the hydrophobic sand in soil; leaching tests were carried out to provide input to this discussion. The study showed that the hydrophobic sand has higher permeability than normal sand when it is saturated with water. However, it needs a considerably longer time in order to reach the saturation stage so recommendations were provided to use a separate layer of hydrophobic sand beneath the normal sand layer where vegetation is planted and avoid using sand mixtures. Based on the leaching tests’ results, it was also concluded that negligible concentrations of the organic silica compounds will be released into soil and ground water and the rates of heavy metals in leaching water were within the allowable limits. However, the possibility of the transformation of the organic compounds, used for normal sand treatment, into silica-free organic compounds was not discussed in this thesis. In other words, the usage of hydrophobic sand for agriculture purposes does not threaten the safety of neither soil nor groundwater concerning the leaching of the chemical compounds and metals that were tested in this study.