Available at: https://digitalcommons.calpoly.edu/theses/1776
Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
Creeks and rivers are often polluted as a result of stormwater runoff that carries various contaminants in to open water bodies, causing adverse environmental and health effects. Low impact development (LID) techniques are currently employed to treat this runoff prior to discharge. Nitrate, however, is not consistently removed by these LID techniques. This study analyzed the ability of several nanoclays to remove nitrate in runoff and determined the feasibility of using them as a soil supplement for LID implementation. Six different nanoclays and HCl-treated clays were compared (pre-modified trimethyl stearyl ammonium nanoclay, pre-modified dimethyl dialkyl amine nanoclay, unmodified hydrophilic bentonite, unmodified halloysite nanoclay, HCl modified hydrophilic bentonite and HCL modified kaolin) to the control clay, unmodified kaolin, for their ability to adsorb nitrate solution by batch adsorption experiments. The findings determined that the pre-modified trimethyl stearyl ammonium nanoclay was the most effective adsorbent, decreasing the nitrate concentration up to 86% for a nitrate to clay ratio of 6.25 mg: 1 g under normal pH (5-6) and temperature (25⁰C) conditions. The HCl acid modification did not prove to provide significant additional benefits to the clays. Column studies were also conducted on the most successful clay, pre-modified trimethyl stearyl ammonium nanoclay, to assess the breakthrough point when 0.1% w/w and 1% w/w of the nanoclay were added to Nevada Sand. The results showed a projected breakthrough pore volume of 17 when the larger fraction was added to the sand, and a corresponding hydraulic conductivity of 12.6 in/hr, which is 35% slower than the un-amended Nevada Sand. Such a high hydraulic conductivity indicated that future work can test larger fractions of clay to sand mixtures to achieve a higher number of pore volumes before the soil reaches its breakthrough point. Future studies can also further explore both batch and column experiments to assess the feasibility of implementing soil amendments to a filtration system by changing the experimental parameters, such as base soil material, types of nanoclays used, and the nanoclay to nitrate ratios. Additionally, synthetic stormwater from runoff should be used as the influent instead of a nitrate-only solution to reflect more realistic scenarios for a potential real-world application.