Impact of Organoclay Content on Hydraulic Performance of Filter Strips to Treat Urban Runoff

Impact of Organoclay Content on Hydraulic Performance of Filter Strips to Treat Urban Runoff

 

Yaren Ozturk ¹, Derya Ayral Cınar ² 

¹ Marmara University, Istanbul, Turkiye

² Gebze Technical University, Kocaeli, Turkiye  

Abstract. 

Due to urbanization and climate change, it has become common for urban runoff to carry pollutants to surface water bodies, wastewater treatment plants, infrastructure systems and groundwater. Pollutants transported include heavy metals, solids, nutrients, pathogens and various organic substances such as pesticides and polycyclic aromatic hydrocarbons (PAH). It is proposed to manage this pollutant load at source before it reaches receiving environments.  Nature-based solutions such as filter ditches, infiltration ponds or rain gardens are considered more efficient to manage urban runoff. Among these methods, filter ditches have the highest potential to treat pollutants. It is thought that the use of organoclays, synthesized by the integration of surfactants into the clay mineral structure, as filter material may increase a common contaminant in urban runoff -PAH- removal compared to conventional clay minerals. In addition to treatment efficiency, another important parameter in designing filter ditches is the hydraulic permeability of the filter material. It is desirable that the infiltration rate of the surface flow is slow enough to allow time for pollutant removal and fast enough to prevent ponding on the filter. This study investigated how organoclays, which are proposed to enhance PAH removal from urban runoff, affect the hydraulic permeability of the filter material. Organoclay synthesized by Ca-montmorillonite and HDTMA is used at different percentages in the filter material mixture and hydraulic permeability was determined. Hydraulic conductivity of sand was 4.5x10^-4 cm/s and it dropped to 2.4x10^-5 cm/s and 2.3x10^-5 cm/s when 10% and 20% clay was used, respectively. On the contrary, organoclay at 10% and 20% did not decrease the hydraulic conductivity significantly (to 1.5x10^-4 cm/s and 1.4x10^-4 cm/s, respectively). As hydraulic conductivity is suggested to be 0.3-1.4 x 10^-4 cm/s for surface runoff treatment systems, it appeared that using 20% organoclay is promising to treat emerging pollutants such as PAHs without comprimising the hydraulic performance of the filter system.

 

Keywords: Nature based solutions, urban runoff, climate change, filter strips, organoclay