Enhanced denitrification by design modifications to the standard permeable pavement structure

In this study, six permeable pavement systems (PPS) with different subbase configurations were tested to evaluate their nitrogen attenuation capabilities from urban stormwater runoff. The PPS subbases were configured based on the following rationale for achieving enhanced physical, chemical and biological treatment of nitrogen compounds commonly found in urban stormwater: (i) a layer of natural zeolite to enhance nitrogen removal by ion exchange and adsorption; (ii) a layer of bark chips as a carbon donor to enhance biodegradation; (iii) a saturated zone to maintain required moisture content and reduced oxygen level for enhanced denitrification and (iv) thin sand layer(s) to limit oxygen transport for creating an anoxic zone within the PPS. A laboratory water sampling and testing program was undertaken from these PPS over a six-month period using synthetic stormwater with different pollutant concentrations while simulating varying rainfall intensities to represent typical design rainfall events considered in urban stormwater management. Our results demonstrate an improved denitrification in the PPS when a saturated zone is maintained and an organic carbon source is added in the PPS subbase. Compared with the traditional PPS, the new PPS is found to attenuate twice the amount of the total inorganic nitrogen in stormwater. Also, the attenuation of nitrogen compounds by the standard PPS is found to be reduced with rainfall duration (e.g., 54% attenuation during the first hour and only 3.5% during the 4th hour of the rainfall). The new PPS is found to attenuate 68% of total inorganic nitrogen even in the 4th hour of the rainfall event. The new PPS has the potential to become an effective stormwater quality improvement device that can contribute towards cleaner urban waterways. (C) 2019 Published by Elsevier Ltd.