Nutrient Removal Rates of Permeable Reactive Concrete

Abstract

Nitrogen and phosphorus contained in stormwater runoff contaminate both surface and groundwaters, causing problems for natural aquatic systems and human health. Pervious concrete specifically designed for pollutant removal, otherwise known as permeable reactive concrete (PRC), may be used as a novel component of existing infrastructure to remove nutrients from runoff. This research compares the removal and retention of dissolved, inorganic nitrate-nitrogen (NO3-N) and orthophosphate-phosphorus (PO4-P) for three PRC mixtures. The control PRC was ordinary portland cement (OPC) and was compared against other mixtures containing 25% replacement with Class C fly ash or with drinking water treatment residual waste (DWTR). Concrete specimens were jar-tested for 72 h in three different concentrations of nitrate or phosphate. The control mixture removed 6% of NO3-N and more than 8% PO4-P, and the fly ash mixture removed up to 39% of NO3-N and more than 91% PO4-P. The DWTR mixture leached NO3-N while removing more than 8% PO4-P. Linear isotherms were determined for the range of nutrient concentrations tested. Column leach tests were conducted on specimens after initial jar testing and used as an indication of removal permanence. Inorganic removal mechanisms were investigated, including crystallographic substitution, adsorption, and physical solute filtering in cement pore space. Results indicate PRC can be one of the leading methods to remove nitrate from surface waters and is as efficient as other methods for orthophosphate removal.