Removal of Metals from Highway Stormwater Runoff Using Enhanced Filtration Media Amendments
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Abstract
Stormwater runoff can introduce contaminants including heavy metals, chloride, and phosphorus compounds, which can have negative impacts on receiving waters. Stormwater filtration systems can offer successful and cost-effective reduction of stormwater contaminants. The objective of this research is to evaluate cost-effective filtration media amendments in column experiments, quantifying contaminant removal under different simulated field conditions. For this research project, field-collected stormwater was spiked at common contaminant levels, buffered for pH, and filtered through sand and Stalite (an expanded slate aggregate) filtration columns amended with biochar or zero-valent iron. The simulated field conditions include baseline flow, alternating contaminant concentrations, antecedent drought, de-icing agents and cold temperature (phase 4.4), and media aging (phase 4.5). Dissolved metals aluminum, chromium, copper, manganese, lead, and zinc were analyzed in phases 4.1 through most of phase 4.4; However, total recoverable metals were also analyzed in samples from the end of phase 4.4 and throughout phase 4.5 due to the relationship between solid particles and metals. Laboratory and statistical analyses showed that aluminum was significantly removed by the Stalite + biochar stormwater filtration system throughout most phases of the project. For example, influent aluminum was 113-450 µg/L during phase 4.3, while effluent through Stalite + biochar exhibited aluminum concentrations less than ~50 µg/L. Chromium was not significantly removed by any of the stormwater filtration systems; however, Stalite and Stalite + biochar displayed lower effluent concentrations than the other stormwater filtration systems throughout most phases. For example, influent chromium was ~0.1-2 µg/L during phase 4.3 while effluent through Stalite + biochar exhibited chromium concentrations below ~0.5 µg/L. Copper was significantly removed by both the Stalite + biochar and Stalite + biochar + iron stormwater filtration systems throughout most phases of the project. For example, influent copper was ~1-7 µg/L, while effluent through Stalite + biochar exhibited copper concentrations less than ~2.5 µg/L. Manganese was significantly removed by the Stalite + iron and Stalite + biochar + iron stormwater filtration systems throughout most phases of the project. For example, influent manganese was 53.2-104 µg/L while effluent through Stalite + biochar + iron exhibited concentrations less than ~5 µg/L. Lead was significantly removed by both the Stalite + biochar and Stalite + biochar + iron stormwater filtration systems throughout most phases of the project. For example, influent lead was ~0-16 µg/L while effluent from Stalite + biochar + iron exhibited concentrations less than ~5 µg/L. Zinc was significantly removed by both the Stalite + biochar and Stalite + biochar + iron stormwater filtration systems throughout all phases of the project. For example, influent zinc was 106-217 µg/L while effluent through Stalite + biochar was less than ~20 µg/L. The Stalite base displayed the most effective removal of metals as opposed to sand. Statistical analyses showed that Stalite + biochar stormwater filtration amended system displayed the most effective overall metals removal, except for chromium.