Laboratory simulation of postfire effects on conventional drinking water treatment and disinfection byproduct formation

Abstract

AbstractWildfires can abruptly transform forests, char vegetation and soils, and create an environment susceptible to postfire erosion and runoff to nearby surface waters serving as potable water supplies. The rising trend in wildfire activity increases the risk to source waters, while postwildfire implications on drinking water treatment are not well understood. A laboratory‐based approach was used to simulate the effects of forest floor heating during wildfire on water quality. Surface soil and litter samples were heated in a furnace and leached to evaluate changes to water‐soluble compounds. Leachates were diluted to a dissolved organic carbon (DOC) concentration of 5.0 ± 1.0 mgC/L. Heated and unheated (control) leachates were compared for dissolved organic matter (DOM) properties, treatability by alum coagulation, and disinfection byproduct formation. Size exclusion chromatography, optical property characterization, and organic nitrogen levels suggest that the DOM character shifted to lower‐molecular‐weight, nitrogen‐enriched aromatic compounds following heating. Raw water total trihalomethane and haloacetic acid precursor yields were not significantly different following heating; however, pairwise responses varied. Chloropicrin precursor yields increased by an average of 155% following heating, while haloacetonitrile precursor yields showed minimal changes. Even at high coagulant doses (>80 mg/L), the heated leachates consistently exhibited a poor coagulation response to turbidity and DOC removal. The DOC removal per mg alum was statistically lower for the heated leachates compared to the control samples (mean Δ = −0.06 mgC/mg‐alum). The adverse effect of heating on the DOC removal of the leachates might be explained by a lower‐molecular‐weight DOM composition. While findings suggest an altered DOM character, utilities may also experience an increase in influent DOC concentrations coupled with higher, or even extreme, sediment loads, resulting in compounding effects on water treatment.