Treatment of Wildfire Ash in Drinking Water

Treatment of Wildfire Ash in Drinking Water

Tanner Miller^1,2, Mrittika Rodela¹, Indranil Chowdhury¹

¹Department of Civil and Environmental Engineering, Washington State University, Pullman, WA

²Department of Earth Sciences - Meteorology, Millersville University, Millersville, PA

Wildfires continue to increase in intensity and frequency due to climate change, deforestation and suppressing forest fires for over 100 years. Ash erosion to downstream water poses a threat to communities as forested water provides source water for two-thirds of the U.S population. For this study, soil samples were collected from the University of Idaho Experimental Forest (UIEF) and burned in a muffle furnace for 2 hours at 250 ℃, 450 ℃ and 650 ℃ to represent wildfire ash. Previously collected wildfire ash samples were also used for comparison. Wildfire ash samples were characterized by color, indication of combustion temperature, using the Munsell color chart. Aluminum Chlorohydrate (ACH) was used to assess its effectiveness on various lab and wildfire ash types at the following dosages: 5 mg/L, 10 mg/L, 15 mg/L, and 20 mg/L. Pre and post-treatment parameters that were examined included turbidity, pH, electrical conductivity (EC), zeta potential, specific ultraviolet absorbance, and dissolved organic matter (DOC). Findings suggest that ACH can reduce the magnitude of zeta potential and turbidity (< 5 NTU) post-coagulation. Minimum application of ACH (5 mg/L) yielded average percent decreases in turbidity of 94.44% and 82.55% for lab and wildfire ashes respectively. Greater values of percentage decreases in turbidity were observed with increasing dosage, in relation to their untreated counterparts. Zeta potential magnitudes showed a decreasing trend with increasing dosage for both lab and wildfire ashes. Near-zero values for zeta potential magnitude were achieved with Obenchain soil (2.15 mV) and 650 ℃ lab ash (0.31 mV) at a dosage of 15 mg/L. EC and pH values, among lab and wildfire samples, expressed almost no variation with increasing dosage. Non-Purgeable Organic Carbon (NPOC) values demonstrated a nearly linear decrease with increasing dosage, with the exception of 450 ℃ and 650 ℃ lab ashes, which proved to be nearly constant with increasing dosage. Specific Ultraviolet Absorbance (SUVA) was affected more in wildfire ashes compared to lab ashes, with little variance displayed in lab ashes. This study will allow water treatment plants to understand the physiochemical characteristics of ash-contaminated water and be able to effectively treat that water for the safety of affected communities.

Keywords: Climate Change, Wildfire Ash, Water Treatment, ACH