Treatment of Severely-Deteriorated Post-Fire Runoff: A Comparison of Conventional and High-Rate Clarification to Demonstrate Key Drinking Water Treatment Capabilities and Challenges

Prior to mixing, ash was sieved through a 1 mm screen to remove any large debris and conifer needles that typically would not be found in water treatment plant influent streams. Three concentrations of ash in river water were prepared (2.0, 10.0, and 20.0 g×L^-1 of ash; five replicates of each) by adding ash to 1000 mL of Elbow River water in 2-L plastic square beakers, and mixed using a jar test apparatus (Phipps & Bird, PB-900 Series Programmable 6-Paddle Jar Tester, Richmond, VA) at 120 RPM for 2 minutes. Turbidity and dissolved organic carbon (DOC) concentrations consistent with or slightly higher than the levels that have been reported following severe wildfire (i.e., >1000 NTU and >15mg×L^-1, respectively) were targeted. These water matrices were black-colored, in a manner consistent with previous reports of severely-deteriorated water conditions after wildfire.

Standard methods were used to evaluate turbidity (Method 2130B; Hach 2100 N turbidimeter, Loveland, CO), pH (4500-H⁺B Electrometric method; Orion 720A pH meter, Thermo Fisher Scientific, Waltham, MA), DOC concentration (filtration through pre-rinsed 0.45 µm Nylaflo membranes, Pall, Port Washington, NY; Method 5310C; Shimadzu TOC-V WP analyzer, Kyoto, Japan), and UVA₂₅₄ (Method 5910B; 1 cm quartz cell; Hach DR 5000 Spectrophotometer, Loveland, CO). Specific ultraviolet absorbance at 254 nm (SUVA) was calculated by dividing UVA₂₅₄ absorbance by the DOC concentration.