Treatment of burned soil leachates by ultrafiltration coupled with coagulation: Insights into membrane fouling

• First study on membrane fouling in coagulation-ultrafiltration of wildfire-impacted soil leachates. • Soil samples collected at a high burn-severity site and a low burn-severity site • High-severity burn leachates show lower pH, turbidity, and DOC with smaller, less aromatic DOM. • Hydrophilic DOM and metal-DOM complexes may contribute to irreversible fouling for high severity soil leachate. • Future studies should broaden soil sample diversity and explore how fire severity, soil and geological conditions This study evaluated the treatability of water leachates from wildfire-impacted soils using a coagulation-ultrafiltration process, aiming to better understand how post-fire changes affect membrane fouling in drinking water treatment. Soil samples were collected from one high burn severity and one low burn-severity site following the Cedar Creek Fire in Oregon, USA. The leachate from the one high severity site exhibited lower pH, turbidity, and dissolved organic carbon, and its dissolved organic matter (DOM) consisted of less aromatic compounds compared to the low-severity leachate. Filtration experiments revealed that, without pre-coagulation, the high-severity leachate caused less membrane fouling than the leachate from the low-severity sample. Pre-coagulation with aluminum chlorohydrate reduced fouling in both cases, though optimal dosages differed. For the low-severity leachate, a 30 mg/L dose improved DOM removal and minimized irreversible fouling, while for the high-severity leachate, effective control was observed at dosages up to 7.5 mg/L, with higher doses (30 mg/L) worsening fouling, potentially via metal-DOM complexes. While our controlled laboratory experiments provide valuable insights, we acknowledge that our lab experiments do not fully replicate field conditions. However, the unique characteristics of the leachate from our burned soil samples, indicate the need for further research to capture the complexities of post-wildfire water quality dynamics and refine treatment strategies for wildfire-impacted watersheds.