Enhancing biofiltration technology for the treatment of wildfire-impacted raw water

Wildfire events significantly contribute to the degradation of surface water quality by introducing ashes and unburnt carbon through runoff, resulting in elevated turbidity, increased levels of total suspended and dissolved solids, and higher concentrations of dissolved organic matter (DOM). Biofiltration has emerged as a sustainable and cost-effective water treatment technology, particularly valued for its environmentally friendly ability to remove DOM. This study evaluated the performance of process intensified biofiltration in removing dissolved organic carbon (DOC) from wildfire-impacted raw water using three bench-scale biofilters composed of different media: sand, granular activated carbon (GAC), and a combination of sand and GAC. The influent was pretreated using aeration and a roughing filter. DOC was tested at three levels: 20, 50, and 100 mg/L. Water quality parameters such as pH, turbidity, temperature, alkalinity, ultraviolet absorbance at 254 nm (UVA₅₂₄), specific ultraviolet absorbance at 254nm (SUVA₅₂₄) – calculated, and microbial activity – adenosine triphosphate (ATP), extracellular polymeric substances (EPS), and dissolved oxygen (DO) were monitored. Results indicate that at 20 mg/L DOC, the sand + GAC biofilter achieved the highest mean DOC removal efficiency of 70 ± 20%, followed by GAC (68 ± 16%) and sand (68 ± 22%). At 50 mg/L, removal efficiencies declined to 54 ± 16% (sand + GAC), 47 ± 19% (GAC), and 33 ± 19% (sand). At 100 mg/L, performance dropped remarkably, with average removals of only 16 ± 26% (sand + GAC), 16 ± 21% (GAC), and 12 ± 22% (sand). UVA₅₂₄ and SUVA₅₂₄ values remained below 2 L/mg·m, indicating the dominance of hydrophilic and low molecular weight organic matter. ATP concentrations peaked at 14 ± 2 mM in the sand biofilter, confirming its superior microbial activity. EPS analysis revealed higher sugar than protein concentrations, with tightly bound EPS peaking at 296 ± 37 mg/g total suspended solids. Elevated influent DOC concentrations were associated with increased pH (up to 9.52 ± 0.12), which may have negatively impacted microbial activity and DOC removal. Statistical analysis revealed a strong negative correlation between DOC concentration and DOC removal efficiency. Furthermore, analysis of variance confirmed that DOC concentration significantly influenced removal efficiency, while media type did not. However, Tukey post-hoc test showed that at DOC concentrations of 20 and 50 mg/L, the biofilters significantly reduced DOC levels, while at 100 mg/L, no significant reduction was observed, indicating diminished effectiveness at higher concentrations. The findings of this study underscore the robustness and adaptability of biofiltration systems in treating wildfire-impacted water, particularly in the effective removal of DOC and turbidity. By providing a nature-based, cost-effective treatment solution, biofiltration offers a sustainable and climate-resilient strategy for safeguarding drinking water sources against emerging contaminants.