Contaminated stormwater runoff from log yards is generated when precipitation comes into contact with wood, woody debris and equipment at outdoor wood sorting, processing and storage facilities. Nine runoff samples collected at a sawmill had biochemical oxygen demand (BOD), chemical oxygen demand (COD), tannins and lignin (T+L), and total suspended solids (TSS) levels ranging from 25 to 745 mg/L, 125 to 4610 mg/L, 10 to 1505 mg/L, and 65 to 2205 mg/L, respectively. Six samples were acutely toxic (EC50 <100%) based on the Microtox assay.
The samples were effectively treated using a laboratory-scale, attached microbial growth reactor. Treatment for 24 hours at 34°C resulted in substantial reductions in BOD (94–100%), COD (86–93%) and T+L (91–97%). Near complete removal of acute toxicity and colour were also observed. Twenty-four-hour treatment at lower temperatures, 24 and 5 C, reduced BOD concentrations by 97 and 76%, COD by 91 and 64%, and T+L by 95 and 67%, respectively.