Treatment of log yard runoff with a continuous fixed film bioreactor

Runoff is generated at log yards when precipitation comes into contact with logs, wood debris, and equipment at outdoor wood processing, sorting and storage facilities. Log yard runoff, which can be toxic and have high levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and tannin and lignin (T&L), is a potential threat to nearby receiving environments. Runoff samples were collected from two sawmills located in British Columbia (BC). The runoff samples collected had BOD ranging from 16 to 371 mg/L, COD from 230 to 2660 mg/L, and tannin and lignin from 200 to 680 mg/L of tannic acid. Four runoff samples were acutely toxic according to the Microtox^® toxicity test. A continuous lab-scale fixed film bioreactor was used to treat the runoff over a range of temperature (5–30 °C) and hydraulic retention times (4–24 h). The reactor was capable of treating runoff with BOD removal ranging from 73.0% to 97.6%, COD removal ranging from 48.0% to 76.9%, and tannin and lignin removal ranging from 27.8% to 60.1%. There appeared to be a transitional change in the makeup of the microbial community in the reactor as the temperature decreased from 15 °C to 10 °C. The reactor was able to remove all acute toxicity at 30 °C, but at lower temperatures treated runoff remained acutely toxic.