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Attached growth biological treatment of stormwater run-off from log yards Woodhouse, Christine Alison

Abstract

Stormwater run-off from log yards, which is frequently toxic, high in solids and poses a significant biological oxygen demand (BOD) on aquatic environments, is a burgeoning environmental concern. The discharge is generated when precipitation comes into contact with wood, debris and equipment at outdoor lumber sorting, processing and storage facilities adjacent to waterways. The treatment of log yard run-off is not common. Nine run-off samples were collected, between May, 2001 and April, 2002, from different locations at the log yard of a Vancouver Island sawmill. Characterization of the samples revealed BOD levels ranging from 25 to 745mg/L, chemical oxygen demand (COD) from 125 to 4610mg/L, tannin and lignin concentrations (T+L) from 10 to 1505mg/L and total suspended solid concentrations (TSS) from 65 to 2205mg/L. Six samples were acutely toxic according to Microtox. A preliminary attempt at elucidating the toxic constituents in the run-off was made. In both samples tested, metals were not found to contribute to run-off toxicity. Wood extractives are the suspected toxicants in these samples, based on related literature. The focus of this project was the treatment of run-off in a lab-scale, attached microbial growth reactor. A biofilm was initially grown, on solid plastic support media, from pulp mill wastewater treatment system seed. Consuming run-off, methanol and supplemental nutrients, a resilient biofilm quickly colonized the reactor. The biofilm effectively treated all five run-off samples tested. Treatment for 24 hours at 34°C resulted in BOD concentration reductions of 94 to 100%, COD of 86 to 93% and T+L of 91 to 97%. Substantial toxicity and colour reductions were also observed. Runoff treatment at 5 and 24°C reduced BOD concentrations by 76 and 97%, COD by 64 and 91%, and T+L by 67 and 95%, respectively.

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