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Treatment of log yard run-off with a continuous attached growth bioreactor Liao, Charles

Abstract

Log yard run-off, 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 the environment. Run-off 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 yards are generally located near bodies of water for the easy transport of logs to the sites; therefore, run-off is likely to enter nearby water sources. Treatment of run-off at log yards is not common. Five run-off samples were collected between September 2004 and July 2005, from two sawmills located in British Columbia (BC). The run-off samples collected had BOD ranging from 16 to 371 mg/L, COD from 230 to 2660 mg/L, tannin and lignin from 200 to 680 mg/L of tannic acid. Four run-off samples were acutely toxic according to the Microtox toxicity test. The purpose of this study was to evaluate the treatability of the run-off with a lab-scale continuous biological attached growth reactor. Biofilm was grown from a mixture of Kraft mill return activated sludge (RAS) and primary treated Kraft mill effluent. The bacteria from the RAS quickly colonized the plastic support material within the reactor. The reactor was used to treat the run-off at different operating conditions. Hydraulic retention time (HRT) and temperature were varied to determine their effect on treatment performance. The reactor showed it was capable of treating run-off 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%, respectively for different operating conditions. In general, the treatment performance increased with increase in temperature and HRT. There appears to be a transition in microbial culture as temperature decreased from 15°C to 10°C, which hindered the reactor performance. The reactor was able to remove all acute toxicity at 30°C, but at lower temperatures, treated run-off remained acutely toxic.

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