Ozone for removal of acute toxicity from logyard run-off

Stormwater run-off from wood handling facilities is garnering increasing attention from environmental regulators. In an effort to develop treatment methods to deal with the problem of toxic run-off from logyard and dryland sorts, we are currently investigating the use of ozone. Samples of logyard run-off were obtained from two British Columbia coastal sawmills. Ranges obtained for measured parameters of these samples were as follows: COD 2400-8700 mg/L, tannins and lignins 160-2500 mg/L, BOD 190-1900 mg/L, acute (Microtox) toxicity EC50 2%-27% v/v. Centrifuged samples were treated with ozone doses up to approximately 0.5 mg ozone/mg COD in a lab-scale reactor. Ozonation was found to significantly reduce toxicity (80%-90%), tannin and lignin (TL) (90%-95%) and dehydroabietic acid (DHA) (95%-100%) levels. There were moderate reductions in COD (30-35%) and BOD (15%-25%). At slightly acidic to neutral pH, pH had no effect on the rate of COD oxidation; TL and toxicity removal were slightly improved in neutral solutions compared to acidic ones, while DHA removal significantly improved.