| Summary: | The forest industry is one of the most important contributors to the economy of the
province of British Columbia. This industry supports many wood processing mills
located throughout the province. Percolation of the rainfall through woodwaste piles and
log storage areas leaches natural chemicals from the wood residuals.
A study was performed on a woodwaste storage site near Mission, B.C., where a number
of wood processing mills are located adjacent to the Fraser River. The objective of this
research was to evaluate the effectiveness of surface flow constructed wetlands for
treatment of woodwaste leachate. The leachate was characterized over the period of the
study. It had very low pH (~3.5), very high and aggressive oxygen demands (5,000-
11,000 mg.L⁻¹ BOD₅ , and 7,000-18,000 mg.L⁻¹ COD) , very high levels of tannin and
lignin (2,800-6,500 mg.L⁻¹) and total VFAs ( 1,800-2,800 mg.L⁻¹), and low levels of
nutrients (< 3 mg.L⁻¹ NH₃ - N , < 0.2 mg.L⁻¹ NOx - N , and < 4 mg.L⁻¹ P0₄-P). Diluted
leachate was directed to six pilot-scale wetland cells, four planted with cattails (Typha
latifolia) and two controls, during a total operational period of 34 weeks. As the leachate
had a very low nutrient content and pH, nutrient addition and pH adjustments were made
to improve contaminant removal. After physical modifications in the site, reductions in
pollutants were consistently achieved. The average removals for BOD and COD were in
the order of 60% and 50% respectively. On average, up to 69% of VFAs and 42% of
tannin and lignin contents were removed. The ThOD comparisons with COD showed that
VFAs and tannin and lignin accounted for over 60% of COD in effluent and influent.
"Planted and nutrient added" cells were more effective in BOD removal from leachate
than the unplanted controls. In addition, the effluent pH values were higher for the
planted cells. No significant differences were observed in removal efficiencies of other
targeted pollutants between the six cells. Climatic conditions (i.e. precipitation,
evaporation and temperature) had a great impact on the performance of the wetlands. In
addition, acclimatization o f the wetlands increased the treatment ratios.
Constructed wetlands proved effective in treatment of woodwaste leachate. Continuous
operation of the system will help to elucidate the seasonal fluctuations. Microbiological
studies can also shed light on the causes of performance variations. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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