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The effectiveness of constructed wetlands for treatment of woodwaste leachate

University of British Columbia

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.

Thesis/Dissertation

application/pdf

2009-08-13

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http://hdl.handle.net/2429/12178

Civil Engineering

University of British Columbia

UBCV

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