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To choose an appropriate dilution ratio to treat woodwaste leachate without inhibition on heterotrophic bacteria, microbial ATP concentration and the rates of heterotrophic leucine incorporation and acetate uptake were compared across surface flow mesocosm wetlands fed with different strengths of influent. Abundances of protozoa and respiring bacteria were investigated in two mesocosm wetlands to elucidate the effects of influent strength on heterotrophic bacteria. The strongest influent or the raw leachate did not show a significant inhibitory effect on leucine incorporation and acetate uptake. Instead, leucine incorporation rates by bacteria in water, epiphytic biofilm and sediment were higher in mesocosm wetlands fed with a stronger influent. There were significantly more respiring planktonic bacteria (451×105 mL−1) and fewer nanoflagellates (3.8×103 mL−1) in the mesocosm fed with a strong influent, while fewer respiring planktonic bacteria (38.7×105 mL−1) and more nanoflagellates (15.4×103 mL−1) in the mesocosm fed with a weak influent. The majority of the total microbial ATP was attributed to sedimentary bacteria, of which >96% were inactive. Heterotrophic activity and its distribution among water, epiphytic biofilm and sediment in the mesocosm wetlands were affected by availability of bacterial substrates and grazing pressure of nanoflagellates. [Copyright &y& Elsevier]

Laboratory tests were conducted on volatilization, adsorption on silt loam, and on the biological treatability of woodwaste leachate. No significant volatilization was found despite the high concentration of volatile fatty acids. Tannin and lignin adsorption reached equilibration within 78 h. Adsorption at a silt loam:leachate volume ratio of 2:25, equivalent to a 2 cm effective soil layer underlying a 25 cm water column in a surface flow constructed wetland, removed 22–42% tannin and lignin and 6–27% chemical oxygen demand at 23 ºC. Tannin and lignin accounted for the majority of the adsorbed chemical oxygen demand. Adsorption followed the Langmuir isotherm, with an adsorption capacity of 36 mg tannin and lignin/g silt loam. Adsorption efficiency for tannin and lignin at 15 °C was 0.44 times that at 23 °C. An aerated reactor removed 62–67% chemical oxygen demand, 65–67% tannin and lignin, and ≥98% volatile fatty acids. A similar anaerobic reactor removed 28–29% chemical oxygen demand, 13–19% tannin and lignin, and 80–94% volatile fatty acids. In long-term operation, biological degradation would be the major mechanism for organic carbon removal from woodwaste leachate in surface flow constructed wetlands. Sediment adsorption would affect treatment performance mainly during initial and transitional operating periods. [ABSTRACT FROM AUTHOR]

Abstract: Four surface-flow mesocosm wetlands were operated at different hydraulic retention times during two periods to treat diluted woodwaste leachate that was acidic, of very high oxygen demand, and toxic. Temperature, dissolved oxygen, and redox potential decreased with increasing water depth. However, there was no significant vertical variation in microbial biomass. No significant development in biomass of planktonic microorganisms was found over 6 weeks of initial operation. It took <1–6 weeks for maturation of the biofilm on submerged plant surfaces and the sedimentary microbial community. Mass reduction efficiencies of chemical oxygen demand, and tannin and lignin increased significantly with hydraulic retention time when 10% leachate was fed with tap water. When a more recalcitrant influent was fed, there was a slight increase of reduction efficiency with increasing hydraulic retention time. Reduction rates increased linearly with mass loading rates up to 0.4kgm−3 d−1 chemical oxygen demand and 0.13kgm−3 d−1 tannin and lignin. Precipitation and evapotranspiration had profound impacts on the overall performance and its variability. Mass balance-based operating data of wetlands with a mature microbial community are required for proper performance assessment. [Copyright &y& Elsevier]

Abstract: Percolation of rainfall through woodwaste piles leaches natural chemicals from the wood residuals that can have adverse impacts on the environment. A study was conducted on a woodwaste storage site, adjacent to the Lower Fraser River, near Mission, BC, Canada. The objective of this research was to evaluate the effectiveness of constructed wetland for treatment of this woodwaste leachate. The leachate was characterized by high oxygen demand, tannin and lignin, and volatile fatty acids (VFAs), but low pH and nutrients. Diluted leachate passed through six pilot-scale wetland cells, four planted with cattail (Typha latifolia) and two unplanted controls, with a hydraulic retention time of 7 days and an average depth of 40cm. Nutrient addition and pH adjustments were made to improve contaminant removal. Reductions in contaminants were consistently achieved, with average removals for BOD, COD, VFAs and tannin and lignin of 60, 50, 69 and 42%, respectively. Climatic conditions had an impact on the performance of the constructed wetland. Further operation of the system will help to elucidate the seasonal fluctuations. Aging of the constructed wetland system increased the treatment performance. [Copyright &y& Elsevier]