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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]

Heterotrophic activities were investigated by measuring ³Hleucine incorporation to bacterial protein and 14C-glucose turnover in surface flow constructed wetlands receiving woodwaste leachate. No significant longitudinal variation was found in heterotrophic activities of bacterioplankton. An open wetland, a vegetated wetland, and a fertilized vegetated wetland were used to examine the effects of vegetation and ammonium nitrate amendment. There was not a significant difference in treatment performance among the three wetlands, except for a significant pH increase and more efficient volatile fatty acids removal in the fertilized wetland. The fertilized wetland had the highest leucine incorporation rate and shortest glucose turnover time accompanied by file lowest glucose mineralization percentage, followed by the open wetland, then the vegetated wetland. Planktonic and sedimentary bacteria contributed to the majority or the total heterotrophic activities; epiphytic bacteria played a minor role. Heterotrophic activities were influenced by the availability of nutrient, electron acceptor, and organic substrate. Water Environ. Res., 78, 671 (2066). [ABSTRACT FROM AUTHOR]

Woodwaste leachate is usually acidic, of high oxygen demand, and toxic. To prevent potential adverse impacts of the raw leachate on heterotrophic bacteria and aquatic plants, woodwaste leachate was diluted before discharge to constructed wetlands. This study compared treatment performance among four vegetated surface flow mesocosm wetlands fed with different dilutions of woodwaste leachate over a period of 12 weeks. During another period of 13 weeks, the effluent of a vegetated wetland fed with the raw leachate was further treated in a vegetated wetland and an open wetland. The highest reduction rates for chemical oxygen demand as well as tannin and lignin were achieved in the wetland fed with the raw leachate. The most diluted (6x) woodwaste leachate yielded the lowest reduction rates and highest reduction efficiencies. Up to 47 mg L-1 volatile fatty acids in influent were depleted through wetlands with a hydraulic retention time of 13 d. Vegetation made insignificant performance differences for treatment of woodwaste leachate. Chemical oxygen demand as well as tannin and lignin were further removed through the wetlands in series, though at lower reduction rates. Wetland performance for treatment of woodwaste leachate was likely regulated by dissolved oxygen concentration and availability of bacterial substrates. [ABSTRACT FROM AUTHOR]

Leachate was generated when precipitation percolated through a pile of woodwaste, including trimmings, off-specification wood chips, shredded bark and roots, and sawdust from several cedar processing mills. The "young" woodwaste leachate produced in the pile's placement period was amber, acidic (pH 3.4-3.7), nutrient-poor (inorganic nitrogen 1.4-3.2 mg L-1, orthophosphate 3.3-4.3 mg P L-1), of very high oxygen demand (chemical oxygen demand 12,559-14,254 mg L-1, tannin and lignin 3066-5150 mg L-1 as tannic acid, volatile fatty acids 1564-2132 mg L-1), and very toxic to aquatic life (96-h median lethal concentration of 0.74% leachate). The leachate at 1.5 years old in the closure period had lower oxygen demand and higher ammonia, and became less acidic and darker. The leachate had a 5-day biochemical oxygen demand to chemical oxygen demand ratio of 0.33 in the placement period and 0.14 in the late closure period. Volatile fatty acids accounted for 6 to 34% chemical oxygen demand, varying as the pile developed and with woodwaste age. Tannin and lignin accounted for 33 to 45% chemical oxygen demand. More than 98% contaminants were in dissolved form. The monthly variation of leachate quality was likely a result of both temperature and precipitation. pH was significantly correlated to chemical oxygen demand, tannin and lignin, and volatile fatty acids. [ABSTRACT FROM AUTHOR]

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]