Laboratory study on potential mechanisms for treatment of woodwaste leachate in surface flow constructed wetlands

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 degrees C. 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 degrees C was 0.44 times that at 23 degrees 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.