Treatment of Landfill Leachate by Short-Rotation Willow Coppice Plantations in a Large-Scale Experiment in Eastern Canada

Abstract

The treatment of leachate by vegetative filters composed of short-rotation willow coppice (SRWC) has been shown to be a cost-effective alternative to conventional and costly methods. However, few studies have considered the treatment capability of willow filters at a scale large enough to meet the industrial requirements of private landfill owners in North America. We report here on a field trial (0.5 ha) in which a willow plantation was irrigated with groundwater (D0) or aged leachate at two different loadings (D1 and D2, which was twice that of D1). Additionally, half of the D2-irrigated plots were amended with phosphorus (D2P). The system, which operated for 131 days, was highly efficient, causing the chemical oxygen demand concentration to drop significantly with the total removal of ammonia (seasonal average removal by a concentration of 99-100%). D2P efficacy was higher than that of D2, indicating that P increased the performance of the system. It also increased the willow biomass 2.5-fold compared to water irrigation. Leaf tissue analysis revealed significant differences in the concentrations of total nitrogen, boron, and zinc, according to the treatment applied, suggesting that the absorption capacity of willows was modified with leachate irrigation. These results indicate that the willow plantation can be effective for the treatment of landfill leachate in respect of environmental requirements.

Keywords: Salix; ammonia and nitrogen removal; landfill leachate; short rotation willow coppice.

Figure 1

Irrigation parameters in 2020. (A) Daily rainfall quantities, cumulative rainfall, and 1980–2005 climate normal; (B) A 10-day moving average reference evapotranspiration (ETo) and cumulative ETo; (C) Modeled 10-day moving average of evapotranspiration; (D) Cumulative daily irrigation volumes (m³) applied by treatment (corresponding to an irrigation area of 804 m²).

Figure 2

Root zone depletion model applied to irrigated treatments with water (D0) or leachate (D1, D2) in 2020.

Figure 3

(A,B): Ammonia (NH₄-H) and nitrate (NO₃-N) concentration (expressed in mg N kg⁻¹ of dry weight, DW) in the soil before (June) and after irrigation (October). Different letters above groupings indicate significant differences at p < 0.05.

Figure 4

Comparison of the yield measured at the end of the growing season in 2020. Different letters above box plots indicate significant differences at p < 0.05. The horizontal line inside each box-whisker represents the median, vertical small rectangles represent interquartile ranges, and circles are data-outliers.

Figure 5

Leaf parameters during the growing season in 2020. (A) Average leaf surface area expressed in cm². (B,C) Average leaf chlorophyll and carotenoids concentrations (expressed in mg g⁻¹ dry weight). Lowercase letters indicate statistical groupings (p < 0.05). The horizontal line inside each box-whisker represents the median, vertical small rectangles represent interquartile ranges, and circles are data-outliers.

Figure 6

Daily temperature 10-day average for the 2020 season and climate norm 1981–2010, and schematic diagram of the experimental setup.

Figure 7

Diagram representing the irrigation system.