Effects of three types of amendments in woodchip-denitrifying bioreactors for tile drainage water treatment

Article no. 106054Excess nutrient inflow from tile-drained agricultural fields significantly contributes to the pollution of surface waters in Lithuania. Therefore, two parallel experiments, each using three pilot-scale woodchip-denitrifying bioreactors, were conducted for 2.5- and 1.5-year periods to test whether activated carbon (C) and flaxseed cake (both 10% v/v) and biochar (10% v/v and 20% v/v made of deciduous wood) additives, respectively, can enhance the removal of nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P) from tile drainage water and reduce C losses from bioreactors. Higher NO3-N removal efficiencies and rates were achieved in bioreactors amended with activated C (10% v/v) and biochar (20% v/v) than in those amended with woodchips alone. Bioreactors amended with 10% v/v flaxseed cake and 10% v/v biochar showed no significant differences from those amended with woodchips alone. The ability to enhance NO3-N removal by the addition of activated C and biochar was particularly evident at lower temperatures (≤10.0 °C). Moreover, activated C has proven to be an effective additive capable of substantially reducing C losses and supporting the lowest C/N (i.e., carbon loss to N removal) ratios. To a lesser extent, these capabilities were also characteristic of biochar-amended woodchips, whereas the addition of flaxseed cake resulted in the highest C/N removal ratios. These experiments also revealed that woodchips, alone or amended with flaxseed cake or activated C, are a suitable media that can allow PO4-P removal. However, the addition of biochar demonstrated large releases of PO4-P and other inorganic elements. Biochar itself was found to be a potential PO4-P source that poses a risk of large startup and over time releases.[...]Vytauto Didžiojo universitetasŽemės ūkio akademij