Treating a lignite pyrolysis wastewater in a constructed subsurface flow wetland

In a pilot-scale, subsurface-flow constructed wetland, treatment experiments were carried out on lignite pyrolysis wastewater which had been stored for a long time in an effluent pond in order to evaluate the removal efficiencies of NH4+-nitrogen and organic components of a large molecular size. The specific wetland conditions (horizontal flow, long hydraulic retention time) encourage both nitrification and denitrification in the same “reactor system” simultaneously. Nitrogen was removed for the entire duration of the experiment. No significant amounts of nitrite were formed. The average efficiency of nitrogen removal corresponded to that of wetland systems used for domestic wastewater treatment cited in the literature. The pilot plant acts like a filter with a limited filtration capacity for low molecular (<1 kDa) and especially large (>0.3 μm) organic components. Consequently, the decolorisation of the water and the removal of the total organics decreased over time. Nevertheless, the decolorisation and the removal of the DOC proportions of organics within the size range of 1 kDa to 0.3 μm increased. Calculations show that it ought to be feasible to use a constructed wetland system as part of a complex remediation programme to improve overall water quality and in particular to remove large amounts of NH4+ nitrogen.