Usuwanie związków azotu z odcieków składowiskowych w pilotowej oczyszczalni hydrofitowej

Landfill leachate contains very high concentrations of ammonia nitrogen and COD. At the same time, BOD5 concentrations are quite low, which makes leachate treatment one of the most difficult and up-to-date problems of environmental engineering. In the recent years constructed wetlands are applied for landfill leachate treatment, alone or as one of treatment stages. The experiences from USA, Canada and Europe (Norway, United Kingdom, Slovenia, Sweden) show good removal efficiencies of surface flow systems (SF). Horizontal subsurface flow systems (HSSF) are less effective. At present the application of vertical flow subsurface beds (VSSF) for landfill leachate treatment is investigated. The vertical flow beds advantage are good conditions for nitrification of ammonia nitrogen. In the article the processes of nitrogen transformation and removal from landfill leachate in a pilot multi-stage constructed wetland consisting of two vertical subsurface flow beds (VSSF-1 and VSSF-2) followed by a horizontal subsurface flow bed (HSSF) were analyzed. The set-up of a pilot system was designed to treat high concentrations of ammonia nitrogen present in the leachate and to provide conditions for the sequence of nitrogen transformation processes (ammonification – nitrification – denitrification). The results from three research periods were discussed. In each period the operational conditions were changed. Different hydraulic loadings, leachate composition (with or without addition of municipal wastewater) and different operation conditions of vertical flow beds were applied. The total nitrogen removal effectiveness varied from 65 to 98%. Nitrification of ammonia nitrogen took place in the vertical flow beds, however the process was incomplete due to too high ammonia nitrogen concentrations in the raw leachate. Denitrification of nitrates in the last bed with horizontal flow of leachate was the limiting process. Quite high concentrations of nitrates were still present in the outflow from the bed. The reason for denitrification inhibition was deficiency of labile organic matter in the leachate inflowing to the HSSF bed. The conclusions for further applications were to use a hydrophyte pond instead of HSSF bed as the last stage of treatment which would increase the amount of easily decomposable organic matter form plant detritus. Also stripping of ammonia nitrogen before the inflow to constructed wetland would increase treatment effectiveness.