DISTRIBUTION OF NITROGEN AND PHOSPHORUS COMPOUNDS IN FILTER MEDIA OF CONSTRUCTED WETLAND

The objective of the present studies is to estimate a distribution of nitrogen and phosphorus compounds in filter media of horizontal filters. The studies were carried out in 2009 within two wastewater treatment facilities of horizontal flow in Lithuania. From both treatment facilities sand samples of different depth and separate profiles in the direction of water flow were taken. These samples were used to determine sandmoisture and concentration of N-NO3, N-NH4 and total P. The measurements of sand moisture showed that the filtration of wastewater through the sand is in process only in the lower layer of sand filter and near the distribution pipe. Moisture regime in the sand influences the composition of nitrogenous compounds in it. In the part of the filter, where sand's moisture is lowest, nitrate concentration is highest. Ammonia concentrations are completely opposite. In the lower part of the filter anaerobic conditions are dominant and nitrification processes stop. Analysis of phosphorus concentrations in filter's sand showed similar tendencies as nitrogen analysis. In the upper part of the sand phosphorus concentration turns out to be 2-3 times lower than in the lower part of the sand. In the filters of horizontal flow, part of the sand contributes little or does not contribute to the wastewater treatment process at all; therefore, it is advisable to use wastewater recirculation for the improvement of nitrogen and phosphorus removal. For that purpose in the part of the filter not included in the treatment process the filter of vertical flow could be arranged.