The effectiveness of pollutant removal from municipal wastewater in vertical flow constructed wetlands

The efficiency of pollution removal from municipal sewage in two vertical flow constructed wetlands consisting of gravel filters with surface area 4 x 5 m, depth 60 cm, covered by reedwas evaluated over a period of two years. The flow of wastewater was about 50 mm per day.Wastewater underwent only mechanical treatment before reed bed B, but reed bed A wassupplied with wastewater after biological treatment with activated sludge. Sewage wassampled before and after filtration every IO days. Measurements were made of sewage supplyand discharge, precipitation and wastewater temperatures. The main indicator of efficiencywas the elimination of suspended solids, carbon, nitrogen and phosphorus from thewastewater during filtration. The elimination of the pollution load was 2-25 g per squaremeter per day for the BOD5 and 0--3.5 g per square meter per day for total nitrogen. Rates ofpollution removal were between 2 and 4 times as high in bed Bas in bed A. The rate ofBOD5 removal and the coefficient k for BOD5 were strongly dependent on temperature for reed bedB; less so far for bed A. The difference between summer and winter indicates that the surfacearea of constructed wetland B should be 3 times bigger during winter to obtain the summerrate ofBOD5 pollution removal in the climatic conditions ofNorth Poland (54a° N).