VEGETATION EFFECTS ON THE PERFORMANCE OF CONSTRUCTED WETLANDS TREATING DOMESCTIC WASTEWATER

The use of constructed wetlands as alternative treatment systems for domestic wastewater has experienced a drastic increase in recent years. However, the contribution of different plant species to the treatment process has not been sufficiently documented. The objective of this study was to assess the treatment efficiency of twelve-constructed wetland systems treating domestic wastewater as a function of vegetation type. The systems studied were planted with cattails, flowering plants, fescue grass, or remained unplanted. Influent and effluent samples were taken on a monthly basis and analyzed for BOD, total nitrogen, ammonium, nitrate, nitrite, inorganic phosphorus, total suspended solids, fecal coliform, and fecal streptococci. The findings suggest a > 86% removal of fecal bacteria in all systems. The vegetated systems were more efficient in treating BOD and total suspended solids than those lacking vegetation. Based on average BOD reduction estimates, the oxygen contribution by the plants in the cattail and the variety systems was up to 3-fold and 1.5-fold higher, respectively, compared to the fescue and unplanted systems. The variety and cattail systems also showed better treatment efficiency for total nitrogen than the fescue or unplanted systems, but ammonium removal was similar in vegetated and unvegetated systems. This suggests that the removal of the extra N was mostly the result of more effective filtering in unvegetated systems and nitrification/ denitrification in vegetated systems. Phosphate removal in the fescue systems appeared to be greater and more consistent than in the other systems, probably due to the presence of a thin soil layer in the upper part of the substrate. The data suggest that seasonal effects also play an important role in the overall treatment performance.