The effects of aeration and the application of the k-C* model in a subsurface flow constructed wetland

Since the horizontal subsurface flow constructed wetland in Kodijarve, Estonia had problems with aeration, a vertical subsurface flow (VSSF) constructed wetland (CW) was built for the purpose of enhancing aeration. This article gives an overview of how the vertical subsurface flow constructed wetland has affected the aeration capacity and purification efficiency of the constructed wetland system in a one-year period of operation. The aeration capacity of the VSSF CW averaged 63.6 g O-2 m(-2) d(-1) during this one-year operational period, and aerobic processes occur more effectively in the system. An area of 0.5 m(2) pe(-1) is most likely too small for sufficient aeration in cold climates, and the short water residence time in the VSSF CW also can hinder nitrification. Also, an analysis of the application of the k-C* model in the horizontal subsurface flow part of the Kodijarve hybrid constructed wetland is presented for BOD, total nitrogen, ammonium and total phosphorus. The k-C* model describes processes in the HSSF CW quite well. The k values are found to be smaller than reported in the literature, mainly because of the low hydraulic loading rates. Low k values in more oxygen dependent processes, such as BOD, N-tot, and NH4-N removal, also indicate insufficient oxygen supply in the system.