Long-Term Effects of Sulfide on Ammonia Oxidation and Nitrite Accumulation in a Seasonally Loaded Vertical Flow Constructed Wetland

A vertical subsurface flow constructed wetland (VF wetland) treating wastewater of a touristically used lodge was studied over a period of eight years. The study aim was to investigate if the design and the operation of VF wetlands can be adjusted to the seasonal loading of recreation facilities. Compared to standard VF wetlands, the plant was designed with a lower specific surface area. The operation was divided into a high load phase during the season and a non-loaded regeneration phase after the season. A further object of the study resulted from the operation of the VF wetland. Since the wetland is located in an area with sulfate-rich drinking water, high sulfide concentrations occur in the wastewater resulting from sulfate-reducing bacteria. While the COD and BOD5 effluent concentrations always stayed within the permissible values, ammonia oxidation was incomplete for several years. The results show the different short- and long-term effects of sulfide on ammonium and nitrite oxidation and their influences on plant operations. It is concluded that nitrite oxidizers are sensitive to sulfide during short-time observations but less sensitive than ammonia-oxidizing bacteria over long periods. Furthermore, the effect of a completely inhibited nitrification on phosphorous removal was studied.