Long term performance of the sand-plant-filter Schattweid (Switzerland)

The human waste concept of the Centre for Applied Ecology Schattweid. Switzerland combines treatment of feces in compost toilets and a constructed wetland for the liquid wastes, The wastewater of 5.1 population equivalents (greywater and urine) is treated in a two chambered settling tank followed by an underground vertical flow sand filter and a horizontal flow constructed wetland. The wastewater system has been in operation since 1985. Its performance has been monitored on COD. NH4-N, NO3-N. NO2-N, Total-P and Total-N almost monthly since then. and on other parameters (Total-Fe. CI) occasionally. COD elimination (91.4 %) and Total-P removal (90.6%) were stable over the years, whereas NH4-N and Total-N elimination have improved markedly from around 55% to 93.0% (NH4-N) and 80.0% (Total-N). Performance in winter was excellent. The addition of an easily degradable carbon source to the plant filter in summer 1991 led to a markedly decreased phosphorus retention and a washout of iron during the experiment.