Anaerobic ammonium oxidation in the old trickling filters at Daspoort Wastewater Treatment Works

Abstract

The century-old trickling filters at the Daspoort Wastewater Treatment Works in Pretoria (Gauteng, South Africa) are known for their remarkable removal of nitrogen from municipal wastewater. Our study was conducted to identify the microbiological processes responsible for this phenomenon and to establish whether anammox bacteria may be involved. An aerobic and anaerobic bench top reactor, both inoculated with biofilm-covered stones from one of the filters, were spiked with ammonia-nitrogen (NH 4+-N) and nitrite-nitrogen (NO 2−-N). These reactors were subsequently monitored by conducting stoichiometric analyses of chemical oxygen demand (COD), NH 4+-N, NO2−-N, and nitrate-nitrogen (NO 3−-N). In the aerobic reactor, the COD concentration decreased over the 56 h batch reaction period and nitrification was revealed by a decrease in NH 4+-N and NO2−-N concentrations. However, the NO 3−-N concentration showed no notable decrease. In contrast, in the anaerobic reactor the concentrations of COD, NH 4+-N, NO2ˉ-N, NO3ˉ-N, as well as total nitrogen decreased during the batch reaction period.

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