Efficient Total Nitrogen Removal in an Ammonia Gas Biofilter through High-Rate OLAND

Ammonia gas is conventionally treated in nitrifying biofilters; however, addition of organic carbon to perform post-denitrification is required to obtain total nitrogen removal. Oxygen-limited autotrophic nitrification/denitrification (OLAND), applied in full-scale for wastewater treatment, can offer a cost-effective alternative for gas treatment. In this study, the OLAND application thus was broadened toward ammonia loaded gaseous streams. A down flow, oxygen-saturated biofilter (height of 1.5 m; diameter of 0.11 m) was fed with an ammonia gas stream (248 +/- 10 ppmv) at a loading rate of 0.86 +/- 0.04 kg N m(-3) biofilter d(-1) and an empty bed residence time of 14 s. After 45 days of operation a stable nitrogen removal rate of 0.67 +/- 0.06 kg N m(-3) biofilter d(-1), an ammonia removal efficiency of 99%, a removal of 75-80% of the total nitrogen, and negligible NO/N2O productions were obtained at water flow rates of 1.3 +/- 0.4 m(3) m(-2) biofilter section d(-1). Profile measurements revealed that 91% of the total nitrogen activity was taking place in the top 36% of the filter. This study demonstrated for the first time highly effective and sustainable autotrophic ammonia removal in a gas biofilter and therefore shows the appealing potential of the OLAND process to treat streams.