Chemoautotrophic denitrification based on ferrous iron oxidation: Reactor performance and sludge characteristics

Abstract

Aiming at treatment of wastewaters with low C/N ratio, a novel ferrous iron-based chemoautotrophic denitrification (Fe-CAD) reactor was developed with inoculum sludge from a municipal sewage plant in Hangzhou, China. The efficiency of the Fe-CAD reactor was remarkable. The volumetric loading rate (VLR) and volumetric removal rate (VRR) of NO3− were 0.26±0.01kg-N/(m3·d) and 0.09±0.03kg-N/(m3·d), while the VLR and VRR of Fe2+ were 3.10±0.24kg-Fe/(m3·d) and 1.69±0.26kg-Fe/(m3·d), respectively. By means of next generation sequencing, the Fe-CAD sludge was found to be rich in ferrous iron-oxidizing nitrate-reducing bacteria including Rhodanobacter, Mizugakiibacter, Sulfuricella, Comamonas and Gallionella. Reaction dynamics of the Fe-CAD sludge were determined by batch experiments. After fitted by Haldane Model, the maximum specific activity (μmax), the saturation concentration (Ki) and the half inhibition concentration (Ks) of NO3− to the Fe-CAD sludge were calculated as 0.24mg-N/(h·gVSS), 72.82mg-N/L and 2722.97mg-N/L, while the μmax, Ki, Ks of Fe2+ were 2.28mg-Fe/(h·gVSS), 203.09mg-Fe/L and 229159.38mg-Fe/L, respectively. The produced ferric iron formed an brilliant yellow iron-encrustation with irregular shape around the functional microorganisms, and the iron-encrustation resulted in a dropped specific activity of the Fe-CAD sludge. Removal or prevention of the iron-encrustation around microbial cells were suggested to be the key to improve the performance of the Fe-CAD reactor.