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

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 +/- 0.01 kg-N/(m(3).d) and 0.09 +/- 0.03 kg-N/ (m(3).d), while the VLR and VRR of Fe2+ were 3.10 +/- 0.24 kg-Fe/(m(3)-d) and 1.69 +/- 0.26 kg-Fe/(m(3).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 Rhodahobacter, Mizugakiibdcter, 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 (mu(max)), the saturation concentration (K-i) and the half inhibition concentration (K-s) of NO3- to the Fe-CAD sludge were calculated as 0.24 mg-N/(h.gVSS), 72.82 mg-N/L and 2722.97 mg-N/L, while the it. mu(max), K-i K-s of Fe2+ were 2.28 mg-Fe/(h.gVSS), 203.09 mg-Fe/L and 22915938 mg-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. (C) 2016 Published by Elsevier B.V.