•VLR and VRR for Fe-CAD reactor were 0.26 ± 0.01 kg-N/(m3·d) and 0.09 ± 0.03 kg-N/(m3·d).•Fe-CAD sludge was dominated by Rhodanobacter, Mizugakiibacter, and Sulfuricella.•Maximum removal rate of NO3− by Fe-CAD sludge was 4.68 mg-N/(L·gVSS·h).•Iron-encrustation caused sludge activity dropping and reactor deterioration.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/(m3·d) and 0.09 ± 0.03 kg-N/(m3·d), while the VLR and VRR of Fe2+ were 3.10 ± 0.24 kg-Fe/(m3·d) and 1.69 ± 0.26 kg-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 0.24 mg-N/(h·gVSS), 72.82 mg-N/L and 2722.97 mg-N/L, while the μmax, Ki, Ks of Fe2+ were 2.28 mg-Fe/(h·gVSS), 203.09 mg-Fe/L and 229159.38 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.Download high-res image (75KB)Download full-size image

•A novel Hanbon was established for simultaneously treating NH4+-N and NO3−-N.•High nitrogen removal rate of 9.0 ± 0.1 kgN·m−3·d−1 was achieved in Hanbon.•Potential capacity of Hanbon process to treat municipal wastewaters was achieved.•Microflora in Hanbon were revealed at both high and low nitrogen loading rate.A novel Heterotrophic Ammonia and Nitrate Bio-removal Over Nitrite (Hanbon) process, combining Short Nitrate Reduction (SNR) with Anaerobic Ammonia Oxidation (Anammox), was developed in a lab-scale continuous up-flow reactor. The substrate effects were investigated to characterize the performance of Hanbon process, and the corresponding microflora information was also revealed. Our results showed that the optimal substrate ratio of NH4+-N:NO3−-N:COD for the Hanbon process was 0.65:1:2.2. The volumetric nitrogen removal rate was up to 9.0 ± 0.1 kgN·m−3·d−1 at high influent substrate concentrations of NH4+-N 375 mg L−1, NO3−-N 750 mg L−1 and COD 1875 mg L−1, which was superior to the reported values of analogous processes. Moreover, the effluent total nitrogen concentration was able to meet the strict discharge standard (less than 10 mg L−1) at low influent substrate concentration of NH4+-N 26 mg L−1, NO3−-N 40 mg·L−1and COD 88 mg L−1. Illumina-based 16S rRNA gene sequencing results showed that Halomonas campisalis and Candidatus Kuenenia stuttgartiensis were the dominant bacteria in the SNR section and Anammox section at high substrate concentration condition. However, Halomonas campaniensis and Candidatus Brocadia brasiliensis were raised significantly at low substrate concentration condition. Hanbon process provided in the present work was flexible of treating wastewater with various nitrogen concentrations, deserving further development.

•Two innovative concepts were proposed to reveal the process characteristics.•The mechanisms of Fe(II)/P ratio and pH effects on phosphorus removal were clarified.•A function was established to predict the ferrous salt dose for phosphorus removal.•The optimal parameters of Fe(II)/P ratio and pH were obtained.Phosphorus pollution is one of the main factors causing water eutrophication. Phosphorus removal by ferrous salt is one of the common methods for phosphorus removal from wastewater. The effects of Fe(II)/P ratio and pH were investigated and new concepts of “balance reaction” and “unbalance reaction” were proposed to reveal their mechanisms. The results showed that the Fe(II)/P ratio had a significant influence on phosphorus removal by ferrous salt with optimal ratio of 2.25. A relationship between residual phosphorus concentration and total Fe(II)/P ratio was established to predict the dose of ferrous salt. pH also had a significant influence on phosphorus removal by ferrous salt with optimal range of 7.0–8.0, and it was found to be the key factor to regulate the competition between Fe3(PO4)2 precipitation and Fe(OH)2 precipitation. The process of phosphorus removal by ferrous salt was an unbalance reaction. And it was ascribed partly to the requirement for a higher residual Fe(II) concentration to get a lower concentration of residual phosphorus in the solution, and partly to the competition between Fe3(PO4)2 precipitation and Fe(OH)2 precipitation.Graphical abstract