Impact of C/N ratio on the fate of simultaneous Ca2+ precipitation, F- removal, and denitrification in quartz sand biofilm reactor.

The coexistence of F-, Ca2+, nitrates, and other pollutants in water body has aroused widespread concern. In this research, a novel quartz sand biofilm reactor was established, aiming to study the key factors of different carbon to nitrogen (C/N) ratios (5:1, 4:1, and 3:1), initial Ca2+ concentration (180 mg L-1, 144 mg L-1, and 108 mg L-1), and hydraulic retention time (HRT) (4 h, 6 h, and 8 h) on simultaneous Ca2+ precipitation, F- removal, and denitrification. Results showed that the removal efficiencies of Ca2+, F-, and nitrate were 55.04%, 82.64%, and 97.69% under the low C/N ratio of 3:1, initial Ca2+ concentration of 180 mg L-1, and HRT of 8 h. 3-D Excitation-Emission Fluorescence Spectroscopy (3-D EEM) demonstrates that extracellular polymeric substances (EPS) was generated during the growth metabolism. Scanning Electron Microscopy (SEM) and X-ray diffractometer images showed that Ca2+, F- removed in the form of CaCO3, Ca5(PO4)3F and CaF2 under Acinetobacter sp. H12 induction. Moreover, high-throughput sequencing results display that the biomineralized bacteria Acinetobacter sp. H12 exerted great influence in the bioreactor. This research will underpin the practical use of multiple pollutants such as F- and Ca2+ wastewater under the different C/N ratios.