Potential of a novel facultative anaerobic denitrifying Cupriavidus sp. W12 to remove fluoride and calcium through calcium bioprecipitation.

This study focused on a novel denitrifying Cupriavidus sp. W12, which can perform microbial induced calcium precipitation (MICP) to remove fluoride (F-) under aerobic and anaerobic conditions. Under anaerobic condition, the removal ratios of F-, calcium (Ca2+), and nitrate (NO3--N) reached 87.52%, 65.03%, and 96.06%, respectively, which were higher than that under aerobic condition (50.17%, 88.21%, and 67.33%, respectively). Higher pH of 8.26 was obtained after 120 h of the strain W12 growth under anaerobic condition than that under aerobic condition (7.77). The F- removal ratio of 98.20% was predicted by the response surface methodology (RSM). Scanning electron microscopy (SEM) images of anaerobic precipitation were dense and porous. CaCO3, Ca5(PO4)3OH, Ca5(PO4)3F, and CaF2 were determined by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Self-aggregation of bacteria and adsorption of biological crystal seeds were the determinant of the precipitates formation. The results of infrared spectrometer (FTIR) and excitation-emission matrix (EEM) showed that anaerobic extracellular polymeric substances (EPS) expression led the proportion of hydroxylapatite in the precipitates increased. As the first report on the anaerobic MICP to remove F-, it provides a theoretical basis for the remediation of F-, Ca2+, and NO3--N in groundwater.