Highly efficient nitrate and phosphorus removal and adsorption of tetracycline by precipitation in a chitosan/polyvinyl alcohol immobilized bioreactor.

Single denitrification using bacteria has been widely investigated, but few studies have focused on the simultaneous removal of nitrate, phosphorus. and tetracycline. Strain L2, an iron-reducing bacteria, was immobilized using chitosan/polyvinyl alcohol to simultaneously remove nitrate and phosphorus. The effects of carbon/nitrogen ratio (1:1, 1.5:1, and 2:1), initial Fe2+ concentration (0, 15, and 30 mg·L-1), and HRT (2, 4, and 6 h) were assessed in bioreactors and optimum conditions were established. Results showed that the nitrate and phosphorus removal efficiency reached 100.00% (2.697 mg·L-1·h-1) and 81.93% (1.533 mg·L-1·h-1) under the conditions of carbon/nitrogen of 2:1, Fe2+ concentration of 30 mg·L-1 and HRT of 6 h. The precipitation of bioreactor, which identified as FeOOH by XRD, had significant adsorption on tetracycline. The results of high-throughput sequencing indicated that strain L2 played a significant role in denitrification. This bioreactor provided effective method for the treatment of polluted water contaminated by nitrate, phosphorus, and tetracycline.

The performance and mechanism of simultaneous removal of fluoride, calcium, and nitrate by calcium precipitating strain Acinetobacter sp. H12.

A calcium precipitating and denitrifying bacterium H12 was used to investigate the F- removal performance and mechanism. The results showed that the strain H12 reduced 85.24% (0.036 mg·L-1·h-1) of F-, 62.43% (0.94 mg·L-1·h-1) of Ca2+, and approximately 100% of NO3- over 120 h in continuous determination experiments. The response surface methodology analysis demonstrated that the maximum removal efficiency of F- was 88.98% (0.062 mg·L-1·h-1) within 72 h under the following conditions: the initial Ca2+ concentration of 250.00 mg·L-1, pH of 7.50, and the initial C4H4Na2O4·6H2O concentration of 800.00 mg·L-1. The scanning electron microscopy images, the X-ray photoelectron spectroscopy, and X-ray diffraction results suggested the following removal mechanism of F-: (1) the bacteria, as the nucleation site, were encapsulated by bioprecipitation to form biological crystal seeds; (2) Biological crystal seeds adsorbed F- to form Ca5(PO4)3F and CaF2; (3) Under the induction of bacteria, calcium, fluoride and phosphate coprecipitated to form Ca5(PO4)3F and CaF2. In addition, the gas chromatography data indicated that F- had little or no effect on the gas composition during denitrification, and the fluorescence spectroscopy analysis also proved that the extracellular polymeric substance (protein) is the site of bioprecipitation nucleation.