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| Effects and mechanism of different calcium sources on the fixation of Pb2+ by urease-producing bacteria in water |
| Received:September 25, 2024 |
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| KeyWord:microbially induced carbonate precipitation;chemical calcium sources;waste calcium sources;Pb2+fixation |
| Author Name | Affiliation | E-mail | | WANG Jinping | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | SUN Chong | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | ZHOU Yuxin | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | HU Dongcheng | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | LIAO Gui | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | LIN Panyuhan | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | CAI Qian | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | ZHENG Dezhi | Sichuan Solid Waste and Chemical Management Center, Chengdu 610032, China | | | WU Jun | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | | | XU Min | College of Environmental Science, Sichuan Agricultural University, Chengdu 611130, China | xumin_xyz@126.com |
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| Abstract: |
| To investigate the effect of different calcium sources on the fixation of Pb2+ by microbially induced carbonate precipitation （MICP）, a strain of urease-producing bacterium NT32 was selected, then analyzed the impact of different calcium sources, including chemical sources（i.e., calcium chloride, calcium acetate, calcium oxide）and waste sources（i.e., egg shells, oyster shells, clam shells）, on the strain′ s capacity to immobilize Pb2+ in aqueous solutions by means of culture tests. Furthermore, the study utilized scanning electron microscopye-energy dispersive spectrometer（SEM-EDS）, X-ray diffraction（XRD）, and Fourier transform infrared spectroscopy（FTIR）to elucidate the mechanisms underpinning the immobilization process. Results indicated optimal growth of the strains within a pH range of 6-9, showcasing their capacity to thrive even at a Pb2+ concentration of 1 000 mg·L-1, implying high tolerance to Pb. It was found that the Pb2+ fixation rate by strain NT32 was low（27.05%）with no-calcium treatment, and the Pb2+ fixation rate was increased by 99.60%, 50.15%, and 87.56% after the additions of calcium chloride, calcium acetate, and calcium oxide. When calcium chloride was added at ratio f 1%（m/V）, the Pb2+ fixation rate（99.60%）and the urease activity（53.1 U · mL-1）were significantly better than other treatments. However, the waste calcium source treatments had less effect in Pb2+ fixation, and the highest Pb2+ fixation rate was observed at 0.5%-clam shell treatment（41.58%）. Characterization findings revealed distinct crystal morphologies of CaCO3 with varying calcium sources. Specifically, calcium chloride predominantly yielded thermodynamically stable calcite, while calcium oxide produce aragonite and calcite, while calcium acetate addition produced aragonite, respectively. Additionally, hydroxyl, carbonyl, carboxyl, and carbonic acid functional groups jointly contribute to Pb2+ fixation, with all treatments yielding carbonate compounds, thereby highlighting the critical role of carbonate precipitation in Pb2+ fixation. In summary, the addition of exogenous calcium can significantly improve the fixation of Pb2+ via urease-producing bacteria, and the chemical calcium source is superior to the waste calcium source. |
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