| Nowadays, the problem of drinking water in China is serious and widespread, the high-fluorine water seriously influence people’s daily life and poses a great threat to people’s health. So it is absolutely essential to control the fluoride amount to the safe limitation. Currently, nanofiltration (NF) technology is widely used for the production of drinking water, which significantly provides more opportunities and higher possibilities than the other defluorination methods, such as precipitation method, adsorption method and membrane technology. The development of nanofiltration membrane was quickly all over the world. But the application research of domestic nanofiltration membrane was very few. So the performance of domestic NF membranes for desalting high-fluorine water was studied. This research will provide technical references to the practical application of domestic NF membranes in the treatment of high-fluorine water, and promote and improve the development of domestic NF membranes. The contents and results of this research mainly included three parts.(1) Basic studies on the performance of domestic nanofiltration membranes for desalting high-fluorine water:The performances of three domestic NF membranes (NF1, NF2 and NF3) for defluorinating high-fluorine water were studied and compared. And the influences of pressure, temperature and pH were studied by a pilot unit test. Then the optimum condition was identified as followings:Pressure 1.0-1.5 MPa, Temperature 15-20 ℃, pH=7.0. Under this condition, the desalination rate, the defhiorination rate and the water flux of NF1 membrane was 48%,53% and 61 L/(m2h), while that of the NF2 membrane was 71%,90% and 43 L/(m2h), and that of the NF3 membrane was 65%,73%, and 61 L/(m2h), respectively. And the Zeta potential of the two NF membranes was detected, the Zeta potential of NF2 and NF3 was-22 and-18 mV.(2) Laboratory research on the performance of domestic nanofiltration membranes for desalting high-fluorine/arsenic water:The performances of NF2 module were studied under the optimum condition. The fluoride concentration, arsenic concentration and total dissolved solids were studied by a lab setup. And as a result of the increasing of fluoride concentration, arsenic concentration and TDS, the desalination rate decreased. According to the research, the permeate water of this NF system could meet the standard, when the initial water under the conditions of CF-< 7.5 mg/L, Cas< 1.25 mg/L, TDS< 2.5 g/L. Meanwhile, the results of long-term operation (72h) showed that the permeability of the membrane remained stable.(3) Studies of nature diatomite as a pretreatment technology for defluorination by domestic nanofiltration:As previous study, domestic nanofiltration is an effective technology for fluoride rejection in drinking water. However, high fluoride concentration severely influences the quality of its product water. Herein, we chose nature diatomite to adsorb fluoride prior to nanofiltration process. The characterization of diatomite was investigated by SEM and XRD and the feasibility was investigated by XPS and FT-IR. The influences of adsorbent dosage, pH, ionic strength and anions were studied by batches of adsorption experiments. And the presence of HA enhanced the adsorption of fluoride at pH<5 while reduced fluoride adsorption at pH>5. The adsorption process fitted the Langmuir isotherm and the adsorption kinetics followed the pseudo-second-order rate equation. In addition, the combination of adsorption process and NF treatment was studied, which confirmed that the nature diatomite can ensure the permeate water of the NF system to meet the standard. Results of this study demonstrated that the nature diatomite is viable and effective to be used as the pretreatment adsorbent for NF system to defluorinate high fluoride water. |
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