Fig. 5 Variations of anions at different voltage compared to the initial value
Conclusions
Soil salinization is becoming a seriously global ecological and environmental problem and has drawn wide attention. In this study, the Vertical Electrokinetic system (V-EK) with multilayer electrodes considered as an “Electric Sieve” was used to mitigate and prevent the soil salinization caused by salts rising from shallow groundwater in coastal area. After the addition of direct current, the final calculated resistances of the soil column under the voltage at 4V, 10V and 20 V were 266, 487 and 1272 Ω, respectively, and showed in the order of 20 V> 10 V> 4 V. The low values of EC (67-230 μs/cm) were observed in the soil within 50 cm below the surface with the voltage at 10 V and 20 V, which was much lower than the minimum EC value (581 μs/cm) in control column. The results revealed that all the cations and anions in the surface soil with different voltage added were significantly declined compared to control column without current addition. The highest Na+ decrements (>99%) in soil column were found between -60 cm and -40 cm after V-EK treatment, which reduce the source ions that would rise to the surface. With voltage at 20 V, the lower concentration of Na+ was detected with a range of 0.06-0.08 mg/g at the surface soil compared to the control column (0.21-0.60 mg/g). Further, Ca2+ and Mg2+ in the surface soil (>-15 cm) reached the decreased percentage of 70-96% and sustained at low concentration. For V-EK tests, Cl- decreased >97% compared with control column at the voltage of 10 V and 20 V, and mainly accumulated around anode (electrode located at -80 cm). The concentrations of Cl- were detected with a range of 0.01-0.02 mg/g and 0.02-0.06 mg/g at the surface soil with the voltage at 20V and 10V respectively, while the concentrations of Cl were 0.84-2.70 mg/g in control test. Results indicated that Cl- could better mitigated and prevented by V-EK treatment test as applied voltage increase. Finally, different salts rising from shallow groundwater were effective inhibited under the application of different voltage at 10 V and 20 V, but slightly effective was observed with voltage at 4 V. Therefore, it is believed that V-EK with multilayer electrodes considered as an “Electric Sieve” could significantly inhibit and mitigate the salts rising from shallow groundwater to surface soil and reducing the soil salinity at the same time. Positive influences of this “Electric Sieve” could be obtained on the saline soil management in agriculture and in landscape works, and even in civil engineering sectors.
Acknowledgments
This work was supported by Tianjin key Scientific and Technological Project [Grant No. 18ZXSZSF00240] and the National Natural Science Foundation of China [No. 41772245]. The authors would like to acknowledge Dr. Song Jin (University of Wyoming) and Paul H. Fallgren (Advanced Environmental Technologies, LLC) for reviewing and editing the English portion of our manuscript.
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