Magnetic and electric field accelerate Phytoextraction of copper Lemna minor duckweed

Abstract

In accordance with the opinion of the World Health Organization and the World Water Council the development of effective technologies for the treatment of wastewater from heavy metals for their discharge into water bodies or reuse is an urgent task nowadays. Phytoremediation biotechnologies is the most environmentally friendly and cheapest way of the treatment of wastewater, suitable for sustainable development principals. The main disadvantage of the phytoremediation is the slow speed of the process. A method for accelerating the process of phytoremediation by the combined effect of magnetic and weak electric fields is proposed. The purpose of this study is to determine the values of the parameters of the magnetic and weak electric fields that are most suitable for extracting cuprum ions from wastewater using the higher aqua plants (Lemna minor). A corresponding technological process based on the results of the study is proposed. The results have shown that the removal of copper cations from sulfate solutions effectively occurs in the initial period of time (1-5 hours) under the influence of a magnetic field with an intensity of H = 2 kA/m. Under the combined influence of an electrical current with density j = 240 μA/cm2 and a magnetic field (H = 2 kA/m) the highest rate of copper extraction by duckweed leaves is achieved. Under these conditions, the greatest growth and development of plant leaves occurs. The paper presents the results of determining of the parameters of the electrochemical release from the eluate of the spent phytomass of duckweed. It has been determined that the release of metal occurs at E = 0.32 V. An original scheme for wastewater treatment from copper with subsequent separation of copper from the spent phytomass of duckweed is proposed. In general, the presented results are a scientific justification of wastewater treatment technologies and a contribution to resolving the crisis in the field of fresh water supply. An important contribution in the circular economy is a technology recommendation proposed for recovering copper from duckweed after wastewater treatment.

Fig 1. Scheme of the environment for experiments.

1 –a constant current source; 2 –magnetic coil; 3 –nickel-cadmium batteries; 4 –a resistance store; 5 –a voltammeter; 6 –an aluminum electrode; 7 –duckweed; 8 –a graphite electrode.

Fig 2. Three-electrode cell with separated Schott filters with cathode and anode spaces.

ae–auxiliary, we–working, nscc–normal reference electrodes with silver chloride.

Fig 3. Comparative results on the effect of MF of different strengths on the process of the copper extraction by Lemna minor duckweed.

t–time (h), Ci is initial concentration Cu²⁺ mg/L = 1 mg/L, C_f Cu2 + is concentration of Cu²⁺, mg/L.

Fig 4. Photo of Lemna minor duckweed in natural conditions.

Fig 5. Photo of Lemna minor duckweed aged for 10 days in a solution of CuSO₄ with concentration C_i = 1 mg/L when influenced to MF H = 4 kA/m.

Fig 6. Microstructural of duckweed leaves Lemna minor without influence in natural condition.

Fig 7. Microstructural of duckweed leaves Lemna minor with the combined influence of a magnetic field and an electric field in the CuSO₄ solution.

Fig 8. Potentiostatic curves obtained when copper was isolated from the eluate of the spent phytomass of Lemna minor duckweed at E = 0.32 V.

The duckweed was previously placed into a copper sulfate solution with Cu²⁺ (Ci = 1 mg/L) under the influence of MF = 2 kA/m, at various current densities j, μA/cm².

Fig 9. Schematic diagram of the phytoremediation of metals from WW.

1 –a WW averager; 2 –a pump for pumping averaged water into a biopond; 3 –a biopond populated by higher aquatic vegetation; 4 –a mesh pan for collecting and holding Lemna minor duckweed during the discharge of purified water; 5 –an installation of a constant magnetic field (can be combined with weak electric fields.); 6 –an equipment for monitoring the residual content of copper cations in solution; 7 –a pump for pumping purified water; 8 –lifting the waste mass by a pallet; 9 –bath for the preparation of the eluate; 10 –a dispenser of sulfuric acid; 11 –a metal electrolysis bath; 12 –a capacity for the collection of neutralized phytomass and its disposal.