Water Resources Research Act Program

Details for Project ID 2020OK196B

Design of Novel Electrocoagulation Systems for Produced Water Treatment

Institute: Oklahoma
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $5,000 Total Non-Federal Funds: $10,000

Principal Investigators: Pankaj Sarin

Abstract: Problem Statement: Electrocoagulation (EC) is a simple and energy efficient method for removal of metals, colloidal solids and particles, and soluble inorganic pollutants from aqueous medium. It involves electrodissolution of sacrificial anodes (e.g. Al or Fe) and formation of hydroxo-metal products as coagulants, while producing hydrogen at the cathode. The hydoxo-species neutralize the electrostatic charges on suspended solids and oil droplets to facilitate agglomeration or coagulation, or even precipitation of certain metals and salts, and their separation from the aqueous phase. EC has been successfully used to treat several types of wastewaters (e.g. from textile industry, metal refineries, and polluted groundwater), however only in the last 5 years there has been a growing interest in its application to treat produced water (PW). The challenges associated with treatment of PW, which includes oil, suspended solids, trace metals, and very high total dissolved solids (TDS) concentrations (e.g. 220,000 pm is average TDS concentration for PW in Oklahoma), are significant. Despite of the high conductivity afforded by high TDS in PWs, a significant advantage for use of EC technology, the available EC systems are limited in treatment of PW primarily due to: (a) formation of an oxide film on the cathode, and (b) low surface area of the electrodes. Prior attempts to overcome the loss in efficiency of EC systems through the use of an AC current (instead of DC) or pulsing of electric field, had only limited success. Development of advanced electrode materials has been identified as one critical area to improve the efficiency of EC technology. Moreover, the use of EC to reduce TDS levels in PW, has not been explored. Optimizing conditions to form hydroxychloride Green Rusts (GR(Cl-), which is a layered double hydroxide of iron having intercalated Cl- ions with a general formula Fe(III)xFe(II)y (OH)3x+2y−z(Cl−)z, is particularly promising to reduce the Cl- ion concentration.Objectives: We propose to develop novel electrodes for EC that will have (a) high surface area, and (b) will allow for easy removal of the oxide layer formed on the cathode. This will be accomplished by embedding an electromagnet in the electrodes (either cathode only, or both). The surface area of the anode will be increased by magnetically attracting iron filings (or magnetic Fe-Al alloy powders) to the surface of the anode by triggering ON of the magnetic field. The cathode on the other hand will be “temporarily†coated with a dust of magnetite (Fe3O4), once again by magnetic attraction. Cleaning of the electrodes will require merely switching the magnetic field OFF and “scrubbing†the electrodes by agitation. Using these novel electrodes, the kinetics of the metal (Fe, or Fe and Al) dissolution at anode and the recovery of a pristine cathode, by removing the oxide layer, will be significantly enhanced. The second objective of the proposed work is to identify conditions to precipitate the formation of GR(Cl-) to decrease the TDS concentrations, in particular the Cl- ion.Methods: The proposed work includes four major tasks: (I) development of electromagnetic electrodes, (II) testing of several combination of developed electrodes for EC of PW using iron filings, Fe/Al alloy powders and magnetite for surface area enhancement, (III) validation of the proposed cleaning of the electrodes by demagnetizing the electrodes in the presence of a secondary magnetic field, and (IV) identifying conditions to promote formation of GR(Cl-). Different anode-cathode electrode combinations will be tested in Task II, and will include pure metal electrodes of Al and Fe for baseline, and (Fe filings)-(Fe3O4), and (Fe-Al alloy)-(Fe3O4). Task IV will involve water quality adjustments, primarily pH and dissolved oxygen concentration, and characterization of the coagulation products through X-ray diffraction, X-ray Fluorescence, and electron microscopy methods.Expected outcomes: This project promises a technological breakthrough for the EC technology, resulting in significant improvement in the efficiency of for PW treatment process. It will be applicable widely, even for waste waters, and not be limited to PW treatment. Based on literature reports, it is anticipated that EC treated PW will be suitable for reverse osmosis treatment, i.e. will have TDS concentration <1000 ppm.List of Project Personnel: (role; position; specific expertise, if applicable)1.Stephen Polkowski (Student Researcher; Graduate Student in Materials Science & Engineering)2.Pankaj Sarin (PI; Associate Professor in Materials Science and Engineering; Corrosion, Oxide materials, Materials characterization, Water treatment)