The Development of Energy Efficient Wastewater Treatment: Electrochemical Oxidation and PFACs liquid-liquid Extraction

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Zhang, Kaihang
Crittenden, John C.
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EAOPs are new, and environmental-friendly techniques that can oxidize organic compounds by direct oxidation and indirect oxidation (hydroxyl radical HO•) on the anode. The benefits of EAOPs are: 1) They are driven by electric power. The stoichiometric connection between power consumption and pollutant removal in EAOP is almost linear. Therefore, they are ease of control. 2) they can generate hydroxyl radical HO• without any chemical additive. However, EAOPs also face several problems for industrial applications. 1) Since the reaction mostly happens on the electrode surface, the mass transfer is the limiting factor in electric efficiency. 2) High operation potential is required for hydroxyl radical generation leading to high energy costs. 3) EAOPs did not have selectivity in terms of the organic compounds. For the third problem, we developed Liquid-liquid extraction to extract and separate specific refractory degradable: PFACs. To improve the EAOPs' energy efficiency, The EAOPs system was optimized at three levels: 1) System level: energy recovery system, and electric power mode; 2) Reactor level: flow-through wire mesh anode 3) Electrode level: electrode material modification. To be specific, a novel EAOP-fuel cell energy recovery system is proposed, and the system performance in varied conditions are summarized. A flow-through multiple layer wire mesh anode reactor is developed for improved mass transfer and PFACs treatment. The Mn2O3-TiO2 NTAs porous anode is developed for optimized electrode conductivity. The anode is tested by both electrochemical oxidation experiments and advanced characterization methods. A pulse potential instead of DC power is used to drive the EAOPs reaction to investigate the frequency and potential amplitude effect on the oxidation. In terms of liquid-liquid extraction, Ionic liquids were used as an extractant for liquid-liquid extraction of PFOA removal from the aqueous phase. The optimized extraction condition is investigated. COSMO-RS, a quantum chemistry-based equilibrium thermodynamics method, is used to screen the ILs for high extraction efficiency. In conclusion, the mass transfer is improved by using the porous anode and multiple-layer wire mesh anodes structure. The mass transfer impact on the overall oxidation is evaluated through the limiting current density analysis. Using the cathodic hydrogen gas for energy recovery reduces the high operation power caused by the operation voltage. The liquid-liquid extraction has the capability of PFACs extraction. In the future, it could be combined with PFACs degradation methods
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