Electric Field-Assisted Nanofiltration for PFOA Removal with Exceptional Flux, Selectivity, and Destruction.

Per- and polyfluoroalkyl substances (PFAS) pose significant environmental and human health risks and thus require solutions for their removal and destruction. However, PFAS cannot be destroyed by widely used removal processes like nanofiltration (NF). A few scarcely implemented advanced oxidation processes can degrade PFAS. In this study, we apply an electric field to a membrane system by placing a nanofiltration membrane between reactive electrodes in a crossflow configuration. The performance of perfluorooctanoic acid (PFOA) rejection, water flux, and energy consumption were evaluated. The reactive and robust SnO2-Sb porous anode was created via a sintering and sol-gel process. The characterization and analysis techniques included field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ion chromatography, mass spectroscopy, porosimeter, and pH meter. The PFOA rejection increased from 45% (0 V) to 97% (30 V) when the electric field and filtration were in the same direction, while rejection capabilities worsened in opposite directions. With saline solutions (1 mM Na2SO4) present, the induced electro-oxidation process could effectively mineralize PFOA, although this led to unstable removal and water fluxes. The design achieved an exceptional performance in the nonsaline feed of 97% PFOA rejection and water flux of 68.4 L/m2 hr while requiring only 7.31 × 10-5 kWh/m3/order of electrical energy. The approach's success is attributed to the proximity of the electrodes and membrane, which causes a stronger electric field, weakened concentration polarization, and reduced mass transfer distances of PFOA near the membrane. The proposed electric field-assisted nanofiltration design provides a practical membrane separation method for PFAS removal from water.

Efficient electrocatalysis for denitrification by using TiO2 nanotube arrays cathode and adding chloride ions.

Electrocatalysis is emerging as a promising alternative to bacterial denitrification for removing nitrate and ammonia from sewage. The technology is highly efficient and robust in actual wastewater treatment scenarios; however, there may be the generation of harmful intermediates (such as nitrite) on the traditional cathode material. In this study, we demonstrated that TiO2 nanotube arrays can be used as an effective cathode to reduce nitrate to ammonia without generation of nitrite. Alongside this, the addition of chloride ions in the solution can further oxidize ammonia to N2. We looked into the key factors influencing the electrocatalytic denitrification, including the current density (2-10 mA/cm2), initial pH values (3-11), and types of anions (HCO3-, Cl-, SO42-). The results showed that 90.8% of nitrate and 59.4% of total nitrogen could be removed in 1.5 h under optimal conditions, with degradation kinetic constants of 1.61 h-1 and 0.79 h-1, respectively. Furthermore, we investigated the formation of intermediate products and explored the electrocatalytic denitrification mechanism: (a) the surface oxygen vacancies and high specific surface area of TiO2 nanotube arrays electrode promote the reduction of nitrate to ammonia and N2; (b) the active chlorine generated at the anode surface can effectively oxidize ammonium to N2.

Enhanced perfluorooctanoic acid degradation by electrochemical activation of peroxymonosulfate in aqueous solution.

Perfluorooctanoic acid (PFOA) was efficiently decomposed at Ti/SnO2-Sb anode via peroxymonosulfate (PMS) activation. PFOA degradation followed both pseudo-zero-order (0-30 min) and pseudo-first-order (30-120 min) kinetics. The pseudo-first-order kinetics constant could increase to 0.0484 min-1 (3.84 times higher than that without PMS) during 30-120 min electrolysis. The inhibited performance in radical scavengers implied both sulfate radical (SO4•-) and hydroxyl radical (•OH) contributed to PFOA degradation. The •OH quantitative detection experiments demonstrated that SO4•- formed from PMS activation could promote •OH generation (from 0.12 mM to 0.24 mM). Electron spin resonance (ESR) tests further proved that SO4•- and •OH were generated during PFOA degradation. According to linear sweep voltammetry (LSV) analyses, the oxygen evolution potential (OEP) value of Ti/SnO2-Sb electrode increased from 1.59 V to 1.72 V (vs SCE) via PMS addition, indicating the inhibited oxygen evolution which was beneficial for the reactive species formation (i.e. •OH, SO4•-). On the basis of intermediates verification and mass balance of carbon and fluorine, PFOA was proposed to be oxidized into short-chain perfluorocarboxylic acids mainly by •OH and SO4•-.

Insights into electrochemical decomposition mechanism of lipopolysaccharide using TiO2 nanotubes arrays electrode.

Electrochemical decomposition of lipopolysaccharide (LPS) was firstly investigated over titania nanotubes (TNTs) arrays electrode. The TNTs layer of this electrode consisted of numerous tubular structures which arranged tightly, and the average diameter of each nanotube is 100 ±â€¯5 nm. The degradation of LPS and polysaccharides followed pseudo-first-order kinetics. The optimal LPS removal ratio was nearly 80 %. The endotoxin toxicity of LPS steadily decreased during the electrolysis process. The acute toxicity of the intermediates increased suddenly at the beginning of electrochemical degradation process (< 5 min), then maintained high inhibition ratio (> 95 %) for about 150 min, and decreased significantly (< 10 %) after electrolysis for 240 min. After 20 min of electrolysis, LPS with molecular weight of 116,854 Da was transformed into small molecular compounds with molecular weights of 59,312 - 12,209 Da. Possible degradation and detoxification mechanisms of LPS including electric-field-force-driving accumulation, adsorption and direct electron transfer on TNTs arrays electrode, and •OH oxidation were proposed. This study underscores that electrochemical technique can be applied to eliminate and decrease the toxicity of LPS from contaminated water.