Removal mechanism of persistent organic pollutants by Fe-C micro-electrolysis

The degradation of persistent organic pollutants (POPs) in the simulated wastewaters was investigated by Fe-C micro-electrolysis system. With phenanthrene (PHE) and 2,4-dichlorophenol (2,4-DCP) as target pollutants, different iron-carbon (Fe-C) micro-electrolysis systems have been established. The effects of initial pH, Fe/C mass ratio, and intake air flow on the degradation and mineralization of PHE and 2,4-DCP were studied. At the initial pH of 5.0, Fe/C of 1.5:1, and an aeration flow rate of 1.5 L/min, after 120 min of reaction, the removal efficiency of FHE and COD was 94.3% and 73%, respectively. Under the conditions of initial pH is 3.0, Fe/C is 1:2, aeration flow rate of 1.5 L/min, and reaction time of 90 min, the best removal efficiency of 2,4-DCP can be obtained in the Fe-C micro-electrolysis system as 97% and COD removal efficiency can reach 76%. The results of kinetic studies show that the Fe-C micro-electrolysis process of PHE and 2,4-DCP follows pseudo-first-order kinetics. Commercial activated carbon (AC) was used for comparison under the same condition. The results indicated that the removal rate of organic pollutants and chemical oxygen demand (COD) of Fe-C micro-electrolysis were superior to that of AC. Analyze the structure of iron after reaction by SEM and XRD. The degradation pathway and mechanism for PHE and 2,4-DCP were proposed based on LC-MS analyses of treated wastewater.

Enhancement of Fe-C micro-electrolysis in water by magnetic field: Mechanism, influential factors and application effectiveness

Fe-C micro-electrolysis system has been widely used in filters, or as an advanced treatment process in some water treatment plants to treat various wastewater. In this study, Fe-C micro-electrolysis process was enhanced by an economical and environmentally friendly method, applied magnetic field. Batch kinetic experiments and scanning electron micrographs demonstrated a more effective micro-electrolysis and more severely corroded on the surface of Fe-C after applying a magnetic field at pH 3.0. An applied magnetic field reduced the charge-transfer resistance and increased the current density in micro-electrolysis system and Fe-C became more prone to electrochemical corrosion. Corrosion products were proved to be Fe²⁺, Fe₃O₄, and C-O, moreover, the formation of them were also increased in the presence of a magnetic field. Base on that, some influential factors like magnetic field flux intensity, Fe-C particle size, pH, Fe-C dosage and its reusability were investigated in this paper. Since Fe²⁺ release was accelerated in micro-electrolysis system by an applied magnetic field, combination of various advanced oxidation processes were designed to explore the application effectiveness of the system. The degradation rate of target contaminant was significantly improved in the presence of a magnetic field, suggesting it could be a reliable method for wastewater treatment.

Effects of different scrap iron as anode in Fe-C micro-electrolysis system for textile wastewater degradation

The degradation of organic contaminants in actual textile wastewater was carried out by iron carbon (Fe-C) micro-electrolysis. Different Fe-C micro-electrolysis systems (SIPA and SISA) were established by using scrap iron particle (SIP) and scrap iron shaving (SIS) as anode materials. The optimal condition of both systems was obtained at the initial pH of 3.0, dosage of 30 g/L and Fe/C mass ratio of 1:1. Commercial spherical Fe-C micro-electrolysis material (SFC) was used for comparison under the same condition. The results indicated that total organic carbon (TOC) and chroma removal efficiencies of SIPA and SISA were superior to that of SFC. Total iron concentration in solution and XRD analysis of electrode materials revealed that the former showed relatively high iron corrosion intensity and the physicochemical properties of scrap iron indeed affected the treatment capability. The UV-vis and 3DEEM analysis suggested that the pollutants degradation was mainly attributed to the combination of reduction and oxidation. Furthermore, the potential degradation pathways of actual textile wastewater were illustrated through the GC-MS analysis. Massive dyes, aliphatic acids, and textile auxiliaries were effectively degraded, and the SIPA and SISA exhibited higher performance on the degradation of benzene ring and dechlorination than that by SFC. In addition, SIPA and SISA exhibited high stability and excellent reusability at low cost. Graphical abstract.

Enhanced anaerobic degradation of Fischer-Tropsch wastewater by integrated UASB system with Fe-C micro-electrolysis assisted

Coupling of the Fe-C micro-electrolysis (IC-ME) into the up-flow anaerobic sludge blanket (UASB) was developed for enhanced Fischer-Tropsch wastewater treatment. The COD removal efficiency and methane production in R₃ with IC-ME assisted both reached up to 80.6 ± 1.7% and 1.38 ± 0.11 L/L·d that higher than those values in R₁ with GAC addition (63.0 ± 3.4% and 0.95 ± 0.09 L/L·d) and R₂ with ZVI addition (74.5 ± 2.8% and 1.21 ± 0.09 L/L·d) under the optimum HRT (5 d). The Fe corrosion as electron donor reduced the ORP values and stimulated the activities of hydrogenotrophic methanogens to lower H₂ partial pressure in R₂ and R₃. Additionally, Fe²⁺ as by-product of iron corrosion, its presence could effectively increase the percentage of protein content in tightly bound extracellular polymeric substances (TB-EPS) to promote better bioflocculation, increasing to 90.5 mg protein/g·VSS (R₂) and 106.3 mg protein/g·VSS (R₃) while this value in R1 was simply 56.6 mg protein/g·VSS. More importantly, compared with R₁, the excess accumulation of propionic acid and butyric acid in system was avoided. The macroscopic galvanic cells around Fe-C micro-electrolysis carriers in R₃, that larger than microscopic galvanic cells in R₂, further accelerate to transfer the electrons from anodic Fe to cathodic carbon that enhance interspecies hydrogen transfer, making the decomposition of propionic acid and butyric acid more thermodynamically feasible, finally facilitate more methane production.