Internal Micro-electrolysis Research Articles

Interaction and selective treatment of lead-zinc flotation wastewater for wastewater recycling using ectrocatalytic internal micro-electrolysis

Lead-zinc flotation wastewater discharge poses a growing risk to environmental safety, and efficient treatment is challenging due to large quantities of water, combined pollution, and the limitations of current approaches. This study discussed the removal differences, available treatment approach, interaction characteristics, and mechanisms of heavy metals (Pb2+ and Zn2+), flotation reagents (butyl xanthate (BX), and dianilino dithiophosphoric acid (DDA)) in single and composite systems using electrocatalytic internal micro-electrolysis (ECIME). Density functional theory (DFT), solubility, and UV spectrum analyses revealed that the high chemical potential of the (BX)2M, (DDA)2M complexes in lead-zinc flotation wastewater played key roles for the solubility and ECIME removal of these pollutants. The complexes significantly inhibited activated carbon (AC) interface adsorption, as well as DDA and (DDA)2M degradation and Fe(II)–Fe(III)–OH flocculation. Prolonging the treatment times for Pb2+, Zn2+, BX, and (BX)2M effectively alleviated the inhibitory effect. However, cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) analysis also highlighted the difficulty of the electrochemical reduction deposition of the Pb2+ and Zn2+ reactions. Comparatively, the DDA and (DDA)2M in composite systems showed higher electrochemical stability, while degradation was highly dependent on high voltage and exhibited temporal hysteresis in the ECIME system. The DDA removal rate only reached 60% after ECIME treatment at 45 V for 90 min, while the values of Pb2+ and Zn2+ (9 V, 30 min) and BX (18 V, 70 min) exceeded 90% and exhibited significantly disadvantage effect when voltage was larger than 18 V. Based on the their distinguishing characteristics of ECIME removal and flotation beneficiation effect, an alternative suggested removing of Pb2+, Zn2+ and BX while preserving DDA and (DDA)2Pb in lead-zinc flotation wastewater could be achieved by regulating the reaction potential and time. By adjusting the ECIME settings to a voltage of 15.2 V, a period of 45 min, and a pH of 5.5, a comprehensive removal rate of 97.59% was achieved. Additionally, recycling wastewater at proportions of 50–70% will not lead to confusion in the selection of lead-zinc ore. The results demonstrated the feasibility and economic efficiency of selective removal and reuse, showing considerable potential for practical application.

Degradation of carbamazepine over MOFs derived FeMn@C bimetallic heterogeneous electro-Fenton catalyst

A highly efficient heterogeneous electro-Fenton (Hetero-EF) catalyst with core-shell structure was successfully prepared by calcination of Mn-doped Mil-53 (Fe) precursor at high temperature. FeMn@C-800/2 prepared at pyrolysis temperature of 800 °C and Fe:Mn molar doping ratio of 2:1 showed the best catalytic performance for the degradation of carbamazepine (CBZ). The characterization, properties and stability of FeMn@C-800/2 were systematically investigated, obtaining the apparent first-order reaction rate of Hetero-EF was 8.9 and 17.8 times higher than that on Fe@C-800 and Mn@C-800 at the optimized conditions of current density 10 mA cm−2, catalyst dosage of 50 mg L−1 and initial pH 4.0, respectively. The incorporation of Mn promoted the generation of more Fe0 and Fe3C during the pyrolysis process, and enhanced the internal micro-electrolysis between Fe0 and carbon shell. At the same time, the presence of Mn0 also promoted the regeneration of Fe2+, and improved the activity of iron-carbon heterogeneous catalysis in the EF process, so as to degrade organic pollutants more effectively. This work would help to gain insight into the design of MOFs derived Fe–Mn bimetal catalyst and its mechanism for enhanced heterogeneous electro-Fenton.

Novel combined IME-O3/OH−/H2O2 process in application for mature landfill leachate treatment

Traditional wastewater treatment methods are often insufficient in the case of mature landfill leachate. Therefore novel methods are in demand. Recently, internal microelectrolysis (IME) has been recognized as an effective method besides AOPs for refractory wastewaters treatment. This study investigated the efficiency of a novel combined three-step process (IME-O3/OH−/H2O2) applied to mature landfill leachate treatment. Waste iron chips and granulated activated carbon (GAC) from nut shells were used in the process. Ozone was applied in doses from 0.28 to 1.4 g/dm3, and the mass ratios of COD/H2O2 were as follows: 1/0, 1/0.5, 1/1 1/1.5, and 1/2. Results showed that the PC is a reasonable pretreatment process before IME. However, COD and TOC removal was up to 22.4% and 37.9%, respectively. It required no additional reagents (before IME acidification is needed). The best total COD removal in the IME process was for Fe/GAC ratio 20/80 g/g in 1 dm3 (76.7%). Studies on the sorption process on GAC showed a significant share in the IME process - 11.2–62.6% of total COD removal. That was an important observation since most other authors ignored the fact of sorption. For optimal parameters of the O3/OH−/H2O2, total COD removal was 95.4%. The values of TOC, absorbance UV254, and color were highly reduced by 91.2%, 94.7%, and 98.2%, respectively. Additionally, biodegradability has been significantly improved up to 0.36.

Removal of methylene blue from aqueous solutions by internal microelectrolysis on the Fe-Cu materials

Fe-Cu material is made by chemical plating method. Materials Fe-Cu is used removal of methylene blue from aqueous solution by internal microelectrolysis. The results show that with optimal conditions for methylene blue decomposition is pH of 4, contact time of 120 minutes, material weight of 1.67 g/L, shaking rate of 300 revolutions per minute (rpm), methylene blue removal efficiency is 93.63 %, with the initial concentration is 245.11 mg/L. The process of decomposition of methylene blue by Fe-Cu material follows the assumed second order kinetic equation with reaction rate constant k = 0.0023 min-1. L.mg-1, The results show that materials Fe-Cu can be applied to remove methylene blue from aqueous solution by internal microelectrolysis

Internal Micro-electrolysis Using Fe/C Material for Pre-Treatment of Concentrated Coking Wastewater

Abstract Untreated coking effluent presents a great challenge for sustainable development of the steel industry and environment preservation. In this study, an internal micro-electrolysis method using Fe/C materials was employed for pretreatment of real coking wastewater with high mass concentration. The Fe/C materials were prepared by Fe powder and graphite powder; and the characteristics of surface morphology, structure, composition of the synthesized materials were examined by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS). The effects of factors namely dosage of Fe/C material, treatment time, initial pH and temperature were investigated via chemical oxygen demand (COD) and phenol removal efficiencies. Optimal treatment efficiency was attained at pH of 4, Fe/C dosage of 40 g/L, treatment time of 360 minutes and temperature of 25°C. After the internal electrolysis process, the values of COD, BOD5, and phenol of the wastewater were 6500, 4850 and 0.1 mg/L, respectively.

Removal of Phenol from Aqueous Solution Using Internal Microelectrolysis with Fe-Cu: Optimization and Application on Real Coking Wastewater

Fe-Cu materials were synthesized using the chemical plating method from Fe powder and CuSO4 5% solution and then characterized for surface morphology, composition and structure by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The as-synthesized Fe-Cu material was used for removal of phenol from aqueous solution by internal microelectrolysis. The internal electrolysis-induced phenol decomposition was then studied with respect to various parameters such as pH, time, Fe-Cu material weight, phenol concentration and shaking speed. The optimal phenol decomposition (92.7%) was achieved under the conditions of (1) a pH value of phenol solution of 3, (2) 12 h of shaking at the speed of 200 rpm, (3) Fe-Cu material weight of 10 g/L, (4) initial phenol concentration of 100.98 mg/L and (5) at room temperature (25 ± 0.5 °C). The degradation of phenol using Fe-Cu materials obeyed the second-order apparent kinetics equation with a reaction rate constant of k of 0.009 h−1L mg−1. The optimal process was then tested against real coking wastewater samples, resulting in treated wastewater with favorable water indicators. Current findings justify the use of Fe-Cu materials in practical internal electrolysis processes.

Internal-micro-electrolysis-enhanced heterogeneous electro-Fenton process catalyzed by Fe/Fe3C@PC core–shell hybrid for sulfamethazine degradation

Core-shell structured hybrid octahedron, which contained a Fe-based nanoparticle core (Fe/Fe3C) and a graphitized porous carbon (PC) shell (Fe/Fe3C@PC), prepared through one-pot pyrolysis using MIL-101(Fe) as the sacrificial template, was used as a novel catalyst for the degradation of sulfamethazine (SMT) by heterogeneous electro-Fenton (Hetero-EF). Fe/Fe3C@PC outperformed common heterogeneous catalysts such as Fe0, Fe3O4 and Fe2O3 due to the synergistic effect between Fe/Fe3C nanoparticles and PC. The rate constant for SMT degradation in the Hetero-EF process was 7.17-folds of that in the heterogeneous Fenton (Hetero-F) process. The plausible catalytic mechanism and degradation pathway for mineralization of SMT by this Hetero-EF process were proposed, confirming the main role of surface-bound hydroxyl radical (OHads) oxidation. Moreover, internal-micro-electrolysis (IME)-enhanced Hetero-EF reaction was verified by experiments and density functional theory (DFT) calculations. Fe/Fe3C@PC could be easily recycled due to magnetism and well recovered via a simple thermal treatment in H2 atmosphere. This work enlightened metal–organic frameworks (MOFs) derived core–shell structured hybrids to be ultra-efficient heterogeneous catalysts and their catalytic mechanism promoting promising utilization in the Hetero-EF process for organic pollutants removal.

Enhanced characteristics and mechanism of Cu(II) removal from aqueous solutions in electrocatalytic internal micro-electrolysis fluidized-bed

For the purification of heavy metal wastewater, internal micro-electrolysis (IME) was considered as an effective method but some disadvantage greatly restricts its application. Electrocatalytic internal micro-electrolysis (ECIME) fluidized bed using iron–carbon particles was proposed to avoid disadvantaging of IME. The principal aim of this study was to investigate the enhanced removal characteristics, mechanism, and kinetic behavior of Cu(II) that none clear before. ECIME reactor shows a better copper removal performance and depends much on the polarization of the external electric field (EEF). Both the reaction rate and removal efficiency of copper electrodeposition improved obviously. Noteworthy is more than 88.0% of Cu(II) in aqueous solutions was removed by enhanced electrodeposition, and only about 10.0% of Cu(II) was absorbed and flocculated through the in situ formed iron hydroxyl compounds. Through scanning electron microscopy (SEM) and electrochemical analysis, copper can effectively electrodeposition on the surface of iron-carbon particles in ECIME reactor and accordingly the enhanced mechanisms were proposed. 1) Iron-carbon particles of ECIME formation of microelectrodes with high surface potential, larger specific area, and active sites through electrode collision and repolarization. 2) Copper electrodeposition on the formed microelectrodes exhibited greater reduction peak potential, reaction overpotential and exchange current density, which influenced by the polarization voltage significantly. 3) The electrocatalytic environment tend to in situ generate iron polymer hydroxyl compounds help to further remove residual Cu(II). ECIME fluidized-bed has promised potential for heavy metal containing wastewater purification and metal recovery. In addition, the proposed reaction models will be useful for field application.

Strengthened Fenton degradation of phenol catalyzed by core/shell Fe–Pd@C nanocomposites derived from mechanochemically synthesized Fe-Metal organic frameworks

We have prepared core/shell structured hollow Fe–Pd@C nanomaterials derived from Fe-metal organic frameworks which were synthesized via cheap, fast and simple mechanochemical technique. The obtained Fe–Pd@C can steadily and continuously release Fe2+ from the galvanic corrosion of Fe0 anode to trigger H2O2 decomposition into hydroxyl radicals and cause fast (10 min) and efficient (mineralization rate 95%) degradation of phenol. The presence of low level of Pd NPs in Fe–Pd@C (mass ratio of the raw material: Fe/Pd = 100:1) facilitated fast Fe3+/Fe2+ redox cycle and thus improved the catalytic performance and pH endurance of the Fe–Pd@C. After recycled four times, Fe–Pd@C remained high catalytic performance and released low level of iron ions (2.5 mg L−1), which reduced the production of iron sludge after usage. In contrast to zero-valent iron (ZVI) and commercial physically mixed Fe/C materials, the core/shell structure of Fe–Pd@C ensured efficient electron transferring from Fe0 to carbon cathode and targets, and prevented the precipitation of iron ions on Fe0 surface, avoiding the deactivation of Fe0 and termination of Fe–C internal micro-electrolysis (IME) and extending their service life. The reactive species quenching experiments and ESR characterization proved the synergistic effect of electrons and hydroxyl free radicals on degradation of phenol. The carbon-centered DMPO radical detected in reaction solution can be regarded as a proof for the strengthened oxidation ability of the combined IME and Fenton reaction.

Long-lasting activity of Fe0-C internal microelectrolysis-Fenton system assisted by Fe@C-montmorillonites nanocomposites

Core/shell type Fe0@carbon (Fe@C) nanocomposites inserted in the interlayer space of montmorillonites (MMT) is prepared by one-step pyrolysis of Fe-metal organic frameworks and MMT. Fe@C-MMT serves as Fenton-like catalyst to degrade organic pollutants based on internal microelectrolysis (IME)-Fenton reactions. The MMT coat accelerates galvanic corrosion of Fe0 to facilitate in-situ generation of Fe2+ and achieves self-regulation of solution pH. Strengthened elimination of phenol and methyl orange with high mineralization efficiency (80%) at initial pH 3–6.5 was achieved in Fe@C-MMT-H2O2 system compared to Fe@C-, ZVI-, and commercial Fe-C-H2O2 systems. The MMT coat retards contact of Fe0 and Fe(II) species on Fe@C-MMT surface with H2O2, leading to rate-controlling consumption of H2O2 to keep the long-lasting efficiency of the IME-Fenton system. Fe@C-MMT suspension with 10 mM of H2O2 can continuously degrade organic pollutants within 40 h. Fe@C-MMT can be recycled for five times and shows good resistance to oxygen and acid corrosion.

Advanced treatment of copper smelting wastewater by the combination of internal micro-electrolysis and electrocoagulation

ABSTRACTIn this study, a combined process of internal micro-electrolysis (IME)–electrocoagulation was developed at lab scale for treating a real copper smelting wastewater. By IME, 92.4% of Cu, 88.6% of Pb, and 72.2% of Zn were removed after 30 min at an initial solution pH of 3, a Fe/C dosage of 40 g/L, and a Fe/C mass ratio of 1:1. Removal of residual metals by electrocoagulation was affected by wastewater pH and current density. Electrocoagulation with iron/aluminum electrodes at a current density of 5 mA/cm2, electrocoagulation time of 30 min, and pH 8 resulted in 99.3% Cu, 99.5% Pb, and 98.6% Zn removal. The final effluent quality could satisfy the National Discharge Standard of China. This work demonstrates that the hybrid system has the potential to be applied for the advanced treatment of high-strength copper smelting wastewater.

ENHANCED EFFICIENCY OF TREATMENT OF TNT WASTEWATER BY INTERNAL ELECTROLYSIS REACTION USE BIMETALIC MATERIALS Fe-Cu

In this article, wastewater containing 2,4,6 trinitrotoluen (TNT) was treated by internal microelectrolysis with bimetal Fe-Cu materials. Components of TNT pollutant content was identified by HPLC method. Examined factors: pH, time, temperature, concentration of Fe-Cu bimetal to efficient treatment of TNT in the wastewater. With conditions at pH 5, bimetal Fe-Cu dosage of 50 g for l litre of wastewater, TNT original content in the wastewater infected about 95-106.4 mg/l, temperature of 25 0C, after 6 hours of processing time, content TNT rest 0.2 - 0.5 mg/l, after 6 hours not observed.

Decomplexation efficiency and mechanism of Cu(II)-EDTA by H2O2 coupled internal micro-electrolysis process.

Internal micro-electrolysis (IE) coupled with Fenton oxidation (IEF) was a very effective technology for copper (Cu)-ethylenediaminetetraacetic acid (EDTA) wastewater treatment. However, the mechanisms of Cu2+ removal and EDTA degradation were scarce and lack persuasion in the IEF process. In this paper, the decomplexation and removal efficiency of Cu-EDTA and the corresponding mechanisms during the IEF process were investigated by batch test. An empirical equation and the oxidation reduction potential (ORP) index were proposed to flexibly control IE and the Fenton process, respectively. The results showed that Cu2+, total organic carbon (TOC), and EDTA removal efficiencies were 99.6, 80.3, and 83.4%, respectively, under the proper operation conditions of iron dosage of 30g/L, Fe/C of 3/1, initial pH of 3.0, Fe2+/H2O2 molar ratio of 1/4, and reaction time of 20min, respectively for IE and the Fenton process. The contributions of IE and Fenton to Cu2+ removal were 91.2 and 8.4%, respectively, and those to TOC and EDTA removal were 23.3, 25.1, and 57, 58.3%, respectively. It was found that Fe2+-based replacement-precipitation and hydroxyl radical (•OH) were the most important effects during the IEF process. •OH played an important role in the degradation of EDTA, whose yield and productive rate were 3.13mg/L and 0.157mg/(Lmin-1), respectively. Based on the intermediates detected by GC-MS, including acetic acid, propionic acid, pentanoic acid, amino acetic acid, 3-(diethylamino)-1,2-propanediol, and nitrilotriacetic acid (NTA), a possible degradation pathway of Cu-EDTA in the IEF process was proposed. Graphical abstract The mechanism diagram of IEF process.

Intensify chemical reduction to remove nitrate from groundwater via internal microelectrolysis existing in nano-zero valent iron/granular activated carbon composite

A composite combination of nano-zero valent iron (nZVI) and granular activated carbon (GAC) was introduced to achieve nitrate transformation into nitrogen with minimum byproducts via chemical reduction. The results showed that nitrate removal was significantly intensified and GAC was an excellent partner of nZVI chemical reduction. Both the dispersion and long-term reactivity of nZVI were improved, and more than 80% of nitrate was removed at 10 g/L nZVI/GAC composite within 90 min in steady state. The byproducts of nitrite and ammonium formed in reduction process were below 0.008 and 0.04 mg/L, respectively, and nitrogen was the main end product, which was confirmed by X-ray photoelectron spectroscopy analysis. Moreover, the kinetic model of nitrate reduction by nZVI/GAC composite can be described well by pseudo-first-order reaction kinetic (R2 = 0.984). The intensification is closely related to the dispersion effect of GAC matrix to nZVI and the promotion effect to electrons transfer between nZVI and nitrate pollutant of internal iron–carbon microelectrolysis existing in such a composite. Therefore, the findings are very beneficial to develop an efficient and low-cost chemical remediation method for nitrate-contaminated groundwater.

Simultaneous removal of organic matter and nitrate from bio-treated leachate via iron–carbon internal micro-electrolysis

Both nitrate and organic matter could be reduced by iron–carbon internal micro-electrolysis by electron competition. The main mechanisms of COD removal include adsorption and coagulation.

Removal of Zinc Ions from Aqueous Solutions by Micro-Electrolysis and Iron Hydroxide Self-Flocculation

This study was performed to determine the feasibility of enhancing removal of zinc ions from aqueous solutions using an iron-carbon internal micro-electrolysis (ICIME) followed by iron hydroxide self-flocculation (IHSF) process. Results shown that the Zn2+ removal using ICIME was improved by IHSF significantly. The pH=3, mass ratio of Fe/AC=2: 1, hydraulic reaction time=30min of ICIME and pH=9, both aeration time and static placing time were 60min of IHSF were proposed as the optimum conditions. Under these conditions, the removal efficiency and residual concentration of Zn2+ from lead and zinc smelting wastewater were reached 99.10%, 1.32mg/L. Meanwhile, other metal ions and the F- also were removed effectively. Lead and zinc smelting wastewater could meet the discharging standard (integrated wastewater discharge standard (GB8978-1996)) of China. The Zn2+ removal was significantly influenced by other metal ions existing in aqueous solutions. Contrast and breakthrough time experiment indicated the Compare with single Fe and ICIME, ICIME followed by IHSF have a higher efficiency and bearing capacity for Zn2+ removal. ICIME removal of Zn2+ enhanced by IHSF is a feasible method.

Treatment of nanofiltration concentrates of mature landfill leachate by a coupled process of coagulation and internal micro-electrolysis adding hydrogen peroxide

In this study, a coupled process of coagulation and aerated internal micro-electrolysis (IME) with the in situ addition of hydrogen peroxide (H2O2) was investigated for the treatment of nanofiltration (NF) concentrate from mature landfill leachate. The acceptable operating conditions were determined as follows: initial pH 4, polymeric aluminium chloride dosage of 525 mg-Al2O3/L in the coagulation process, H2O2 dosage of 0.75 mM and an hydraulic retention time of 2 h in an aerated IME reactor. As a result, the removal efficiencies for chemical oxygen demand (COD), total organic carbon, UV254 and colour were 79.2%, 79.6%, 81.8% and 90.8%, respectively. In addition, the ratio of biochemical oxygen demand (BOD5)/COD in the final effluent increased from 0.03 to 0.31, and that of E2/E4 from 12.4 to 38.5, respectively. The results indicate that the combined process is an effective and economical way to remove organic matters and to improve the biodegradability of the NF concentrate. Coagulation process reduces the adverse impact of high-molecular-weight organic matters such as humic acids, on the aerated IME process. A proper addition of H2O2 in the aerated IME can promote the corrosion of solid iron (Fe2+/Fe3+) and cause a likely domino effect in the enhancement of removal efficiencies.

Degradation efficiency and mechanism of azo dye RR2 by a novel ozone aerated internal micro-electrolysis filter

A newly designed ozone aerated internal micro-electrolysis filter (OIEF) was developed to investigate its degradation efficiencies and correlated reaction mechanisms of RR2 dye. Complete decolorization and 82% TOC removal efficiency were stably achieved in OIEF process. Based on the comprehensive experimental results, an empirical equation was proposed to illustrate the effects of initial dye concentration and ozone dosage rate on color removal. The results indicated that OIEF process could be operated at wide pH range without significant treatment efficiencies change, while the optimum pH for RR2 dye degradation was 9.0. There were 15, 8 and 6 kinds of identified intermediates during ozonation, IE and OIEF treatment processes, respectively. Less identified intermediates and their lower concentrations in OIEF may attribute to its rather excellent mineralization performance. It was found that ozonation, Fe2+/Fe3+ catalyzed ozonation, the redox reactions of electro-reduction and electro-oxidation are the most important mechanisms in OIEF process. The catalytic effect of Fe2+/Fe3+ would induce mutual conversion between dissolved Fe2+ and Fe3+, and then decrease the dissolution rate of ZVI. The excellent treatment performance proved that the OIEF process is one promising technology applied for reactive azo dyes and other refractory wastewater treatment.

Dual-cell reduction and group effect in an internal microelectrolysis reactor

To address some of the fundamental questions regarding the functions of cathodes and anodes (e.g., iron and granular active carbon) and what happens when numerous particles (microscopic galvanic cells) are combined in the widely used and efficient wastewater treatment of an internal microelectrolysis (IME) reactor, we employed a specifically designed dual-cell IME reactor with single-couple electrodes and a narrow cell IME reactor with multi-couple electrodes. The simultaneous removal of 6.36mgL−1 and 2.93mgL−1 of 2,4-dichlorophenol within 30min from the graphite cathode and the iron anode cells, respectively, was observed in the dual-cell reactor. The innovative concept behind this phenomenon is that the anode, which is generally believed to be oxidative, could probably be reductive in an IME reactor. Thus, it is important to understand the unique performance of IME reactors. The group effect, which provides a 45% increase of open-circuit potential with just two additional electrode couples in aqueous solution, was tested and verified in a multi-couple electrode reactor. It suggests a complex potential distribution in the IME reactor and that compounds even with high redox potential could possibly be reduced, which was generally believed to be difficult to accomplish.

Enhanced MBR by internal micro-electrolysis for degradation of anthraquinone dye wastewater

Anthraquinone dyes are very common and refractory pollutants in a wide variety of textile wastewaters and the treatments of these wastewaters have attracted much attention up to now. In this study, a novel enhanced membrane bioreactor (MBR) by internal micro-electrolysis (IE) was successfully applied for treatment of reactive brilliant blue X-BR dye wastewater owing to its high organic matter and nitrogen removal. The main interests were taken in exploring the effect of iron ions released from the IE on properties of biomass and membrane filtration. A hybrid MBR (HMBR) with iron ions fed and an iron controlled MBR (CMBR) were operated in parallel. The biomasses in various MBRs were characterized by sludge volume index (SVI), particle size distributions, concentration of the bound extracellular polymeric substance (EPS), and microscopic structure of the sludge flocs. The results demonstrated that alleviation of membrane fouling in HMBR for a long time was mainly caused by the improvement of settleability and compactability of flocs, as well as the increase in the particle size. As a skeleton frame of aggregations, bound EPS effectively enhanced the bioflocculation of small particles, which was beneficial in controlling membrane biofouling. However, in the last phase, membrane permeability in HMBR continued to drop and tended to be lower than that in CMBR, which mostly attributed to the severely inorganic fouling besides the negative impact of EPS on membrane filterability. Therefore, iron ions control was critical in operation of the enhanced IE/MBR system.