Iron-carbon Micro-electrolysis Research Articles

Long-term evaluating the strengthening effects of iron-carbon mediator for coking wastewater treatment in EGSB reactor

Coking wastewater (CWW) treatment is difficult due to its complex composition and high biological toxicity. Iron-carbon mediators was used to enhance the treatment of CWW through iron-carbon microelectrolysis (ICME). The results indicated that the removal rate of COD and phenolic compounds were enhanced by 24.1 % and 23.5 %, while biogas production and methane content were promoted by 50 % and 7 %. Microbial community analysis indicated that iron-carbon mediators had a transformative impact on the reactor's performance and dependability by enriching microorganisms involved in direct and indirect electron transfer, such as Anaerolineae and Methanothrix. The mediator also produced noteworthy gains in LB-EPS and TB-EPS, increasing by roughly 109.3 % and 211.6 %, respectively. PICRISt analysis demonstrated that iron-carbon mediators effectively augment the abundance of functional genes associated with metabolism, Citrate cycle, and EET pathway. This study provides a new approach for CWW treatment.

Enhanced reduction of sulfate by iron-carbon microelectrolysis: interaction mechanism between microelectrolysis and microorganisms.

Sulfate wastewater has a wide range of sources and greatly harms water, soil, and plants. Iron-carbon microelectrolysis (IC-ME) is a potentially sustainable strategy to improve the treatment of sulfate (SO42-) wastewater by sulfate-reducing bacteria (SRB). In this study, an iron-carbon mixed micro-electrolysis bioreactor (R1), iron-carbon layered bioreactor (R2), activated carbon bioreactor (R3), and scrap iron filing bioreactor (R4) were constructed by up-flow column experimental device. The performance and mechanism of removing high-concentration sulfate wastewater under different sulfate concentrations, hydraulic retention times (HRT), and chemical oxygen demand (COD)/SO42- were discussed. The results show that the iron-carbon microelectrolysis-enhanced SRB technology can remove high-concentration sulfate wastewater, and the system can still operate normally at low pH. In the high hydraulic loading stage (HRT = 12h, COD/SO42- = 1.4), the SO42- removal rate of the R1 reactor reached 98.08%, and the ORP value was stable between - 350 and - 450mV, providing a good ORP environment for SRB. When HRT = 12h and influent COD/SO42- = 1.4, the R1 reactor sulfate removal rate reached 96.7%. When the influent COD/SO42- = 0.7, the sulfate removal rate was 52.9%, higher than the control group. Biological community analysis showed that the abundance of SRB in the R1 reactor was higher than that in the other three groups, indicating that the IC-ME bioreactor could promote the enrichment of SRB and improve its population competitive advantage. It can be seen that the synergistic effect between IC-ME and biology plays a vital role in the treatment of high-concentration sulfate wastewater and improves the biodegradability of sulfate. It is a promising process for treating high-concentration sulfate wastewater.

Continuous treatment of chromium picolinate and efficient chromium removal without hexavalent chromium accumulation using the modified Fe-C micro-electrolysis process

Cr(pic)3, an emerging contaminant, is easily degraded to hexavalent chromium (Cr(VI)) in environment, which exacerbates its risk. Because of the complexing structure, removal of this organic chromium is rather difficult through the simple adsorption and precipitation. Herein, disposal of Cr(pic)3 via the modified iron-carbon (Fe-C) micro-electrolysis (abbreviated as Fe-C) process (H2O2 was added simultaneously as the reactant) was first developed in this work. The modified process could accelerate the de-complexation of Cr(pic)3 and promote Cr removal at a lower H2O2 dosage than the Fenton process. Cr(VI) was not accumulated in the process. Almost all the Cr(pic)3 could be degraded and the residual chromium (all was trivalent chromium Cr(III)) was decreased from 520 to 52.7 μg/L within 30 min under optimized conditions in batch experiments (i.e., pHinitial = 3.0, pHfinal = 7.0, [H2O2]0 = 0.3 mM, [Fe-C fillers]0 = 0.1 g/L, respectively). Mechanisms of Cr(pic)3 de-complexation and Cr removal were elucidated based on the products detected and characteristics of the precipitates. Adsorption was the main mechanism for Cr(III) removal. It exchanged the hydroxyl ligand with the iron hydro(oxides) to form inner sphere complex. Factors that potentially affected the performance of the modified Fe-C process were investigated, including the operational parameters and the composition of water matrix. Moreover, the feasibility and stability of the established method were further confirmed by the column test, which realized the continuous operation and maintained the residual Cr in the effluent constant below 10.0 μg/L. Collectively, these findings consistently indicated that the modified Fe-C process is a robust and promising approach for the industrial disposal of Cr(pic)3.

Iron-carbon micro-electrolysis facilitates autotrophic denitrification and Feammox in tidal flow constructed wetlands for enhanced nitrogen removal and reduced N2O emissions

This study focused on developing a tidal flow constructed wetland (CW) with an iron-carbon (Fe-C) substrate to enhance nitrogen removal efficiency. The results demonstrated significant improvements in the removal of NH4+-N and TN in the iron-carbon tidal flow constructed wetland (IC-TFCW) compared to traditional gravel CW. IC-TFCW achieved a 23.82 % and 31.01 % more effective removal, resulting in reductions of 82.45 % and 74.13 %, respectively. The large specific surface area and electron transfer effect of the Fe-C substrate facilitated pollutant retention and proliferation of denitrifying microorganisms. However, the Fe-C substrate inhibited plant growth and rhizosphere microorganisms, reducing plant nitrogen uptake by 2.69-fold. Galvanic cell reaction in the Fe-C substrate facilitated the release of iron and its oxides and promoted iron cycling under the alternating aerobic-anoxic conditions induced by tidal flow. This led to the enrichment of autotrophic denitrifying and Fe-reducing bacteria by 14.89 and 1.1 times, and increase in the relative abundance of denitrification genes nar (narG, narH, narI) and nap (napA, napB) by 60.94 %. The Fe2+ released during the galvanic cell reaction contributed electrons to denitrification, while the reduction of Fe3+ facilitated the Anammox process, resulting in the Feammox reaction. This created an autotrophic denitrification pathway (autotrophic denitrification and Feammox), synergizing with the heterotrophic denitrification pathway and the iron cycling process to significantly increase TN removal and reduce N2O emissions per unit of TN removed by up to 36.99 %. These findings elucidate the various denitrification pathways present in CW and provide insights into improving denitrification efficiency.

Review in application of blast furnace dust in wastewater treatment: material preparation, integrated process, and mechanism.

Blast furnace dust (BFD) is the solid powder and particulate matter produced by dust removal process in ironmaking industry. The element composition of BFD is complex, and a direct return to sintering will lead to heavy metal enrichment and blast furnace lining corrosion. In recent years, the application of BFD in wastewater treatment has attracted widespread attention. Based on the mechanisms of action of BFD in wastewater, this paper discusses in detail the application of BFD in iron-carbon micro-electrolysis, biological enhancement, adsorption, flocculation, and Fenton/Fenton-like reactions. Iron oxides and carbon in BFD are key substances. Thus, BFD has great potential as a raw material in wastewater treatment, and the waste utilization of BFD can be realized. However, the difference in elements and composition of BFD limits its large-scale application. We can classify BFD according to different proportions of elements. In the future, it is necessary to focus on the service life of BFD in water and whether it shall bring secondary pollution to water.

Effect and mechanism of iron-carbon micro-electrolysis pretreatment of organic peroxide production wastewater.

The wastewater from organic peroxide production has high chemical oxygen demand (COD) concentration and poor biodegradability, so it is necessary to find a cost-effective treatment method. The iron-carbon microelectrolysis (IC-ME) technology was used to pretreat the organic peroxide production wastewater, and the influence of reaction conditions on the removal effect of pollutants and the degradation mechanism were studied. The effects of initial pH, iron filings, iron-carbon ratio, and reaction time on the wastewater treatment were investigated by single-factor and response surface optimization experiments, and the degradation mechanism was analyzed by three-dimensional fluorescence spectroscopy, UV-Vis, and gas chromatography mass spectrometry (GC-MS). The experimental results showed that the COD removal efficiency was 35.67% and the biodegradability of wastewater was increased from 0.113 to 0.173 under the conditions of initial pH of 3.1, the dosage of iron filings of 30.5g/L, the ratio of iron-carbon of 1.01, and the reaction time of 122.8min, and the process of IC-ME for degrading COD of wastewater from the production of organic peroxide was consistent with the secondary reaction. The IC-ME process could decompose macromolecular organic compounds such as tyrosine proteins and aromatic proteins, and improve the biodegradability of wastewater. It provides a theoretical reference for the practical application of IC-ME to treat this type of wastewater.

Enhanced denitrification driven by a novel iron-carbon coupled primary cell: chemical and mixotrophic denitrification

Iron-carbon micro-electrolysis system is a promising method for promoting electron transfer in nitrate removal. However, many traditional approaches involving simple physical mixing inevitably suffered from the confined iron-carbon contact area and short validity period, leading to the overuse of iron. Here, a ceramsite-loaded microscale zero-valent iron (mZVI) and acidified carbon (AC) coupled-galvanic cell (CMC) was designed to support chemical, autotrophic and heterotrophic denitrification. Long-term experiments were conducted to monitor the nitrogen removal performance of denitrification reactors filled with CMC and thus optimized the denitrification performance by improving fabrication parameters and various operating conditions. The denitrification contributions test showed that the chemical denitrification pathway contributed most to nitrate removal (57.3%), followed by autotrophic (24.6%) and heterotrophic denitrification pathways (18.1%). The microbial analysis confirmed the significant aggregation of related denitrifying bacteria in the reactors, while AC promoted the expression of relevant nitrogen metabolism genes because of accelerated uptake and utilization of iron complexes. Meanwhile, the electrochemical analysis revealed a significantly improved electron transfer capacity of AC compared to pristine carbon. Overall, our study demonstrated the application of a novel mZVI-AC coupled material for effective nitrate removal and revealed the potential impact of CMC in the multipathway denitrification process.Graphical

Study on the transformation of nitrate nitrogen by manganese-catalyzed iron-carbon micro-electrolysis and microbial coupling.

Nitrate-nitrogen pertains to the nitrogen component of the overall nitrate present in a given sample in order to reduce nitrate nitrogen pollution in water, nitrate nitrogen removal methods based on iron-carbon micro-electrolysis have become a key research focus. The process and mechanism of nitrate nitrogen removal by microbial coupling was comprehensively explored in a novel iron-carbon micro-electrolysis (ICME) system. In order to establish the transformation pathway of nitrate nitrogen in water, the transformation paths of nitrate nitrogen in water before and after coupling microorganisms in three groups of continuous flow reaction devices, namely sponge iron (s-Fe0), sponge iron + biochar (s-Fe0/BC) and sponge iron + biochar + manganese sand (s-Fe0/BC/MS), were studied. The morphology and composition changes of sponge iron were analyzed by means of characterization, and the microbial population changes in the three groups were analyzed by high-throughput sequencing. Results showed that the nitrate conversion rate in the s-Fe0, s-Fe0/BC and s-Fe0/BC/MS systems reached 99.48%, 99.57% and 99.36%, respectively, with corresponding ammonia nitrogen generation, rates of 3.77%, 9.34% and 11.24% and nitrogen generation rates of 95.71%, 90.23% and 88.12%. Scanning electron microscopy imaging showed that in the s-Fe0/BC and s-Fe0/BC/MS systems the surface of sponge iron was highly corroded, with granular substances in the corrosion product clusters. X-ray photoelectron spectroscopy analysis found that the relative contents of Fe2O3 in the surface oxides of sponge iron after microbial coupling were 38.02% and 71.27% in the s-Fe0/BC and s-Fe0/BC/MS systems, while the relative Fe3O4 contents were 61.98% and 28.72%, respectively. Microbial high-throughput sequencing analysis revealed that the Chao and Ace index values in the s-Fe0 system were 871.89 and 880.78, while in the s-Fe0/BC system they were 1012.05 and 1017.29, and in the s-Fe0/BC/MS system were 1241.09 and 1198.29, respectively. The relative proportion of Thauera in the s-Fe0, s-Fe0/BC, and s-Fe0/BC/MS systems was 16.76%,14.25% and 10.01%, while the proportion of Acetoanaerobium was 15.36%, 13.27% and 11.11%, and the proportion of Chloroflexi was 0%, 1.11% and 2.18%, respectively. Furthermore, FAPROTAX function annotation found that the expression levels of chemoheterotrophs in the s-Fe0, s-Fe0/BC and s-Fe0/BC/MS systems were 43 316 OTU, 37 289 OTU and 34 205 OTU, while nitrate respiration expression levels were 16 230 OTU, 15 483 OTU and 9149 OTU, with nitrogen respiration expression levels of 16 328 OTU, 15 493 OTU and 9154 OTU, respectively. These findings suggest that nitrate is converted into nitrogen gas and ammonia nitrogen through the actions of the coupled system of sponge iron/biochar/manganese sand and microorganisms. The catalytic effect of MnO2 promotes the conversion of Fe2+ to Fe3+, generating more electrons, allowing denitrifying bacteria to reduce more nitrate nitrogen, effectively coupling the manganese-catalyzed ICME reaction and microbial denitrification. The micro-electrolysis system and the addition of manganese sand enhanced biodiversity within the s-Fe0/BC/MS system. The heterotrophic bacteria Thauera and Acetoanaerobium were the dominant microorganisms in all three systems, although the micro-electrolysis system with added manganese sand significantly reduced the proportion of facultative bacteria Thauera and Acetoanaerobium and promoted the growth of autotrophic Chloroflexi bacteria. The ecological functions of the three systems were mainly nitrate respiration and nitrogen respiration. By comparing the expression levels of nitrate respiration and nitrogen respiration in s-Fe0/BC and s-Fe0/BC/MS systems, it can be seen that the addition of manganese sand reduced microbial activity.

How the subsurface wastewater infiltration systems with iron‑carbon micro-electrolytic substrate achieve high pollutants removal: A metabolomic view

Being an ecological engineering water treatment technology, subsurface wastewater infiltration system (SWIS) combines ecological principles with anaerobic and aerobic processes. Iron‑carbon micro-electrolysis (ICME) is a rapidly developing SWIS substrate type in recent years. In this study, microbial metabolomics was introduced into SWIS aiming to reveal the “black box” of enhanced nitrogen removal in SWIS assisted by ICME (namely ICMESWIS). Ultra performance liquid chromatography-mass spectrometry (UPLC-MS), principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and univariate analysis were carried out to classify the samples from SWIS and ICMESWIS. The results showed that compared with SWIS, 28.5 ± 2.6 %, 33.7 ± 1.3 % and 19.3 ± 0.4 % improvements were found for NO3−-N, NH4+-N and NO2−-N removals in ICMESWIS. According to the model's variable importance factor and fold change >2, metabolites with large differences were screened out. Metabolites, such as 1-(4-nitrophenyl)piperidine (ESI-) and 2-amino-1,3,4-octadecanetriol (ESI-) presented higher abundance in ICMESWIS, in consistent with the higher degradation of pollutants. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that nitrification, nitrate reduction, dissimilatory nitrate reduction, denitrification, anaerobic ammonia oxidation (anammox) are the main nitrogen removal pathways in ICMESWIS.

Fenton Oxidation Combined with Iron–Carbon Micro-Electrolysis for Treating Leachate Generated from Thermally Treated Sludge

In this study, Iron–Carbon Micro-Electrolysis (ICME), Fenton oxidation, and their combination were investigated to treat the leachate obtained from a wastewater treatment plant located in southern China. The results show that the Fenton-ICME process was the most efficient one. After the leachate was treated with the Fenton-ICME process, the COD concentration was reduced from the initial 35,772 mg/L to 13,522 mg/L, and the removal efficiency was up to 62.2%. In addition, the biological oxygen demand (BOD) to COD ratio increased by 40% at optimal conditions. This suggests that the biodegradability of the leachate has been increased, facilitating the biodegradation of the leachate after it is mixed with the raw wastewater. By studying the characteristic variation of the leachate treated with the Fenton-ICME process, it was found that the combined process mainly removes organic compounds such as aromatic compounds, ketones, and aldehydes. The separated sludge does not have a crystalline structure, and the iron in it mainly exists in the form of trivalent iron. It reveals that the Fenton-ICME process has great potential to be used as a pretreatment of leachate.

Iron-carbon micro-electrolysis material enhanced high-solid anaerobic digestion: Performance and microbial mechanism

Iron-carbon micro-electrolysis (ICME) materials are widely used as composite conductive materials for wastewater treatment to promote the degradation of volatile solids (VS), but there is virtually no research on their effect on high-solid anaerobic digestion (HSAD). This study aimed to investigate the effect of 10–50 g/L ICME dosages on HSAD and to reveal the microbial enhancement mechanism. The batch experiments (working volume of 400 mL) were conducted in a constant temperature water bath shaker. The results showed that the ICME materials promoted methane production by HSAD. The highest methane production rate was 297.79 mL/ g VS at a dosage of 50 g/L, which was 28% higher than that of the control. Scanning electron microscopy results showed that the ICME materials increased the attachment area of microorganisms. Further analyses of microbial community indicated that ICME materials facilitate symbiotic metabolism of syntrophic acetate-oxidizing bacteria (Synergistaceae) and hydrogenotrophic methanogens (Methanospirillum). This potentially promotes the conversion of the acetoacetic methanogenesis pathway to the syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathways. This study revealed ICME material enhancement in HSAD as well as new insights into the microbial mechanisms.

Mechanistic insights into removal of bisphenol A from activate peroxymonosulfate by Fe-C coupled biochar with the assistance of electric-field activation

Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution, Limitations such as short reaction lifetime and hardening of Fe-C usually make it insufficient to achieve the desired treatment effect.The research is a new type of electric field in the auxiliary, promote biochar activation peroxymonosulfate (PMS) by micro electrolysis produce active free radicals to degradation of organic pollutants in water. namely IC-BC/PMS-EC，Using biochar as electron shuttle, electric field was introduced in the process of iron-carbon microelectrolysis activation of PMS promoted the electron transfer in the solution， The results showed that the reaction system could achieve 100% removal effect in 20 min. Fe2+/Fe3+ released by Fe-C was below the ambient concentration, which constituted a stable cycle in the electrocatalytic system and efficiently activated PMS. The work found that applied electric field and Fe-C micro-electrolysis activation both improved the efficiency of persulfate advanced oxidation progress. The activated system superimposition strengthened on coupled action and enhanced the performance for the degradation of organic pollutants in water. In summary, IC-BC/PMS-EC system is an economical, efficient and promising new system in the process of activating PMS to degrade pollutants.

Sludge-derived iron-carbon material enhancing the removal of refractory organics in landfill leachate: Characteristics optimization, removal mechanism, and molecular-level investigation

Mature landfill leachate is a refractory organic wastewater, and needs physical and chemical pretreatments contemporaneously, e.g. iron-carbon micro-electrolysis (IC-ME). In this study, a novel iron-carbon (Fe-C) material was synthesized from waste activated sludge to be utilized in IC-ME for landfill leachate treatment. The pyrolysis temperature, mass ratio of iron to carbon, and solid-liquid ratio in leachate treatment were optimized as 900 °C with 1.59 and 34.7 g/L. Under these optimal conditions, the chemical oxygen demand (COD) removal efficiency reached 79.44 %, which was 2.6 times higher than that of commercial Fe-C material (30.1%). This excellent COD removal performance was indicated to a better mesoporous structure, and uniform distribution of zero-valent iron in novel Fe-C material derived from sludge. The contribution order of COD removal in IC-ME treatment for landfill leachate was proven as coagulation, adsorption, and redox effects by a contrast experiment. The removal of COD includes synthetic organic compounds, e.g. carcinogens, pharmaceuticals and personal care products. The contents of CHO, CHON, and CHOS compounds of dissolved organic matter (DOM) in the leachate were decreased, and both the molecular weight and unsaturation of lipids, lignin, and tannic acids concentration were also reduced. Some newly generated small molecular DOM in the treated leachate further confirmed the existence of the redox effect to degrade DOM in leachate. The total cost of sludge-derived Fe-C material was only USD$ 152.8/t, which could save 76% of total compared with that of commercial Fe-C materials. This study expands the prominent source of Fe-C materials with excellent performance, and deepens the understanding of its application for leachate treatment.

Evaluating the stability and performance of a novel core-shell ZVI@C-montmorillonite particle for anaerobic treatment of chloramphenicol wastewater

ZVI@C-MP is a novel composite particle consisting of zero-valent iron (ZVI) enclosed within a carbon shell. The purpose of this composite material is to enhance the anaerobic treatment of wastewater containing chloramphenicol (CAP). This approach aims to address the initial challenge of excessive corrosion experienced by ZVI, followed by its subsequent passivation and inactivation. ZVI@C-MP was synthesized through a hydrothermal process and calcination, with montmorillonite as binder, it exhibits stability, iron-carbon microelectrolysis (ICME) properties, and strong adsorption for CAP. Its ICME actions include releasing iron ions (0.70 mg/L) and COD (11.3 mg/L), generating hydrogen (3.82%), and raising the pH from 6.30 to 7.71. With minimal structural changes, it achieved release equilibrium. ZVI@C-MP boasts high removal efficiency of CAP (98.96%) by adsorption, attributed to surface characteristics (surface area: 167.985 m2/g; pore volume: 0.248 cm3/g). The addition of ZVI@C-MP increases COD removal (10.16%), methane production (72.86%), and reduces extracellular polymeric substances (EPS) from 70.58 to 52.72 mg/g MLVSS. It reduces microbial by-products and toxic effects, enhancing CAP biodegradation and microbial metabolic activity. ZVI@C-MP's electrical conductivity and biocompatibility bolster functional flora for interspecies electron transfer. It's a novel approach to antibiotic wastewater treatment.

Enhanced nitrogen removal performance of microorganisms to low C/N ratio black-odorous water by coupling with iron-carbon micro-electrolysis

Black-odorous water was caused by urbanization, industrial sewage and domestic sewage. Black-odorous water with low carbon nitrogen ratio (C/N) may inhibit the activity of microorganisms due to the lack of C source during microbial treatment. In this study, iron-carbon micro-electrolysis (ICME) was used to couple nitrifying and denitrifying bacteria. The external factors affecting microbial activity were optimized through experiments, and the effect of low C/N wastewater was studied. The optimal external factors were temperature of 30 ℃, C/N of 3, DO of 3 mg/L and iron-carbon dosage of 150 g/L. Coupled with ICME, it was found that the removal rate of nitrate nitrogen in water increased by 50.74 %, indicating that ICME could make up for the deficiency of microbial C source and improve the removal rate of nitrate nitrogen in low C/N black-odorous water. The improvement of removal rate had much to do with ICME's role as electron donor to provide electrons for denitrification. In addition, the performance of wastewater treatment by this process is tested. The maximum load of ammonia nitrogen, COD, nitrate and total nitrogen was increased to 0.1928, 1.7732, 0.2691 and 0.5181 kg/(m3·d), respectively. High-throughput sequencing results showed that the species of dominant plant population changed after ICME coupling, but the abundance increased significantly, which further indicated that ICME played a synergic role in microbial nitrogen removal, which was related to the release of trace iron by ICME. This study can provide some guidance for the treatment of black-odorous water with high ammonia nitrogen and low C/N.

Enhancing methane production from food waste with iron-carbon micro-electrolysis in a two-stage process

A two-stage process, consisting of a leach-bed reactor (LBR) and an up-flow anaerobic sludge blanket reactor (UASB), has been commonly adopted to improve food waste anaerobic digestion. However, its application is limited due to low hydrolysis and methanogenesis efficiencies. This study proposed a strategy of incorporating iron-carbon micro-electrolysis (ICME) into the UASB and recirculating its effluent to the LBR to improve the two-stage process efficiency. Results showed that the integration of the ICME with the UASB significantly increased the CH4 yield by 168.29%. The improvement of the food waste hydrolysis in the LBR mainly contributed to the enhanced CH4 yield (approximately 94.5%). The enrichment of hydrolytic-acidogenic bacterial activity, facilitated by the Fe2+ generated through ICME, might be the primary cause of the improved food waste hydrolysis. Moreover, ICME enriched the growth of hydrogenotrophic methanogens and stimulated the hydrogenotrophic methanogenesis pathway in the UASB, contributing partially to the enhanced CH4 yield.

An internal circulation iron–carbon micro-electrolysis reactor for aniline wastewater treatment: Parameter optimization, degradation pathways and mechanism

Aniline is a vital industrial raw material. However, highly–toxic aniline wastewater usually deteriorated effluent quality, posed a threat to human health and ecosystem safety. Therefore, this study reported a novel internal circulation iron–carbon micro-electrolysis (ICE) reactor to treat aniline wastewater. The effects of reaction time, pH, aeration rate and iron–carbon (Fe/C) ratio on the removal rate of aniline and the chemical oxygen demand were investigated using single-factor experiments. This process exhibited high aniline degradation performance of approximately 99.86% under optimal operating conditions (reaction time = 20 min, pH = 3, aeration rate = 0.5 m3·h−1, and Fe/C = 1:2). Based on the experimental results, the response surface method was applied to optimize the aniline removal rate. The Box–Behnken method was used to obtain the interaction effects of three main factors. The result showed that the reaction time had a dominant effect on the removal rate of aniline. The highest aniline removal rate was obtained at pH of 2, aeration rate of 0.5 m3·h−1 and reaction time of 30 min. Under optional experimental conditions, the aniline content of effluent was reduced to 3 mg·L–1 and the removal rate was as high as 98.24%, within the 95% confidence interval (97.84%–99.32%) of the predicted values. The solution was treated and the reaction intermediates were identified by high–performance liquid chromatography, ultraviolet–visible spectroscopy, Fourier–transform infrared spectroscopy, gas chromatography–mass spectrometry, and ion chromatography. The main intermediates were phenol, benzoquinone, and carboxylic acid. These were used to propose the potential mechanism of aniline degradation in the ICE reactor. The results obtained in this study provide optimized conditions for the treatment of industrial wastewater containing aniline and can strengthen the understanding of the degradation mechanism of iron–carbon micro-electrolysis.

Study on nitrate removal from wastewater by micro-electrolysis and construction of iron-carbon micro-electrolysis reactor (ICMER)

This study explored the potential of using iron-carbon micro-electrolysis (ICMER) to remove nitrate from artificially simulated wastewater. Various factors that mainly influence the removal efficiency of nitrate from wastewater were studied using batch experiments. The results showed that the mixing of iron and activated carbon formed a galvanic cell to effectively remove nitrates at the optimal Fe/C ratio of 3:1 (88.22% for NO3–-N and 33.54% for TN). Moreover, the removal of nitrates was not influenced by the changes in temperature (removal efficiency stabilized within the range of 88.98%-90.26% for the temperatures range of 10-50℃). In addition, the results from the continuous flow ICMER reactor showed that the removal efficiencies of nitrate and TN were 83.77% and 61.66%, respectively, with the Fe/C ratio of 3:1. Coexisting anions showed a significant influence on the removal efficiency of nitrates from wastewater. This study provides a reference for developing ICMER technology to remove nitrates from various wastewater systems.

Iron-carbon micro-electrolysis simultaneously enhanced nutrient and heavy metal removal in constructed wetlands for purifying polluted groundwater with variable hydraulic loadings

Heavy metal and nitrate pollution, as a primary water quality issue in shallow groundwater, is posing a severe threat to public health from drinking groundwater. In this study, iron-carbon (Fe-C) fillers were applied in constructed wetlands (CWs) to enhance the nutrient and heavy metal removal simultaneously, while the interaction of effective nitrate reduction and heavy metals mitigation under variable influent hydraulic loadings was also investigated. Groundwater is not conducive to biological heterotrophic denitrification due to its low dissolved organic matter content. Fe-C fillers can form plentiful microscopic galvanic cells and act as inorganic electron donors to promote the autotrophic denitrification process. The results showed that Fe-C micro-electrolytic CWs showed excellent simultaneous removal of nutrients and heavy metals. The nitrate nitrogen (NO3–-N) removal rate was as high as 75.77% due to the increased autotrophic denitrification process, while the removal of total nitrogen (TN) and total phosphorus (TP) could reach 73.72 % and 89.04% with a low nitrous oxide (N2O) emission of 12.12 μg m-2h−1. Besides, the removal rates of chromium (Cr) and lead (Pb) reached 98.96% and 97.09%, respectively. However, the presence of heavy metals might inhibit denitrification by competing with nitrite for electrons and generating free radicals, which decreased the denitrification by 10.02–39.05% particularly with the increasing of the hydraulic loading. On the other hand, heavy metals promoted TP removal by forming metal phosphate precipitates and complexations with phosphorus. This study provides comprehensive insights into processes and mechanism of simultaneous nutrient and heavy metal removal in CW.

Red mud-derived iron carbon catalyst for the removal of organic pollutants in wastewater

In order to reduce the environmental hazards of red mud (RM) and realize its resource utilization, in this study, RM-based iron-carbon micro-electrolysis material (RM-MEM) were prepared by a carbothermal reduction process using RM as raw material. The influence of the preparation conditions on the phase transformation and structural characteristics of the RM-MEM were investigated during the reduction process. The ability of RM-MEM to remove organic pollutants from wastewater was evaluated. The results showed that RM-MEM prepared at a reduction temperature of 1100 °C, a reduction time of 50 min and a coal dosage of 50% had the best removal effect for the degradation of methylene blue (MB). When the initial MB concentration was 20 mg L−1, the amount of RM-MEM material was 4 g L−1, the initial pH was 7, and the degradation efficiency reached 99.75% after 60 min. When RM-MEM is split into carbon free and iron free parts for use, the degradation effect becomes worse. Compared to other materials, RM-MEM has lower cost and better degradation. X-ray diffraction (XRD) analysis showed that hematite was transformed to zero-valent iron with the increase in the roasting temperature. Scanning electron microscopy (SEM) and energy spectroscopy (EDS) analysis showed that micron-sized ZVI particles were formed in the RM-MEM, and increasing the carbon thermal reduction temperature was beneficial to the growth of zero-valent iron particles.