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Biogenic ferrous sulfide nanoparticles (bio-FeS) as low-cost and green-synthesized nanomaterial are promising for heavy metals removal, but the need for complicated extraction, storage processes and the production of iron sludge still restrict their practical application. Here, a self-regenerable bio-hybrid consisting of bacterial cells and self-assembled bio-FeS was developed to efficiently remove chromium (Cr(VI)). A dense layer of bio-FeS was distributed on the cell surface and in the periplasmic space of Shewanella oneidensis MR-1, endowing the bacterium with good Cr(VI) tolerance and unusual activity for bio-FeS-mediated Cr(VI) reduction. An artificial transmembrane electron channel was constituted by the bio-FeS to facilitate extracellular electron pumping, enabling efficient regeneration of extracellular bio-FeS for continuous Cr(VI) reduction. The bio-hybrid maintained high activity within three consecutive treatment-regeneration cycles for treating both simulated Cr(VI)-containing wastewater (50 mg/L) and real electroplating wastewater. Importantly, its activity can be facilely and fully restored through bio-FeS re-synthesis or regeneration with replenished fresh bacteria. Overall, the bio-hybrid merges the self-regeneration ability of bacteria with high activity of bio-FeS , opening a promising new avenue for sustainable treatment of heavy metal- containing wastewater.

Dosing ferrous ions (ZVI/Fe2+), combining with oxidants (e.g., H2O2) (ZVI/H2O2), sulfidation treatment (S-ZVI), and introducing a weak magnetic field (ZVI/WMF) have been widely used to enhance the performance of zerovalent iron (ZVI) for reductive removal of contaminants. Taking Se(VI) as a probe contaminant, this study systematically compared the performances of different ZVI systems (i.e., ZVI/Fe2+, ZVI/H2O2, S-ZVI, and ZVI/WMF) for contaminant removal. All the four tested methods could greatly improve the performance of ZVI for Se(VI) removal. Se(VI) was removed by S-ZVI at S/Fe molar ratio of 0.05 with a much greater rate constant than other enhanced-ZVI technologies while the maximum amount of Se(VI) removal was obtained in ZVI/Fe2+ system with Fe2+ applied at 0.5 mM among the four tested enhanced-ZVI technologies at initial pH 6.0. In addition, Se(VI) removal by ZVI/Fe2+ was least influenced by initial pH compared to the other tested enhanced-ZVI systems, implying its good adaptability of pH. The application of these tested methods could significantly increase the electron efficiency from ∼0.5% to 4.06–8.72% and Fe2+ application was much more efficient in enhancing the electron efficiency than the other three methods. Finally, the perspective of these enhanced-ZVI technologies was compared in terms of their reactivity, selectivity, chemical cost, and pH adaptability and some suggestions for their possible application were provided.

A novel iron-cycling process based on core-shell iron granules, which contained zero-valent iron (Fe0) in the core and maghemite (γ-Fe2O3) on the shell (Fe0@FeIII granules), was proposed to in-situ control hydrogen sulfide in the sediments of the polluted urban rivers. The Fe0@FeIII granules added in the top sediment layer removed 97% of sulfide generated by sulfate-reducing bacteria in the sediments, and the sulfide removal capacity of virgin granules was 163 mg S/g Fe (114 mg S/g granule). The Fe0@FeIII granules removed the formed sulfide through the abiotic sulfide oxidation and precipitation, and they also stimulated the microbial iron reduction, which competitively consumed wastewater-derived organics and partially inhibited the sulfate reduction in the sediments. The used Fe0@FeIII granules were easily regenerated through magnetic separation from sediments and air exposure for 12 h, which enhanced the sulfide removal capacities of the regenerated granules by 12%–22%, compared to the virgin granules. During the air exposure, ferrous products (i.e., iron sulfide and surface-associated FeII) on the granule shell were completely oxidized to poorly ordered FeIII hydroxides (γ-FeOOH and amorphous FeOOH) having larger specific surface areas and higher reactivity to sulfide than γ-Fe2O3 on the virgin granules. Meanwhile, the Fe0 in the core was also partially oxidized through the indirect electron transfer, which was facilitated by the electrically conductive iron oxide minerals (Fe3O4 and Fe2O3) and the microbial electron carriers (e.g., Geobacter). The oxidation of Fe0 core contributed additional FeIII hydroxides to the sulfide control. The Fe0@FeIII granules were reused for four times in a 293-day trial, and their overall sulfide removal capacity was at least 920 mg S/g Fe. The proposed iron-cycling process can be a chemical-saving, energy-saving and cost-effective approach for the hydrogen sulfide control in the sediments of polluted urban rivers, as well as lakes, aquaculture ponds and marine.

The simultaneous degradation of seventeen emerging concern pollutants in effluent from the municipal wastewater treatment plant (MWTP) of Bogotá-Colombia was studied using high frequency ultrasound (375 kHz). The considered compounds in the effluent corresponded to pharmaceuticals (diclofenac, carbamazepine, venlafaxine, ciprofloxacin, norfloxacin, valsartan, losartan, irbesartan, sulfamethoxazole, clarithromycin, azithromycin, erythromycin, metronidazole, trimethoprim and the high potentiality of the sono-photo-Fenton/oxalic acid system for the pollutants elimination in real-world wastewater matrices. clindamycin); cocaine and its major metabolite benzoylecgonine. Due to limitation of the MWTP for the pollutants elimination, ultrasound was applied to remove these compounds. Interestingly, ultrasonic physical action led to releasing of ciprofloxacin, norfloxacin, diclofenac and sulfamethoxazole from suspended solids, whereas the chemical effects induced degradation of the rest of compounds. For the latter ones, an interesting correlation between the sonodegradation and arithmetic multiplication between hydrophobicity and concentration of pollutants was established. Afterwards, the sonochemical process was complemented with ferrous ions (sono-Fenton), ferrous ions plus light (sono-photo-Fenton) or ferrous ions plus light in presence of oxalic acid (sono-photo-Fenton/oxalic acid). Additionally, to clarify fundamental aspects of the different systems, individual treatments in distilled water of a model pollutant (valsartan) were performed. The complemented processes significantly enhanced all compounds degradation, following the order: sono-photo-Fenton/oxalic acid > sono-photo-Fenton ~ sono-Fenton > sonochemistry. The Fe2+ addition improved the pollutants elimination by generation of more hydroxyl radicals in the solution bulk. Meanwhile, oxalic acid avoided Fe3+ precipitation favoring the iron catalytic cycle. Thus, the work demonstrates

Cell lysis in sludge pretreatment by advanced oxidation process (AOP) has a great effect on sludge dewaterability. Cell lysis caused by reactive radicals (e.g. hydroxyl radical) was dependent on the reaction site of AOP. However, little is known about the accurate radical generation site of AOP in sludge pretreatment. In this study, two kinds of oxidation behaviors from different oxidants (HOCl vs. H2O2) catalyzed by ferrous iron were comparatively investigated. Higher amount of living cells (84.3%) and hydroxyl radicals (9.86 × 10−5 M), and more fragmentized sludge flocs (particle sizes of D50 was 50.1 vs. 57.3 μm of RS) were detected in sludge conditioned by Fe2+/H2O2, which implied that Fenton reaction mainly happened at surface and outside of sludge flocs (such as EPS layer and liquid phase). Thus, it could be regarded as “extracellular oxidation”. Fewer living cells (undetectable), fewer amount of hydroxyl radicals (undetectable in sludge), and more integrated sludge flocs (particle size of D50 was 56.1 vs. 57.3 μm of RS) were determined in sludge conditioned by Fe2+/Ca(ClO)2. Hence, it could be regarded as “Intracellular oxidation”. In addition, sludge pretreatment based on Fe2+/Ca(ClO)2 could achieve simultaneous deep-dewatering performance and total coliforms inactivation. Based on response surface methodology, the optimal dosages of Fe2+ and Ca(ClO)2 were proposed as 106.1 and 234.5 mg/g volatile solids respectively, without any acidification of sludge. Under these optimal dosages, the water content of dewatered sludge cake was 51.9 ± 0.1 wt% and the pH of the final filtrate was 5.8 ± 0.2. Total coliforms of sludge could be inactivated in 10 s after Fe2+/Ca(ClO)2 addition.

Algal extracellular organic matter (EOM) released from Microcystis aeruginosa can cause severe membrane fouling during algae-laden water treatment. To solve this problem, three typical sulfate radical-based advanced oxidation processes (SR-AOPs), i.e., ferrous iron/peroxymonosulfate (Fe(II)/PMS), UV/PMS and UV/Fe(II)/PMS, were employed as membrane pretreatment strategies. Their performance on mitigating EOM fouling of a ceramic UF membrane was systematically investigated and compared in the present study. The results indicated that SR-AOPs pretreatments could promote the reduction of DOC and UV254, and the removal performance showed an apparent regularity of UV/Fe(II)/PMS > Fe(II)/PMS > UV/PMS. The pretreatments were very effective for decomposing high-MW biopolymers (>20,000 Da) into low-MW humic substances (1000–20,000 Da), thus reducing the accumulation of high-MW biopolymers on membrane surface. With respect to membrane fouling control, Fe(II)/PMS significantly mitigated both reversible and irreversible membrane fouling, whereas UV/PMS only reduced reversible fouling, and exhibited little effect on irreversible fouling. By contrast, UV/Fe(II)/PMS showed the best performance for fouling reduction due to the synergistic effect of UV and Fe(II) for PMS activation. The dominating fouling mechanism was governed by both pore blockage and cake filtration, likely due to the bimodal MW distribution of EOM, and SR-AOPs pretreatments delayed the transition from pore blockage to cake filtration. In addition, SR-AOPs prior to UF membrane were also very effective to improve the removal of micropollutants (i.e., ATZ, SMT and p-CNB). These results demonstrate the potential application of SR-AOPs as pretreatment for membrane fouling control during algae-laden water treatment.

The bound water in waste activated sludge (WAS) is trapped in extracellular polymeric substances (EPS) in the form of gel-like structure, leading to a great challenge in the sludge deep dewatering. Traditional flocculation conditioning is unable to destroy EPS and ineffective to remove the bound water in WAS. In this study, we employed integration of Fe(II)-sulfite oxidation and polyacrylamide flocculation (F/S-PAM) treatment for removing the bound water and improving sludge dewaterability under aerobic conditions. Meanwhile, the floc microstructure and EPS properties were examined to understand the mechanisms of F/S-PAM conditioning. F/S produced SO3·− radicals which could decompose the EPS in sludge, releasing bound water into free water. In addition, the formed Fe(III) from F/S led to re-coagulation of decomposed EPS, and C=O groups of tryptophan played the leading role in Fe-EPS association binding, causing transformation of the secondary structure of proteins (especially β-sheets and α-helices). Then, the introduction of PAM caused re-flocculation of disintegrated sludge flocs, enhancing the sludge filterability. This work provides a novel and cost-effective method for efficient removal of bound water in sludge, and subsequence improvement in sludge dewaterability.

Fe-based materials used to adsorb P are commonly considered to be limited by the increased Fe lability, while Fe in drinking water treatment residue (DWTR) shows stable P adsorption abilities. Accordingly, this study aimed to gain insight into Fe lability in DWTR as compared to FeCl3 and Fe2(SO4)3 using Fe fractionation, EXAFS, and high-throughput sequencing technologies. The results showed that compared to Fe2(SO4)3 and FeCl3, Fe was relatively stable in the DWTR under the effects of organic matter, sulfides, and anaerobic conditions. Typically, the addition of FeCl3 and Fe2(SO4)3 enhanced Fe mobility in sediment and overlying water, promoting the formation of Fe-humin acid and ferrous sulfides (FeS and FeS2). However, the addition of DWTR, even at relatively high doses of Fe, has limited impact on Fe mobility. The addition remarkably increased oxidizable Fe in sediment (by approximately 63%), causing Fe to be dominated by oxidizable and residual fractions (like those in raw DWTR); EXAFS analysis also suggested that Fe-humin acid increased substantially with the addition of DWTR, becoming the main Fe species in sediment (with a relative abundance of 50.1%). Importantly, the Fe distributions were stable in sediment with DWTR added, which demonstrated that organic matter stabilized the Fe in the DWTR. Further analysis indicated that all materials promoted the enrichment of bacterial genera potentially related to Fe metabolism (e.g., Bacteroides, Dok59, and Methanosarcina). Fe2O3 in the FeCl3 and Fe2(SO4)3 groups and Fe-HA in the DWTR group were the key species affecting the microbial communities. Overall, the stabilizing effect of organic matter on Fe in DWTR could be used to develop Fe-based materials to enhance Fe stability for environmental remediation.

The application of in situ electrochemical generation of ferrous (Fe(II)) ions for phosphorus (P) removal in wastewater treatment was investigated with attention to the efficacy, kinetics and mechanism. At concentrations typical of municipal wastewater, P could be removed by in situ Fe(II) with removal efficiency higher than achieved on addition of FeSO4 and close to that of FeCl3 under both anoxic and oxic conditions. The generation of alkalinity due to water electrolysis at the cathode created much higher pH conditions compared to FeSO4 dosing thereby resulting in very different pathways of Fe solid phase formation and associated P removal mechanisms. The remarkably similar dependence of P removal on accumulated Fe for all investigated currents, initial P concentrations and DO conditions indicated that kinetic aspects did not play a role in P removal during in situ Fe(II) dosing. Thermodynamic modelling was undertaken to investigate possible solid phase formation pathways under anoxic conditions and these insights were extended to oxic conditions. The exclusive formation of ferrous hydroxide during anoxic in situ Fe(II) dosing implied that P removal occurred via coprecipitation and adsorption. Under oxic conditions, the high pH conditions would have resulted in rapid Fe(II) oxidation and formation of ferric oxyhydroxides with associated coprecipitation and adsorption effecting P removal in a similar pattern to that observed under anoxic conditions. In situ Fe(II) dosing represents a versatile option for chemical P removal with the precise control of Fe dosage to optimize FeP forms for possible P recovery.

Water utilities worldwide spend annually billions of dollars to control sulfide-induced corrosion in sewers. Iron salts chemically oxidize and/or precipitate dissolved sulfide in sewage and are especially used in medium- and large-size sewers. Iron salt dosing rates are defined ad hoc, ignoring variation in sewage flows and sulfide levels. This often results in iron overdosing or poor sulfide control. Online dosing control can adjust the chemical dosing rates to current (and future) state of the sewer system, allowing high-precision, stable and cost-effective sulfide control. In this paper, we report a novel and robust online control strategy for the dosing of ferrous salt in sewers. The control considers the fluctuation of sewage flow, pH, sulfide levels and also the perturbation from rainfall. Sulfide production in the pipe is predicted using auto-regressive models (AR) based on current flow measurements, which in turn can be used to determine the dose of ferrous salt required for cost-effective sulfide control. Following comprehensive model-based assesment, the control was successfully validated and its effectiveness demonstrated in a 3-week field trial. The online control algorithm controlled sulfide below the target level (0.5 mg S/L) while reducing chemical dosing up to 30%.

Remarkable atrazine degradation in the S(IV) autoxidation process catalyzed by Fe2+-Mn2+ (Fe2+/Mn2+/sulfite) was demonstrated in this study. Competitive kinetic experiments, alcohol inhibiting methods and electron spin resonance (ESR) experiments proved that sulfur radicals were not the major oxidation species. Mn(III) was demonstrated to be the primary active species in the Fe2+/Mn2+/sulfite process based on the comparison of oxidation selectivity. Moreover, the inhibiting effect of the Mn(III) hydrolysis and the S(IV) autoxidation in the presence of organic contaminants indicated the existence of three Mn(III) consumption routes in the Fe2+/Mn2+/sulfite process. The absence of hydroxyl radical and sulfate radical was interpreted by the competitive dynamics method. The oxidation capacity of the Fe2+/Mn2+/sulfite was independent of the initial pH (4.0-6.0) because the fast decay of S(IV) decreased initial pH below 4.0 rapidly. The rate of ATZ degradation was independent of the dissolved oxygen (DO) because that the major DO consumption process was not the rate determining step during the production of SO5•-. Phosphate and bicarbonate were confirmed to have greater inhibitory effects than other environmental factors because of their strong pH buffering capacity and complexing capacity for Fe3+. The proposed acetylation degradation pathway of ATZ showed the application of the Fe2+/Mn2+/sulfite process in the research of contaminants degradation pathways. This work investigated the characteristics of the Fe2+/Mn2+/sulfite process in the presence of organic contaminants, which might promote the development of Mn(III) oxidation technology.

To assess the fate and long-term reactivity of bimetallic nanoparticles used in groundwater remediation, it is important to trace the physicochemical transformation of nanoparticles during aging in water. This study investigated the short-term (within 5 d) and long-term (up to 90 d) aging process of Fe/Ni bimetallic nanoparticles (Fe/Ni BNPs) in simulated groundwater and the consequent effect on the particle reactivity. Results indicate that the morphological, compositional and structural transformation of Fe/Ni BNPs happened during the aging. In the 5-d short-term aging, Fe0 corrosion occurred rapidly and was transformed to ferrous ions which were adsorbed onto the surface of Fe/Ni BNPs, accompanied by the elevation of solution pH and the negative redox potential. In the long-term aging, scanning electron microscopy (SEM) images show that the particles transformed from spherical to rod-like and further to sheet-like and needle-like. X-ray diffraction (XRD) analysis reveals that the main aging product was magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) after aging for 60–90 d. Energy dispersive spectrometer (EDS) analysis demonstrates that the mass ratio of Fe/Ni increased with aging, revealing that Ni were possibly gradually entrapped and covered by the iron oxides. Besides, the release of Ni into solution was also detected during the aging. The reactivity of the aged Fe/Ni BNPs was examined by studying its performance in tetracycline (TC) removal. The aged Fe/Ni BNPs within 2 d kept similar removal efficiency of TC as the fresh particles. However, the removal efficiency of TC by Fe/Ni BNPs aged for 5–15 d dropped by 20–50% due to aggregation and oxidation of particles, and the removal efficiency further decreased slowly with the prolongation of aging time up to 90 d. This reveals that Fe/Ni BNPs were vulnerable to passivation in water environments.

Sewer deterioration caused by sulfide-induced concrete corrosion is spreading worldwide. Within the strategies to overcome this problem, dosing iron salts into the pipeline has attracted more attention. However, there is not yet research that evaluates this method whether it is overall environmentally friendly. Here, we conducted a comparative Life Cycle Assessment (LCA) to adjudge the benefits of dosing ferric chloride over non-dosing option in three different H2S concentration levels (High, Medium, Low). Compared with taking no precautions, dosing ferric chloride performs better for all impact categories only in High H2S situation, which can reduce the environmental impacts by 10% to 50%. In Medium H2S situation, dosing ferric chloride shows lower environmental impacts of Global Warming, Fossil Fuel Depletion, Acidification, and Eutrophication, while leads to the deterioration of Human Toxicity and Freshwater Ecotoxicity by 10% and 13%, respectively. In Low H2S situation, dosing ferric chloride performs even worse for all impact categories. Therefore, from an LCA perspective, this study recommends iron salts dosing technology to be applied in severe corrosion conditions caused by high H2S concentrations. Contribution analysis shows that asphalt and diesel consumed during the sewer construction and renovation dominate all impact categories for non-dosing option, whereas the main contributor of Human Toxicity and Freshwater Ecotoxicity is shifted to ferric chloride production in dosing option, average at around 50%. Sensitivity analysis on the length of pipes protected by iron salts confirms that the initial dosing location is more preferable to be set at upstream of the sewer system. From an LCA perspective, as alternatives to ferric chloride, ferrous chloride is superior in all impact categories, and ferric sulfate could reduce the toxicity-related impacts and other effects at the expense of exacerbation of acidification. In the end, a systematic optimization of salts dosing should be considered in urban sewer management practice.

Elevated As(III) and Fe(II) in shallow reducing groundwater can be frequently re-oxidized by introducing O2 due to natural/anthropogenic processes, thus leading to oxidative precipitation of As as well as Fe. Nevertheless, the geochemical process may be impacted by co-existing engineered black carbon due to its considerable applications, which remains poorly understood. Taking rice husk-derived biochar prepared at 500 °C as an example, we explored its impact on the process particularly for the As(III) oxidation and (im)mobilization during the oxygenation. The presence of the biochar had a negligible effect on the As(III) oxidation and immobilization extents within 1 d, while accelerating their rates. However, the immobilized As(III) was significantly liberated from the formed Fe(III) minerals afterward within 21 d, which was 2.2-fold higher than that in the absence of the biochar. The enhanced As(III) liberation was attributed to the presence of the surface silicon-carbon structure, consisting of the outer silicon and inner carbon layers, of the rice husk-derived biochar. The outer silicon components, particularly for the dissolved silicate primarily promoted the As(III) release via ligand exchange, while significantly impeding the transformation of ferrihydrite to lepidocrocite and goethite still resulted secondarily in the As(III) release. Our findings reveal the possible impact of biochar on the environmental behavior and fate of As(III) in the Fe(II)-rich groundwater during the oxygenation. This work highlights that biochar, particularly for its structural features should be a concern in re-mobilizing As in such scenarios when the oxygenation time reaches several days or weeks.

The addition of iron salts is one of the most commonly used dosing strategies for sulfide control in sewers. However, iron salts decrease the sewage pH which not only reduces the effectiveness of sulfide precipitation but also enhances the release of residual sulfide to the sewer atmosphere. Equally important, concentrated iron salt solutions are corrosive and their frequent transport, handling, and on-site storage often come with Occupational Health and Safety (OH&S) concerns. Here, we experimentally demonstrated a novel sulfide control approach using electrochemical systems with parallel placed iron electrodes. This enabled combining anodic dissolved iron species release with cathodic hydroxyl anion production, which alleviates all the aforementioned concerns. A long-term experiment was successfully carried out achieving an average sulfide removal efficiency of 95.4 ± 4.4% at low voltage input of 2.90 ± 0.54 V over the course of 8 weeks. This electrochemical method was demonstrated to successfully achieve efficient sulfide control. In addition, it increases the sewage pH, thereby overcoming the drawbacks associated with the pH decrease in the case of conventional iron salt dosing. Ferrous ions were produced at an overall coulombic efficiency (CE) of 98.2 ± 1.2%, whereas oxygen evolution and direct sulfide oxidation were not observed. Short-term experiments showed that increasing either inter-electrode gap or current density increased the cell voltage associated with the increase in the ohmic drop of the system. Overall, this study highlights the practical potential of in-situ generation of dissolved iron species and simultaneous hydroxyl anion generation for efficient sulfide control in sewers.

Ferrous-tetrapolyphosphate complexes (Fe(II)-TPP) activate oxygen and hydrogen peroxide to produce reactive oxidants capable of degrading organic compounds. In this study, the Fe(II)-TPP/O2 and Fe(II)-TPP/H2O2 systems were assessed for oxidative degradation of microcystin-LR (MC-LR), the most toxic and abundant cyanotoxin. The degradation of MC-LR was optimized for both the Fe(II)-TPP/O2 and Fe(II)-TPP/H2O2 systems when the molar ratio of TPP:Fe(II) was approximately 5.7-5.9. The optimal H2O2 dose for MC-LR degradation by Fe(II)-TPP/H2O2 was found to be 320 μM. The Fe(II)-TPP/O2 and Fe(II)-TPP/H2O2 systems exhibited two pH optima for MC-LR degradation i.e., ∼7 and 9, which can be attributed to pH-dependent reactivity changes of the resultant oxidants (most likely the ferryl-tetrapolyphostate complex, Fe(IV)-TPP). Liquid chromatography-mass spectrometry identified 22 compounds produced by the oxidation of MC-LR, including four primary oxidation products. One of the primary products, in particular, was formed via oxidative cleavage of the alkene group in the Mdha moiety of MC-LR. This compound and its secondary oxidation products are rarely found when MC-LR is transformed by other oxidants and is believed to reflect a unique reaction pathway involving Fe(IV)-TPP. Meanwhile, the hepatotoxicity of the reaction solution decreased concurrently with a decrease on MC-LR concentration.

International audience; Accurate identification of phosphorus (P) forms is crucially important for understanding the geochemical cycle of P; however, until now the role of ferrous iron P (Fe(II)-P) buried in sediments has been completely ignored in nearly all sequential extraction procedures developed. Using sediment cores sampled from Donghu Lake in Wuhan, China, this study explored a modified version of widely used sequential P extraction method (SEDEX; Ruttenberg, 1992) in which Fe(II)-P was identified as an independent fraction. Based on the high selectivity of the extractant (0.2% 2,2′–bipyridine+0.1 M KCl) and the dissolution equilibrium of P, procedures for extracting Fe(II)-P were optimized using a 1:100 solid:liquid ratio and extraction at 50 ± 1 °C for 24 h. The sedimentary P extracted was divided into five fractions: loosely-bound P, Fe(II)-P, CDB-P, Ca-P and O-P. Fe(II)-P was the predominant fraction in fresh sediments in Donghu Lake, accounting for 15.7–49.9% of TP, with a mean of 31.6%. The mean values of Ca-P, O-P, CDB-P and loosely-bound P were 28.4%, 22.7%, 17.1% and 4.3%, respectively. Combined with component analysis of extracts and recovery experiments of standard reference minerals (vivianite, Fe3(PO4)2·8H2O) in natural sediments, extraction of Fe(II)-P with 0.2% 2,2-bipridine and 0.1 M KCl was robust, with a good recovery rate (88.7–100.6%) and little of the Ca-P dissolved. It is possible to use this innovative SEDEX not only to distinguish the contribution of different P matrices in fresh sediments, but also to investigate the transformation of sedimentary P under different redox conditions. Therefore, greater focus on Fe(II)-P is necessary, because it is a major sink for the geochemical process of sedimentary P.

Autotrophic iron-dependent denitrification (AIDD) is arising as a promising process for nitrogen removal from wastewater with a low carbon to nitrogen ratio. However, there is still a debate about the existence of such a process in activated sludge systems. This work provides evidence and elucidated the feasibility of autotrophic Fe(II)-oxidizing nitrate-reducing culture for nitrogen removal by long-term reactor operation, batch experimental verification, unstructured kinetic modeling and microbial community analyses. A relatively stable nitrate removal rate was achieved coupled with the oxidation of ferrous ions in 3-month operation of reactor. The kinetic modeling suggests that the iron oxidation was a growth-associated process in AIDD. Utilization of extracellular polymeric substances (and/or soluble microbial products) as electron donor for denitrification by heterotrophic denitrifiers was not mainly responsible for nitrogen removal in the reactor. After long-term operation of the reactor with activated sludge as inoculum, the enrichment culture KS-like consortium, dominated by Fe(II) oxidizer, Gallionellaceae, was successfully acclimated for autotrophic Fe(II)-oxidizing nitrate reduction. This work extents our understanding about the existence of such an autotrophic Fe(II)-oxidizing nitrate-reducing culture in both natural and engineered systems, and opens a door for its potential application in wastewater treatment.

Emerging water treatment technologies using ferrous and zero-valent iron show promising virus mitigation by both inactivation and adsorption. In this study, iron electrocoagulation was investigated for virus mitigation in drinking water via bench-scale batch experiments. Relative contributions of physical removal and inactivation, as determined by recovery via pH 9.5 beef broth elution, were investigated for three mammalian viruses (adenovirus, echovirus, and feline calicivirus) and four bacteriophage surrogates (fr, MS2, P22, and ΦX174). Though no one bacteriophage exactly represented mitigation of the mammalian viruses in all water matrices, bacteriophage ΦX174 was the only surrogate that showed overall removal comparable to that of the mammalian viruses. Bacteriophages fr, MS2, and P22 were all more susceptible to inactivation than the three mammalian viruses, raising concerns about the suitability of these common surrogates as indicators of virus mitigation. To determine why some bacteriophages were particularly susceptible to inactivation, mechanisms of bacteriophage mitigation due to electrocoagulation were investigated. Physical removal was primarily due to inclusion in flocs, while inactivation was primarily due to ferrous iron oxidation. Greater electrostatic attraction, virus aggregation, and capsid durability were proposed as reasons for virus susceptibility to ferrous-based inactivation. Results suggest that overall treatment claims based on bacteriophage mitigation for any iron-based technology should be critically considered due to higher susceptibility of bacteriophages to inactivation via ferrous oxidation.

As obligate anaerobes, anammox bacteria are sensitive to oxygen, which might hinder the maximization of anammox activity. However, there are very few effective strategies to rapidly recover anammox activity after its deterioration under exposure of oxygen. In this study, the activity recovery of anammox bacteria encountering dissolved oxygen (DO) exposure (0.2 and 2.0 mg L−1) were compared by three strategies in short-term experiments, nZVI, Fe(II) dosing, and N2 purging. nZVI is more effective in recovering anammox activity with a high DO exposure (2 mg L−1), compared to a low DO exposure (0.2 mg L−1). After inhibiting by 2.0 mg L−1 DO, anammox activity recovery (normalized to the control) was ranked in the order of nZVI (5 mg L−1) addition (63 ± 8.2%) > Fe(II) (5 mg L−1) addition (41 ± 8.0%) >N2 purging (39 ± 4.0%). In contrast to Fe(II) ion additions, the shell structure of nZVI combined with the buffering effect of biomass-extracellular polysaccharide (EPS) prevented the sharp pH variation and excessive dissolved Fe(II)/Fe(III) in solution. Under such circumstances, nZVI addition (5 and 25 mg L−1) increased the intracellular reactive oxygen species (ROS) to a moderate level (

Phosphorus (P) can be retained in mineral association with ferrous iron (Fe) as vivianite, Fe(II)3(PO4)2 ∙ 8 H2O, in lake sediments. The mineral is formed and remains stable under anoxic non-sulphidogenic conditions and, therefore, acts as a long-term P sink. In laboratory experiments under anoxic conditions, we investigated whether P adsorbed to amorphous Fe(III)-hydroxide functioned as a precursor phase of vivianite when added to different sediments as a treatment. The untreated sediments served as controls and were naturally Fe-rich (559 µmol/g DW) and Fe-poor (219 µmol/g DW), respectively. The solid P binding forms analysed by sequential extraction and X-ray diffraction were related to coinciding pore water analyses and the bacterial community compositions of the sediments by bacterial 16S rRNA gene amplicon sequencing. In the treatments, within a period of 40 d, 70 % of the redox-sensitive Fe(III)-P was transformed into redox-stable P, which contained vivianite. The mineral was supersaturated in the pore water, but the presence of Fe(III)-P functioning as a precursor was sufficient for measurable vivianite formation. The composition of the microbial community did not differ significantly (PERMANOVA, p = 0.09) between treatment and control of the naturally Fe-rich sediment. In the naturally Fe-poor sediment, the microbial community changed significantly (PERMANOVA, p = 0.001) in response to the addition of Fe(III)-P to the sediment. The freshly formed redox-stable P was not retransferred to a redox-sensitive compound by aeration for 24 h until 90 % O2 saturation was reached in the sediment slurry. We conclude that 1) Fe(III)-hydroxide bound P, resulting from oxic conditions at the sediment-water interface, is immobilised during anoxic conditions and stable even after re-oxygenation; 2) the process is feasible within the time scales of anoxic lake stratification periods; and 3) in relatively Fe-poor lakes, Fe dosing can provide excess Fe to form the precursor.

To enhance the advanced oxidation process based on persulfate, CuO was introduced into the Fe2+/PS system to achieve a synergistic effect between Fe and Cu. Results showed that Fe2+ was able to adsorb onto the CuO surface to form Fe(II) and further reduced Cu(II) into Cu(I), which can further release into the solution to participate in oxidation reactions. In this case, SO4·− can be generated via Fe2+ and Cu+ reactions with PS and ·OH from Cu+ reaction with dissolved oxygen (DO). The degradation efficiency of APAP was studied under the optimal condition (initial pH 6.5, PS = 0.8 g L−1, Fe2+ = 0.7 mM, CuO = 0.3 g L−1), and the results indicated that the Fe2+/CuO/PS system can achieve a higher degradation rate of APAP (92% within 90 min) rather than Fe2+/PS and CuO/PS system (79% and 10%). Quenching experiment was performed to verify the active radicals in the Fe2+/CuO/PS system. Sulfate and hydroxyl radicals were generated in the Fe2+/CuO/PS system. Besides, some critical factors, such as Fe2+ concentration, catalyst dosage, PS concentration, initial pH (buffers and nonbuffers), and dissolved oxygen were evaluated in bath experiments. Results indicated that dissolved oxygen was essential in the Fe2+/CuO/PS system. APAP degradation experiments were conducted in surface water, and the intermediates were detected via GC-MS. The results indicated that the Fe2+/CuO/PS system is effective in the treatment of APAP in natural waters.

Stonecutters Island Sewage Treatment Works is one of the largest sewage treatment plants in the world and consists mainly of a chemically enhanced primary treatment (CEPT) unit and a disinfection unit. It has long been realized that most of the dosed chlorine (15 mg/L) is lost at the beginning part of the disinfection unit during disinfection of the CEPT effluent. Lab-scale tests were therefore conducted in this study to determine the causes. Because ferric chloride is used in CEPT, ferrous iron in the CEPT effluent (from the reduction of ferric iron) was initially thought to be the main chlorine consumer. However, the chlorine consumption by ferrous iron was found to be 1.2 mg/L at most. Suspended solids and sulfide also did not contribute significantly to the chlorine consumption. Batch tests were therefore conducted to evaluate the effects of mixing condition and chlorine stock solution concentration on the chlorine consumption. Less chlorine was consumed upon increased mixing. Using a high-concentration chlorine stock solution (25000 mg/L) resulted in a 3-times-higher chlorine consumption in the absence of mixing than using a low-concentration chlorine stock solution (2500 mg/L). By correlating the losses of ammonia and total nitrogen with the chlorine consumption, we hypothesized that the use of a high-concentration chlorine stock solution under poor mixing leads to a localized high ratio of chlorine to ammonia, resulting in breakpoint chlorination and an unusually excessive chlorine consumption. A novel apparatus was developed to quantify the nitrogen gas generated during chlorination of a simulated wastewater, and the mass balance of nitrogen-containing species (i.e., ammonia, nitrogen gas, nitrite and nitrate) during the chlorination was inspected. The good fit between the measured chlorine consumption and that back-calculated from nitrogen-containing species verified our hypothesis. Finally, it needs mentioning that the high chlorine consumption and the breakpoint chlorination may occur during chlorine disinfection of any sewage effluents with relatively high ammonia levels; thus it is suggested that either not-too-high concentrations of chlorine stock solutions or sufficient mixing should be applied during disinfection of the sewage effluents.

Phosphate recovery from sewage sludge is essential in a circular economy. Currently, the main focus in centralized municipal wastewater treatment plants (MWTPs) lies on struvite recovery routes, land application of sludge or on technologies that rely on sludge incineration. These routes have several disadvantages. Our study shows that the mineral vivianite, Fe2(PO4)3 × 8H2O, is present in digested sludge and can be the major form of phosphate in the sludge. Thus, we suggest vivianite can be the nucleus for alternative phosphate recovery options. Excess and digested sewage sludge was sampled from full-scale MWTPs and analysed using x-ray diffraction (XRD), conventional scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), environmental SEM-EDX (eSEM-EDX) and Mossbauer spectroscopy. Vivianite was observed in all plants where iron was used for phosphate removal. In excess sludge before the anaerobic digestion, ferrous iron dominated the iron pool (≥50%) as shown by Mossbauer spectroscopy. XRD and Mossbauer spectroscopy showed no clear correlation between vivianite bound phosphate versus the iron content in excess sludge. In digested sludge, ferrous iron was the dominant iron form (>85%). Phosphate bound in vivianite increased with the iron content of the digested sludge but levelled off at high iron levels. 70–90% of all phosphate was bound in vivianite in the sludge with the highest iron content (molar Fe:P = 2.5). The quantification of vivianite was difficult and bears some uncertainty probably because of the presence of impure vivianite as indicated by SEM-EDX. eSEM-EDX indicates that the vivianite occurs as relatively small (20–100 μm) but free particles. We envisage very efficient phosphate recovery technologies that separate these particles based on their magnetic properties from the complex sludge matrix.

Iron dosing of membrane bioreactors (MBRs) is widely used as a means of meeting effluent phosphorus targets but there is limited understanding of the nature of iron and phosphorus-containing solids that are formed within the bioreactor (an important issue in view of the increasing interest in recovering phosphorus from wastewaters). Of particular challenge is the complexity of the MBR system and the variety of reactions that can occur on addition of iron salts to a membrane bioreactor. In this study, the performances of bench scale MBRs with dosing of either ferrous or ferric salts were monitored for a period of four months. The distributions of Fe and P-species in the Fe-conditioned sludges were determined using X-ray absorption spectroscopy (XAS) at the Fe K-edge and the P K-edge. Regardless of whether iron was dosed to the anoxic or aerobic chambers and regardless of whether ferrous (Fe(II)) or ferric (Fe(III)) iron was dosed, iron present in the minerals in the conditioned sludges was consistently in the +III oxidation state. Fitting of the Fe K-edge EXAFS spectra revealed that an Fe(III)-phosphate species was the main Fe species present in all cases with the remaining fraction dominated by lepidocrocite (γ-FeOOH) in the Fe(II)-dosed case and ferrihydrite (am-FeOOH) in the Fe(III)-dosed case. Approximately half the phosphorus in the activated sludge samples was present as a distinct Fe-PO4 mineral (such as strengite or an amorphous ferric hydroxyl phosphate analogue of strengite) and half as phosphorus adsorbed to an iron oxyhydroxide mineral phase indicating that both co-precipitation and adsorption of phosphorus by iron contribute to removal of phosphorus from the MBR supernatant.

Batch tests were conducted to investigate the roles of dissolved Fe(2+) and corrosion products, and the involved mechanisms in selenate (Se(VI)) removal by zero-valent iron (ZVI). The results showed that insignificant Se(VI) removal (4-7.5%) was observed in the presence of ZVI or Fe(2+) alone. However, external supply of dissolved ferrous ion dramatically enhanced Se(VI) removal in the presence of ZVI. Selenate removal efficiency increased with increasing Fe(2+) concentration. Selenate removal sustained only if Fe(2+) was supplied continuously. Both sequential extraction experiments and XPS analysis showed that selenate was reduced step by step, with elemental selenium and adsorbed selenite as the dominant reductive products. Selenite and elemental selenium could be further reduced to selenide, with continuous Fe(2+) supply and sufficient reaction time. In the ZVI-Se(VI)-Fe(2+) system, ZVI was the major electron donor for selenate reduction. Fe(2+) functioned as electron donor as well and was consumed with a Fe(2+):Se stoichiometry of ∼1:1. It also facilitated the transformation of the passive layer of iron coatings to a medium (e.g., magnetite) favoring electron transfer and thus enhanced selenate reduction. Iron corrosion products were media for electron transfer and reactive interfaces for selenium adsorption and reduction. These findings provided a new approach to overcome ZVI surface passivation for long-term application.

A novel Mn(VII)–Fe(II) pre-treatment was proposed to simultaneously enhance the removal of Microcystis aeruginosa by aluminum chloride (AlCl3) coagulation and enabled lowering the dose of Al as effective coagulation can be achieved only by Al, however, at higher doses. In this process, permanganate [Mn(VII)] and ferrous sulfate [Fe(II)] were dosed sequentially prior to Al. The application of Fe(II) not only avoids the extensive oxidation of M. aeruginosa by Mn(VII) but also introduces Fe(III) formed in situ into the system. Results show that, at Al doses of 83.3–108.3 μM, Mn(VII)–Fe(II) pretreatment (Mn(VII) dose: 8.3–16.7 μM; Fe(II) dose: 39.5 μM) is capable of enhancing M. aeruginosa removal by 73.4–81.4%. In contrast, only 0–65.4% and 2.7–8.2% increase in M. aeruginosa removal is achieved by Mn(VII) and Fe(II) pre-treatment, respectively. The ESI-MS spectrum shows that the freshly formed Fe(III) hydrolyzes much more slowly than pre-formed Fe(III) does, and this effect results in its higher efficiency towards the removal of M. aeruginosa. Moreover, in the co-existing system, Fe tends to hydrolyze preferentially and the presence of Fe salts improves the precipitation of Al and vice versa. Thus, the use of Fe and Al as dual-coagulants is practically valuable to control the residual level of coagulant(s) besides its improvement on the removal of M. aeruginosa.

Coagulation and ozonation have been widely used as pretreatments for ultrafiltration (UF) membrane in drinking water treatment. While beneficial, coagulation or ozonation alone is unable to both efficiently control membrane fouling and product water quality in many cases. Thus, in this study an emerging alternative of ferrous iron/peroxymonosulfate (Fe(II)/PMS), which can act as both an oxidant and a coagulant was employed prior to UF for treatment of natural surface water, and compared with conventional coagulation and ozonation. The results showed that the Fe(II)/PMS-UF system exhibited the best performance for dissolved organic carbon removal, likely due to the dual functions of coagulation and oxidation in the single process. The fluorescent and UV-absorbing organic components were more susceptible to ozonation than Fe(II)/PMS treatment. Fe(II)/PMS and ozonation pretreatments significantly increased the removal efficiency of atrazine, p-chloronitrobenzene and sulfamethazine by 12-76% and 50-94%, respectively, whereas coagulation exerted a minor influence. The Fe(II)/PMS pretreatment also showed the best performance for the reduction of both reversible and irreversible membrane fouling, and the performance was hardly affected by membrane pore size and surface hydrophobicity. In addition, the characterization of hydraulic irreversible organic foulants confirmed its effectiveness. These results demonstrate the potential advantages of applying Fe(II)/PMS as a pretreatment for UF to simultaneously control membrane fouling and improve the permeate quality.

Ferric iron is widely dosed in wastewater treatment plants dealing with sulfide for septicity control, which generates a great amount of iron-rich chemical sludge that is challenging and costly to dispose. This study investigates the feasibility of using this iron sludge as the electron donor for autotrophic denitrification, not only realizing high nitrogen removal efficiency without additional carbon source requirement, but also partially mitigating iron-rich chemical sludge disposal and reduce sludge production by enriching low-yield autotrophic denitrifiers in the system. Both batch tests and performance monitoring of a lab-scale up-flow anaerobic sludge blanket reactor with a more than 300 days of operation were conducted. All the results confirmed the feasibility of using iron sludge as electron donor for autotrophic denitrification. The nitrate reduction rate with iron sludge was highly influenced by the type of ferrous electron donor and the electron donor/acceptor ratio. Ferrous hydroxide had significantly higher nitrate reduction rate than ferrous sulfide at the same electron donor/acceptor ratio. The nitrate reduction rate also accelerated with the increase of the electron donor/acceptor ratio. However, if the total surface area of the iron sludge is considered for comparison, it was shown that ferrous hydroxide and ferrous sulfide provided similar nitrate reduction rates of around 0.02 mmol N/m2/d in this study, indicating total surface area would be the key parameter for denitrification efficiency for the solid phase electron donor.

In present work, the treatment of aromatic compounds of simulated wastewater was performed by Fenton and NaOCl/Fe2+ processes. The model solution was prepared based on the wastewater composition of Diisocyanate unit of Karoon Petrochemical Company/Iran containing Diamino-toluenes, Nitro-phenol, Mononitro-toluene, Nitro-cresol, and Dinitro-toluene. Experiments were conducted in a batch mode to examine the effects of operating variables such as pH, oxidant dosages, ferrous ion concentration and numbers of feeding on COD removal. Taguchi experimental design was used to determine the optimum conditions. The COD removal efficiency under optimum conditions (suggested by Taguchi design) in Fenton and NaOCl/Fe2+ processes was 88.7% and 83.4%, respectively. The highest contribution factor in Fenton process belongs to pH (47.47%) and in NaOCl/Fe2+ process belongs to NaOCl/pollutants (50.26%). High regression coefficient (R2: 0.98) obtained for Taguchi method, indicates that models are statistically significant and are in well agreement with each other. The NaOCl/Fe2+ process utilizing a conventional oxidant, in comparison to hydrogen peroxide, is an efficient cost effective process for COD removal from real wastewater, although the removal efficiency is not as high as in Fenton process; however it is a suitable process to replace Fenton process in industrial scale for wastewater involved aromatic compounds with high COD. This process was successfully applied in Karoon Petrochemical Company/Iran.

A pilot scale membrane bioreactor (3.7 m 3 /day capacity), configured for alternate pointferrous sulphate addition, was evaluated in a fourteen month trial to comply with aneffluent discharge requirement of less than 0.15 mg-P/L at the 50 th percentile and less than0.30 mg-P/L at the 90th percentile. Ferrous sulphate was added at a molar ratio (Fe(II):PO 4 )of 2.99 in the filtration chamber for 85 days and 2.60 in the primary anoxic zone for 111days. Addition of ferrous salts to the anoxic zone achieved a final effluent phosphorousconcentration (mg-P/L) of

International audience; This work aimed at decontaminating biologically treated domestic wastewater effluent from pharmaceutical residues by using sulphate radical based homogeneous photo-Fenton involving persulphate (PS) as an oxidant, ferrous iron (Fe(II)) as a catalyst and simulated solar irradiation as a light source. This is the first time that the beneficiary use of solar energy in PS/Fe(II)/UV–Vis system was evaluated by using carbamazepine (CBZ) as a probe compound. In wastewater, CBZ was fully degraded in 30 min for an initial CBZ concentration of 50 μM and an optimal PS:Fe(II) molar ratio of 2:1 thanks to the high selectivity in reactivity of the sulphate radical limiting scavenging effects of organic matter and inorganic ions. Seventeen by-products were identified using liquid chromatography-high resolution-mass spectrometry allowing for the establishment of degradation pathways. CBZ first underwent degradation through one electron transfer oxidation processes due to sulphate radical reactivity followed by hydroxylation processes through hydroxyl radical formed by Fe(III) photoreduction. The sequential generation of sulphate radical and hydroxyl radical has made PS/Fe(II)/UV–Vis a kinetically effective process in removing CBZ from wastewater without the accumulation of toxic intermediates and opens new remediation strategies for tertiary treatment in domestic wastewater treatment plants.

Ferrous iron/peroxymonosulfate (Fe(II)/PMS) oxidation was employed as a pretreatment method for ultrafiltration process to control membrane fouling caused by natural organic matter, including humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA), and their mixture (HA-SA-BSA). To evaluate the mechanism of fouling mitigation, the effects of Fe(II)/PMS pretreatment on the characteristics of feed water were examined. The degradation of atrazine (ATZ) was also investigated and the species of generated radicals were preliminarily determined. Under the test exposure (15 and 50 μM), Fe(II)/PMS pretreatment effectively mitigated membrane fouling caused by HA, SA and HA-SA-BSA mixture, and the performance improved with the increase of Fe(II) or PMS dose; whereas aggravated BSA fouling at lower doses and fouling alleviation was observed only at a higher dose (50/50 μΜ). The fouling mitigation was mainly attributed to the effective reduction of organic loadings by coagulation with in-situ formed Fe(III). Its performance was comparable or even slightly higher than single coagulation with Fe(III), most likely due to the oxidation by Fe(II)/PMS process. Fe(II)/PMS oxidation showed better performance in reducing DOC and UV254, fluorescence intensities of fluorescent components and UV-absorbing compounds than single coagulation. In addition, Fe(II)/PMS pretreatment was efficient in ATZ degradation due to the generation of sulfate and hydroxyl radicals, whereas coagulation was ineffective to remove it.

Nanoscale zerovalent iron (nZVI)-mediated oxidation reaction is increasingly being used for enhanced treatment of water or wastewater processes; however, the fate and eco-toxicological effects of nZVI in the surface aquifer remain unclear. We investigated bioaccumulation and lethal-to-sublethal toxic effects on early life development of Japanese medaka (Oryzias latipes) with 7-day exposure to 25–200 mg/L of well-characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nZVI (CMC-nZVI), nanoscale iron oxide (nFe3O4) or ferrous ion [Fe(II)aq]. The CMC-nZVI solution had the greatest acute mortality and developmental toxic effects in embryos, with lesser and the least effects with Fe(II)aq and nFe3O4. The toxicity of CMC-nZVI was ascribed to its high reactivity in the oxygenic solution, which led to a combination of hypoxia and production of reactive oxygen species (ROS) and Fe(II)aq. nFe3O4 (50–100 mg/L) was more bioavailable to embryos and bioaccmulative in hatchlings than suspended CMC-nZVI. The antioxidant balance was differentially altered by induced intracellular ROS in hatchlings with all 3 iron species. We revealed causal toxic effects of nZVI and its oxidized products in early life stages of medaka fish using different organizational levels of biomarker assays. The toxicity results implicate a potential eco-toxicological impact of nZVI on the aquatic environment.

This paper reports on the reusability and the optimal reuse of iron-rich sludge for an electrochemical Fenton-type process using sequencing batch mode and separation batch mode reuse models. In the sequencing batch mode, processes of electrochemical treatment, neutralization, sedimentation, and re-dissolution of iron sludge were all performed in the same reactor, whereas the neutralization and sedimentation of iron sludge in the separation batch mode was carried out in an iron recovery tank separated from the electrochemical reactor. The effects of iron speciation at different pH levels were discussed. It was found that ferric ions at a pH ≤2.5 were suitable for this electrochemical Fenton-type process where ferrous ions acted as hydroxyl radical scavengers, generating brownish deposits on the cathode at pH 3. When the sequencing batch mode was applied, the current efficiency in the Fenton-type process after the iron recovery declined due to the formation of insoluble deposits on the electrodes, which decreased at lower pH. The deposits were mainly formed during the neutralization and sedimentation steps after the electrochemical process. Fortunately, iron from the sludge could be reused for the electrochemical process when the separation batch mode was used, with 100% iron recovery and no decline in current efficiency.

In this research, we conducted trichloroethylene (TCE) reduction in a column filled with iron and iron-reducing bacteria (IRB) and developed a mathematical model to investigate the critical reactions between active species in iron/IRB/contaminant systems. The formation of ferrous iron (Fe(II)) in this system with IRB and zero-valent iron (ZVI, Fe(0)) coated with a ferric iron (Fe(III)) crust significantly affected TCE reduction and IRB respiration in various ways. This study presents a new framework for transformation property and reducing ability of both dissolved (Fe(II)(dissolved)) and solid form ferrous iron (Fe(II)(solid)). Results showed that TCE reduction was strongly depressed by Fe(II)(solid) rather than by other inhibitors (e.g., Fe(III) and lactate), suggesting that Fe(II)(solid) might reduce IRB activation due to attachment to IRB cells. Newly exposed Fe(0) from the released Fe(II)(dissolved) was a strong contributor to TCE reduction compared to Fe(II)(solid). In addition, our research confirmed that less Fe(II)(solid) production strongly supported long-term TCE reduction because it may create an easier TCE approach to Fe(0) or increase IRB growth. Our findings will aid the understanding of the contributions of iron media (e.g., Fe(II)(solid), Fe(II)(dissolved), Fe(III), and Fe(0)) to IRB for decontamination in natural groundwater systems.

In CSTRs, ferrous iron was biologically oxidized followed by crystallization of scorodite (FeAsO 4 ·2H 2 O) at pH 1.2 and 72 °C. The CSTRs were fed with 2.8 g L −1 arsenate and 2.4 g L −1 ferrous and operated at an HRT of 40 h, without seed addition or crystal recirculation. Both oxidation and crystallization were stable for periods up to 200 days. The arsenic removal efficiency was higher than 99% at feed Fe/As molar ratios between 1 and 2, resulting in effluents with 29 ± 18 mg As L −1 . Arsenic removal decreased to 40% at feed Fe/As molar ratios between 2 and 5. Microorganisms were not affected by arsenic concentrations up to 2.8 g As 5+ L −1 . The bioscorodite solid yield was 3.2 g/g arsenic removed. Bioscorodite crystals precipitated as aggregates, causing scaling on the glass wall of the reactor. The observed morphology through SE microscopy of the precipitates appeared amorphous but XRD analysis confirmed that these were crystalline scorodite. Arsenic leaching of bioscorodite was 0.4 mg L −1 after 100 days under TCLP conditions, but when jarosite had been co-precipitated leaching was higher at 0.8 g L −1 . The robustness of the continuous process, the high removal efficiency and the very low arsenic leaching rates from bioscorodite sludge make the process very suitable for arsenic removal and disposal.

An enhanced result in organic pollutants degradation and simultaneous electricity production has been achieved by establishing a novel Fenton-photocatalytic fuel cell (Fenton-PFC) system in which TiO 2 nanotube arrays (TNA) was designed as a photoanode and ferrous ions were added. The proposed Fenton-PFC system can expand the radical reaction for organic pollutants degradation from the surface of electrodes to the whole solution system due to a continuous photoelectric Fenton reaction without continually adding any external voltage and ferrous ions. The cyclic reactions between ferrous ions (Fe 2+ /Fe 3+ ) and radicals and related species (HO , HO 2 , O 2 − and H 2 O 2 etc.) can be achieved at electrodes surface via a self-bias voltage yielded by the PFC. More importantly, the proposed Fenton-PFC system has hardly any sludge due to an effective radical reaction using a small amount of ferrous ions. The degradation rate of refractory organics, such as methyl orange, methylene blue, congo red and tetracycline, increased from 34.99%, 43.75%, 40.58% and 34.40% (the traditional PFC without Fe 2+ ) to 97.34%, 95.36%, 93.23% and 73.80% (the Fenton-PFC within Fe 2+ ) respectively after 60 min operation. Meanwhile, the electricity generation is up to 1.21–2.04 times larger than the traditional PFC. The proposed Fenton-PFC system provides a more economical and efficient way for energy recovery and wastewater treatment.

Results from a laboratory-scale study evaluating virus control by a hybrid iron electrocoagulation – microfiltration process revealed only 1.0–1.5 log MS2 bacteriophage reduction even at relatively high iron dosages (∼13 mg/L as Fe) for natural surface water containing moderate natural organic matter (NOM) concentrations (4.5 mg/L dissolved organic carbon, DOC). In contrast, much greater reductions were measured (6.5-log at pH 6.4 and 4-log at pH 7.5) at similar iron dosages for synthetic water that was devoid of NOM. Quantitative agreement with Faraday’s law with 2-electron transfer and speciation with phenanthroline demonstrated electrochemical generation of soluble ferrous iron. Near quantitative extraction of viruses by dissolving flocs formed in synthetic water provided direct evidence of their removal by sorption and enmeshment onto iron hydroxide flocs. In contrast, only approximately 1% of the viruses were associated with the flocs formed in natural water consistent with the measured poor removals. 1–2 logs of virus inactivation were also observed in the electrochemical cell for synthetic water (no NOM) but not for surface water (4.5 mg/L DOC). Sweep flocculation was the dominant destabilization mechanism since the ζ potential did not reach zero even when 6-log virus reductions were achieved. Charge neutralization only played a secondary role since ζ potential → 0 with increasing iron electrocoagulant dosage. Importantly, virus removal from synthetic water decreased when Suwanee River Humic Acid was added. Therefore, NOM present in natural waters appears to reduce the effectiveness of iron electrocoagulation pretreatment to microfiltration for virus control by complexing ferrous ions. This inhibits (i) Fe 2+ oxidation, precipitation, and virus destabilization and (ii) virus inactivation through reactive oxygen species intermediates or by direct interactions with Fe 2+ ions.

Electrochemical dechlorination of trichloroethylene (TCE) in aqueous solution is investigated in a closed, liquid-recirculation system. The anodic reaction of cast iron generates ferrous species, creating a chemically reducing electrolyte (negative ORP value). The reduction of TCE on the cathode surface is enhanced under this reducing electrolyte because of the absence of electron competition. In the presence of the iron anode, the performances of different cathodes are compared in a recirculated electrolysis system. The copper foam shows superior capability for dechlorination of aqueous TCE. Electrolysis by cast iron anode and copper foam cathode is further optimized though a multivariable experimental design and analysis. The conductivity of the electrolyte is identified as an important factor for both final elimination efficiency (FEE) of TCE and specific energy consumption. The copper foam electrode exhibits high TCE elimination efficiency in a wide range of initial TCE concentration. Under coulostatic conditions, the optimal conditions to achieve the highest FEE are 9.525 mm thick copper foam electrode, 40 mA current and 0.042 mol L(-1) Na(2)SO(4). This novel electrolysis system is proposed to remediate groundwater contaminated by chlorinated organic solvents, or as an improved iron electrocoagulation process capable of treating the wastewater co-contaminated with chlorinated compounds.

Nanoscale zero-valent iron (NZVI) is increasingly used for reducing chlorinated organic contaminants in soil or groundwater. However, little is known about what impact the particles will have on the biochemical processes and the indigenous microbial communities. Nanoiron reactivity is affected by the structure and morphology of nanoparticles that complicates the applicability in bioremediation. In this study, the effect of precursors (ferrous sulfate and ferric chloride) and reducing agents (sodium dithionite and sodium borohydride) on the morphology and the reactivity of NZVIs was investigated. We also studied the impact of differently synthesized NZVIs on microbial community, which take part in reductive dechlorination. We demonstrated that both the applied iron precursor and the reducing agent had influence on the structure of the nanoparticles. Spherical nanoparticles with higher Fe0 content (>90%) was observed by using sodium borohydride as reducing agent, while application of sodium dithionite as reducing agent resulted nanostructures with lower Fe0 content (between 68,7 and 85,5%). To determine the influence of differently synthesized NZVIs on cell viability anaerobic enriched microcosm were used. NVZI was used in 0.1 g/L concentration in all batch experiments. Relative amount of Dehalococcoides, sulfate reducers (SRBs) and methanogens were measured by quantitative PCR. We found that the relative amount of Dehalococcoides slowly decreased in all experiments independently from the precursor and reducing agent, whereas the total amount of microbes increased. The only clear distinction was in relative amount of sulfate reducers which were higher in the presence of NZVIs synthesized from sodium dithionite.

Formation of the greenhouse gas nitrous oxide in water treatment systems is predominantly studied as a biological phenomenon. There are indications that also chemical processes contribute to these emissions. Here we studied the formation of nitric oxide (NO) and nitrous oxide (N(2)O) due to chemical nitrite reduction by ferrous iron (Fe(II)). Reduction of nitrite and NO coupled to Fe(II) oxidation was studied in laboratory-scale chemical experiments at different pH, nitrite and iron concentrations. The continuous measurement of both NO and N(2)O emission showed that nitrite reduction and NO reduction have different kinetics. Nitrite reduction shows a linear dependency on the nitrite concentration, implying first order kinetics in nitrite. The nitrite reduction seems to be an equilibrium based reaction, leading to a constant NO concentration in the liquid. The NO reduction rate is suggested to be most dependent on reactive surface availability and the sorption of Fe(II) to the reactive surface. The importance of emission of NO and N(2)O coupled to iron oxidation is exemplified by iron reduction experiments and several examples of environments where this pathway can play a role.

The mechanisms of iron precipitation and crystallization in a fluidized-bed reactor were investigated. Within the typical Fenton's reagent dosage and pH range, ferric ions as a product from ferrous ion oxidation would be supersaturated and would subsequently precipitate out in the form of ferric hydroxide after the initiation of the Fenton reaction. These precipitates would simultaneously crystallize onto solid particles in a fluidized-bed Fenton reactor if the precipitation proceeded toward heterogeneous nucleation. The heterogeneous crystallization rate was controlled by the fluidized material type and the aging/ripening period of the crystallites. Iron crystallization onto the construction sand was faster than onto SiO(2), although the iron removal efficiencies at 180 min, which was principally controlled by iron hydroxide solubility, were comparable. To achieve a high iron removal rate, fluidized materials have to be present at the beginning of the Fenton reaction. Organic intermediates that can form ferro-complexes, particularly volatile fatty acids, can significantly increase ferric ion solubility, hence reducing the crystallization performance. Therefore, the fluidized-bed Fenton process will achieve exceptional performance with respect to both organic pollutant removal and iron removal if it is operated with the goal of complete mineralization. Crystallized iron on the fluidized media could slightly retard the successive crystallization rate; thus, it is necessary to continuously replace a portion of the iron-coated bed with fresh media to maintain iron removal performance. The iron-coated construction sand also had a catalytic property, though was less than those of commercial goethite.

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe III /H 2 O 2 (pH = 2.85), Fe III NTA/H 2 O 2 (neutral pH), Fe II /O 2 , Fe II NTA/O 2 , Fe II /H 2 O 2 and Fe II NTA/H 2 O 2 (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe II NTA/H 2 O 2 and Fe III NTA/H 2 O 2 at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k Atrazine / k pCBA and k Fenuron / k pCBA , respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers ( tert- butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe II NTA/O 2 , Fe II NTA/H 2 O 2 and Fe III NTA/H 2 O 2 is initiated by hydroxyl radicals.

The microwave-hydrothermal decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in aqueous solution using persulfate activated by zero-valent iron (ZVI) at 60 and 90 degrees C was examined. The results of laboratory study reveal that when PFOA is treated with 5mM persulfate (PS) and ZVI at 90 degrees C for 2h, 67.6% of PFOA is effectively decomposed to form shorter-chain perfluorinated carboxylic acids (PFCAs) and fluoride ions, with 22.5% defluorination efficiency. Introducing ZVI into the PFOA solution with PS addition will lead to synergetic effect that accelerates the PFOA decomposition rate, and reduces the reaction time. ZVI not only decomposes PFOA, but also releases ferrous ions to lower the activation energy of PS while forming sulfate free radicals at a lower reaction temperature. The combined use of ZVI and persulfate will lead to significant savings in energy consumption and reduction of process time.