Addition Of Ferrous Iron Research Articles

Boron isotopes of Manganese ores from the northern part of the Kalahari Manganese Deposit, South Africa

Abstract The world-class deposits of the Kalahari Manganese Field (KMF) in South Africa constitute a key resource of manganese (Mn) ore for the global steel industry. Many aspects of the origin of high metal-grade ores in the northernmost KMF remain unresolved, especially with respect to the complex hydrothermal history of these ores and the source/s of fluids responsible for epigenetic metal enrichment. In this study, the geochemistry of boron (B) is employed as a potential proxy for such processes, and the results are contextualised against an assumed low metal-grade precursor. Samples collected from the northern part of the Kalahari Manganese Deposit allow for the distinction of three Mn ore types, of which the precursor ore is the closest candidate, petrographically and geochemically, to primary/diagenetic Mn deposition. This precursor ore is dominated by Mn-carbonate and braunite, and records B concentrations in the order of a few 100s to 1 000s ppm and positive δ11B values at an average of 11 ± 6‰. Ferruginous Mn ores appear to have formed from decarbonation of precursor ore and metasomatic ferric iron addition, particularly in the stratigraphically upper Mn ore bed, which is closest to the overlying Olifantshoek and Kalahari unconformities. Ferruginous Mn ores appear depleted in B (ca. 500 ppm on average) and have lower boron isotope values (δ11B: 0 ± 3‰). Hydrothermally Mn-enriched ores, in contrast, are dominated by hausmannite, braunite-II and bixbyite and record highest B concentrations (up to 10 000s ppm) and δ11B values as high as 41‰, pointing to metasomatic introduction of B by circulating evaporitic brines. While further research is needed to comprehensively unravel the geochemical intricacies of B within the complex interplay of fluids and rocks in the Hotazel region, the findings of this study still strongly suggest that B holds promise as a tracer for alteration processes in the KMF.

Evaluation of ecological impacts with ferrous iron addition in constructed wetland under perfluorooctanoic acid stress

In this study, ferrous ion (Fe(II)) had the potential to promote ecological functions in constructed wetlands (CWs) under perfluorooctanoic acid (PFOA) stress. Concretely, Fe(II) at 30 mg/L and 20–30 mg/L even led to 11.37% increase of urease and 93.15–243.61% increase of nitrite oxidoreductase respectively compared to the control. Fe(II) promotion was also observed on Nitrosomonas, Nitrospira, Azospira, and Zoogloea by 1.00–6.50 folds, which might result from higher expression of nitrogen fixation and nitrite redox genes. These findings could be explanation for increase of ammonium removal by 7.47–8.75% with Fe(II) addition, and reduction of nitrate accumulation with 30 mg/L Fe(II). Meanwhile, both Fe(II) stimulation on PAOs like Dechloromonas, Rhodococcus, Mesorhizobium, and Methylobacterium by 1.58–2.00 folds, and improvement on chemical phosphorus removal contributed to higher total phosphorus removal efficiency under high-level PFOA exposure. Moreover, Fe(II) raised chlorophyll content and reduced the oxidative damage brought by PFOA, especially at lower dosage. Nevertheless, combination of Fe(II) and high-level PFOA caused inhibition on microbial alpha diversity, which could result in decline of PFOA removal (by 4.29–12.83%). Besides, decrease of genes related to nitrate reduction demonstrated that enhancement on denitrification was due to nitrite reduction to N2 pathways rather than the first step of denitrifying process.

A Novel Natural Siderophore Antibiotic Conjugate Reveals a Chemical Approach to Macromolecule Coupling.

Inspired by natural sideromycins, the conjugation of antibiotics to siderophores is an attractive strategy to facilitate "Trojan horse" delivery of antibiotics into bacteria. Genome analysis of a soil bacterium, Dactylosporangium fulvum, found a "hybrid" biosynthetic gene cluster responsible for the production of both an antibiotic, pyridomycin, and a novel chlorocatechol-containing siderophore named chlorodactyloferrin. While both of these natural products were synthesized independently, analysis of the culture supernatant also identified a conjugate of both molecules. We then found that the addition of ferric iron to purified chlorodactyloferrin and pyridomycin instigated their conjugation, leading to the formation of a covalent bond between the siderophore-catechol and the pyridomycin-pyridine groups. Using model reactants, this iron-based reaction was found to proceed through a Michael-type addition reaction, where ferric iron oxidizes the siderophore-catechol group into its quinone form, which is then attacked by the antibiotic pyridyl-nitrogen to form the catechol-pyridinium linkage. These findings prompted us to explore if other "cargo" molecules could be attached to chlorodactyloferrin in a similar manner, and this was indeed confirmed with a pyridine-substituted TAMRA fluorophore as well as with pyridine-substituted penicillin, rifampicin, and norfloxacin antibiotic analogues. The resultant biomimetic conjugates were demonstrated to effectively enter a number of bacteria, with TAMRA-chlorodactyloferrin conjugates causing fluorescent labeling of the bacteria, and with penicillin and rifampicin conjugates eliciting antibiotic activity. These findings open up new opportunities for the design and facile synthesis of a novel class of biomimetic siderophore conjugates with antibiotic activity.

A sustainable approach for gold recovery from refractory source using novel BIOX-TC system

This study developed a sustainable method for gold extraction from low-grade refractory ore by combining acidic biooxidation and thiocyanate (SCN) leaching (BIOX-TC) in one system to avoid neutralization and minimize the complexity of the process. Among leachant candidates, thiocyanate was proposed as a less toxic reagent for gold leaching. Furthermore, thiocyanate requires ferric iron as an oxidant for gold extraction and ferric iron can be provided by the microorganisms during biooxidation. In the first step, acidic biooxidation was done using a mixture of acidophiles including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans resulting in 59.6% sulfur oxidation. A preliminary static incubation of Acidithiobacillus thiooxidans also improved biooxidation efficiency achieving higher sulfur oxidation of 87.8%. Following biooxidation, thiocyanate leaching using 0.2 M SCN was performed under three different conditions: (1) in a separate flask with 0.01 M ferric iron addition; (2) in-situ leaching, in the biooxidation flask with the mixed bacterial culture); (3) in-situ leaching in the biooxidation flask with the bacterial culture and with 0.01 M additional ferric iron. It was found that in-situ thiocyanate leaching of the biooxidized ore in the presence of the bacterial culture and without ferric iron addition resulted in the highest gold recovery (86.9%). The biooxidation mechanism and its kinetics have been extensively discussed in this paper.

Chromium (VI) Inhibition of Low pH Bioleaching of Limonitic Nickel-Cobalt Ore

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.

High-frequency ultrasound processes as alternative methods for degrading meropenem antibiotic in water

β-lactam, more specifically carbapenems, are antibiotics used as last resort pharmaceuticals to deal with infections. Despite the medical relevance, they are considered contaminants of emerging concern in water because of their recalcitrance to conventional systems in the municipal wastewater treatment plants. This work aimed to show alternative methods based on the use of high-frequency ultrasound (200-1000 kHz) at a laboratory scale to degrade meropenem (a representative carbapenem antibiotic) in water. The ability of the sonochemical method alone to eliminate meropenem was tested initially. Then, the improvements of degradation by the addition of ferrous iron, or Fe (II) plus UVA light (sono-Fenton, or sono-photo-Fenton methods) were assessed. Finally, the effect of the best ultrasound-based method on the removal of biological activity of meropenem was determined.• Three high-frequency ultrasound processes were applied to degrade meropenem in water.• Sono-photo-Fenton degraded 67% of imipenem at 60 min of treatment and decreased significantly H2O2 accumulation.• Antimicrobial activity was removed after only 30 min of sono-photo-Fenton action.

Biofilm Formation Is Crucial for Efficient Copper Bioleaching From Bornite Under Mesophilic Conditions: Unveiling the Lifestyle and Catalytic Role of Sulfur-Oxidizing Bacteria.

Biofilm formation within the process of bioleaching of copper sulfides is a relevant aspect of iron- and sulfur-oxidizing acidophilic microorganisms as it represents their lifestyle in the actual heap/dump mining industry. Here, we used biofilm flow cell chambers to establish laminar regimes and compare them with turbulent conditions to evaluate biofilm formation and mineralogic dynamics through QEMSCAN and SEM-EDS during bioleaching of primary copper sulfide minerals at 30°C. We found that laminar regimes triggered the buildup of biofilm using Leptospirillum spp. and Acidithiobacillus thiooxidans (inoculation ratio 3:1) at a cell concentration of 106 cells/g mineral on bornite (Cu5FeS4) but not for chalcopyrite (CuFeS2). Conversely, biofilm did not occur on any of the tested minerals under turbulent conditions. Inoculating the bacterial community with ferric iron (Fe3+) under shaking conditions resulted in rapid copper recovery from bornite, leaching 40% of the Cu content after 10 days of cultivation. The addition of ferrous iron (Fe2+) instead promoted Cu recovery of 30% at day 48, clearly delaying the leaching process. More efficiently, the biofilm-forming laminar regime almost doubled the leached copper amount (54%) after 32 days. In-depth inspection of the microbiologic dynamics showed that bacteria developing biofilm on the surface of bornite corresponded mainly to At. Thiooxidans, while Leptospirillum spp. were detected in planktonic form, highlighting the role of biofilm buildup as a means for the bioleaching of primary sulfides. We finally propose a mechanism for bornite bioleaching during biofilm formation where sulfur regeneration to sulfuric acid by the sulfur-oxidizing microorganisms is crucial to prevent iron precipitation for efficient copper recovery.

Altered Pseudomonas Strategies to Inhibit Surface Aspergillus Colonies.

Pseudomonas aeruginosa and Aspergillus fumigatus infections frequently co-localize in lungs of immunocompromised patients and individuals with cystic fibrosis (CF). The antifungal activity of P. aeruginosa has been described for its filtrates. Pyoverdine and pyocyanin are the principal antifungal P. aeruginosa molecules active against A. fumigatus biofilm metabolism present in iron-limited or iron-replete planktonic P. aeruginosa culture filtrates, respectively. Using various P. aeruginosa laboratory wild-type strains (PA14, PAO1, PAK), we found antifungal activity against Aspergillus colonies on agar. Comparing 36 PA14 and 7 PAO1 mutants, we found that mutants lacking both major siderophores, pyoverdine and pyochelin, display higher antifungal activity on agar than their wild types, while quorum sensing mutants lost antifungal activity. Addition of ferric iron, but not calcium or magnesium, reduced the antifungal effects of P. aeruginosa on agar, whereas iron-poor agar enhanced antifungal effects. Antifungal activity on agar was mediated by PQS and HHQ, via MvfR. Among the MvfR downstream factors, rhamnolipids and elastase were produced in larger quantities by pyoverdine–pyochelin double mutants and showed antifungal activity on agar. In summary, antifungal factors produced by P. aeruginosa on agar differ from those produced by bacteria grown in liquid cultures, are dependent on quorum sensing, and are downregulated by the availability of ferric iron. Rhamnolipids and elastase seem to be major mediators of Pseudomonas’ antifungal activity on a solid surface.

Dissolution of Manganese (IV) Oxide Mediated by Acidophilic Bacteria, and Demonstration That Manganese (IV) Can Act as Both a Direct and Indirect Electron Acceptor for Iron-Reducing Acidithiobacillus spp.

Experiments were carried out to examine the oxido-reduction of manganese by extremely acidophilic Acidithiobacillus spp. grown with either elemental sulfur or molecular hydrogen as electron donor. While there was no evidence for manganese (II) oxidation, dissolution of solid phase manganese dioxide was observed in cultures grown aerobically on both electron donors, though this appeared not to involve reduction of the metal. Solubilization of MnO2 was much enhanced in cultures incubated anaerobically, even though biomass was smaller, and pH values increased significantly as a consequence of acid dissolution being accompanied by manganese (IV) reduction. Increases in cell numbers correlated with concentrations of soluble manganese in anaerobic cultures grown on hydrogen, demonstrating that iron-oxidizing/reducing Acidithiobacillus spp. can grow in the absence of oxygen using manganese (IV) as sole electron acceptor. Addition of ferric iron to anaerobic cultures further enhanced the reductive dissolution of MnO2 as a result of its reduction to ferrous iron which then reacted with the solid manganese phase, and confirming that Mn (IV) reduction by iron-reducing acidophiles can proceed both directly and indirectly, involving iron as a shuttle vector. The implications of these findings to developing technologies for bio-processing oxidized metal ore deposits are discussed.

Ferrugination of biocrusts grown on crushed ferricrete: Potential for slope stabilisation

Bioremediation of degraded lands using biological soil crusts (i.e., biocrusts; complex association between soil, microorganisms, and extracellular polymeric substances) is an emerging biotechnological strategy to control surface erosion. Here, we examined the use of biocrusts for the stabilisation of iron ore mine waste. Simulating naturally occurring biomineralisation of microbial mats on ferricrete, we promoted the ferrugination of biocrusts on crushed iron-rich waste material, aiming to form iron biocement. The biocrusts on our 50-cm experimental slopes (comprised primarily of cyanobacteria, green algae, and fungi) aggregated crushed ferricrete fragments through the secretion of extracellular polymeric substances. Provided with an external source of ferrous iron, the biocrusts also acted as organic scaffolds for the precipitation of iron oxides. The mineralisation of the biocrusts led to the formation of biocemented aggregates that mechanically stabilised the crushed iron-rich waste material. The biocrusts, with and without biomineralisation, enhanced hydraulic conductivity and minimised erosion. The addition of ferrous iron without an organic framework resulted in a powdery coating of individual fragments, rather than consolidation of the substrate. Our findings demonstrate the potential of synthetic biocement as a long-term stabilisation strategy for waste rock stockpiles, engineered slopes, and mine remediation requiring the reformation of iron-rich duricrust.

Effect of Ferrous Iron Addition on Ammonium Nitrogen Removal and Microbial Communities in Horizontal Subsurface Flow Constructed Wetlands

This study explored the influence of ferrous iron (Fe2+) addition on ammonium nitrogen (NH4-N) removal and microbial communities in horizontal subsurface flow constructed wetlands (HSSFs) at different carbon/nitrogen (C/N) ratios. Fe2+ addition could improve NH4-N removal under the C/N ratio of 2.1 and alter the microbial community structure. The microbial diversity and functional genes at the C/N ratio of 2.1 were enhanced by the addition of 50 mg/L Fe2+, with the increases observed in NH4-N and total nitrogen (TN) removal. This indicates the enhancement of nitrogen removal by Fe2+ addition with the presence of high organic matter. However, the enhancement of Fe2+ on chemical oxygen demand removal was not obvious overall. The relative abundance of functional genes and those related to energy metabolism, xenobiotic biodegradation, and metabolism decreased significantly in HSSFs with Fe2+ at C/N ratio of 1.1, whereas they increased in HSSFs with the addition of 50 mg/L Fe2+ at C/N ratio of 2.1.

Mitigating Membrane Fouling Based on In Situ •OH Generation in a Novel Electro-Fenton Membrane Bioreactor.

A novel electro-Fenton membrane bioreactor was constructed to investigate the effect of electro-Fenton on mitigating membrane fouling. Herein, porous carbon (PC), carbon nanotubes (CNTs) and Fe2+ were spun into hollow fiber membranes (Fe-PC-CHFM), then served as cathode and filtration core simultaneously. The H2O2 can be in situ produced by O2 reduction with electro-assistance, and further induce hydroxyl radicals (•OH) generation with loaded Fe2+ on the surface of Fe-PC-CHFM. In addition, Fe3+/Fe2+ cycle can be realized effectively by the electro-assistance, avoiding ferrous iron addition. During over 100-day operation, the electro-Fenton membrane bioreactor achieved 93% of COD and 88% of NH4+-N removal at a HRT of 8 h. At the end of operation, the membranes in electro-Fenton membrane bioreactor still exhibited obviously mesh-like structure similarly to initial level. Importantly, merely 15 min with an operation voltage of -0.8 V was sufficient to completely recover permeate flux of the fouled Fe-PC-CHFM. The energy consumption used for membrane fouling control was barely 8.64 × 10-5 kW·h/m3. Therefore, this novel energy-saved electro-Fenton membrane bioreactor process could provide an envisaging prospective and promising method for practice wastewater membrane treatment.

Ferrous Iron Addition Decreases Methane Emissions Induced by Rice Straw in Flooded Paddy Soils

Straw returning to fields is a common agricultural practice for enhancing soil fertility and organic matter although it induces substantial CH4 emissions from flooded paddy soils. The characteristi...

Bacterial influence on storage and mobilisation of metals in iron-rich mine tailings from the Salobo mine, Brazil

In this study we investigated the potential effects of promoting bacterial activity on tailings from the Salobo iron-oxide copper‑gold (IOCG) mine, Brazil. In particular we focussed on (1) the potential for mobilising additional Cu and (2) the effects of long-term storage on other metals. Unlike typical sulphide-ore tailings, the pH of the Salobo tailings is circumneutral and these tailings are dominated by Fe-bearing silicates and magnetite, with minor micrometre-scale encapsulated Cu-bearing sulphides. While these tailings do not produce acid mine drainage, an endemic strain of Acidithiobacillus ferrooxidans was isolated from the mine site. These bacteria were used in laboratory column leaching experiments of tailings material, which ran for up to 395 days, without the addition of ferrous iron. Bacteria-tailings interactions were typically maintained at a pH > 5, due to silicate-mediated pH buffering. This was eventually overcome after ~200 days by regular addition of acidic (pH 2.2) nutrient solution, as well as growth and acid generation by bacteria. Copper dissolution was not significantly enhanced by bacterial activity compared to abiotic control experiments while pH was >5. However, as the experiments were progressively acidified, additional Cu was mobilised in the biotic systems. The mineral alteration reactions produced abundant ferrihydrite precipitates within the tailings, which was enhanced by bacterial activity as the pH decreased. Adsorption of metal cations to these precipitates ensured that effluent solutions had only low levels (<0.5 mg/l) of dissolved trace metals such as As, Co, Pb, Zn, Se, Ni and Cr. These adsorption processes will strongly inhibit metal leaching from the tailings during long-term storage, as long as the iron oxidising bacteria are producing the requisite excess of ferrihydrite and the pH is >5. This case study shows that bacterially-mediated silicate weathering, in Fe(II)-bearing silicate rich tailings with only minor sulphides and Acidithiobacillus ferrooxidans can enhance the environmental stability of the tailings.

Controlling the mobility of chromium and molybdenum in MSWI fly ash in a washing process

Fly ash from a cogeneration plant near Sundsvall in Sweden was treated in an ash-washing facility. The leaching of chromium (Cr) and molybdenum (Mo) from the ash residue exceeded the limit values for non-hazardous landfills. In this study factors that influence the leaching of Cr and Mo were identified and methods that can reduce the leaching were evaluated. The results revealed that the mobility of Cr and Mo are mainly controlled by pH and redox reactions and sequential extraction tests also showed that the fraction of highly soluble species of Cr and Mo increased after washing due to pH reactions in the ash during the process. Stabilization of the pH at ∼8 through carbonation of the washed ash and a lowering of the redox potential by adding ferrous iron to the process resulted in decreased leaching. Treatment with carbon dioxide yielded a decrease (from 10.7 to 8.2) in the pH and, hence, the leaching of Cr and Mo by 93 and 91%, respectively. And the addition of ferrous iron reduced the leaching of Cr by 50%. Carbonation of the ash can be achieved via treatment with flue gases from the power plant or treatment with landfill gas at the disposal site.

Echinochrome A Release by Red Spherule Cells Is an Iron-Withholding Strategy of Sea Urchin Innate Immunity

Cellular immune defences in sea urchins are shared amongst the coelomocytes - a heterogeneous population of cells residing in the coelomic fluid (blood equivalent) and tissues. The most iconic coelomocyte morphotype is the red spherule cell (or amebocyte), so named due to the abundance of cytoplasmic vesicles containing the naphthoquinone pigment echinochrome A. Despite their identification over a century ago, and evidence of antiseptic properties, little progress has been made in characterising the immunocompetence of these cells. Upon exposure of red spherule cells from sea urchins, i.e., Paracentrotus lividus and Psammechinus miliaris, to microbial ligands, intact microbes, and damage signals, we observed cellular degranulation and increased detection of cell-free echinochrome in the coelomic fluid ex vivo. Treatment of the cells with ionomycin, a calcium-specific ionophore, confirmed that an increase in intracellular levels of Ca²⁺ is a trigger of echinochrome release. Incubating Gram-positive/negative bacteria as well as yeast with lysates of red spherule cells led to significant reductions in colony-forming units. Such antimicrobial properties were counteracted by the addition of ferric iron (Fe³⁺), suggesting that echinochrome acts as a primitive iron chelator in echinoid biological defences.

Formation, reactivity and aging of amorphous ferric oxides in the presence of model and membrane bioreactor derived organics

Iron salts are routinely dosed in wastewater treatment as a means of achieving effluent phosphorous concentration goals. The iron oxides that result from addition of iron salts partake in various reactions, including reductive dissolution and phosphate adsorption. The reactivity of these oxides is controlled by the conditions of formation and the processes, such as aggregation, that lead to a reduction in accessible surface sites following formation. The presence of organic compounds is expected to significantly impact these processes in a number of ways. In this study, amorphous ferric oxide (AFO) reactivity and aging was investigated following the addition of ferric iron (Fe(III)) to three solution systems: two synthetic buffered systems, either containing no organic or containing alginate, and a supernatant system containing soluble microbial products (SMPs) sourced from a membrane bioreactor (MBR). Reactivity of the Fe(III) phases in these systems at various times (1–60 min) following Fe(III) addition was quantified by determining the rate constants for ascorbate-mediated reductive dissolution over short (5 min) and long (60 min) dissolution periods and for a range (0.5–10 mM) of ascorbate concentrations. AFO particle size was monitored using dynamic light scattering during the aging and dissolution periods. In the presence of alginate, AFO particles appeared to be stabilized against aggregation. However, aging in the alginate system was remarkably similar to the inorganic system where aging is associated with aggregation. An aging mechanism involving restructuring within the alginate-AFO assemblage was proposed. In the presence of SMPs, a greater diversity of Fe(III) phases was evident with both a small labile pool of organically complexed Fe(III) and a polydisperse population of stabilized AFO particles present. The prevalence of low molecular weight organic molecules facilitated stabilization of the Fe(III) oxyhydroxides formed but subsequent aging observed in the alginate system did not occur. The reactivity of the Fe(III) in the supernatant system was maintained with little loss in reactivity over at least 24 h. The capacity of SMPs to maintain high reactivity of AFO has important implications in a reactor where Fe(III) phases encounter alternating redox conditions due to sludge recirculation, creating a cycle of reductive dissolution, oxidation and precipitation.

Impact of Ferrous Iron on Microbial Community of the Biofilm in Microbial Fuel Cells.

The performance of microbial electrochemical cells depends upon microbial community structure and metabolic activity of the electrode biofilms. Iron as a signal affects biofilm development and enrichment of exoelectrogenic bacteria. In this study, the effect of ferrous iron on microbial communities of the electrode biofilms in microbial fuel cells (MFCs) was investigated. Voltage production showed that ferrous iron of 100 μM facilitated MFC start-up compared to 150 μM, 200 μM, and without supplement of ferrous iron. However, higher concentration of ferrous iron had an inhibitive influence on current generation after 30 days of operation. Illumina Hiseq sequencing of 16S rRNA gene amplicons indicated that ferrous iron substantially changed microbial community structures of both anode and cathode biofilms. Principal component analysis showed that the response of microbial communities of the anode biofilms to higher concentration of ferrous iron was more sensitive. The majority of predominant populations of the anode biofilms in MFCs belonged to Geobacter, which was different from the populations of the cathode biofilms. An obvious shift of community structures of the cathode biofilms occurred after ferrous iron addition. This study implied that ferrous iron influenced the power output and microbial community of MFCs.

Effects of ferrous iron on the performance and microbial community in aerobic granular sludge in relation to nutrient removal.

Lab-scale experiments were conducted to investigate the effects of ferrous iron on nutrient removal performance and variations in the microbial community inside aerobic granular sludge for 408days. Two reactors were simultaneously operated, one without added ferrous iron (SBR1), and one with 10mg Fe2+ L-1 of added ferrous iron (SBR2). A total of 1mg Fe2+ L-1 of added ferrous iron was applied to SBR1 starting from the 191st day to observe the resulting variations in the nutrient removal performance and the microbial community. The results show that ammonia-oxidizing bacteria (AOB) could not oxidize ammonia due to a lack of iron compounds, but they could survive in the aerobic granular sludge. Limited ferrous iron addition encouraged nitrification. Enhanced biological phosphorus removal (EBPR) from both reactors could not be maintained regardless of the amount of ferrous iron that was applied. EBPR was established in both reactors when the concentration of mixed liquor suspended solid (MLSS) and the percentage of Accumulibacteria increased. A total of 10mgFe2+ L-1 of added ferrous iron had a relatively adverse effect on the growth of AOB species compared to 1mgFe2+ L-1 of added ferrous iron, but it encouraged the growth of Nitrospira sp. and Accumulibacteria, which requires further study. It could be said that the compact and stable structure of aerobic granular sludge preserved AOB and NOB from Fe-deficient conditions, and wash-out during the disintegration period. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:716-725, 2017.

Treatment of landfill leachate by continuously reused ferric oxyhydroxide sludge-activated hydrogen peroxide

The ferric oxyhydroxide sludge-activated Fenton-based oxidation and its application for landfill leachate treatment were studied. The mechanism of iron dissolution form the surface of ferric oxyhydroxides was proposed. The impact of humic substances, corresponding to 11% of COD, on the iron dissolution and the subsequent hydrogen peroxide activation was assessed. An innovative H2O2/sludge system with the addition of ferrous iron, which was operated in sequencing batch mode, was determined to be a promising technique for the effective degradation of an organic load and for the reduction of the produced residual ferric waste. The observed results indicated the effective removal of COD, DOC, BOD7 and total phenols (TPh) in the H2O2/sludge/Fe2+ system at a H2O2/[O]COD and H2O2/Fe2+ molar ratio of 1.5/1 and 50/1, respectively, during ten sludge reuse cycles in a sequencing batch reactor (SBR). Accordingly, the removal of the organic contaminants after the 1st/10th reuse cycle was 63/55% (COD), 51/44% (DOC), and 79/79% (TPh). Moreover, a rough estimation of the biodegradability of the SBR effluent is given as the BOD7/COD ratio, which indicated the potential use of a biological post-treatment to improve the overall quality of the effluent. The sludge-activated Fenton-based treatment also resulted in more effective thickening of the ferric oxyhydroxide sludge and in a lower content of adsorbed organic compounds in the solid residue compared with the sludge formed after a single Fenton treatment.