Biodegradation of nitrilotriacetic acid (NTA) and ferric-NTA complex by aerobic microbial granules

Triple Synergism Effect of Ammonium Nitrilotriacetate on the Chemical Mechanical Polishing Performance of Ruthenium Barrier Layers

As the feature size of integrated circuits continues to decrease, ruthenium (Ru) has been suggested as the successor to traditional Ta/TaN bilayers for barrier layer materials due to its unique properties. This research delves into the effects of ammonium nitrilotriacetate (NTA(NH4 )3 ) on the chemical mechanical polishing (CMP) performance of Ru in H2 O2 -based slurry. The removal rate (RR) of Ru surged from 47 to 890 Å min-1 , marking an increase of about 17 times. The essence of this mechanism lies in the triple synergistic effects of NTA(NH4 )3 in promoting ruthenium (Ru) removal: 1) The interaction betweenNH 4 + ${\mathrm{NH}}_{\mathrm{4}}^{\mathrm{+}}$ from NTA(NH4 )3 and SiO2 abrasives; 2) The chelating action of [(NH4 )N(CH2 COO)3 ]2-  from NTA(NH4 )3 on Ru and its oxides; 3) The ammoniation and chelation of Ru and its oxides byNH 4 + ${\mathrm{NH}}_{\mathrm{4}}^{\mathrm{+}}$ from NTA(NH4 )3 , which enhance the dissolution and corrosion of oxidized Ru, making its removal during the barrier layer CMP process more efficient through mechanical means. This research introduces a synergistic approach for the effective removal of Ru, shedding light on potential applications of CMP in the field of the integrated circuits.

A novel diagnostic method for distinguishing between Fe(IV) and •OH by using atrazine as a probe: Clarifying the nature of reactive intermediates formed by nitrilotriacetic acid assisted Fenton-like reaction

In this work, we found that the distribution of two specific atrazine (ATZ) oxidation products (desethyl-atrazine (DEA) and desisopropyl-atrazine (DIA)) was different in oxidation processes involving aqueous ferryl ion (Fe(IV)) species and ^•OH. Specifically, the molar ratio of produced DEA to DIA (i.e., [DEA]/[DIA]) increased from 7.5 to 13 with increasing pH from 3 to 6 when ATZ was oxidized by Fe(IV), while the treatment of ATZ by ^•OH led to the [DEA]/[DIA] value of 2 which was independent of pH. Moreover, ATZ showed high reactivity towards Fe(IV) over a wide pH range, especially at near-neutral pH, at which ATZ oxidation in Fe(II)/peroxydisulfate system was even much faster than another well-defined Fe(IV) scavenger, the sulfoxides. By using this approach, it was obtained that the [DEA]/[DIA] value remained at 2 during ATZ transformation by the nitrilotriacetic acid (NTA) assisted Fenton-like (Fe(III)/H₂O₂) system, which was independent of solution pH and reactants dosage. This result clarified that ^•OH was the primary reactive intermediate formed in the NTA assisted Fe(III)/H₂O₂ system. This study not only developed a novel sensitive diagnostic tool for distinguishing Fe(IV) from ^•OH, but also provided more credible evidence to the nature of reactive intermediate in a commonly controversial system.

Effect of the gradual increase of Na2SO4 on performance and microbial diversity of aerobic granular sludge

Aerobic granular sludge (AGS) is a promising technology in treating saline wastewater. The effects of sodium sulfate on contaminant removal performance and sludge characteristics of AGS were studied. The results showed that under the stress of sodium sulfate, AGS kept good removal performance of ammonia nitrogen (NH+ 4-N), chemical oxygen demand (COD), and total nitrogen (TN), with removal efficiency reaching 98.7%, 91.5% and 62.7%, respectively. When sodium sulfate reached 14700 mg/L, nitrite oxidizing bacteria (NOB) were inhibited and nitrite accumulation occurred, but it had little impact on total phosphorus (TP) removal. Under the stress of sodium sulfate, compactness and settling performance of AGS was enhanced. The microbial community greatly varied and the microbial diversity of aerobic granular sludge has decreased under the stress of sodium sulfate. The study reveals that AGS has great potential in application on treating saline wastewater.

Aerobic granular sludge for high-strength ammonium wastewater treatment: Effect of COD/N ratios, long-term stability and nitrogen removal pathways

Aerobic granular sludge (AGS) technology is increasingly considered for wastewater treatment. AGS stability particularly under lower COD/N ratios is an impediment for AGS technology. This study evaluated AGS stability and nitrogen removal at different loading rates of 0.03 to 4 kg NH4+-N m-3 d-1 and COD/N ratios of 18.3 to 0.13. Ammoniacal and total nitrogen removals were high at 99.9% and 99.3%, respectively, during 440 days. MiSeq sequencing revealed a reduction in bacterial diversity and enrichment of ammonia oxidizing bacteria (AOB), anammox and denitrifying bacteria. Quantitative PCR showed enrichment of AOB, anammox bacteria, Nitrospira and denitrifiers. Chemical data and bacterial community supported occurrence of nitritation and anammox pathways. AGS had stable granular structure with excellent settling properties at lower COD/N ≤ 1. Removal of high-strength ammonium could be partly explained by the existing nitrogen pathways suggesting novel mechanisms. Nevertheless, results presented here support implementation of AGS process for ammonium wastewaters.

Effects of PASP/NTA and TS on the phytoremediation of pyrene-nickel contaminated soil by Bidens pilosa L

Bidens pilosa L. (B. pilosa) is considered as an effective phytoremediation plant. In this study, polyaspartic acid (PASP), aminotriacetic acid (NTA) and tea saponin (TS) was combined with B. pilosa. to strengthen the phytoremediation efficiency. The removal rate of pyrene reached 95.8% with B. pilosa alone. The release of Ni in NTA and NTA-TS treatments was 20-30 times than untreated contaminant soil. The Ni concentration in roots of B. pilosa increased by 63.1% and 58.6% in PASP and PASP-TS treatments, respectively. The Ni concentration in leaves of B. pilosa increased by 55.9% and 186% in NTA and NTA-TS treatments, respectively. The growth of B. pilosa was significantly promoted in PASP and PASP-TS treatments. PASP, NTA and TS significantly promoted soil microbial activities. The results showed that B. pilosa was beneficial to pyrene removal. PASP and NTA had positive effects on absorption of Ni by B. pilosa.

Efficient degradation of pharmaceutical micropollutants in water and wastewater by FeIII-NTA-catalyzed neutral photo-Fenton process

Ferric-nitrilotriacetate complex (Fe^III-NTA) has been adopted to catalyze the photo-Fenton degradation of emerging pharmaceutical micropollutants in water and wastewater at neutral pH. The generation of hydroxyl radicals (HO) in UVA/Fe^III-NTA/H₂O₂ was identified by using electron spin resonance (ESR) trapping technique. The effects of critical parameters (e.g., NTA:Fe^III molar ratio, Fe^III-NTA and H₂O₂ dosages) on the steady-state HO concentrations were studied in terms of the degradation of carbamazepine (CBZ, as a model compound) in Milli-Q water. In addition, the degradation of pharmaceuticals mixtures (including CBZ, crotamiton (CRMT) and ibuprofen (IBP)) in wastewater effluents from a biological aerated filter (BAF) by UVA/Fe^III-NTA/H₂O₂ was studied in continuous-flow mode. The results showed that the efficacies of Fe^III-NTA in catalyzing photo-Fenton degradation of pharmaceuticals in wastewater effluents were comparable to those obtained by Fe^III-ethylenediamine-N,N'-disuccinic acid (Fe^III-EDDS), and far exceeded other Fe^III-L complex (e.g., citric acid, malonic acid, oxalic acid and tartaric acid). More than 92% degradation efficiencies of CBZ, CRMT and IBP were obtained in continuous-flow mode under the given conditions of 0.178 mM Fe^III-NTA (1:1), 4.54 mM H₂O₂, UVA intensity 4.05 mW cm^-2, hydraulic retention time (HRT) 2 h, influent pH 7.6 (±0.2) and temperature 20 °C. The results presented herein suggest that Fe^III-NTA-catalyzed neutral photo-Fenton reaction can be an alternative tertiary process for the treatment of pharmaceutical micropollutants in secondary wastewater effluents.

Artificial neural network modelling for organic and total nitrogen removal of aerobic granulation under steady-state condition

Aerobic granulation is a recent technology with high level of complexity and sensitivity to environmental and operational conditions. Artificial neural networks (ANNs), computational tools capable of describing complex non-linear systems, are the best fit to simulate aerobic granular bioreactors. In this study, two feedforward backpropagation ANN models were developed to predict chemical oxygen demand (Model I) and total nitrogen removal efficiencies (Model II) of aerobic granulation technology under steady-state condition. Fundamentals of ANN models and the steps to create them were briefly reviewed. The models were respectively fed with 205 and 136 data points collected from laboratory-, pilot-, and full-scale studies on aerobic granulation technology reported in the literature. Initially, 60%, 20%, and 20%, and 80%, 10%, and 10% of the points in the corresponding datasets were randomly chosen and used for training, testing, and validation of Model I, and Model II, respectively. Overall coefficient of determination (R²) value and mean squared error (MSE) of the two models were initially 0.49 and 15.5, and 0.37 and 408, respectively. To improve the model performance, two data division methods were used. While one method is generic and potentially applicable to other fields, the other can only be applied to modelling the performance of aerobic granular reactors. R² value and MSE were improved to 0.90 and 2.54, and 0.81 and 121.56, respectively, after applying the new data division methods. The results demonstrated that ANN-based models were capable simulation approach to predict a complicated process like aerobic granulation.

Recognition of Proteins by Metal Chelation-Based Fluorescent Probes in Cells

Fluorescent probes such as thiol-reactive and Ni2+-nitrilotriacetate (NTA) based probes provide a powerful toolbox for real-time visualization of a protein and a proteome in living cells. Herein, we first went through basic principles and applications of thiol-reactive based probes in protein imaging and recognition. We then summarize a family of metal-NTA based fluorescence probes in the visualization of His6-tagged protein and identification of metalloproteins at proteome-wide scale. The pros and cons of the probes, as well as ways to optimize them, are discussed.

Design of Novel Oligomeric Mixed Ligand Complexes: Preparation, Biological Applications and the First Example of Their Nanosized Scale

A successful oligomerization of ternary metal complexes, cobalt (II), nickel (II), copper (II), zinc (II), chromium (III) and ferric sulfate (III) with nitrilotriacetic acid (NTA) as a primary ligand and glutamic acid as a secondary ligand, has been demonstrated. The formation of oligomers arose from the presence of the sulfate moiety, which operates as a bridged bidentate ligand that coordinates with other metal moieties. The novel oligomers exhibited octahedral structures, which bonded together through the sulfate moiety. In silico predictions were conducted to gauge the bioactivity, physico-chemical and pharmacokinetic properties. The biological activities of these oligomers as well as their tumor inhibitory behavior have been explored. This work also presents a facile and novel method of preparing these materials in nanosize, using Cetyltrimethylammonium bromide (CTAB) and polyvinyl alcohol (PVA) as capping ligands. The size and shape of the nanomaterials have been confirmed using the transmission electron microscope (TEM) and the scanning electron microscope (SEM).

Textile dye biodecolourization and ammonium removal over nitrite in aerobic granular sludge sequencing batch reactors

Biodecolourization of azo dye and removal of ammonium by aerobic granular sludge (AGS) was investigated under different growth conditions. AGS not previously exposed to azo dye was able to effectively decolourize azo dye under anaerobic and microaerophilic conditions. Azo dye, total organic carbon and ammoniacal nitrogen removal efficiencies of 89-100%, 79-95% and 92-100%, respectively, were achieved in the AGS reactor operated for 80days under microaerophilic conditions. Removal of carbon, nitrogen and phosphorus was not impacted by azo dye loading. Azo dye, organic carbon and ammonium were majorly removed in the anoxic period wherein bulk dissolved oxygen was ranged from 0.5 and <0.08mgL^-1. Removal of 60mgL^-1 NH₄⁺-N was associated only with smaller amounts of nitrite build-up (∼5mgL^-1 NO₂^--N) and negligible nitrate concentrations. Profiles of nitrogen compounds in individual sequencing batch reactor cycles supported the occurrence of ammonium removal over nitrite pathway. Bacterial community analysis showed enrichment of specific microorganisms capable of decolourizing azo dyes in the dye-decolourizing AGS. Dye decolourization and nutrient removal by AGS under microaerophilic conditions is a novel finding and can be further developed for treating textile wastewaters onsite or after dilution with sewage.

Aerobic granular sludge technology: Mechanisms of granulation and biotechnological applications

Aerobic granular sludge (AGS) is a novel microbial community which allows simultaneous removal of carbon, nitrogen, phosphorus and other pollutants in a single sludge system. AGS is distinct from activated sludge in physical, chemical and microbiological properties and offers compact and cost-effective treatment for removing oxidized and reduced contaminants from wastewater. AGS sequencing batch reactors have shown their utility in the treatment of abattoir, live-stock, rubber, landfill leachate, dairy, brewery, textile and other effluents. AGS is extensively researched for wide-spread implementation in sewage treatment plants. However, formation of AGS takes relatively much longer time while treating low-strength wastewaters like sewage. Strategies like increased volumetric flow by means of short cycles and mixing of sewage with industrial wastewaters can promote AGS formation while treating low-strength sewage. This article reviewed the state of research on AGS formation mechanisms, bioremediation capabilities and biotechnological applications of AGS technology in domestic and industrial wastewater treatment.

Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems

Nitrogen and phosphorous are key pollutants in wastewater to be removed and recovered for sustainable development. Traditionally, nitrogen removal is practiced through energy intensive biological nitrification and denitrification entailing a major cost in wastewater treatment. Recent innovations in nitrogen removal aim at reducing energy requirements and recovering ammonium nitrogen. Bioelectrochemical systems (BES) are promising for recovering ammonium nitrogen from nitrogen rich waste streams (urine, digester liquor, swine liquor, and landfill leachate) profitably. Phosphorus is removed from the wastewater in the form of polyphosphate granules by polyphosphate accumulating organisms. Alternatively, phosphorous is removed/recovered as Fe-P or struvite through chemical precipitation (iron or magnesium dosing). In this article, recent advances in nutrients removal from wastewater coupled to recovery are presented by applying a waste biorefinery concept. Potential capabilities of BES in recovering nitrogen and phosphorous are reviewed to spur future investigations towards development of nutrient recovery biotechnologies.

Statistical investigation on the role of supporting electrolytes during NTA degradation on BDD anodes

This work reported a comparative study on the electrochemical incineration of nitrilotriacetic acid (NTA) in the presence of different supporting electrolytes (Na2SO4 and NaCl). Galvanostatic electrolyses were conducted in an undivided electrochemical cell containing boron-doped diamond (BDD) anode and platinum cathode. Initial solution pH, flow rate, applied current density, and supporting electrolyte concentration were selected as variables, besides the mineralization efficiency of NTA that was selected as response. Central composite rotatable design and response surface methodology were employed here to examine the statistical significance of the selected variables, as well as to determine the optimal conditions of the degradation process. Under the same operating conditions, two regression models were thus constructed to illustrate the differing impact of supporting electrolytes in BDD anode cells. The kinetics for NTA degradation followed different reaction orders for the two scenarios (in the absence and presence of NaCl), indicating the complex interaction between hydroxyl radicals and active chlorine. Despite this, the experimental results demonstrated that effective mineralization of NTA might also be achieved in the presence of chlorides (of lower concentrations). Besides, in the case of chlorides, the average mass transfer coefficient of the system was found to be strongly dependent on the initial solution pH. Lastly, a plausible reaction sequence concerning the electrolytic oxidation of NTA in chloride media was also proposed.

Chemometric study on the electrochemical incineration of nitrilotriacetic acid using platinum and boron-doped diamond anode

This study investigated the electrochemical incineration of nitrilotriacetic acid (NTA) at boron-doped diamond (BDD) and platinum (Pt) anodes. Trials were performed in the presence of sulfate electrolyte media under recirculation mode. The parameters that influence the degradation efficiency were investigated, including applied current density, flow rate, supporting electrolyte concentration and reaction time. To reduce the number of experiments, the system had been managed under chemometric technique named Doehlert matrix. As a consequence, the mineralization of NTA demonstrated similar behavior upon operating parameters on these two anodes. Further kinetic study indicated that the degradations followed pseudo-first-order reactions for both BDD and Pt anodes, and the reaction rate constant of the former was found to be higher than that of the latter. Such difference could be interpreted by results from fractal analysis. In addition, a reaction sequence for NTA mineralization considering all the detected intermediates was also proposed.

Umbelliferone β-d-galactopyranoside inhibits chemically induced renal carcinogenesis via alteration of oxidative stress, hyperproliferation and inflammation: possible role of NF-κB

Umbelliferone (7-hydroxycoumarin) compound possesses strong anti-inflammatory and free radical scavenging activity.

Cadmium accumulation and apoplastic and symplastic transport in Boehmeria nivea (L.) Gaudich on cadmium-contaminated soil with the addition of EDTA or NTA

A Cd-tolerant plant species named Boehmeria nivea (L.) Gaudich (ramie) was applied to study its Cd accumulation and translocation mechanisms with the addition of ethylene diamine tetracetic acid (EDTA) or nitrilotriacetic acid (NTA).

Biogenic nanopalladium production by self-immobilized granular biomass: application for contaminant remediation

Microbial granules cultivated in an aerobic bubble column sequencing batch reactor were used for reduction of Pd(II) and formation of biomass associated Pd(0) nanoparticles (Bio-Pd) for reductive transformation of organic and inorganic contaminants. Addition of Pd(II) to microbial granules incubated under fermentative conditions resulted in rapid formation of Bio-Pd. The reduction of soluble Pd(II) to biomass associated Pd(0) was predominantly mediated by H2 produced through fermentation. X-ray diffraction and scanning electron microscope analysis revealed that the produced Pd nanoparticles were associated with the microbial granules. The catalytic activity of Bio-Pd was determined using p-nitrophenol and Cr(VI) as model compounds. Reductive transformation of p-nitrophenol by Bio-Pd was ∼20 times higher in comparison to microbial granules without Pd. Complete reduction of up to 0.25 mM of Cr(VI) by Bio-Pd was achieved in 24 h. Bio-Pd synthesis using self-immobilized microbial granules is advantageous and obviates the need for nanoparticle encapsulation or use of barrier membranes for retaining Bio-Pd in practical applications. In short, microbial granules offer a dual purpose system for Bio-Pd production and retention, wherein in situ generated H2 serves as electron donor powering biotransformations.

Biodegradation of tributyl phosphate, an organosphate triester, by aerobic granular biofilms

Tributyl phosphate (TBP) is commercially used in large volumes for reprocessing of spent nuclear fuel. TBP is a very stable compound and persistent in natural environments and it is not removed in conventional wastewater treatment plants. In this study, cultivation of aerobic granular biofilms in a sequencing batch reactor was investigated for efficient biodegradation of TBP. Enrichment of TBP-degrading strains resulted in efficient degradation of TBP as sole carbon or along with acetate. Complete biodegradation of 2mM of TBP was achieved within 5h with a degradation rate of 0.4 μmol mL(-1) h(-1). TBP biodegradation was accompanied by release of inorganic phosphate in stoichiometric amounts. n-Butanol, hydrolysed product of TBP was rapidly biodegraded. But, dibutyl phosphate, a putative intermediate of TBP degradation was only partially degraded pointing to an alternative degradation pathway. Phosphatase activity was 22- and 7.5-fold higher in TBP-degrading biofilms as compared to bioflocs and acetate-fed aerobic granules. Community analysis by terminal restriction length polymorphism revealed presence of 30 different bacterial strains. Seven bacterial stains, including Sphingobium sp. a known TBP degrader were isolated. The results show that aerobic granular biofilms are promising for treatment of TBP-bearing wastes or ex situ bioremediation of TBP-contaminated sites.

Efficiency of biodegradable EDDS, NTA and APAM on enhancing the phytoextraction of cadmium by Siegesbeckia orientalis L. grown in Cd-contaminated soils

Chelant assisted phytoextraction has been proposed to enhance the efficiency of remediation. This study evaluated the effects of biodegradable ethylene diamine tetraacetate (EDDS), nitrilotriacetic (NTA) and anionic polyacrylamide (APAM) on the tolerance and uptake of Siegesbeckia orientalis L. at 10 and 100 mg kg(-1) Cd-contaminated soils. On the 80th and 90th days of transplanting, pots were treated with EDDS and NTA at 0 (control), 1 and 2 mmol kg(-1) soils, and APAM at 0 (control), 0.07 and 0.14 g kg(-1). Generally, the root and shoot biomass of S. orientalis in all treatments reduced not significantly compared with the control, and the activities of peroxidase and catalase in leaves generally increased by the application of chelants (P<0.05). The concentrations of Cd in the shoots were increased significantly by addition of all chelants. As a result, the Cd accumulation of S. orientalis under treatments with higher dosages of the three chelants on the 80th day were 1.40-2.10-fold and 1.12-1.25-fold compared to control at 10 and 100 mg kg(-1) Cd, respectively. Under the addition of 2 mmol kg(-1) NTA on the 80th day, the highest metal extraction ratio reached 1.2% and 0.4% at 10 and 100 mg kg(-1) Cd soils, respectively. Therefore, the applications of EDDS, NTA and APAM may provide more efficient choices in chemical-enhanced phytoextraction.

Microbial degradation of polyacrylamide by aerobic granules

To deal with polyacrylamide (PAM) wastewater, granular sludge formed in glucose-fed sequencing batch reactors (SBR) was employed to cultivate PAM-degrading granules. Three replicated SBRs were operated with increasing PAM concentration in the influent from 67 to 670 mg L(-1), and the hydraulic retention time was increased at the same time from 1 d to 6 d during the six-phase of the 43 d acclimation period. The well-acclimated PAM-degrading granules were different from the seeding granules in colour, mean diameter, biomass density and settle ability, and could use PAM as the sole carbon and nitrogen source. In the batch experiments, PAM degradation rate by granules was determined as 2.23 mg PAM g(-1) MLSS h(-1). According to the analysis of the intermediates of PAM biodegradation, PAM was degraded initially through hydrolysis of the amide group, and no acrylamide monomer was detected. With the help of LC/MS, the main intermediate was identified as polyacrylic acid with a low molecular weight. Therefore, the PAM-degrading granular sludge may be employed for removing PAM in the wastewater produced from tertiary oil recovery that uses polymeric flooding technology.

P-nitrophenol biodegradation by aerobic microbial granules

Mixed microbial consortia in the form of aerobic microbial granules (AMG) capable of xenobiotic degradation can be developed from activated sludge or by adaptation of microbial granules pre-grown on labile carbon sources. Both of these approaches were investigated for the cultivation of AMG capable of p-nitrophenol (PNP) biodegradation. Attempts to cultivate AMG from activated sludge using PNP as the sole carbon source were not successful due to poor microbial growth and washout of the inoculated activated sludge. As part of the second approach, parallel sequencing batch reactors (SBRs) were inoculated with pre-grown AMG and operated by feeding both acetate and PNP together (RA), PNP alone (RB) or acetate alone (RC). Acetate/PNP mineralization and nitrification were monitored in the three SBRs. PNP biodegradation was quickly established in both RA and RB. PNP removal rates were found to be 47 and 55 mg g VSS(-1) h(-1) in RA and RB, respectively. PNP biodegradation during the SBR cycle consisted of distinct lag, exponential and deceleration phases. However, with higher concentrations of PNP (>50 mg l(-1)), disintegration of granules was observed in RA and RB. When PNP was the sole carbon source, it inhibited the development of aerobic granules from activated sludge and caused disintegration of pre-cultivated aerobic granules. When PNP was the co-substrate along with acetate, the structural and functional integrity (including nitrification) of the granular sludge was maintained. This report highlights the importance of a labile co-substrate for maintaining the physical and functional integrity of granular sludge, when used for toxic waste degradation.

Denitrification of synthetic concentrated nitrate wastes by aerobic granular sludge under anoxic conditions

The aim of the present work was to determine the denitrification potential of aerobic granular sludge for concentrated nitrate wastes. We cultivated mixed microbial granules in a sequencing batch reactor operated at a superficial air velocity of 0.8 cm s(-1). The denitrification experiments were performed under anoxic conditions using serum bottles containing synthetic media with 225-2250 mg L(-1) NO3-N. Time required for complete denitrification varied with the initial nitrate concentration and acetate to nitrate-N mass ratio. Complete denitrification of 2250 mg L(-1) NO3-N under anoxic conditions was accomplished in 120 h. Nitrite accumulation was not significant (<5 mg N L(-1)) at initial NO3-N concentrations below 677 mg L(-1). However, denitrification of higher concentrations of nitrate (≥900 mg N L(-1)) resulted in buildup of nitrite. Nevertheless, nitrite buildups observed in present study were relatively lower compared to that reported in previous studies using flocculent activated sludge. The experimental results suggest that acetate-fed aerobic granular sludge can be quickly adapted to treat high strength nitrate waste and can thus be used as seed biomass for developing high-rate bioreactors for efficient treatment of concentrated nitrate-bearing wastes.

SO2907, a putative TonB-dependent receptor, is involved in dissimilatory iron reduction by Shewanella oneidensis strain MR-1

Shewanella oneidensis strain MR-1 utilizes soluble and insoluble ferric ions as terminal electron acceptors during anaerobic respiration. The components of respiratory metabolism are localized in the membrane fractions which include the outer membrane and cytoplasmic membrane. Many of the biological components that interact with the various iron forms are proposed to be localized in these membrane fractions. To identify the iron-binding proteins acting either as an iron transporter or as a terminal iron reductase, we used metal-catalyzed oxidation reactions. This system catalyzed the oxidation of amino acids in close proximity to the iron binding site. The carbonyl groups formed from this oxidation can then be labeled with fluoresceinamine (FLNH(2)). The peptide harboring the FLNH(2) can then be proteolytically digested, purified by HPLC and then identified by MALDI-TOF tandem MS. A predominant peptide was identified to be part of SO2907 that encodes a putative TonB-dependent receptor. Compared with wild type (wt), the so2907 gene deletion (ΔSO2907) mutant has impaired ability to reduce soluble Fe(III), but retains the same ability to respire oxygen or fumarate as the wt. The ΔSO2907 mutant was also impacted in reduction of insoluble iron. Iron binding assays using isothermal titration calorimetry and fluorescence tryptophan quenching demonstrated that a truncated form of heterologous-expressed SO2907 that contains the Fe(III) binding site, is capable of binding soluble Fe(III) forms with K(d) of approximate 50 μm. To the best of our knowledge, this is the first report of the physiological role of SO2907 in Fe(III) reduction by MR-1.

Degradation of chelating agents in aqueous solution using advanced oxidation process (AOP)

This article presents an overview with critical analysis of technical applicability of advanced oxidation process (AOP) in removing chelating agents from aqueous solution. Apart from the effect of metals for chelating agents as a major influencing factor, selected information such as pH, oxidant's dose, concentrations of pollutants and treatment performance is presented. The performance of individual AOP is compared. It is evident from our literature survey that photocatalysis with UV irradiation alone or coupled with TiO(2), ozonation and Fenton's oxidation are frequently applied to mineralize target pollutants. Overall, the selection of the most suitable AOP depends on the characteristics of effluents, technical applicability, discharge standard, regulatory requirements and environmental impacts.

Immobilization of Cr(VI) and its reduction to Cr(III) phosphate by granular biofilms comprising a mixture of microbes

We assessed the potential of mixed microbial consortia, in the form of granular biofilms, to reduce chromate and remove it from synthetic minimal medium. In batch experiments, acetate-fed granular biofilms incubated aerobically reduced 0.2 mM Cr(VI) from a minimal medium at 0.15 mM day(-1) g(-1), with reduction of 0.17 mM day(-1) g(-1) under anaerobic conditions. There was negligible removal of Cr(VI) (i) without granular biofilms, (ii) with lyophilized granular biofilms, and (iii) with granules in the absence of an electron donor. Analyses by X-ray absorption near edge spectroscopy (XANES) of the granular biofilms revealed the conversion of soluble Cr(VI) to Cr(III). Extended X-ray absorption fine-structure (EXAFS) analysis of the Cr-laden granular biofilms demonstrated similarity to Cr(III) phosphate, indicating that Cr(III) was immobilized with phosphate on the biomass subsequent to microbial reduction. The sustained reduction of Cr(VI) by granular biofilms was confirmed in fed-batch experiments. Our study demonstrates the promise of granular-biofilm-based systems in treating Cr(VI)-containing effluents and wastewater.

The application of molecular techniques to the study of wastewater treatment systems

Wastewater treatment systems tend to be engineered to select for a few functional microbial groups that may be organized in various spatial structures such as activated sludge flocs, biofilm or granules and represented by single coherent phylogenic groups such as ammonia-oxidizing bacteria (AOB) and polyphosphate-accumulating organisms (PAO). In order to monitor and control engineered microbial structure in wastewater treatment systems, it is necessary to understand the relationships between the microbial community structure and the process performance. This review focuses on bacterial communities in wastewater treatment processes, the quantity of microorganisms and structure of microbial consortia in wastewater treatment bioreactors. The review shows that the application of molecular techniques in studies of engineered environmental systems has increased our insight into the vast diversity and interaction of microorganisms present in wastewater treatment systems.

Characterization, modeling and application of aerobic granular sludge for wastewater treatment

Recently extensive studies have been carried out to cultivate aerobic granular sludge worldwide, including in China. Aerobic granules, compared with conventional activated sludge flocs, are well known for their regular, dense, and strong microbial structure, good settling ability, high biomass retention, and great ability to withstand shock loadings. Studies have shown that the aerobic granules could be applied for the treatment of low- or high-strength wastewaters, simultaneous removal of organic carbon, nitrogen and phosphorus, and decomposition of toxic wastewaters. Thus, this new form of activate sludge, like anaerobic granular sludge, could be employed for the treatment of municipal and industrial wastewaters in near future. This chapter attempts to provide an up-to-date review on the definition, cultivation, characterization, modeling and application of aerobic granular sludge for biological wastewater treatment. This review outlines some important discoveries with regard to the factors affecting the formation of aerobic granular sludge, their physicochemical characteristics, as well as their microbial structure and diversity. It also summarizes the modeling of aerobic granule formation. Finally, this chapter highlights the applications of aerobic granulation technology in the biological wastewater treatment. It is concluded that the knowledge regarding aerobic granular sludge is far from complete. Although previous studies in this field have undoubtedly improved our understanding on aerobic granular sludge, it is clear that much remains to be learned about the process and that many unanswered questions still remain. One of the challenges appears to be the integration of the existing and growing scientific knowledge base with the observations and applications in practice, which this paper hopes to partially achieve.

Is sludge retention time a decisive factor for aerobic granulation in SBR?

This study investigated the role of sludge retention time (SRT) in aerobic granulation under negligible hydraulic selection pressure. Results showed that no successful aerobic granulation was observed at the studied SRTs in the range of 3-40 days. A comparison analysis revealed that hydraulic selection pressure in terms of the minimum settling velocity would be much more effective than SRT for enhancing heterotrophic aerobic granulation in sequencing batch reactor (SBR). It was shown that SRT would not be a decisive factor for aerobic granulation in SBR.

Kinetics of reduction of Fe(III) complexes by outer membrane cytochromes MtrC and OmcA of Shewanella oneidensis MR-1

Because of their cell surface locations, the outer membrane c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 have been suggested to be the terminal reductases for a range of redox-reactive metals that form poorly soluble solids or that do not readily cross the outer membrane. In this work, we determined the kinetics of reduction of a series of Fe(III) complexes with citrate, nitrilotriacetic acid (NTA), and EDTA by MtrC and OmcA using a stopped-flow technique in combination with theoretical computation methods. Stopped-flow kinetic data showed that the reaction proceeded in two stages, a fast stage that was completed in less than 1 s, followed by a second, relatively slower stage. For a given complex, electron transfer by MtrC was faster than that by OmcA. For a given cytochrome, the reaction was completed in the order Fe-EDTA > Fe-NTA > Fe-citrate. The kinetic data could be modeled by two parallel second-order bimolecular redox reactions with second-order rate constants ranging from 0.872 microM(-1) s(-1) for the reaction between MtrC and the Fe-EDTA complex to 0.012 microM(-1) s(-1) for the reaction between OmcA and Fe-citrate. The biphasic reaction kinetics was attributed to redox potential differences among the heme groups or redox site heterogeneity within the cytochromes. The results of redox potential and reorganization energy calculations showed that the reaction rate was influenced mostly by the relatively large reorganization energy. The results demonstrate that ligand complexation plays an important role in microbial dissimilatory reduction and mineral transformation of iron, as well as other redox-sensitive metal species in nature.

Formation of aerobic granules in the presence of a synthetic chelating agent

This paper examines the development of aerobic granular sludge in the presence of a synthetic chelating agent, nitrilotriacetic acid (NTA), in sequencing batch reactors (SBR). The growth of seed sludge at 0.26 mM, 0.52 mM and 1.05 mM of NTA was found to be significantly lower as compared to that in the absence of NTA. Aerobic granulation was significantly enhanced in the three SBRs (R2, R3 and R4), which were fed with 0.26 mM, 0.52 mM and 1.05 mM of NTA as a co-substrate, in comparison to the acetate-alone fed SBR (R1). After 2 months of operation, the mean diameter of the biomass stabilized at 0.35 mm in R1 (acetate alone), as compared to 2.18 mm in R4 (1.05 mM NTA+acetate). NTA degradation was established in SBRs, with almost complete removal during the SBR cycle. Batch experiments also showed efficient degradation of NTA by the aerobic granules.

Bioaugmentation of aerobic microbial granules with Pseudomonas putida carrying TOL plasmid

This paper describes results of a successful bioaugmentation experiment on aerobic granular sludge using Pseudomonas putida KT2442 cells bearing the TOL (pWWO) plasmid. The methodology was designed to monitor incorporation of the added donor cells into pre-existent microbial granules and the subsequent plasmid transfer to the autochthonous microbial community using shake flask microcosms. Expression of reporter proteins (GFP and DsRed) allowed in situ monitoring of donor cell attachment and plasmid transfer to the recipient cells using confocal laser scanning microscopy. Concomitant with donor integration and transconjugant proliferation in the granules, a significant increase in degradation of benzyl alcohol (used as sole substrate) was observed in the augmented microcosms. In contrast, control microcosms (with non-augmented granules) did not show any noticeable increase in the degradation of the substrate. This study shows that bioaugmentation of aerobic granular sludge via donor colonization and plasmid transfer is feasible for enhanced biodegradation.

Biodegradation of pyridine using aerobic granules in the presence of phenol

Aerobic granules cultivated with 500 mg/L phenol medium effectively degraded pyridine at a concentration of 250-2500 mg/L; maximum degradation rate was 73.0 mg pyridineg/VSS/h at 250 mg/L pyridine concentration. Phenol concentrations of 500-2000 mg/L limited pyridine degradation in a competitive inhibition pattern, as interpreted using Michaelis-Menten kinetics with corresponding parameters V(max), K(m) and K(I) of 63.7 mg/Lh(-1), 827.8 and 1388.9 mg/L, respectively. Fluorescent staining and confocal laser scanning microscopy (CLSM) tests suggested that an active biomass accumulated at the granule outer layer. Denaturing gradient gel electrophoresis (DGGE) fingerprint profile demonstrated that dominating microbial strains exist in phenol and pyridine-degrading aerobic granules.