[show abstract][hide abstract] ABSTRACT: Electrochemically active bacteria (EAB) have the ability to transfer electrons to electron acceptors located outside the cell, and they are widely present in diverse environments. In spite of their important roles in geochemical cycles, environmental remediation and electricity generation, so far, only a limited number and types of EAB have been isolated and characterized. Thus, effective and rapid EAB identification methods are highly desirable. In this protocol, we describe a photometric protocol for the visualization and high-throughput identification and isolation of EAB. The protocol relies on the fast electron acquisition and color change ability of an electrochromic material, namely a tungsten trioxide (WO3) nanorod assembly. The extracellular electron transfer (EET) from EAB to the WO3 nanorod assembly probe is accompanied by a bioelectrochromic reaction made evident by the color change of the probe. This protocol enables researchers to rapidly identify EAB and evaluate their EET ability either qualitatively with the naked eye or quantitatively by image analysis. We have also successfully used this protocol to isolate EAB from environmental samples. The time needed to complete this protocol is ∼2 d, with the actual EAB identification process taking about 5 min.
[show abstract][hide abstract] ABSTRACT: The concentration of nitrate in aquatic systems is rising with the development of modern industry and agriculture, causing a cascade of environmental problems. Here we describe a previously unreported nitrate formation process. Both indoor and outdoor experiments are conducted to demonstrate that nitrate may be formed from abundant atmospheric nitrogen and oxygen on nano-sized titanium dioxide surfaces under UV or sunlight irradiation. We suggest that nitric oxide is an intermediate product in this process, and elucidate its formation mechanisms using first-principles density functional theory calculations. Given the expanding use of titanium dioxide worldwide, such a titanium dioxide-mediated photocatalysis process may reveal a potentially underestimated source of nitrate in the environment, which on one hand may lead to an increasing environmental pollution concern, and on the other hand may provide an alternative, gentle and cost-effective method for nitrate production.
[show abstract][hide abstract] ABSTRACT: Electrochemically active bacteria (EAB) are ubiquitous in environment and have important application in the fields of biogeochemistry, environment, microbiology and bioenergy. However, rapid and sensitive methods for EAB identification and evaluation of their extracellular electron transfer ability are still lacking. Herein we report a novel photometric method for visual detection of EAB by using an electrochromic material, WO(3) nanoclusters, as the probe. This method allowed a rapid identification of EAB within 5 min and a quantitative evaluation of their extracellular electron transfer abilities. In addition, it was also successfully applied for isolation of EAB from environmental samples. Attributed to its rapidness, high reliability, easy operation and low cost, this method has high potential for practical implementation of EAB detection and investigations.
[show abstract][hide abstract] ABSTRACT: Flocculation process is one of the most widely used techniques for water and wastewater treatment, and also for sludge dewatering. Synthesis of natural biopolymers or modification of natural biopolymers as environmentally friendly flocculants is highly desired in the field of environmental protection. In this work, a water soluble copolymer flocculant, STC-g-PDMC (starch-graft-poly (2-methacryloyloxyethyl) trimethyl ammonium chloride) was synthesized through grafting a monomer, (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC), onto starch initiated by potassium persulphate. Acetone and ethanol were used for copolymer precipitation and purification in the synthesis, which diminished the toxicity during the synthesis process. The graft copolymer was characterized using Fourier-transform infrared spectroscopy, (1)H nuclear magnetic resonance, X-ray powder diffraction, thermogravimetric analysis and elemental analysis. The prepared STC-g-PDMC exhibited a highly effective flocculation capability for kaolin suspensions compared with starch and polyacrylamide as control. The charge neutralization effect played an important role in the flocculation process at low flocculant dosages. When it was used as dewatering agent for anaerobic sludge, the conditioned sludge could be easily filtered after the dosage reached 0.696% of the dry weight of sludge. Such a graft copolymer is a promising green agent for wastewater treatment and sludge dewatering applications.
[show abstract][hide abstract] ABSTRACT: Microorganisms capable of extracellular electron transfer play important roles in biogeochemical redox processes and have been of great interest in the fields of energy recovery, waste treatment, and environmental remediation. In this study, a new electrochemically active bacterium was identified with a high-throughput method using WO3 nanoclusters as probes. The 16S rRNA gene sequence designated the strain as Lysinibacillus sphaericus D-8, a Gram-positive bacterium. Its electrochemical activity was characterized in a two-chamber microbial fuel cell and a three-electrode electrochemical cell. Strain D-8 produced 92 mW/m2 of power using lactate as the electron donor. The electrochemical impedance spectroscopy results confirmed the electrochemical activity of this strain. Cyclic voltammetry analysis indicated that the presence of soluble redox active compounds might play an important role in the extracellular electron transfer by L. sphaericus D-8. This work might be the first report that demonstrates the electrochemical activity of Lysinibacillus species.
[show abstract][hide abstract] ABSTRACT: The flocculation of microorganisms plays a crucial role in bioreactors, and is substantially affected by pH. However, the mechanism for such an effect remains unclear. In this work, with an integrated approach, the pH dependence of structure and surface property of microbial extracellular polymeric substances (EPS), excreted from Bacillus megaterium TF10, and accordingly its flocculation is elucidated. From the Fourier transform infrared spectra and acid−base titration test results, the main functional groups and buffering zones in the EPS responsible for the microbial flocculation are indentified. The laser light scattering analysis reveals that the deprotonated or protonated states of these functional groups in EPS result in more dense and compact structure at a lower pH because of hydrophobicity and intermolecular hydrogen bonds. The zeta potential measurements identify the isoelectric point and indicate that the electrostatic repulsion action of EPS is controlled by pH. The highest flocculation efficiency is achieved near the isoelectric point (pH 4.8). These results clearly demonstrate that the EPS structure, surface properties, and accordingly the microbial flocculation are dependent heavily on pH in solution.
[show abstract][hide abstract] ABSTRACT: Two monomers, acrylamide (AM) and (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) were grafted onto chitosan simultaneously in acid-water solution initiated by the highly efficient and environmentally friendly gamma ray radiation at ambient temperatures. The copolymer obtained was analyzed using Fourier-transform infrared, X-ray powder diffraction and thermogravimetric analysis. The cationic degree of the copolymer was determined by the colloid titration method. Its flocculation properties were evaluated in 0.25% (wt) kaolin suspensions and its significant superiority over PAM (polyacrylamide) and chitosan was observed. The results of zeta potential measurement demonstrated that the flocculation mechanism of the copolymer was distinct when it was used as a flocculant under different conditions. The images and the settling rate test of the floccules after treating by the flocculant showed that the capacities of bridging and charge neutralization of the graft copolymer were improved after the grafting of AM and DMC. Jar tests with pulp mill wastewater demonstrated that the flocculation efficiency of the graft copolymer was much better than that of PAM.
[show abstract][hide abstract] ABSTRACT: Pulp mill wastewater was treated using the coagulation-flocculation process with aluminum chloride as the coagulant and a modified natural polymer, starch-g-PAM-g-PDMC [polyacrylamide and poly (2-methacryloyloxyethyl) trimethyl ammonium chloride], as the flocculant. A novel approach with a combination of response surface methodology (RSM) and uniform design (UD) was employed to evaluate the effects and interactions of three main influential factors, coagulant dosage, flocculant dosage and pH, on the treatment efficiency in terms of the supernatant turbidity and lignin removals as well as the water recovery. The optimal conditions obtained from the compromise of the three desirable responses, supernatant turbidity removal, lignin removal and water recovery efficiency, were as follows: coagulant dosage of 871 mg/L, flocculant dosage of 22.3 mg/L and pH 8.35. Confirmation experiments demonstrated that such a combination of the UD and RSM is a powerful and useful approach for optimizing the coagulation-flocculation process for the pulp mill wastewater treatment.
Water Research 09/2011; 45(17):5633-40. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Extracellular polymeric substances (EPS), a complex high-molecular-weight mixture of polymers excreted by microorganisms and produced from cell lysis, may have a high bioflocculation activity. In this work, the EPS excreted from Bacillus megaterium TF10, which was isolated from a soil sample, were systematically characterized to give insights into the relationship between their specific constituents and structure with their flocculation capacity. The results of microscopic observation, zeta potential, and TF10 EPS structure analysis show that the bridging mechanism was mainly responsible for the flocculation of the TF10. The constituents with a large molecular weight (1037-2521 kDA) and functional groups had contributed to the flocculation. GC-MS and NMR analyses demonstrate that the polysaccharides had long chain composed of rhamnose as well as glucose and galactose with uronic acids, acetyl amino sugars, and proteins as the side chains. The proteins in TF10 had no flocculation ability because of their special secondary structure and molecular weight diffusion characters. The EPS from Bacillus megaterium TF10 were found to exhibit a high flocculation activity, and the polysaccharides in EPS, which have the structure of the long backbone with active side chains, were identified as the active constituents for the high flocculation activity.
[show abstract][hide abstract] ABSTRACT: Photocatalytic oxidation mediated by TiO(2) is a promising oxidation process for degradation of organic pollutants, but suffers from the decreased photocatalytic efficiency attributed to the recombination of photogenerated electrons and holes. Thus, a cost-effective supply of external electrons is an effective way to elevate the photocatalytic efficiency. Here we report a novel bioelectrochemical system to effectively reduce p-nitrophenol as a model organic pollutant with utilization of the energy derived from a microbial fuel cell. In such a system, there is a synergetic effect between the electrochemical and photocatalytic oxidation processes. Kinetic analysis shows that the system exhibits a more rapid p-nitrophenol degradation at a rate two times the sum of rates by the individual photocatalytic and electrochemical methods. The system performance is influenced by both external resistor and electrolyte concentration. Either a lower external resistor or a lower electrolyte concentration results in a higher p-nitrophenol degradation rate. This system has a potential for the effective degradation of refractory organic pollutants and provides a new way for utilization of the energy generated from conversion of organic wastes by microbial fuel cells.
Environmental Science and Technology 07/2010; 44(14):5575-80. · 5.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: The contribution of extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), to the aggregation of both aerobic and anaerobic sludge is explored using the extended DLVO theory. It is observed that the aggregation abilities of both sludge samples decrease with the extraction of LB-EPS and TB-EPS, implying the crucial roles of EPS in sludge aggregation. Furthermore, through analyzing the interaction energy curves of sludge before and after the EPS extraction using the extended DLVO theory, it is found that both LB-EPS and TB-EPS have a substantial contribution to the sludge aggregation. The interaction energy of LB-EPS is always negative, suggesting that the LB-EPS always display a positive effect on the sludge aggregation. On the other hand, the interaction energy of TB-EPS is not always negative, depending on the separation distance between sludge cells. These results imply that the LB-EPS and TB-EPS have different contributions to the sludge aggregation.
Environmental Science and Technology 06/2010; 44(11):4355-60. · 5.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this work, pulp mill wastewater was treated using a novel copolymer flocculant with a high water-solubility, which was synthesized through grafting (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) onto chitosan initiated by potassium persulphate. The experimental results demonstrate that the two main problems associated with the utilization of chitosan as a flocculant, i.e., low molecular weight and low water-solubility, were concurrently sorted out. The physicochemical properties of this flocculant were characterized with Fourier-transform infrared spectroscopy, (1)H nuclear magnetic resonance spectroscopy, X-ray powder diffraction and field emission scanning electron microscopy. Reaction parameters influencing the grafting percentage, such as temperature, reaction time, initiator concentration and monomer concentration, were optimized using an orthogonal array design matrix. With an increase in grafting percentage, the water-solubility of the flocculant was improved, and it became thoroughly soluble in water when the grafting percentage reached 236.4% or higher. Its application for the treatment of pulp mill wastewater indicates that it had an excellent flocculation capacity and that its flocculation efficiency was much better than that of polyacrylamide. The optimal conditions for the flocculation treatment of pulp mill wastewater were also obtained.
Water Research 09/2009; 43(20):5267-75. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: A water-soluble cationic flocculant, a copolymer of acrylamide (AM) and acryloylamino-2-hydroxypropyl trimethyl ammonium chloride (AMHP), was synthesized through dispersion polymerization method in aqueous ammonium sulfate ((NH4)2SO4) solution. The polymerization was initiated by gamma-radiation using poly(2-methylacryloylxyethyl trimethyl ammonium chloride) (PDMC) as the stabilizer. The obtained copolymer was characterized by using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), colloidal titration and optical microscopy. Its flocculation properties were evaluated with 0.25 wt% kaolin suspensions using a standard jar test. The zeta potential of supernatant at different flocculant dosage was simultaneously measured. The results demonstrate the superiority of the copolymer over the commercial polyacrylamide as a flocculant.
[show abstract][hide abstract] ABSTRACT: A water-soluble cationic flocculant, the copolymer of acrylamide (AM) and acryloylamino-2-hydroxypropyl trimethyl ammonium chloride (AMHP), has been synthesized through dispersion polymerization in aqueous ammonium sulfate ((NH4)2SO4) solution. The polymerization was initiated by potassium persulfate (KPS) using poly(2-methylacryloylxyethyl trimethyl ammonium chloride) (PDMC) as the stabilizer. The copolymer obtained was characterized using Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, colloidal titration and optical microscopy. Its flocculation properties were evaluated with 0.25 wt% kaolin suspensions using a standard jar test. The zeta potential of the supernates at different flocculant dosages was measured simultaneously. The results demonstrate the superiority of the copolymer over the commercial polyacrylamide as a flocculant.
[show abstract][hide abstract] ABSTRACT: A microbial fuel cell (MFC) was explored as a pretreatment method to remove dissolved organic matter (DOM) from polluted lake water and simultaneously generate electricity. After the MFC treatment, the total organic carbon concentration in the raw lake water was reduced by 50%, the physicochemical nature of DOMs was substantially altered. Protein-like substances in lake water were utilized as a major substrate for the MFC, while humic-like substances were refractory to the biodegradation. A further investigation into the bovine serum albumin utilization in an MFC confirms that the electricity generation was closely associated with the removal of protein-like substrates. Toxicity assessment by Salmonella typhimurium Sal94 indicates that the genotoxic agents in the polluted lake water were almost completely removed after the MFC treatment. This approach of coupling microbially-catalyzed electricity generation with DOM removal may offer a potential avenue for energy-efficient bioremediation of lake water.