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Microcystin (MC) elimination is a global challenge that is necessary for the health of humans and ecosystems. Biodegradation of MC, one of the most environmental-friendly methods, had previously been focused on the aerobic condition. In this study, two enrichment cultures from Taihu sediments possessed high capacity for MC-leucine arginine (MC-LR) anaerobic biodegradation. Meanwhile, it was firstly found that MC-LR underwent similar degradation process under anaerobic conditions to that in aerobic condition. Furthermore, a novel degradation pathway, hydrolyzing of Ala-Mdha to form a new linear MC-LR intermediate, was proposed under anaerobic conditions. Combining MC-LR degradation with microbial community analysis, this study deduced that Candidatus Cloacamonas acidaminovorans str. Evry may play an important role in the degradation of MC-LR. These findings suggest an additional pathway involved in the environmental cycle of MC-LR, which implies that the biotransformation of MC-LR might play an important role in eliminating MC-LR in eutrophic lake sediments under anaerobic conditions., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. We report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacterium Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). These results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In the recent years, anaerobic membrane bioreactor (AnMBR) technology is being considered as a very attractive alternative for wastewater treatment due to the striking advantages such as upgraded effluent quality. However, fouling control is still a problem for the application of AnMBR. This study investigated the performance of an AnMBR using mesh filter as support material to treat low-strength wastewater via in-situ biogas sparging. It was found that mesh AnMBR exhibited high and stable chemical oxygen demand (COD) removal efficiencies with values of 95 ± 5 % and an average methane yield of 0.24 L CH4/g CODremoved. Variation of transmembrane pressure (TMP) during operation indicated that mesh fouling was mitigated by in-situ biogas sparging and the fouling rate was comparable to that of aerobic membrane bioreactor with mesh filter reported in previous researches. The fouling layer formed on the mesh exhibited non-uniform structure; the porosity became larger from bottom layer to top layer. Biogas sparging could not change the composition but make thinner thickness of cake layer, which might be benefit for reducing membrane fouling rate. It was also found that ultrasonic cleaning of fouled mesh was able to remove most foulants on the surface or pores. This study demonstrated that in-situ biogas sparging enhanced the performance of AnMBRs with mesh filter in low-strength wastewater treatment. Apparently, AnMBRs with mesh filter can be used as a promising and sustainable technology for wastewater treatment.

Microbial extracellular polymeric substances (EPS) excreted from microorganisms were a complex natural biological polymer mixture of proteins and polysaccharides, which played an important roles in the transport of metals, such as Ag(+). Electroactive bacteria, is an important class of environmental microorganisms, which can use iron or manganese mineral as terminal electron acceptors to generate energy for biosynthesis and cell maintenance. In this work, the EPS extracted of three electroactive bacteria (Shewanella oneidensis, Aeromonas hydrophila, and Pseudomonas putida) were used for reducing Ag(+) and forming silver nanoparticles (AgNPs). Results showed that all the three microbial EPS could reduce Ag(+) to AgNPs. The formed AgNPs were characterized in depth by the UV-visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The main components in the EPS from the three electroactive bacteria were analyzed. The presence of cytochrome c in these EPS was confirmed, and they were found to contribute to the reduction of Ag(+) to AgNPs. The results indicated that the EPS of electroactive bacteria could act as a reductant for AgNPs synthesis and could provide new information to understand the fate of metals and their metal nanoparticles in the natural environments.

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.

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.

Soluble microbial products (SMP) generated by microbial populations can adversely affect the efficiency of biological wastewater treatment systems and secondary effluent quality. In this work, both experimental and modeling approaches were used to investigate the formation of SMP by both heterotrophic and autotrophic bacteria. Strategies to control and reduce SMP in activated sludge systems were thus evaluated. SMP produced by heterotrophs were found to account for more than 92% of total SMP. The SMP produced by autotrophs contributed to less than 8% of the total SMP, with 5% attributable to the ammonia-oxidizing bacteria (AOB) and 3% to the nitrite-oxidizing bacteria (NOB). When external organic substrate was present, the utilization-associated products (UAP) were the main component of SMP. When external organic substrate was completely consumed, biomass-associated products (BAP) from the hydrolysis of extracellular polymeric substances (EPS) dominated the SMP. The model developed in this study described the fractions and dynamics of UAP and BAP produced by heterotrophs, AOB and NOB. Solids retention time of the reactor had a significant effect on SMP production, while the effect of the hydraulic retention time was only minor. Decreasing the solids retention time from 15 to 0.5 d reduced SMP production in the reactor by 62%., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In this work, nitrogen loss in the nitrite oxidation step of the nitrification process in an aerobic-granule-based reactor was characterized with both experimental and modeling approaches. Experimental results showed that soluble microbial products (SMP) were released from the nitrite-oxidizing granules and were utilized as a carbon source by the heterotrophs for denitrification. This was verified by the fluorescence in situ hybridization (FISH) analysis. Microelectrode tests showed that oxygen diffusion limitation did result in an anoxic micro-zone in the granules and allowed sequential utilization of nitrate as an electron acceptor for heterotrophic denitrification with SMP as a carbon source. To further elucidate the nitrogen loss mechanisms, a mathematic model was formulated to describe the growth of nitrite oxidizers, the formation and consumption of SMP, the anoxic heterotrophic growth on SMP and nitrate, as well as the oxygen transfer and the substrate diffusion in the granules. The results clearly indicate that the heterotrophs grown on the SMP released by the autotrophs are responsible for the nitrogen loss in the nitrifying granules, and give us a better understanding of the aerobic granules for nitrogen removal. Biotechnol. Bioeng. 2011;108: 2844-2852. © 2011 Wiley Periodicals, Inc., (Copyright © 2011 Wiley Periodicals, Inc.)

In this work, the heterotrophic growth on the microbial products of autotrophs and the effecting factors were evaluated with both experimental and modeling approaches. Fluorescence in situ hybridization (FISH) analysis illustrated that ammonia oxidizers (AOB), nitrite oxidizers (NOB), and heterotrophs accounted for about 65%, 20%, and 15% of the total bacteria, respectively. The mathematical evaluation of experimental data reported in literature indicated that heterotrophic growth in nitrifying biofilm (30-50%) and granules (30%) was significantly higher than that of nitrifying sludge (15%). It was found that low influent ammonium resulted in a lower availability of soluble microbial products (SMP) and a slower heterotrophic growth, but high ammonium (>150 mg N L(-1)) feeding would lead to purely AOB dominated sludge with high biomass-associated products contained effluent, although the absolute heterotrophic growth increased. Meanwhile, the total active biomass concentration increased gradually with the increasing solids retention time, whereas the factions of active AOB, NOB, and heterotrophs varied a lot at different solids retention times. This work could be useful for better understanding of the autotrophic wastewater treatment systems., (Copyright © 2010 Wiley Periodicals, Inc.)

Microbial products formed in biological wastewater treatment systems are closely related to system performance and status, and many of them have fluorescence spectral characteristics. In this work, the fluorescence spectral characteristics of the supernatants from an anaerobic hydrogen-producing bioreactor were studied using three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy. Since the components of the microbial products are complex, the parallel factor analysis (PARAFAC) method was used to extract the real spectra from the overlapped spectra. Two principal components were identified from the EEM spectra. The peaks at excitation-emission maxima of 280/350 and 350/440 nm were, respectively, attributed to the fluorescence of proteins and NADH. Their real concentrations were quantified using the PARAFAC coupled with the second-order calibration method. Results show that the formation rate of proteins was correlated to the production rate of hydrogen and volatile fatty acids, as well as the substrate degradation rate. A close correlation between the hydrogen partial pressure and the two fluorophores was found out. This study provides a reliable and convenient approach, which could be potentially used for monitoring the wastewater treatment reactor performance through measuring the fluorescence spectra of the supernatant.

A model azo dye, methyl orange (MO), was reduced through in situ utilization of the electrons derived from the anaerobic conversion of organics in a microbial fuel cell (MFC). The MO reduction process could be described by a pseudo first-order kinetic model with a rate constant of 1.29 day(-1). Electrochemical impedance spectroscopic analysis shows that the cathode had a high polarization resistance, which could decrease the reaction rate and limit the electron transfer. To improve the MO reduction efficiency, the cathode was modified with redox mediators to enhance the electron transfer. After modification with thionine, the polarization resistance significantly decreased by over 50%. As a consequence, the MO decolorization rate increased by over 20%, and the power density was enhanced by over three times. Compared with thionine, anthraquinone-2, 6-disulfonate modified cathode has less positive effect on the MFC performance. These results indicate that the electrode modification with thionine is a useful approach to accelerate the electrochemical reactions. This work provides useful information about the key factors limiting the azo dye reduction in the MFC and how to improve such a process.

A review concerning the definition, extraction, characterization, production and functions of extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment reactors is given in this paper. EPS are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater. They are a major component in microbial aggregates for keeping them together in a three-dimensional matrix. Their characteristics (e.g., adsorption abilities, biodegradability and hydrophilicity/hydrophobicity) and the contents of the main components (e.g., carbohydrates, proteins, humic substances and nucleic acids) in EPS are found to crucially affect the properties of microbial aggregates, such as mass transfer, surface characteristics, adsorption ability, stability, the formation of microbial aggregates etc. However, as EPS are very complex, the knowledge regarding EPS is far from complete and much work is still required to fully understand their precise roles in the biological treatment process., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Fermentative hydrogen production, as a process for clean energy recovery from organic wastewater, is limited by its low hydrogen yield due to incomplete conversion of substrates, with most of the fermentation products being volatile fatty acids (VFAs). Thus, further recovery of the energy from VFAs is expected. In this work, microbial fuel cell (MFC) was applied to recover energy in the form of electricity from mixed VFAs of acetate, propionate, and butyrate. Response surface methodology was adopted to investigate the relative contribution and possible interactions of the three components of VFAs. A stable electricity generation was demonstrated in MFCs after the enrichment of electrochemically active bacteria. Analysis showed that power density was more sensitive to the composition of mixed VFAs than coulombic efficiency. The electricity generation could mainly be attributed to the portion of acetate and propionate. However, the two components showed an antagonistic effect when propionate exceeded 19%, causing a decrease in coulombic efficiency. Butyrate was found to exert a negative impact on both power density and coulombic efficiency. Denaturing gradient gel electrophoresis profiles revealed the enrichment of electrochemically active bacteria from the inoculum sludge. Proteobacteria (Beta-, Delta-) and Bacteroidetes were predominant in all VFA-fed MFCs. Shifts in bacterial community structures were observed when different compositions of VFA mixtures were used as the electron donor. The overall electron recovery efficiency may be increased from 15.7% to 27.4% if fermentative hydrogen production and MFC processes are integrated.

In this work, both experimental and modeling approaches are used to explore the formation of soluble microbial products (SMP) by activated sludge under anoxic conditions. With substrate consumption, the SMP concentration increases gradually. Utilization associated products (UAP) are the main fraction of SMP when substrate is present; whereas biomass associated products (BAP) are the major content of SMP as substrate is completely consumed. The fraction of the accumulated SMP accounts for 3-4% of initial organic substrate. Three dimensional excitation emission matrix analysis results indicate that the SMP concentration increases in the denitrification process. The accumulation of nitrite up to 22.6 mg/l under anoxic conditions has no significant effect on the SMP formation. With a consideration of SMP formation under anoxic conditions, an ASM3-based denitrification model is developed. The results show that the developed model is able to capture the relationship between the SMP formation and the substrate consumption by activated sludge in the denitrification process.

Anaerobic ammonium oxidation (anammox) is a promising new process to treat high-strength nitrogenous wastewater. Due to the low growth rate of anaerobic ammonium-oxidizing bacteria, efficient biomass retention is essential for reactor operation. Therefore, we studied the settling ability and community composition of the anaerobic ammonium-oxidizing granules, which were cultivated in an upflow anaerobic sludge blanket (UASB) reactor seeded with aerobic granules. With this seed, the start-up period was less than 160 days at a NH(4)(+)-N removal efficiency of 94% and a loading rate of 0.064 kg N per kg volatile suspended solids per day. The formed granules were bright red and had a high settling velocity (41 to 79 m h(-1)). Cells and extracellular polymeric substances were evenly distributed over the anaerobic ammonium-oxidizing granules. The high percentage of anaerobic ammonium-oxidizing bacteria in the granules could be visualized by fluorescent in situ hybridization and electron microscopy. The copy numbers of 16S rRNA genes of anaerobic ammonium-oxidizing bacteria in the granules were determined to be 4.6 x 10(8) copies ml(-1). The results of this study could be used for a better design, shorter start-up time, and more stable operation of anammox systems for the treatment of nitrogen-rich wastewaters.

Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were 0.21 g chemical oxygen demand (COD) g(-1) N, 0.09 h(-1), and 9.1 mg N L(-1), respectively, whereas the corresponding values for NOB were 0.05 g COD g(-1) N, 0.11 h(-1), and 4.85 mg N L(-1), respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules.

In this work the extracellular polymeric substances (EPS) produced by mixed microbial community in activated sludge are characterized using gel-permeating chromatography (GPC), 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy measurement and mathematical modeling. Chromatograms of extracted EPS exhibit seven peaks, among which proteins have four peaks and polysaccharides have three peaks. Evolution of the chromatogram area indicates that the quantity of produced EPS increases significantly in the substrate utilization process. With the parallel factor analysis (PARAFAC) approach, two components of the polymer matrix are identified by the EEM analysis, one as EPS proteins at Ex/Em 280/340 nm and one matrix associated as fulvic-acid-like substances at 320/400 nm. The proteins and fulvic-acid-like substances in the EPS increase in the substrate utilization phase, but decrease in the endogenous phase. To have a better insight into EPS production, the kinetic modeling of EPS is performed with regard to their molecular weight distribution and chemical natures identified by GPC and EEM. In this way, the dynamics of these important microbial products are better understood.

Microbial fuel cells (MFCs) are devices that use bacteria as the catalysts to oxidize organic and inorganic matter and generate current whereas microbial electrolysis cells (MECs) are a reactor for biohydrogen production by combining MFC and electrolysis. In an MEC, an external voltage must be applied to overcome the thermodynamic barrier. Here we report an MEC-MFC-coupled system for biohydrogen production from acetate, in which hydrogen was produced in an MEC and the extra power was supplied by an MFC. In this coupled system, hydrogen was produced from acetate without external electric power supply. At 10 mM of phosphate buffer, the hydrogen production rate reached 2.2 +/- 0.2 mL L(-1) d(-1), the cathodic hydrogen recovery (RH2) and overall systemic Coulombic efficiency (CEsys) were 88 to approximately 96% and 28 to approximately 33%, respectively, and the overall systemic hydrogen yield (Y(sysH2)) peaked at 1.21 mol-H2 mol-acetate(-1). The hydrogen production was elevated by increasing the phosphate buffer concentration, and the highest hydrogen production rate of 14.9 +/- 0.4 mL L(-1) d(-1) and Y(sysH2) of 1.60 +/- 0.08 mol-H2 mol-acetate(-1) were achieved at 100 mM of phosphate buffer. The performance of the MEC and the MFC was influenced by each other. This MEC-MFC-coupled system has a potential for biohydrogen production from wastes, and provides an effective way for in situ utilization of the power generated from MFCs.

Three-dimensional excitation-emission-matrix (EEM) fluorescence spectrometry was used to characterize the extracellular and intracellular substances of activated sludge in a sequencing batch reactor (SBR). Parallel factor analysis (PARAFAC) was applied to extract the pure spectra from the overlapped spectra. Three main components, proteins, fulvic- and humic-like substances, were identified from the extracellular substances. Their fluorescence peaks were at an excitation/emission (Ex/Em) of 280/350, 340/400 and 390/450 nm, respectively. The fluorescence of the extracellular proteins had a similar changing pattern with the wastewater chemical oxygen demand, the fulvic-like substance did not vary significantly in a cycle and the humic-like substances accumulated in the substrate uptake phase but decreased later. Proteins and nicotinamide adenine dinucleotide, reduced form (NADH), were identified as the two main intracellular fluorophores, and their fluorescence peaks (Ex/Em) were at 280/340 and 350/450 nm, respectively. The fluorescence intensity scores of the intracellular fluorophores were closely related to the bioreactor performance. Thus, the results of this work provide a foundation for potential utilization of the EEM fluorescence spectroscopy to monitor the activated sludge systems for wastewater treatment.