Assessment of heavy metal contamination and Hg-resistant bacteria in surface water from different regions of Delhi,India

The present study aims to monitor the surface water quality of different regions in Delhi (India). With many physical and chemical properties, all samples had a high load of pollution in which Najafgarh drain (Nd) exhibited maximum and laboratory tap water (Ltw) minimum contamination. Water samples contained notable amounts of heavy metals including Cr, Cd, As, Cu, Pb and Hg. A total of 88 Hg-resistant bacteria were isolated from all the regions except Ltw. Among all the samples, the density of Hg-resistant bacteria was highest in sample of Nd and their morphotype heterogeneity was highest in sample collected from river Yamuna nearby Kashmiri gate (Kg). Different strains showed different patterns of resistance to different heavy metals and antibiotics. Multiple antibiotic resistance (MAR) indices were high in two samples, the highest reported in a sample taken from river Yamuna nearby Majnu ka tila (Mkt) (0.34). The 12.5% and 24.45% isolates showed β- and α-hemolytic natures, respectively that might be of pathogenic concern. In this account, high concentrations of heavy metals and their resistant bacteria in surface water have severely damaged the quality of water and their resources and produced high risk to the associated life forms.     

Spatial variation in ciliate communities with respect to water quality in the Delhi NCR stretch of River Yamuna,India

The River Yamuna emerges from Saptarishi Kund, Yamunotri and merge with River Ganges at Allahabad, India. Anthropogenic stress has affected the water quality of the river Yamuna drastically in the stretch traversing Delhi and its satellite towns (National Capital Region, NCR). In the present study, effect of water quality on the microbial life in the River Yamuna was analyzed using ciliate communities (Protista, Ciliophora) as bio-indicators. Water samples were collected from six sampling sites chosen according to the levels of pollution along the river and water quality was analysed using standard physicochemical factors. As the river traverses Delhi NCR, water quality deteriorates considerably as indicated by the Water Quality Index at the selected sampling sites. Seventy-four ciliate species representing nine classes were recorded. Based on the Shannon diversity index, maximum species diversity was found at the point where the river enters Delhi. The saprobity index showed the river water was beta-mesosaprobic when the river enters Delhi and alpha-mesosaprobic at downstream sites after the first major drain outfall. Significant relationship between the spatial variation in ciliate communities and abiotic parameters indicate that ciliates can be used as effective bioindicators of pollution in the River Yamuna.     

Fabrication of stainless steel mesh gas diffusion electrode for power generation in microbial fuel cell

This study reports the fabrication of a new membrane electrode assembly by using stainless steel mesh (SSM) as raw material and its effectiveness as gas diffusion electrode (GDE) for electrochemical oxygen reduction in microbial fuel cell (MFC). Based on feeding glucose (0.5 g L(-1)) substrate to a single-chambered MFC, power generation using SSM-based GDE was increased with the decrease of polytetrafluoroethylene (PTFE) content applied during fabrication, reaching the optimum power density of 951.6 mW m(-2) at 20% PTFE. Repeatable cell voltage of 0.51 V (external resistance of 400 Ω) and maximum power density of 951.6 mW m(-2) produced for the MFC with SSM-based GDE are comparable to that of 0.52 V and 972.6 mW m(-2), respectively obtained for the MFC containing typical carbon cloth (CC)-made GDE. Besides, Coulombic efficiency (CE) is found higher for GDE (SSM or CC) with membrane assembly than without, which results preliminarily from the mitigation of Coulombic loss being associated with oxygen diffusion and substrate crossover. This study demonstrates that with its good electrical conductivity and much lower cost, the SSM-made GDE suggests a promising alternative as efficient and more economically viable material to conventional typical carbon for power production from biomass in MFC.     

Increased power production from a sediment microbial fuel cell with a rotating cathode

The application of a rotating cathode in a river sediment microbial fuel cell increased the oxygen availability to the cathode, and therefore improved the cathode reaction rate, resulting in a higher power production (49 mW/m²) compared to a nonrotating cathode system (29 mW/m²). The increased dissolved oxygen in the water of our lab-scale sediment MFC, however, resulted in a less negative anode potential and a higher anodic charge transfer resistance, which constrained the maximum power density. Thus, an optimum balance between the superior cathode reaction rates and the inferior anode reaction rates due to higher dissolved oxygen levels must be ascertained.     

Evaluation of procedures to acclimate a microbial fuel cell for electricity production

A microbial fuel cell (MFC) is a relatively new type of fixed film bioreactor for wastewater treatment, and the most effective methods for inoculation are not well understood. Various techniques to enrich electrochemically active bacteria on an electrode were therefore studied using anaerobic sewage sludge in a two-chambered MFC. With a porous carbon paper anode electrode, 8 mW/m² of power was generated within 50 h with a Coulombic efficiency (CE) of 40%. When an iron oxide-coated electrode was used, the power and the CE reached 30 mW/m² and 80%, respectively. A methanogen inhibitor (2-bromoethanesulfonate) increased the CE to 70%. Bacteria in sludge were enriched by serial transfer using a ferric iron medium, but when this enrichment was used in a MFC the power was lower (2 mW/m²) than that obtained with the original inoculum. By applying biofilm scraped from the anode of a working MFC to a new anode electrode, the maximum power was increased to 40 mW/m². When a second anode was introduced into an operating MFC the acclimation time was not reduced and the total power did not increase. These results suggest that these active inoculating techniques could increase the effectiveness of enrichment, and that start up is most successful when the biofilm is harvested from the anode of an existing MFC and applied to the new anode.     

Electricity generation and microbial community analysis of alcohol powered microbial fuel cells

Two different microbial fuel cell (MFC) configurations were investigated for electricity production from ethanol and methanol: a two-chambered, aqueous-cathode MFC; and a single-chamber direct-air cathode MFC. Electricity was generated in the two-chamber system at a maximum power density typical of this system (40+/-2 mW/m2) and a Coulombic efficiency (CE) ranging from 42% to 61% using ethanol. When bacteria were transferred into a single-chamber MFC known to produce higher power densities with different substrates, the maximum power density increased to 488+/-12 mW/m2 (CE = 10%) with ethanol. The voltage generated exhibited saturation kinetics as a function of ethanol concentration in the two-chambered MFC, with a half-saturation constant (Ks) of 4.86 mM. Methanol was also examined as a possible substrate, but it did not result in appreciable electricity generation. Analysis of the anode biofilm and suspension from a two-chamber MFC with ethanol using 16S rDNA-based techniques indicated that bacteria with sequences similar to Proteobacterium Core-1 (33.3% of clone library sequences), Azoarcus sp. (17.4%), and Desulfuromonas sp. M76 (15.9%) were significant members of the anode chamber community. These results indicate that ethanol can be used for sustained electricity generation at room temperature using bacteria on the anode in a MFC.     

Comparative study of commercial 4-methylumbelliferyl-beta-D-glucuronide preparations with the Standard Methods membrane filtration fecal coliform test for the detection of Escherichia coli in water samples.

The performance capabilities of two commercial 4-methylumbelliferyl-beta-D-glucuronide preparations were evaluated for the detection of Escherichia coli from water samples. Eighty-three water samples were collected from a treated water reservoir, and 32 samples were collected from untreated surface water. There was a statistically significant difference between the two commercial preparations compared with the Standard Methods membrane filtration fecal coliform (MFC) method for the detection of E. coli from treated water samples. However, there was no difference between the two methods and the MFC test for E. coli detection from the untreated surface water samples. The disagreement between the two commercial products and the MFC method was primarily due to the occurrence of false-negative results with the two commercial products. The data indicate that the occurrence of false-negative samples could be attributed to impaired substrate specificity and sensitivity of the two tests for E. coli detection. There was no apparent relationship between the occurrence of false-negative results and heterotrophic plate counts in samples.     

Comparative study of commercial 4-methylumbelliferyl-beta-D-glucuronide preparations with the Standard Methods membrane filtration fecal coliform test for the detection of Escherichia coli in water samples.

The performance capabilities of two commercial 4-methylumbelliferyl-beta-D-glucuronide preparations were evaluated for the detection of Escherichia coli from water samples. Eighty-three water samples were collected from a treated water reservoir, and 32 samples were collected from untreated surface water. There was a statistically significant difference between the two commercial preparations compared with the Standard Methods membrane filtration fecal coliform (MFC) method for the detection of E. coli from treated water samples. However, there was no difference between the two methods and the MFC test for E. coli detection from the untreated surface water samples. The disagreement between the two commercial products and the MFC method was primarily due to the occurrence of false-negative results with the two commercial products. The data indicate that the occurrence of false-negative samples could be attributed to impaired substrate specificity and sensitivity of the two tests for E. coli detection. There was no apparent relationship between the occurrence of false-negative results and heterotrophic plate counts in samples.     

Electricity generation using a baffled microbial fuel cell convenient for stacking

To make sure that microbial fuel cells (MFCs) are more convenient to stack, a baffled single-chambered MFC with two groups of electrodes sharing only one anode chamber was designed and the performance was examined. The experiments showed that the prototype MFC generated electrical power (maximum of 133 mW/m(2)) while removing up to 88% of chemical oxygen demand (COD) in 91 h. Volumetric power increased as electrode area per anode compartment volume increased, indicating that the MFC with two groups of electrodes was better than that with one group. Power density as a function of wastewater concentration was modeled according to saturation kinetics, with a maximum power density of P(max)=164 mW/m(2) (fixed 100 Omega resistor) and half-saturation concentration of K(s)=259 mg/l. The hydraulic retention time (HRT) was examined as a factor influencing the power generation. When it was 15.5h, the voltage and the power density reached the maximum 0.413 V and 108 mW/m(2).     

微生物燃料电池中脱色希瓦氏菌S12的产电特性研究

为了确定脱色希瓦氏菌S12的电化学活性,采用循环伏安法(cyclic voltammograms, CV)对厌氧培养的菌株S12进行曲线扫描,所得曲线表明S12具有一定的电化学活性,可以用来进行产电实验.研究了不同电子供体和供体浓度对菌株S12产电的影响,结果表明,以浓度为10mmol/L的不同有机酸(甲酸钠、乳酸钠和丙酮酸钠)分别作为电子供体时,乳酸钠产电量最大,其最大功率密度Pmax为21.93mW/m2增加乳酸钠的浓度,菌株S12的产电量也相应增加,当乳酸钠的浓度为20mmol/L时,所产生的最大功率密度达55.72 mW/m2.     

Effects of the Pt loading side and cathode-biofilm on the performance of a membrane-less and single-chamber microbial fuel cell

In order to analyze the effect of cathode's Pt loading side on the performance of single-chamber microbial fuel cells (MFCs), power generation of a bamboo charcoal membrane-less air-cathode MFC was examined. The maximum power outputs obtained were 0.144 and 1.16 mW, while the maximum voltage outputs were 0.400 and 0.500 V (external resistance was 500 Omega), respectively, when the Pt loading side facing to the air and to the anode chamber solution; after a long time of operation with the side of cathode loaded Pt facing to anode chamber solution, a biofilm was developed on the inner side of cathode. With the formation of this biofilm, the power outputs of MFC increased first, and then decreased to 0.8 mW; oxidation-reduction potentials (ORP) dropped first, and then achieved the level of stability. Coulombic efficiency (CE) increased at a certain extent. In addition, the impact of cathode-biofilm on the loss of water in anode chamber solution was determined.     

Viability of Escherichia coli O157:H7 in natural river water determined by the use of flow cytometry

The enzymatic activity and viability of Escherichia coli O157:H7 in natural river water was determined by flow cytometry. River water was collected at two sites (an agricultural area and an industrial area) on the Aigawa River (Osaka, Japan). To facilitate estimation of the physiology of E. coli O157 in natural river water, bacterial cells in the water were stained with 6-carboxyfluorescein diacetate (6CFDA) and propidium iodide (PI). The cells were sorted into two populations, using a flow cytometer, based on their esterase activity. Each population was stained with E. coli O157:H7 fluorescent antibody (FA), and E. coli O157:H7 cells were observed in the esterase-active population. River water samples collected at the same points were incubated with yeast extract containing antibiotics to prevent cell division, and bacterial cells in the incubated samples were stained with PI and FA. Escherichia coli O157:H7 existed in both the viable (elongated and/or fattened) and inactive bacterial population determined by flow cytometry. These results indicate that E. coli O157:H7 may retain metabolic activity and growth potential in the natural aquatic environment.     

微生物燃料电池中脱色希瓦氏菌S12的产电特性研究

为了确定脱色希瓦氏菌S12的电化学活性, 采用循环伏安法(cyclic voltammograms, CV)对厌氧培养的菌株S12进行曲线扫描, 所得曲线表明S12具有一定的电化学活性, 可以用来进行产电实验。研究了不同电子供体和供体浓度对菌株S12产电的影响, 结果表明, 以浓度为10 mmol/L 的不同有机酸(甲酸钠、乳酸钠和丙酮酸钠)分别作为电子供体时, 乳酸钠产电量最大, 其最大功率密度Pmax为21.93 mW/m2, 增加乳酸钠的浓度, 菌株S12的产电量也相应增加, 当乳酸钠的浓度为20 mmol/L时, 所产生的最大功率密度达55.72 mW/m2。     

A comparison of air and hydrogen peroxide oxygenated microbial fuel cell reactors

In this study, a two-compartment continuous flow microbial fuel cell (MFC) reactor was used to compare the efficiencies of cathode oxygenation by air and by hydrogen peroxide. The MFC reactor had neither a proton-selective membrane nor an electron transfer mediator. At startup, the cathodic compartment was continuously aerated and the anodic compartment was fed with a glucose solution. An increase of electrical power generation from 0.008 to 7.2 mW m(-2) of anode surface with a steady-state potential of 215-225 mV was observed within a period of 12 days. The performance of the air-oxygenated MFC reactor progressively declined over time because of biofilm proliferation in the cathodic compartment. Oxygenation of the cathodic compartment using 300 mL d(-1) of 0.3% hydrogen peroxide solution resulted in a power density of up to 22 mW m(-2) (68.2 mA m(-2)) of anode surface at a potential of 340-350 mV. The use of H2O2 for oxygenation was found to improve the long-term stability of the MFC reactor.     

Improved performance of membrane free single-chamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes

Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened by 45% and 51%, respectively as compared to that for MFC-AT equipped with an unmodified anode. Moreover, the power output of MFCs with modified anodes was significantly improved. In comparison with MFC-AT which had a maximum power density of 1304 mW/m², the MFC-N achieved a maximum power density of 1641 mW/m². The nitric acid-treated anode in MFC-A increased the power density by 58% reaching 2066 mW/m². XPS analysis of the treated and untreated anode materials indicated that the power enhancement was attributable to the changes of surface functional groups.     

Air-cathode structure optimization in separator-coupled microbial fuel cells

Microbial fuel cells (MFC) with 30% wet-proofed air cathodes have previously been optimized to have 4 diffusion layers (DLs) in order to limit oxygen transfer into the anode chamber and optimize performance. Newer MFC designs that allow close electrode spacing have a separator that can also reduce oxygen transfer into the anode chamber, and there are many types of carbon wet-proofed materials available. Additional analysis of conditions that optimize performance is therefore needed for separator-coupled MFCs in terms of the number of DLs and the percent of wet proofing used for the cathode. The number of DLs on a 50% wet-proofed carbon cloth cathode significantly affected MFC performance, with the maximum power density decreasing from 1427 to 855 mW/m² for 1–4 DLs. A commonly used cathode (30% wet-proofed, 4 DLs) produced a maximum power density (988 mW/m²) that was 31% less than that produced by the 50% wet-proofed cathode (1 DL). It was shown that the cathode performance with different materials and numbers of DLs was directly related to conditions that increased oxygen transfer. The coulombic efficiency (CE) was more affected by the current density than the oxygen transfer coefficient for the cathode. MFCs with the 50% wet-proofed cathode (2 DLs) had a CE of >84% (6.8 A/m²), which was substantially larger than that previously obtained using carbon cloth air-cathodes lacking separators. These results demonstrate that MFCs constructed with separators should have the minimum number of DLs that prevent water leakage and maximize oxygen transfer to the cathode.     

Electricity generation in a membrane-less microbial fuel cell with down-flow feeding onto the cathode

A novel membrane-less microbial fuel cell (MFC) with down-flow feeding was constructed to generate electricity. Wastewater was fed directly onto the cathode which was horizontally installed in the upper part of the MFC. Oxygen could be utilized readily from the air. The concentration of dissolved oxygen in the influent wastewater had little effect on the power generation. A saturation-type relationship was observed between the initial COD and the power generation. The influent flow rate could affect greatly the power density. Fed by the synthetic glucose wastewater with a COD value of 3500 mg/L at a flow rate of 4.0 mL/min, the developed MFC could produce a maximum power density of 37.4 mW/m². Its applicability was further evaluated by the treatment of brewery wastewater. The system could be scaled up readily due to its simple configuration, easy operation and relatively high power density.     

Power production in MFCs inoculated with Shewanella oneidensis MR‐1 or mixed cultures

Power densities and oxidation–reduction potentials (ORPs) of MFCs containing a pure culture of Shewanella oneidensis MR‐1 were compared to mixed cultures (wastewater inoculum) in cube shaped, 1‐, 2‐, and 3‐bottle batch‐fed MFC reactor configurations. The reactor architecture influenced the relative power produced by the different inocula, with the mixed culture generating 68–480% more power than MR‐1 in each MFC configuration. The mixed culture produced the maximum power density of 858 ± 9 mW m^?2 in the cubic MFC, while MR‐1 produced 148 ± 20 mW m^?2. The higher power by the mixed culture was primarily a result of lower internal resistances than those produced by the pure culture. Power was a direct function of ohmic resistance for the mixed culture, but not for strain MR‐1. ORP of the anode compartment varied with reactor configuration and inoculum, and it was always negative during maximum power production but it did not vary in proportion to power output. The ORP varied primarily at the end of the cycle when substrate was depleted, with a change from a reductive environment during maximum power production (approximately ?175 mV for mixed and approximately ?210 mV for MR‐1 in cubic MFCs), to an oxidative environment at the end of the batch cycle (～250 mV for mixed and ～300 mV for MR‐1). Mixed cultures produced more power than MR‐1 MFCs even though their redox potential was less negative. These results demonstrate that differences between power densities produced by pure and mixed cultures depend on the MFC architecture. Biotechnol. Bioeng. 2010; 105: 489–498. © 2009 Wiley Periodicals, Inc.     

Performance and microbial diversity of palm oil mill effluent microbial fuel cell

Aim: To evaluate the bioenergy generation and the microbial community structure from palm oil mill effluent using microbial fuel cell. Methods and Results: Microbial fuel cells enriched with palm oil mill effluent (POME) were employed to harvest bioenergy from both artificial wastewater containing acetate and complex POME. The microbial fuel cell (MFC) showed maximum power density of 3004 mW m^?2 after continuous feeding with artificial wastewater containing acetate substrate. Subsequent replacement of the acetate substrate with complex substrate of POME recorded maximum power density of 622 mW m^?2. Based on 16S rDNA analyses, relatively higher abundance of Deltaproteobacteria (88·5%) was detected in the MFCs fed with acetate artificial wastewater as compared to POME. Meanwhile, members of Gammaproteobacteria, Epsilonproteobacteria and Betaproteobacteria codominated the microbial consortium of the MFC fed with POME with 21, 20 and 18·5% abundances, respectively. Conclusions: Enriched electrochemically active bacteria originated from POME demonstrated potential to generate bioenergy from both acetate and complex POME substrates. Further improvements including the development of MFC systems that are able to utilize both fermentative and nonfermentative substrates in POME are needed to maximize the bioenergy generation. Significance and Impact of the Study: A better understanding of microbial structure is critical for bioenergy generation from POME using MFC. Data obtained in this study improve our understanding of microbial community structure in conversion of POME to electricity.     

On the dynamic response of the anode in microbial fuel cells

A study of the dynamic response of a microbial fuel cell (MFC) using membrane electrode assemblies (MEAs) designed for air breathing cathode operation is reported. The MFC used four MEAs simultaneously and has a low internal resistance. An increased concentration of glucose produced a non-linear increase in the maximum current reached. The time to reach the maximum current increased with increasing glucose concentrations of 1-7 mM; varying from approximately 2.4 to 4.2h. The rate at which the current density increased with time was the same for all glucose concentrations up to current densities close to the maximum values. The peak power density varied approximately linearly with glucose concentrations from 2 to 77 mW/m(2) (1-7 mM) with a 1 kΩ resistance. The cell response appeared to be linked to a slow process of fuel transport to the bacteria and their metabolic processes. The dynamic response of the anode was analysed in terms of a substrate mass transport model. The application of different current ranges did not significantly change the dynamic response of either the anode community or the MFC polarization characteristics. Thus, it is likely that the bacterial communities that form under MFC operation contain sufficiently "dominant" electro-active species that are capable of producing high power for MFCs.