Effect of sulfide to nitrate ratios on the simultaneous anaerobic sulfide and nitrate removal

Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg (m³ d)⁻¹ and 0.99 kg (m³ d)⁻¹, respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.     

Simultaneous sulfide and nitrate removal in anaerobic reactor under shock loading

The performance of anaerobic reactor for simultaneous sulfide and nitrate removal under substrate shock loading was studied. The response to the shock loading could be divided into three stages i.e. disturbance, inertial and recovery periods. The effect of the shock loading was directly proportional to the intensity of the shock loads. The reactor performance was stable at a relatively lower intensity (1.5 times shock load), while it was considerably affected by higher intensity (higher than 2.0 times shock load). Nevertheless, the reactor performance recovered from disturbances at all the tested shock loads. The effluent sulfide-sulfur concentration was found as sensitive parameter, which increased up to 18 times of that at steady state; it could be used as an indicator of the reactor’s performance.     

Control of malodorous hydrogen sulfide compounds using microbial fuel cell

In this study, a microbial fuel cell (MFC) was used to control malodorous hydrogen sulfide compounds generated from domestic wastewaters. The electricity production demonstrated a distinct pattern of a two-step increase during 170 h of system run: the first maximum current density was 118.6 ± 7.2 mA m^?2 followed by a rebound of current density increase, reaching the second maximum of 176.8 ± 9.4 mA m^?2. The behaviors of the redox potential and the sulfate level in the anode compartment indicated that the microbial production of hydrogen sulfide compounds was suppressed in the first stage, and the hydrogen sulfide compounds generated from the system were removed effectively as a result of their electrochemical oxidation, which contributed to the additional electricity production in the second stage. This was also directly supported by sulfur deposits formed on the anode surface, which was confirmed by analyses on those solids using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy as well as an elemental analyzer. To this end, the overall reduction efficiencies for HS^? and H₂S_(g) were as high as 67.5 and 96.4 %, respectively. The correlations among current density, redox potential, and sulfate level supported the idea that the electricity signal generated in the MFC can be utilized as a potential indicator of malodor control for the domestic wastewater system.     

Influence of diligent disintegration on anaerobic biomass and performance of microbial fuel cell

Objectives

To enhance the performance of microbial fuel cells (MFC) by increasing the surface area of cathode and diligent mechanical disintegration of anaerobic biomass.

Results

Tannery effluent and anaerobic biomass were used. The increase in surface area of the cathode resulted in 78% COD removal, with the potential, current density, power density and coulombic efficiency of 675 mV, 147 mA m^?2, 33 mW m^?2 and 3.5%, respectively. The work coupled with increased surface area of the cathode with diligent mechanical disintegration of the biomass, led to a further increase in COD removal of 82% with the potential, current density, power density and coulombic efficiency of 748 mV, 229 mA m^?2, 78 mW m^?2 and 6% respectively.

Conclusions

Mechanical disintegration of the biomass along with increased surface area of cathode enhances power generation in vertical MFC reactors using tannery effluent as fuel.

     

Archaea-based microbial fuel cell operating at high ionic strength conditions

In this work, two archaea microorganisms (Haloferax volcanii and Natrialba magadii) used as biocatalyst at a microbial fuel cell (MFC) anode were evaluated. Both archaea are able to grow at high salt concentrations. By increasing the media conductivity, the internal resistance was diminished, improving the MFC’s performance. Without any added redox mediator, maximum power (P _max) and current at P _max were 11.87/4.57/0.12 μW cm⁻² and 49.67/22.03/0.59 μA cm⁻² for H. volcanii, N. magadii and E. coli, respectively. When neutral red was used as the redox mediator, P _max was 50.98 and 5.39 μW cm⁻² for H. volcanii and N. magadii, respectively. In this paper, an archaea MFC is described and compared with other MFC systems; the high salt concentration assayed here, comparable with that used in Pt-catalyzed alkaline hydrogen fuel cells, will open new options when MFC scaling up is the objective necessary for practical applications.     

Effect of ammonium and nitrate on current generation using dual-cathode microbial fuel cells

These studies were conducted to determine the effects of various concentrations of ammonium and nitrate on current generation using dual-cathode microbial fuel cells (MFCs). Current generation was not affected by ammonium up to 51.8+/-0.0 mg/l, whereas 103.5+/-0.0 mg/l ammonium chloride reduced the current slightly. On the other hand, when 60.0+/-0.0 and 123.3+/-0.1 mg/l nitrate were supplied, the current was decreased from 10.23+/-0.07 mA to 3.20+/-0.24 and 0.20+/-0.01 mA, respectively. Nitrate did not seem to serve as a fuel for current generation in these studies. At this time, COD and nitrate removal were increased except at 123+/-0.1 mg NO(3)(-)/l. These results show that proper management of ammonium and nitrate is very important for increasing the current in a microbial fuel cell.     

Assessment of organic removal in series- and parallel-connected microbial fuel cell stacks

Microbial fuel cells (MFCs) degrade organic contaminants in wastewater while simultaneously producing electricity, but must be stacked to yield adequate voltage and current. This study examined the evolution of the chemical oxygen demand (COD) removal rate and efficiency in two identical individual MFCs (i-MFCs) in series- and parallel-connected stacks (sc- and pc-MFCs, respectively) under batch and continuous operation. The stack voltage and current increased in the respective series and parallel connections of the two i-MFCs (MFC unit 1 and MFC unit 2). Voltage reversal was observed in the sc- MFC below an external load of 100 Ω. Regardless of occurrence of the voltage reversal, organic reduction between i-MFCs and sc-MFCs showed no significant difference (gap of < 9% and < 6% in COD removal rate and efficiency, respectively); additionally, organic removals between the two individual MFCs in series indicated differences less than 9% of COD removal rate and 5% of COD removal efficiency in batch mode. Continuous operation also yielded similar organic removals as the MFCs in individual and series connection (voltage reversal occurred) mode, even over 8 days operation. Parallel connection yielded identical organic removals and currents in the two individual MFCs of the pc-MFC, even though the two separate i-MFCs showed different organic removal rates and current productions. This study provides the guide for the application of stacked MFCs for power source and efficient organic pollutant removal in wastewater treatment process.     

亚硝酸盐型同步厌氧生物脱氮除硫工艺的运行性能

采用上流式厌氧污泥床(UASB)反应器研究了亚硝酸盐型同步厌氧生物脱氮除硫工艺的性能。该工艺具有很高的硫化物和亚硝酸盐转化潜能,最大容积硫化物去除率和容积硝酸盐去除率分别为13.4kg/(m3·d)和2.3kg/(m3·d);所能耐受的最大进水硫化物和亚硝酸盐浓度分别为880mg/L和252.7mg/L;最适进水硫化物和亚硝酸盐浓度分别为460mg/L和132.3mg/L,最适水力停留时间为4h。硫化物和亚硝酸盐的表观半抑制浓度分别为403.9mg/L和120.8mg/L,两者之间的联合毒性为拮抗作用。     

Effect of vitamins and cell constructions on the activity of microbial fuel cell battery

Construction of efficient performance of microbial fuel cells (MFCs) requires certain practical considerations. In the single chamber microbial fuel cell, there is no border between the anode and the cathode, thus the diffusion of the dissolved oxygen has a contrary effect on the anodic respiration and this leads to the inhibition of the direct electron transfer from the biofilm to the anodic surface. Here, a fed-batch single chambered microbial fuel cells are constructed with different distances 3 and 6?cm (anode- cathode spacing), while keeping the working volume is constant. The performance of each MFC is individually evaluated under the effects of vitamins & minerals with acetate as a fed load. The maximum open circuit potential during testing the 3 and 6?cm microbial fuel cells is about 946 and 791?mV respectively. By decreasing the distance between the anode and the cathode from 6 to 3?cm, the power density is decreased from 108.3?mW?m^?2 to 24.5?mW?m^?2. Thus, the short distance in membrane-less MFC weakened the cathode and inhibited the anodic respiration which affects the overall performance of the MFC efficiency. The system is displayed a maximum potential of 564 and 791?mV in absence & presence of vitamins respectively. Eventually, the overall functions of the acetate single chamber microbial fuel cell can be improved by the addition of vitamins & minerals and increasing the distance between the cathode and the anode.     

A microbial fuel cell operating at low pH using the acidophile Acidiphilium cryptum

For the first time, a microbial fuel cell has been developed using an acidophile, Acidiphilium cryptum, as the anode biocatalyst. Electricity production using its natural electron acceptor, iron, as the electron mediating agent at pH values < or =4.0 was demonstrated. Accumulation of Fe(III) at the electrode, however, restricted current output. The combination of nitrilotriacetic acid and Phenosafranin as electron mediators increased the power output to 12.7 mW/m(2) in a two-chamber air-sparged fuel cell. Direct electron transfer from the microorganisms to the anode was also investigated but was not detected under the conditions studied.     

Effect of bacterial cell size on electricity generation in a single-compartmented microbial fuel cell

A single-compartmented microbial fuel cell composed of a graphite felt anode modified with Neutral Red (NR-anode) and a porous Fe(II)-carbon cathode (FeC-cathode) were compared for electricity generation from Microbacterium sp. and Pseudomonas sp. under identical conditions. Pseudomonas sp. was more than four times the size of Microbacterium sp. based on SEM images. In cyclic voltammetry, the redox reaction between Microbacterium sp and electrode was three times the rate observed between Pseudomonas sp. and the electrode based on the Y-axis (current) variation of cyclic voltammogram. The electric power generated by Microbacterium sp. was approx 3–4 times higher than that with Pseudomonas sp. during incubation for more than 150 days in the fuel cell.     

An evaluation of aerobic and anaerobic sludges as start-up material for microbial fuel cell systems

The operation of microbial fuel cells (MFCs) seeded with the same quantities of aerobic or anaerobic sludge has been compared. The two sludges consisted of mixed cultures obtained from the aerobic reactor and anaerobic digester, respectively, of a municipal Wastewater Treatment Plant (WWTP). Both the sludges were diluted with their sedimentation supernatant to avoid modifying their metabolism. The results show that the type of sludge has a major impact on the performance of the system. Seeding an MFC with anaerobic acclimated sludge leads to a more rapid start-up of electricity production and the absence of a lag period. In the MFC seeded with anaerobic sludge, the steady-state operation conditions were achieved in less than 10 days, while in the aerobic sludge-seeded MFC more than 20 days were necessary to achieve this regime. The anaerobic sludge also led to better performance of the MFC. Thus, maximum power densities above 300mWm(-2) were obtained for such systems (i.e. two times higher than that achieved with the aerobic sludge-seeded MFC in the same setup). This better performance is a direct consequence of the greater availability of Chemical Oxygen Demand (COD) in anaerobic sludge. However, the performance is not a consequence of the coulombic efficiency in the use of the COD to produce electricity because the aerobic sludge-seeded MFC doubles this figure with respect to the anaerobic sludge-seeded system.     

Process of simultaneous hydrogen sulfide removal from biogas and nitrogen removal from swine wastewater

The feasibility of a new flowchart describing simultaneous hydrogen sulfide removal from biogas and nitrogen removal from wastewater was investigated. It took 30 days for the reactor inoculated with aerobic sludge to attain a removal rate of 60% for H₂S and NO_x–N simultaneously. It took 34 and 48 days to attain the same removal rate for the reactor without inoculated sludge and the reactor inoculated with anaerobic sludge respectively. The reactor without inoculated sludge still operated successfully, despite requiring a slightly longer startup time. The packing material was capable of enhancing the removal efficiency of reactors. Based on the concentration of NO_x–N and H₂S in the effluent, the loading rate and the ability of the system to resist shock loading, the performance of the reactor filled with hollow plastic balls was greater than that of the reactor filled with elastic packing and the reactor filled with Pall rings.     

Effect of nitrate on anaerobic azo dye reduction

The aim of the study was to investigate the effect of nitrate on anaerobic color removal efficiencies. For this aim, anaerobic–aerobic sequencing batch reactor (SBR) fed with a simulated textile effluent including Remazol Brilliant Violet 5R azo dye was operated with a total cycle time of 12 h, including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (nitrate) and performance of the system was determined by monitoring color removal efficiency, nitrate removal, nitrite formation and removal, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2 dioxygenase), and formation and removal of aromatic amines. Variations of population dynamics of microorganisms exposed to various amount of nitrate were identified by denaturing gradient gel electrophoresis (DGGE). It was found that nitrate has adverse effect on anaerobic color removal efficiency and color removal was achieved after denitrification process was completed. It was found that nitrate stimulates the COD removal efficiency and accelerates the COD removal in the first hour of anaerobic phase. About 90 % total COD removal efficiencies were achieved in which microorganism exposed to increasing amount of nitrate. Population dynamics of microorganisms exposed to various amount of nitrate were changed and diversity was increased.     

Integrated organic and nitrogen removal with electricity generation in a tubular dual-cathode microbial fuel cell

This study presented a dual-cathode microbial fuel cell (MFC) that was designed to accomplish nitrification in its outer cathode and denitrification in the inner cathode. The MFC was continuously operated for more than 150 days and achieved organic removal of 85–99% in the anode, depending on the initial organic loading rates. More than 96% of the ammonium was removed, while the total nitrogen removal was between 66.7 and 89.6%, largely affected by the remaining nitrate in the effluent of the inner cathode. The coulombic efficiency suggested that the nitrate was primarily removed by bioelectrochemcial denitrification in the inner cathode, especially at the low nitrogen loading rates. However, a higher nitrogen loading rate encouraged nitrate migration through the anion exchange membrane, thereby being removed by conventional denitrification. The preliminary energy analysis suggested that the energy production in the dual-cathode MFC could potentially support its pumping system. To achieve an energy-neutral system, aeration must be omitted in the future design and passive oxygen supply should be considered with a proper design of the outer cathode. Those results demonstrated the feasibility of using a tubular dual-cathode MFC to remove both organics and nitrogen while producing electricity.     

Effect of electron mediators on current generation and fermentation in a microbial fuel cell

Effects of select electron mediators [9,10-anthraquinone-2,6-disulfonic acid disodium salt (AQDS), safranine O, resazurin, methylene blue, and humic acids] on metabolic end-products and current production from cellulose digestion by Clostridium cellulolyticum in microbial fuel cells (MFCs) were studied using capillary electrophoresis and traditional electrochemical techniques. Addition of the mediator resazurin greatly enhanced current production but did not appear to alter the examined fermentation end-products compared to MFCs with no mediator. Assays for lactate, acetate, and ethanol indicate that the presence of safranine O, methylene blue, and humic acids alters metabolite production in the MFC: safranine O decreased the examined metabolites, methylene blue increased lactate formation, and humic acids increased the examined metabolites. Mediator standard redox potentials (E ₀) reported in the literature do not coincide with redox potentials in MFCs due presumably to the electrolytic complexity of media that supports bacterial survival and growth. Current production in MFCs: (1) can be effected by the mediator redox potential while in the media, which may be significantly shifted from E ₀, and (2) depended on the ability of the mediator to access the bacterial electron source, which may be cytoplasmic. In addition, some electron mediators had significant effects on metabolic end-products and therefore the metabolism of the organism itself. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Simultaneous analysis of physiological and electrical output changes in an operating microbial fuel cell with Shewanella oneidensis

Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high‐throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR‐1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR‐1, with both air‐exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR‐1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR‐1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points. Biotechnol. Bioeng. 2009;103: 524–531. Published 2009 Wiley Periodicals, Inc.