Search

Pretreatment of municipal sludge has the potential to improve anaerobic digestion by increasing the ultimate biodegradability of particulate chemical oxygen demand (PCOD) to methane (CH4) gas. However, the effect of pretreatment, that is, increased soluble COD from solubilization of PCOD, makes it difficult to correctly estimate hydrolysis kinetics in biochemical methane potential tests. In this study, batch digestion tests were used to evaluate the general impact of alkaline and thermal pretreatment of waste activated sludge (WAS) and to determine a different method to estimate hydrolysis rates from pretreated streams. Throughout the 60-day batch experiments, liquid and gas samples were collected and analyzed for total (TCOD) and semi-soluble (SSCOD) COD, total (TSS) and volatile (VSS) suspended solids, pH, volatile fatty acids (VFAs), and ammonium concentration. Pretreatments significantly decreased VSS concentrations at the start of digestion, but all samples showed similar VSS destruction to the control at the end of the experiments. Ultimate CH4 production was significantly increased by alkaline and thermal pretreatments, which produced 203 and 219 mL CH4 gVSS−1, respectively, versus 175 mL CH4 gVSS−1 in the control. Although CH4 generation was a good proxy for solids hydrolysis of untreated WAS, CH4 generation significantly overestimated the rate of hydrolysis of pretreated solids. The overestimation was due to the abundance of SSCOD available at the start of the experiment being converting to CH4. Incorporating SSCOD or VFAs into the hydrolysis kinetics resulted in much slower hydrolysis rates that were similar to those measured by VSS destruction directly (e.g., 0.08 d−1 with SSCOD + CH4 vs. 0.19 d−1 from CH4 alone for thermal pretreatment vs. 0.05 d−1 with VSS alone). The slower kinetics indicate that the necessity to understand the trade-offs between the performance advantages of pretreatment (i.e., solids destruction and energy conversion) versus the operational and financial impacts on large-scale digestion. [ABSTRACT FROM AUTHOR]

Abstract Background Buffering to achieve pH control is crucial for successful trichloroethene (TCE) anaerobic bioremediation. Bicarbonate (HCO3−) is the natural buffer in groundwater and the buffer of choice in the laboratory and at contaminated sites undergoing biological treatment with organohalide respiring microorganisms. However, HCO3− also serves as the electron acceptor for hydrogenotrophic methanogens and hydrogenotrophic homoacetogens, two microbial groups competing with organohalide respirers for hydrogen (H2). We studied the effect of HCO3− as a buffering agent and the effect of HCO3−-consuming reactions in a range of concentrations (2.5-30 mM) with an initial pH of 7.5 in H2-fed TCE reductively dechlorinating communities containing Dehalococcoides, hydrogenotrophic methanogens, and hydrogenotrophic homoacetogens. Results Rate differences in TCE dechlorination were observed as a result of added varying HCO3− concentrations due to H2-fed electrons channeled towards methanogenesis and homoacetogenesis and pH increases (up to 8.7) from biological HCO3− consumption. Significantly faster dechlorination rates were noted at all HCO3− concentrations tested when the pH buffering was improved by providing 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as an additional buffer. Electron balances and quantitative PCR revealed that methanogenesis was the main electron sink when the initial HCO3− concentrations were 2.5 and 5 mM, while homoacetogenesis was the dominant process and sink when 10 and 30 mM HCO3− were provided initially. Conclusions Our study reveals that HCO3− is an important variable for bioremediation of chloroethenes as it has a prominent role as an electron acceptor for methanogenesis and homoacetogenesis. It also illustrates the changes in rates and extent of reductive dechlorination resulting from the combined effect of electron donor competition stimulated by HCO3− and the changes in pH exerted by methanogens and homoacetogens.

Food waste and biopolymers, plastics derived from plants, are unexploited sources of energy when discarded in landfills without energy recovery. In addition, polylactic acid (PLA) and food waste have complimentary characteristics for anaerobic digestion; both are organic and degrade under anaerobic conditions. Lab-scale reactors were set up to quantify the solubilization of pretreated amorphous and crystalline PLA. Biochemical methane potential (BMP) assays were performed to quantify CH4 production from both treated and untreated PLA in the presence of food waste and anaerobic digested sludge. Amorphous and crystalline PLA reached near-complete solubilization at 97% and 99%, respectively, when alkaline pretreatment was applied. The PLA that received alkaline treatment produced the most of CH4 throughout the run time of 70 days. The PLA without treatment resulted in 54% weight reduction after anaerobic digestion. Results from this study show that alkaline pretreatment has the greatest solid reduction of PLA and maximum production of CH4 when combined with food waste and anaerobic digested sludge. [ABSTRACT FROM AUTHOR]

ABSTRACT When anode-respiring bacteria (ARB) respire electrons to an anode in microbial electrochemical cells (MXCs), they harvest only a small amount of free energy. This means that ARB must have a high substrate-oxidation rate coupled with a high ratio of electrons used for respiration compared to total electrons removed by substrate utilization. It also means that they are especially susceptible to inhibition that slows anode respiration or lowers their biomass yield. Using several electrochemical techniques, we show that a relatively high total ammonium-nitrogen (TAN) concentration (2.2 g TAN/L) induced significant stress on the ARB biofilms, lowering their true yield and forcing the ARB to boost the ratio of electrons respired per electrons consumed from the substrate. In particular, a higher respiration rate, measured as current density ( j), was associated with slower growth and a lower net yield, compared to an ARB biofilm grown with a lower ammonium concentration (0.2 g TAN/L). Further increases in influent TAN (to 3 and then to 4.4 g TAN/L) caused nearly complete inhibition of anode respiration. However, the ARB could recover from high-TAN inhibition after a shift of the MXC's feed to 0.2 g TAN/L. In summary, ARB biofilms were inhibited by a high TAN concentration, but could divert more electron flow toward anode respiration with modest inhibition and recover when severe inhibition was relieved. Biotechnol. Bioeng. 2017;114: 1151-1159. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Selective fermentation (SF), a novel alternative for microalgae-derived biofuel, ferments carbohydrates and proteins in microalgae biomass to volatile fatty acids (VFAs), which makes it easy to extract the lipid with low-toxicity solvents. A further advantage of SF is that the lipids are biohydrogenated to more valuable fuel precursors. This work evaluated SF using semi-continuous studies at pH values of 5 and 7 and with solids retention times (SRTs) of 2 to 15 days. SRT > 2 day enhanced VFA recovery from the non-lipid fractions by 4-fold (vs feed biomass), conserved the lipids, increased lipid wet-extraction (lipids assayed as fatty acid methyl esters, FAME) by at least 6900-fold (vs feed biomass), and shifted the FAME profile toward more saturated fatty acids through biohydrogenation. The performance benefits were accompanied by selective enrichment of biohydrogenating strains, e.g., Prevotella and Porphyromonodaceae , along with other fermenting bacteria that generate VFAs and H 2 , e.g., Veillonellaceae . SF with a 5-day SRT had greater lipid wet extraction, compared to 2-day SRT, due to increased cell disruption and solvent permeability. By integrating multiple downstream processes into one step, SF offers important advantages for sustainable biofuel production from microalgae. [ABSTRACT FROM AUTHOR]

Microalgae-derived lipids are good sources of biofuel, but extracting them involves high cost, energy expenditure, and environmental risk. Surfactant treatment to disrupt Scenedesmus biomass was evaluated as a means to make solvent extraction more efficient. Surfactant treatment increased the recovery of fatty acid methyl ester (FAME) by as much as 16-fold vs. untreated biomass using isopropanol extraction, and nearly 100% FAME recovery was possible without any Folch solvent, which is toxic and expensive. Surfactant treatment caused cell disruption and morphological changes to the cell membrane, as documented by transmission electron microscopy and flow cytometry. Surfactant treatment made it possible to extract wet biomass at room temperature, which avoids the expense and energy cost associated with heating and drying of biomass during the extraction process. The best FAME recovery was obtained from high-lipid biomass treated with Myristyltrimethylammonium bromide (MTAB)- and 3-(decyldimethylammonio)-propanesulfonate inner salt (3_DAPS)-surfactants using a mixed solvent (hexane : isopropanol = 1 : 1, v/v) vortexed for just 1 min; this was as much as 160-fold higher than untreated biomass. The critical micelle concentration of the surfactants played a major role in dictating extraction performance, but the growth stage of the biomass had an even larger impact on how well the surfactants disrupted the cells and improved lipid extraction. Surfactant treatment had minimal impact on extracted-FAME profiles and, consequently, fuel-feedstock quality. This work shows that surfactant treatment is a promising strategy for more efficient, sustainable, and economical extraction of fuel feedstock from microalgae. [ABSTRACT FROM AUTHOR]

Biofuels derived from microalgae have promise as carbon-neutral replacements for petroleum. However, difficulty extracting microalgae-derived lipids and the co-extraction of non-lipid components add major costs that detract from the benefits of microalgae-based biofuel. Selective fermentation could alleviate these problems by managing microbial degradation so that carbohydrates and proteins are hydrolyzed and fermented, but lipids remain intact. We evaluated selective fermentation of Scenedesmus biomass in batch experiments buffered at pH 5.5, 7, or 9. Carbohydrateswere fermented up to 45%within the first 6 days, protein fermentation followed after about 20 days, and lipids (measured as fatty acid methyl esters, FAME) were conserved. Fermentation of the non-lipid components generated volatile fatty acids, with acetate, butyrate, and propionate being the dominant products. Selective fermentation of Scenedesmus biomass increased the amount of extractable FAME and the ratio of FAME to crude lipids. It also led to biohydrogenation of unsaturated FAME to more desirable saturated FAME (especially to C16:0 and C18:0), and the degree of saturation was inversely related to the accumulation of hydrogen gas after fermentation. Moreover, the microbial communities after selective fermentation were enriched in bacteria from families known to perform biohydrogenation, i.e., Porphyromonadaceae and Ruminococcaceae. Thus, this study provides proof-of-concept that selective fermentation can improve the quantity and quality of lipids that can be extracted from Scenedesmus. [ABSTRACT FROM AUTHOR]

Primary sludge (PS) is a renewable and sustainable energy source, but pretreatment often is required to accelerate hydrolysis of organic solids. Pulsed electric field (PEF) treatment has been proven effective for waste activated sludge (WAS), but its impact on PS is not known. We evaluated the impacts of PEF pretreatment of PS on energy recovery by methanogenesis and fermentation to volatile fatty acids (VFAs). PEF treatment achieved successful microbial inactivation of PS and it modestly enhanced conversion of PS chemical oxygen demand to methane (by ∼8%) and to VFAs by fermentation (by ∼7%) by increasing hydrolysis rates. Thus, the impact of PEF treatment was small for PS alone, compared to the much more significant increases in methane conversion from WAS or WAS+PS. This difference points to the value of optimizing ratios of PS:WAS for PEF treatment, whether the goal is methanogenesis or fermentation to VFAs. [ABSTRACT FROM AUTHOR]

Chloroform and methanol are superior solvents for lipid extraction from photosynthetic microorganisms, because they can overcome the resistance offered by the cell walls and membranes, but they are too toxic and expensive to use for large-scale fuel production. Biomass from the photosynthetic microalga Scenedesmus , subjected to a commercially available pre-treatment technology called Focused-Pulsed® (FP), yielded 3.1-fold more crude lipid and fatty acid methyl ester (FAME) after extraction with a range of solvents. FP treatment increased the FAME-to-crude-lipid ratio for all solvents, which means that the extraction of non-lipid materials was minimized, while the FAME profile itself was unchanged compared to the control. FP treatment also made it possible to use only a small proportion of chloroform and methanol, along with isopropanol, to obtain equivalent yields of lipid and FAME as with 100% chloroform plus methanol. [ABSTRACT FROM AUTHOR]

Cyanobacteria are considered good models for biohydrogen production because they are relatively simple organisms with a demonstrable ability to generate H2 under certain physiological conditions. However, most produce only little H2, revert readily to H2 consumption, and suffer from hydrogenase sensitivity to O2. Strains of the cyanobacteria Lyngbya aestuarii and Microcoleus chthonoplastes obtained from marine intertidal cyanobacterial mats were recently found to display much better H2 production potential. Because of their ecological origin in environments that become quickly anoxic in the dark, we hypothesized that this differential ability may have evolved to serve a role in the fermentation of the photosynthate. Here we show that, when forced to ferment internal substrate, these cyanobacteria display desirable characteristics of physiological H2 production. Among them, the strain L. aestuarii BL J had the fastest specific rates and attained the highest H2 concentrations during fermentation of photosynthate, which proceeded via a mixed acid fermentation pathway to yield acetate, ethanol, lactate, H2, CO2, and pyruvate. Contrary to expectations, the H2 yield per mole of glucose was only average compared to that of other cyanobacteria. Thermodynamic analyses point to the use of electron donors more electronegative than NAD(P)H in Lyngbya hydrogenases as the basis for its strong H2 production ability. In any event, the high specific rates and H2 concentrations coupled with the lack of reversibility of the enzyme, at the expense of internal, photosynthetically generated reductants, makes L. aestuarii BL J and/or its enzymes, a potentially feasible platform for large-scale H2 production. [ABSTRACT FROM AUTHOR]

Thermincola ferriacetica is a recently isolated thermophilic, dissimilatory Fe(III)-reducing, Gram-positive bacterium with capability to generate electrical current via anode respiration. Our goals were to determine the maximum rates of anode respiration by T. ferriacetica and to perform a detailed microscopic and electrochemical characterization of the biofilm anode. T. ferriacetica DSM 14005 was grown at 60 °C on graphite-rod anodes poised at -0.06 V (vs) SHE in duplicate microbial electrolysis cells (MECs). The cultures grew rapidly until they achieved a sustained current density of 7-8 A m-2 with only 10 mM bicarbonate buffer and an average Coulombic Efficiency (CE) of 93%. Cyclic voltamme- try performed at maximum current density revealed a Nernst-Monod response with a half saturation potential (EKA) of -0.127 V (vs) SHE. Confocal microscopy images revealed a thick layer of actively respiring cells of T. ferriacetica (∼38 /μm), which is the first documentation for a gram positive anode respiring bacterium (ARB). Scanning electron microscopy showed a well-developed biofilm with a very dense network of extracellular appendages similar to Geobacter biofilms. The high current densities, a thick biofilm (∼ μm) with multiple layers of active cells, and Nemst-Monod behavior support extracellular electron transfer (EET) through a solid conductive matrix - the first such observation for Gram-positive bacteria. Operating with a controlled anode potential enabled us to grow T. ferriacetica that can use a solid conductive matrix resulting in high current densities that are promising for MXC applications. [ABSTRACT FROM AUTHOR]

One of the limitations currently faced by microbial electrochemical cell (MXC) technologies lies in the shortage of different organisms capable of forming a biofilm and channeling electrons from substrates to the anode at high current densities. Using a poised anode (-0.30 V vs Ag/AgCl) and acetate as the electron donor in a MXC, we demonstrated the presence of highly efficient anode-respiring bacteria (ARB) able to produce high current densities (>1.5 A/m2 anode) in seven out of thirteen environmental samples. These included marshes, lake sediments, saline microbial mats, and anaerobic soils obtained from geographically diverse locations. Our microbial ecology analysis, using pyrosequencing, shows that bacteria related to the genus Geobacter, a known and commonly found ARB, dominate only two of the biofilm communities producing high current; other biofilm communities contained different known and/or novel ARB. The presence of ARB in geographically diverse locations indicates that ARB thrive in a wide range of ecosystems. Studying ARB from different environmental conditions will allow us to better understand the ubiquity of anode respiration, compare the capabilities of different ARB consortia, and find ARB with useful metabolic capacities for future applications. [ABSTRACT FROM AUTHOR]

This study demonstrated the utility in correlating performance and community structure of a trichloroethene (TCE)-dechlorinating microbial consortium; specifically dechlorinators, fermenters, homoacetogens, and methanogens. Two complementary approaches were applied: predicting trends in the microbial community structure based on an electron balance analysis and experimentally assessing the community structure via pyrosequencing and quantitative polymerase chain reaction (qPCR). Fill-and-draw reactors inoculated with the DehaloR⁁2 consortium were operated at five TCE-pulsing rates between 14 and 168 µmol/10-day-SRT, amended with TCE every 2 days to give peak concentrations between 0.047 and 0.56 mM (6-74 ppm) and supplied lactate and methanol as sources of e- donor and carbon. The complementary approaches demonstrated the same trends: increasing abundance of Dehalococcoides and Geobacter and decreasing abundance of Firmicutes with increasing TCE pulsing rate, except for the highest pulsing rate. Based on qPCR, the abundance of Geobacter and Dehalococcoides decreased for the highest TCE pulsing rate, and pyrosequencing showed this same trend for the latter. This deviation suggested decoupling of Dehalococcoides growth from dechlorination. At pseudo steady-state, methanogenesis was minimal for all TCE pulsing rates. Pyrosequencing and qPCR showed suppression of the homoacetogenic genera Acetobacterium at the two highest pulsing rates, and it was corroborated by a decreased production of acetate from lactate fermentation and increased propionate production. Suppression of Acetobacterium, which can provide growth factors to Dehalococcoides, may have contributed to the decoupling for the highest TCE-pulsing rate. Biotechnol. Bioeng. 2012;109: 2230-2239. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

we evaluated the consumption of hydrogen gas at the anode of a microbial electrolysis cell (MEC) and characterized the significance of new interactions between anode respiring bacteria (ARB) and homo-acetogens. we demonstrated the significance of biofilm limitation for direct consumption of H2 over acetate by ARB, using the deep biofilm model. Selective inhibition of the major competing hydrogen sink at the biofllm anode, methanogenesis, resulted in significant increase in electron recovery as electric current (-10-12 Aim2). The presence of acetate at high concentration in the anode compartment and detection of formate, a known intermediate of the acetyl-C0A pathway, provide evidence towards the role of homoacetogenic bacteria. We also assessed the activity of homoacetogens with reverse transcription quantitative PCR targeting formyltetrahydrofolate synthetase (FTHFS) transcripts, and observed a comparable decrease in the FTHFS transcript numbers with current density and acetate concentrations as we decreased the HRT below 4.5 h. The biofilm anode community was predominated by Deltaproteobacteria (70% of total readouts) along with a fraction of the homoacetogenic genus, Acetobacterium (4% of total readouts), established by pyrosequencing targeting the V6 region of the loS rRNA. Homoacetogens seem to play a major role as syntrophic members of the biofilm anode community when electron recovery is high. [ABSTRACT FROM AUTHOR]

Abstract: Homo-acetogens in the anode of a microbial electrolysis cell (MEC) fed with H2 as sole electron donor allowed current densities similar to acetate-fed biofilm anodes (∼10A/m2). Evidence for homo-acetogens included accumulation of acetate at high concentrations (up to 18mM) in the anode compartment; detection of formate, a known intermediate during reductive acetogenesis by the acetyl-CoA pathway; and detection of formyl tetrahydrofolate synthetase (FTHFS) genes by quantitative real-time PCR. Current production and acetate accumulation increased in parallel in batch and continuous mode, while both values decreased simultaneously at short hydraulic retention times (1h) in the anode compartment, which limited suspended homo-acetogens. Acetate produced by homo-acetogens accounted for about 88% of the current density of 10A/m2, but the current density was sustained at 4A/m2 at short hydraulic retention time because of a robust partnership of homo-acetogens and anode respiring bacteria (ARB) in the biofilm anode. [ABSTRACT FROM AUTHOR]

We evaluated the feasibility of using waste activated sludge (WAS) from a wastewater treatment plant as an internal electron donor to fuel denitrification, by increasing its bioavailability with Focused-Pulsed (FP) technology. The focused-pulsed treatment of WAS (producing FP-WAS) increased the semi-soluble chemical oxygen demand (SSCOD) by 26 times compared with the control WAS. The maximum denitrification rate of FP-WAS (0.25 g nitrate-nitrogen [NO3-·N]/g volatile suspended solids [VSS]·d) was greater than for untreated WAS (0.05 g NO3-·N/g VSS·d) and methanol (0.15 NO3-·N/g VSS·d). Centrifuging out the larger suspended solids created FP-centrate, which had a rate (0.14 g NO3-·N/g VSS·d) comparable with that of methanol. Thus, FP treatment of WAS created SSCOD, which was an internal electron donor that was able to drive denitrification at a rate similar to or greater than methanol. One trade-off of using FP-WAS for denitrification is an increase in total Kjeldahl nitrogen (TKN) loading. While FP-WAS achieved the lowest total nitrogen and NO3-·N concentrations in the batch denitrification test, its final ammonia-nitrogen (NH3-N) concentration was the highest, as a result of the release of organic nitrogen from the FP-treated biomass; FP-centrate had less release of total soluble nitrogen. While the return of total nitrogen (TN) is small compared with the SSCOD, the effects of the added nitrogen loading need to be considered. Water Environ. Res., 82, 2316 (2010). [ABSTRACT FROM AUTHOR]

In microbial fuel cells and electrolysis cells (MXCs), anode-respiring bacteria (ARB) oxidize organic substrates to produce electrical current. In order to develop an electrical current, ARB must transfer electrons to a solid anode through extracellular electron transfer (EET). ARB use various EET mechanisms to transfer electrons to the anode, including direct contact through outer-membrane proteins, diffusion of soluble electron shuttles, and electron transport through solid components of the extracellular biofilm matrix. In this review, we perform a novel kinetic analysis of each EET mechanism by analyzing the results available in the literature. Our goal is to evaluate how well each EET mechanism can produce a high current density (>10 A m−2) without a large anode potential loss (less than a few hundred millivolts), which are feasibility goals of MXCs. Direct contact of ARB to the anode cannot achieve high current densities due to the limited number of cells that can come in direct contact with the anode. Slow diffusive flux of electron shuttles at commonly observed concentrations limits current generation and results in high potential losses, as has been observed experimentally. Only electron transport through a solid conductive matrix can explain observations of high current densities and low anode potential losses. Thus, a study of the biological components that create a solid conductive matrix is of critical importance for understanding the function of ARB. [ABSTRACT FROM AUTHOR]