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PubMed2006

Identification of the microbiological community in biogas systems and evaluation of microbial risks from gas usage.

The plans for introducing biogas produced from organic waste to the pipe system for natural gas has raised concerns about the risk of transmitting disease via the gas. To assess this risk, condensate water from gas pipes and gas from different parts of a biogas upgrading system were sampled and cultured for microbial content. On average, 10(5) cfu ml-1 were found in the condensate water throughout the system, while in the gas between 10 and 100 cfu m-3 were found. The microorganisms were subjected to further identification and found to represent a wide variety, e.g. fungi and spore-forming and non-spore-forming bacteria, including species such as Enterobacteriaceae. The number of microorganisms found in the biogas corresponded to the densities in sampled natural gas, which also held 10-100 cfu m-3. Since no pathogens were identified and since the exposure to gas from e.g. cookers and refuelling of cars may only result in the inhalation of small volumes of gas, the risk of spreading disease via biogas was judged to be very low.

Bacteria↗
PubMed2004

Bioelectric power generation.

In the recent article by Chaudhuri and Lovley, a fuel cell is described in which a microorganism, Rhodoferax ferrireducens, is used to oxidize glucose to carbon dioxide at neutral pH. This reaction occurs via direct bioelectrocatalysis: the microorganism uses the anode itself as the terminal oxidant to which liberated electrons are transferred, and does so with 83% efficiency. These findings are significant because they demonstrate a new approach for harvesting energy from the environment using microorganisms.

Bioelectric Energy Sources↗
PubMed2004

Production of bioenergy and biochemicals from industrial and agricultural wastewater.

The building of a sustainable society will require reduction of dependency on fossil fuels and lowering of the amount of pollution that is generated. Wastewater treatment is an area in which these two goals can be addressed simultaneously. As a result, there has been a paradigm shift recently, from disposing of waste to using it. There are several biological processing strategies that produce bioenergy or biochemicals while treating industrial and agricultural wastewater, including methanogenic anaerobic digestion, biological hydrogen production, microbial fuel cells and fermentation for production of valuable products. However, there are also scientific and technical barriers to the implementation of these strategies.

Bacteria↗
PubMed2005

Crop biotechnology provides an opportunity to develop a sustainable future.

The current reliance on petro-based fuels and chemicals is not sustainable. New technologies typically take approximately 25 years to penetrate the market; consequently, the development of viable alternatives is required in the near future. Plant-based systems capture solar energy and can be produced in a renewable manner. However, the harvestable parts are not well optimized for energy transfer and this has been a significant limitation to the development of economically viable and sustainable biomass energy systems. Biotechnology has provided a new toolset that can be used to design and optimize the capture of solar energy through crops. Further development of biotechnology and genomics tools will enable the development of crops with specific traits that are optimized for biofuels and bioenergy. The implementation of such a system will enable a sustainable platform for centuries to come and should be given a high priority in society.

Agriculture↗
PubMed2005

Microbial fuel cells: novel biotechnology for energy generation.

Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy from biodegradable, reduced compounds. MFCs function on different carbohydrates but also on complex substrates present in wastewaters. As yet there is limited information available about the energy metabolism and nature of the bacteria using the anode as electron acceptor; few electron transfer mechanisms have been established unequivocally. To optimize and develop energy production by MFCs fully this knowledge is essential. Depending on the operational parameters of the MFC, different metabolic pathways are used by the bacteria. This determines the selection and performance of specific organisms. Here we discuss how bacteria use an anode as an electron acceptor and to what extent they generate electrical output. The MFC technology is evaluated relative to current alternatives for energy generation.

Biodegradation, Environmental↗
PubMed2005

White biotechnology: differences in US and EU approaches?

Several predominantly political movements advocate white, or industrial, biotechnology as a means to alleviate economic, ecological and societal problems in petroleum-dependent industrialized nations worldwide. US and European approaches differ significantly and we believe that, in the long-term, only economic drivers will be able to bring about the broad use of renewable resources and a bio-based economy. As long as the cost of fossil fuel and feedstock for key chemicals have not passed their respective critical thresholds, industrial biotechnology and its products will need political support and funding, particularly in the energy and bulk-chemicals sectors. Other uses of industrial biotechnology, however, such as biocatalytic conversions of fine and specialty chemicals and the manufacture of high-value products, such as nutriceuticals, cosmeceuticals and performance chemicals offer dynamic growth opportunities both for established chemical industries, as well as emerging entrepreneurial enterprises.

Bioelectric Energy Sources↗
PubMed2006

Environmental biocatalysis: from remediation with enzymes to novel green processes.

Modern biocatalysis is developing new and precise tools to improve a wide range of production processes, which reduce energy and raw material consumption and generate less waste and toxic side-products. Biocatalysis is also achieving new advances in environmental fields, from enzymatic bioremediation to the synthesis of renewable and clean energies and biochemical cleaning of 'dirty' fossil fuels. Despite the obvious benefits of biocatalysis, the major hurdles hindering the exploitation of the repertoire of enzymatic processes are, in many cases, the high production costs and the low yields obtained. This article will discuss these issues, pinpointing specific new advances in recombinant DNA techniques amenable to future biocatalyst development, in addition to drawing the attention of the biotechnology community to the active pursuit and development of environmental biocatalysis, from remediation with enzymes to novel green processes.

Biodegradation, Environmental↗
PubMed2004

Emissions from a controlled fire in municipal solid waste bales.

Environmental and safety aspects of seasonal storage of baled municipal solid waste to be used as fuel for energy production (waste fuel), was investigated and experiments were carried out on burning of bales. The flammability, combustion processes and emissions were studied by simulating, in small-scale, potential effects of a possible fire in full-scale bale storage area. Despite the high water content and the high density of the bales, after setting fire, the bales burned well, even though no risk for self-ignition exists. The following parameters of the combustion product were measured continuously: O2, CO2, CO, SO2, NO, NO2, NOx, THC, smoke gas rate and the temperature of the smoke. Soot particles in the smoke were collected and analysed for Hg, Pb, Cd, As, Ni, Cr, Mn, Cu, Co, Sb and V concentrations. The analysis of the moisture content, concentrations of Hg, Cd, HCl, HF, HBr, NH3, polyaromatic hydrocarbons (PAH), chlorinated and brominated dioxins (PCDD/F and PBrDD/F, respectively) were carried out. It was found that the PCDD/F levels (TEQs) varied according to the system used: 12.53 ng (I-TEF-88)/Nm3; 14.09 ng (I-TEF-99)/Nm3; 13.86 ng (Eadons)/Nm3. The PAH concentration was 3.04 microg/Nm3. The contents of the metals in the smoke (with the exceptions of Pb and Cd with mean values of 1.74 and 0.36 mg/m3, respectively) were below the limit values established by the Swedish Ministry of Environment for emissions from incineration plants [Swedish Ministry of Environment, (2002:1060), Förordning 2002:1060 om avfallsförbränning. Available from http://www.notisum.se/rnp/SLS/LAG/20021060.HTM]/EU-directive [(2000/76/EC), Directive 2000/76/EC, of the European Parliament and of the Council of 4 December 2000 on the Incineration of Waste. http://www.Scotland. gov.uk/library5/environment/iecda.pdf]. The HCl concentration was 10 times higher than the limit value (mean value of 99 mg/m3).

Air Pollutants↗
PubMed2004

Prediction of syngas quality for two-stage gasification of selected waste feedstocks.

This paper compares the syngas produced from methane with the syngas obtained from the gasification, in a two-stage reactor, of various waste feedstocks. The syngas composition and the gasification conditions were simulated using a simple thermodynamic model. The waste feedstocks considered are: landfill gas, waste oil, municipal solid waste (MSW) typical of a low-income country, the same MSW blended with landfill gas, refuse derived fuel (RDF) made from the same MSW, the same RDF blended with waste oil and a MSW typical of a high-income country. Energy content, the sum of H2 and CO gas percentages, and the ratio of H2 to CO are considered as measures of syngas quality. The simulation shows that landfill gas gives the best results in terms of both H2+CO and H2/CO, and that the MSW of low-income countries can be expected to provide inferior syngas on all three quality measures. Co-gasification of the MSW from low-income countries with landfill gas, and the mixture of waste oil with RDF from low-income MSW are considered as options to improve gas quality.

Bioelectric Energy Sources↗
PubMed2005

Alternative strategies for energy recovery from municipal solid waste Part B: Emission and cost estimates.

This two-part paper assesses four strategies for energy recovery from Municipal Solid Waste (MSW) by dedicated Waste-To-Energy (WTE) plants. In strategy 1, the residue of Material Recovery (MR) is fed directly to a grate combustor, while in strategy 2 the grate combustor comes downstream of light mechanical treatment. In strategies 3 and 4, the MR residue is converted into Refuse Derived Fuel (RDF), in a fluidized cumbuster bed. The results of Part A, devoted to mass and energy balances, clearly show that pre-treating the MR residue in order to increase the heating value of the feedstock fed to the WTE plant has marginal effects on the energy efficiency of the WTE plant. When considering the efficiency of the whole strategy of waste management, the energy balances show that the more thorough the pre-treatment, the smaller the amount of energy recovered per unit of MR residue. Starting from the heat/mass balances illustrated in Part A, Part B examines the environmental impacts and economics of the various strategies by means of a Life Cycle Assessment (LCA). Results show that treating the MR residues ahead of the WTE plant does not provide environmental or economic benefits. RDF production worsens almost all impact indicators because it reduces net electricity production and thus the displacement of power plant emissions; it also increases costs, because the benefits of improving the quality of the material fed to the WTE plant do not compensate the cost of such improvement.

Bioelectric Energy Sources↗
PubMed2005

Alternative strategies for energy recovery from municipal solid waste Part A: Mass and energy balances.

This two-part paper assesses four strategies for energy recovery from municipal solid waste (MSW) by dedicated waste-to-energy (WTE) plants generating electricity through a steam cycle. The feedstock is the residue after materials recovery (MR), assumed to be 35% by weight of the collected MSW. In strategy 1, the MR residue is fed directly to a grate combustor. In strategy 2, the MR residue is first subjected to light mechanical treatment. In strategies 3 and 4, the MR residue is converted into RDF, which is combusted in a fluidized bed combustor. To examine the relevance of scale, we considered a small waste management system (WMS) serving 200,000 people and a large WMS serving 1,200,000 people. A variation of strategy 1 shows the potential of cogeneration with district heating. The assessment is carried out by a Life Cycle Analysis where the electricity generated by the WTE plant displaces electricity generated by fossil fuel-fired steam plants. Part A focuses on mass and energy balances, while Part B focuses on emissions and costs. Results show that treating the MR residue ahead of the WTE plant reduces energy recovery. The largest energy savings are achieved by combusting the MR residue "as is" in large scale plants; with cogeneration, primary energy savings can reach 2.5% of total societal energy use.

Bioelectric Energy Sources↗
PubMed2006

Water hyacinths as a resource in agriculture and energy production: a literature review.

Water hyacinths are becoming a problem in lakes, ponds and waterways in many parts of the world. This paper contains a literature study of different ways to use water hyacinths, mainly in agricultural or alternative energy systems. The literature review indicated that water hyacinths can be rich in nitrogen, up to 3.2% of DM and have a C/N ratio around 15. The water hyacinth can be used as a substrate for compost or biogas production. The sludge from the biogas process contains almost all of the nutrients of the substrate and can be used as a fertiliser. The use of water hyacinth compost on different crops has resulted in improved yields. The high protein content makes the water hyacinth possible to use as fodder for cows, goats, sheep and chickens. Water hyacinth, due to its abundant growth and high concentrations of nutrients, has a great potential as fertiliser for the nutrient deficient soils of Africa and as feed for livestock. Applying the water hyacinths directly without any other processing than sun drying, seems to be the best alternative in small-scale use due to the relatively small losses of nutrients and workload required. To meet the ever-growing energy demand, biogas production could be one option but it requires investments and technological skills that would impose great problems in developing countries where the water hyacinth is often found. Composting as an alternative treatment has the advantage of a product that is easy to work into the soil compared with dried water hyacinths, because of the decomposed structure. Harvesting and transport of water hyacinths can be conducted manually on a small scale and does not require a new harvesting technique to be introduced. Transporting of fresh water hyacinths means, if used as fertiliser in amounts large enough to enhance or effect crop growth, an unreasonably large labour requirement. Based on the labour need and the limited access to technology, using dried water hyacinths, as green manure is a feasible alternative in many developing countries.

Agriculture↗
PubMed2006

A technical, economic, and environmental analysis of energy production from newspaper in Ireland.

The production of newspaper corresponds to 37 kg per person per annum in Ireland. Newspaper becomes a waste product in a short period of time; only 13% of domestic waste paper is recycled (data on newspaper is not available). Four scenarios, which generate energy from newspaper, are analysed. These scenarios may be summarised as follows: lignocellulosic biomass conversion to ethanol (transport fuel); co-digestion with the organic fraction of municipal solid waste and production of CH4-enriched biogas (transport fuel); co-firing with the residue of municipal solid waste in an incinerator; and gasification of newspaper as a sole fuel. Two of the scenarios involve transport fuel production; two involve the production of electricity and heat. Two of the scenarios involve newspaper as the sole ingredient; two involve co- utilisation of newspaper with another waste stream. Assuming no economic market for heat, then only the transport scenarios have the potential to be economic; indeed the biogas scenario is shown to be extremely competitive generating a potential profit of euro 227/t newspaper. A greenhouse-gas analysis indicates that the biogas scenario generated the best net greenhouse-gas savings. However when a market for heat is available, gasification was shown to be most advantageous.

Bioelectric Energy Sources↗
PubMed2005

Electricity generation from cysteine in a microbial fuel cell.

In a microbial fuel cell (MFC), power can be generated from the oxidation of organic matter by bacteria at the anode, with reduction of oxygen at the cathode. Proton exchange membranes used in MFCs are permeable to oxygen, resulting in the diffusion of oxygen into the anode chamber. This could either lower power generation by obligate anaerobes or result in the loss in electron donor from aerobic respiration by facultative or other aerobic bacteria. In order to maintain anaerobic conditions in conventional anaerobic laboratory cultures, chemical oxygen scavengers such as cysteine are commonly used. It is shown here that cysteine can serve as a substrate for electricity generation by bacteria in a MFC. A two-chamber MFC containing a proton exchange membrane was inoculated with an anaerobic marine sediment. Over a period of a few weeks, electricity generation gradually increased to a maximum power density of 19 mW/m(2) (700 or 1000 Omega resistor; 385 mg/L of cysteine). Power output increased to 39 mW/m(2) when cysteine concentrations were increased up to 770 mg/L (493 Omega resistor). The use of a more active cathode with Pt- or Pt-Ru, increased the maximum power from 19 to 33 mW/m(2) demonstrating that cathode efficiency limited power generation. Power was always immediately generated upon addition of fresh medium, but initial power levels consistently increased by ca. 30% during the first 24 h. Electron recovery as electricity was 14% based on complete cysteine oxidation, with an additional 14% (28% total) potentially lost to oxygen diffusion through the proton exchange membrane. 16S rRNA-based analysis of the biofilm on the anode of the MFC indicated that the predominant organisms were Shewanella spp. closely related to Shewanella affinis (37% of 16S rRNA gene sequences recovered in clone libraries).

Bacterial Physiological Phenomena↗
PubMed2005

Electricity generation using membrane and salt bridge microbial fuel cells.

Microbial fuel cells (MFCs) can be used to directly generate electricity from the oxidation of dissolved organic matter, but optimization of MFCs will require that we know more about the factors that can increase power output such as the type of proton exchange system which can affect the system internal resistance. Power output in a MFC containing a proton exchange membrane was compared using a pure culture (Geobacter metallireducens) or a mixed culture (wastewater inoculum). Power output with either inoculum was essentially the same, with 40+/-1mW/m2 for G. metallireducens and 38+/-1mW/m2 for the wastewater inoculum. We also examined power output in a MFC with a salt bridge instead of a membrane system. Power output by the salt bridge MFC (inoculated with G. metallireducens) was 2.2mW/m2. The low power output was directly attributed to the higher internal resistance of the salt bridge system (19920+/-50 Ohms) compared to that of the membrane system (1286+/-1Ohms) based on measurements using impedance spectroscopy. In both systems, it was observed that oxygen diffusion from the cathode chamber into the anode chamber was a factor in power generation. Nitrogen gas sparging, L-cysteine (a chemical oxygen scavenger), or suspended cells (biological oxygen scavenger) were used to limit the effects of gas diffusion into the anode chamber. Nitrogen gas sparging, for example, increased overall Coulombic efficiency (47% or 55%) compared to that obtained without gas sparging (19%). These results show that increasing power densities in MFCs will require reducing the internal resistance of the system, and that methods are needed to control the dissolved oxygen flux into the anode chamber in order to increase overall Coulombic efficiency.

Air Pollution↗
PubMed2005

Hydrogen and electricity production from a food processing wastewater using fermentation and microbial fuel cell technologies.

Hydrogen can be produced from fermentation of sugars in wastewaters, but much of the organic matter remains in solution. We demonstrate here that hydrogen production from a food processing wastewater high in sugar can be linked to electricity generation using a microbial fuel cell (MFC) to achieve more effective wastewater treatment. Grab samples were taken from: plant effluent at two different times during the day (Effluents 1 and 2; 735+/-15 and 3250+/-90 mg-COD/L), an equalization tank (Lagoon; 1670+/-50mg-COD/L), and waste stream containing a high concentration of organic matter (Cereal; 8920+/-150 mg-COD/L). Hydrogen production from the Lagoon and effluent samples was low, with 64+/-16 mL of hydrogen per liter of wastewater (mL/L) for Effluent 1, 21+/-18 mL/L for Effluent 2, and 16+/-2 mL/L for the Lagoon sample. There was substantially greater hydrogen production using the Cereal wastewater (210+/-56 mL/L). Assuming a theoretical maximum yield of 4 mol of hydrogen per mol of glucose, hydrogen yields were 0.61-0.79 mol/mol for the Cereal wastewater, and ranged from 1 to 2.52 mol/mol for the other samples. This suggests a strategy for hydrogen recovery from wastewater based on targeting high-COD and high-sugar wastewaters, recognizing that sugar content alone is an insufficient predictor of hydrogen yields. Preliminary tests with the Cereal wastewater (diluted to 595 mg-COD/L) in a two-chambered MFC demonstrated a maximum of 81+/-7 mW/m(2) (normalized to the anode surface area), or 25+/-2 mA per liter of wastewater, and a final COD of <30 mg/L (95% removal). Using a one-chambered MFC and pre-fermented wastewater, the maximum power density was 371+/-10 mW/m(2) (53.5+/-1.4 mA per liter of wastewater). These results suggest that it is feasible to link biological hydrogen production and electricity producing using MFCs in order to achieve both wastewater treatment and bioenergy production.

Bioelectric Energy Sources↗
PubMed2005

Electricity generation from swine wastewater using microbial fuel cells.

Microbial fuel cells (MFCs) represent a new method for treating animal wastewaters and simultaneously producing electricity. Preliminary tests using a two-chambered MFC with an aqueous cathode indicated that electricity could be generated from swine wastewater containing 8320 +/- 190 mg/L of soluble chemical oxygen demand (SCOD) (maximum power density of 45 mW/m2). More extensive tests with a single-chambered air cathode MFC produced a maximum power density with the animal wastewater of 261 mW/m2 (200 omega resistor), which was 79% larger than that previously obtained with the same system using domestic wastewater (146 +/- 8 mW/m2) due to the higher concentration of organic matter in the swine wastewater. Power generation as a function of substrate concentration was modeled according to saturation kinetics, with a maximum power density of P(max) = 225 mW/m2 (fixed 1000 omega resistor) and half-saturation concentration of K(s) = 1512 mg/L (total COD). Ammonia was removed from 198 +/- 1 to 34 +/- 1 mg/L (83% removal). In order to try to increase power output and overall treatment efficiency, diluted (1:10) wastewater was sonicated and autoclaved. This pretreated wastewater generated 16% more power after treatment (110 +/- 4 mW/m2) than before treatment (96 +/- 4 mW/m2). SCOD removal was increased from 88% to 92% by stirring diluted wastewater, although power output slightly decreased. These results demonstrate that animal wastewaters such as this swine wastewater can be used for power generation in MFCs while at the same time achieving wastewater treatment.

Animal Husbandry↗
PubMed2006

Biological hydrogen production by Clostridium acetobutylicum in an unsaturated flow reactor.

A mesophilic unsaturated flow (trickle bed) reactor was designed and tested for H2 production via fermentation of glucose. The reactor consisted of a column packed with glass beads and inoculated with a pure culture (Clostridium acetobutylicum ATCC 824). A defined medium containing glucose was fed at a flow rate of 1.6 mL/min (0.096 L/h) into the capped reactor, producing a hydraulic retention time of 2.1 min. Gas-phase H2 concentrations were constant, averaging 74 +/- 3% for all conditions tested. H2 production rates increased from 89 to 220 mL/hL of reactor when influent glucose concentrations were varied from 1.0 to 10.5 g/L. Specific H2 production rate ranged from 680 to 1270 mL/g glucose per liter of reactor (total volume). The H2 yield was 15-27%, based on a theoretical limit by fermentation of 4 moles of H2 from 1 mole of glucose. The major fermentation by-products in the liquid effluent were acetate and butyrate. The reactor rapidly (within 60-72 h) became clogged with biomass, requiring manual cleaning of the system. In order to make long-term operation of the reactor feasible, biofilm accumulation in the reactor will need to be controlled through some process such as backwashing. These tests using an unsaturated flow reactor demonstrate the feasibility of the process to produce high H2 gas concentrations in a trickle-bed type of reactor. A likely application of this reactor technology could be H2 gas recovery from pre-treatment of high carbohydrate-containing wastewaters.

Animals↗