Biogas and Anaerobic Digestion – Taking a Second Look
ID: 3928

Abstract: Shulin Chen

Anaerobic digestion has attracted renewed interests due to its potential environmental benefits in addition to bioenergy production. Compared with other types of biofuel technologies, anaerobic digestion has the advantage of using low grade feedstock such as mixed wastes that are either free or negative in cost. A much wider adoption of anaerobic digestion technology, however, is still with limit such as economics. A major barrier related to anaerobic digestion application is the perception that this technology is so mature that not much further research and development is necessary. On the contrary, this paper argues that anaerobic digestion research is urgently need as the technology has a great potential to contribute to the solutions to the climate change issues as well as bioenergy. Using examples of current research and commercialization efforts, this paper makes two main points. First, anaerobic digestion should be looked at differently, not only as a waste treatment process as it was considered in the past, but also a biorefinery system that can turn wastes into a suites of products, including biogas either for power generation or as transportation fuel, fertilizers derived from recovered nutrients, and partially degraded fibers for various applications. Second, the development in biotechnology and engineering sciences in the last a couple of decades has provided many new possibilities to improve the performance of the technology. Applying these new knowledge and new tools will greatly enhance the capability of anaerobic digestion to advance this technology for various new applications such as converting organic fraction of municipal wastes and other types of industrial solid wastes.











Manfred Ringpfeil

Biogas as most effective basis of profoundly climate-neutral raw material for industry

Manfred Ringpfeil & Matthias Gerhardt

BIOPRACT GmbH, Berlin, Germany



Biogas contains roughly equal amounts of methane and carbon dioxide. In practice it is formed from biomasses. Processes are known transferring about 90 % of the biomass energy into the methane component of the biogas. This methane contains carbon coming directly (plant biomasses) or indirectly (animal and microbial biomasses as well as residues of plant-converting industries) from atmospheric carbon dioxide. Therefore, it is climate-neutral. It is called bio-methane.



This climate neutrality will be maintained in all further products produced from that bio-methane as well as the accompanying carbon dioxide. However, the chemical properties of them are identical with those of methane and carbon dioxide derived from fossil sources. Thus, the already available production processes worked out for fossil methane and carbon dioxide can be applied 1:1 for climate-neutral methane and carbon dioxide, too.



Most of these production processes are destined to produce high-volume low-added value products. Production of biogas and its separation into methane and carbon dioxide must comply with the requirements for mass processes. Currently, production of biogas is organized in many small units distributed all over the country. To organize mass production needs to separate the two gases on-site and to use the available gas grid to transport the bio-methane to central processing sites.



The distributed biogas production has to fulfil the requirements of mass production, i.e.

high yield of product, as well as high velocity and stability of processing. Unlike biological ethanol production, biogas production needs several different bacterial consortia responsible for the single steps of conversion – hydrolysis, acidogenesis, acetogenesis, acetoclastic and hydrogenotrophic methanogenesis.



Process management has to take care for unobstructed interaction of these consortia enabling stability, high velocity and yield. Adding externally produced biocatalysts does accelerate single steps as e.g. hydrolysis. Adding externally produced bioactive compounds does strengthen single consortia as e.g. the methane-producing ones. These process-intensifying measures are objects of research and application at Biopract.



The advantages to establish the biogas process in climate protection are up to the facts, that in contrast to ethanol formation, nearly all organic compounds can be implied into the production of climate-neutral energy carriers and that biogas separates voluntarily from its aqueous production phase.



Carbon dioxide from biogas can be released into the atmosphere without disadvantage but better should be used to produce e.g. algal biomass as a source of climate-neutral products leading to an additional removal of the atmosphere’s load of carbon dioxide.











Serge Guiot

Biomass-based energy demand is increasing. Several bioconversion routes exist to turn biomass into gas or liquid fuels. A significant portion of biomass is however difficultly and/or slowly biodegradable by microorganisms, due to its heterogeneous and polymeric nature. When relatively dry (moisture less than 40%), an alternative might be to gasify biomass, which results in a synthetic gas (syngas) mainly composed of carbon monoxide (CO), CO2 and hydrogen. Syngas can be used directly to power industrial boilers, gas turbines or fuel cells to make electricity. Syngas can also be steam reformed and purified into methane, which could be used locally for energy needs, or re-injected in the natural gas grid. In Canada and particularly Quebec, this likely would return a higher revenue as compared to electricity. Sustainable means of CH4 production are thus essential. Thermochemical processes are well established. They normally involve high pressure and/or temperature, may be problematic when impurities are present and tend to have low product specificity.

To circumvent these disadvantages and use milder treatments with minimal chemical and energy, we can harness the power of microorganisms to convert the syngas compounds into gas biofuels. A small number of microbes can reduce the CO from syngas into methane. In short, the syngas can be a substrate for those carboxydotrophic methanogenic archaea that grow chemolithoautotrophically on CO and H2, such as Methanobacterium thermoautotrophicum, or Methanothermobacter wolfeii, both thermophiles (55-65 ºC).

However this research domain is yet in its infancy. Actual batch culture of M. wolfei under 100% CO at 70ºC showed an activity rate in the range of 200 mmol CO/g protein.hr with an CH4 yield around 0.9 mol CH4/mol CO.

Moreover because the aqueous solubility of CO and H2 is low, syngas fermentations are typically limited by the gas-to-liquid mass transfer rate, which represents a major engineering challenge for development of large-scale syngas fermentation facilities cost-effectively compatible with upstream gasifier productivity. Suitable bioreactor concepts therefore require optimal gas/liquid mass transfer characteristics. For that purpose, we are using an hollow fiber bioreactor, where the syngas conveyed at elevated pressure inside the fibers (inner and outer diameter 0.8 and 1.4 mm, respectively; 20 fibers per cm2 of cartridge cross-section) diffuses through the M. wolfei biofilm attached outside the fiber, while liquid is recycled in the cartridge countercurrently over the fibers. We will present preliminary performance results of such a reactor fed on the continuous mode with a reconstituted syngas made of 35% CO, 35% H2, 30% CO2, under a variety of operational conditions.













Diane Saber

Interest in biomethane from anaerobic digestion of waste for injection into natural gas pipeline networks in North America has dramatically increased due to environmental, political, and economic drivers. Sources of this increasingly popular new fuel include landfill waste, wastewater treatment sludge, agricultural waste, food-processing waste, and dairy waste. Historically, biogas has been used primarily for on-site electrical power generation or other site specific energy needs; however, operators of distribution and pipeline systems are now frequently approached to purchase and/or take delivery of biogas. Many wish to take advantage of the opportunity to transport and/or distribute a “green product” or renewable energy source but are somewhat reluctant due to limited experience with this product. Currently, gas quality specifications only exist for geologically formed natural gas; therefore, many distribution and pipeline operators lack certainty about the quality and possible effects of biomethane on pipeline networks and end use equipment.

The Gas Technology Institute (GTI), a not-for-profit research center for the natural gas industry, is finalizing a document titled: Pipeline Quality Biomethane: North American Guidance Document for Delivery of Dairy Waste Derived Biomethane into Existing Natural Gas Networks. This document will cover parameters for effective introduction of biomethane to traditional natural gas supplies. In this effort, GTI has conducted a project consisting of three Tasks: 1) compiling information which details the status of domestic and international technology and approaches for biogas production, 2) conducting an extensive comparative testing program consisting of 44 samples of “raw biogas”, “partially cleaned biogas” and “cleaned biogas” (biomethane) for examination of primary and trace constituents, and, 3) preparation of the Guidance Document which will serve as an industry reference document. This presentation will be specific to the results of Tasks 2 and 3 of the project. The document is reviewed and approved by the natural gas industry.

This GTI project is specific to the conversion of dairy waste into pipeline quality biomethane. However, it is also part of a larger, phased effort within the US and Canadian natural gas industry that encompasses:

• Biomethane parameters specific to landfill gas, wastewater sludge, agricultural waste, food processing waste, and other non-traditional sources of methane.

• Conversion of biomass (organic material) sources, in general, to pipeline quality biomethane.



The purpose of the work and the Guidance Document is to identify key analytical parameters for successful introduction of dairy-produced biomethane into existing supplies. The Guidance Document will serve as a template to which specific gas requirements may be added, based upon local distribution company (LDC) requirements and tariffs and end user needs. The GTI project will provide key information for natural gas suppliers, biomethane developers, dairy farmers and others for incorporating biomethane, a promising green, renewable energy source, into existing transmission/distribution pipeline systems or for specific end-use purposes.









Moderator: Shulin Chen, Washington State University (United States)

Presenter 1: Advancing Anaerobic Digestion Biotechnology For New Applications
Shulin Chen, Washington State University, (United States)  []

Presenter 2: Biogas as most effective basis of profoundly climate-neutral raw material for industry 
Manfred Ringpfeil, BIOPRACT, GmbH, (Germany)  []

Presenter 3: Bio-upgrading of syngas into natural gas (methane) 
Serge Guiot, National Research Council Canada - Biotechnology Research Institute, (Canada)  []

Presenter 4 (if necessary): Pipeline Quality Biomethane From Dairy Waste Conversion:  
Diane Saber, Gas Technology Institute, (United States)  []

Panel Organizer:
Matthew Carr, Biotechnology Industry Organization, (United States)

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