Biomass Feasibility
www.BiomassFeasibility.com

The Renewable Energy Institute offers three types of Biogas Feasibility Reviews & Studies:

Phase I Biomass Preliminary Screening Review - Depending on the specific type of study, location, amount of time we require, and any additional requirements that may be added by the client.  This  review averages about $10,000.00 to $20,000.00 and requires 30 to 60 days to complete and may include a site visit to one of our affiliated plants.

Phase II Biomass Feasibility Study and Analysis - Provides a solid basis for moving a potential renewable energy project forward.  The cost for this depends on the type, location, amount of time we require, and any additional requirements that may be included by the client. This study can cost from $50,000.00 and run as high as $100,000.00 and requires 90 to 120 days, on average, to complete. Final result is usually a basis for a loan or other investment funding.

Phase III Biomass Detailed Concept, Engineering and Design Analysis - the actual renewable energy project is conceived, designed and engineered. Final result is usually ready for a company to start construction. A Phase III can take about 6 months to complete and will cost anywhere from 5% to 10% of the overall cost of the project.     

Our Feasibility Reviews, Studies and Analyses are led by one of our engineers and PhD's that serve on our Scientific Advisory Board. They are each recognized leaders in the renewable energy industry and/or academia.  Our goal is to help you determine whether your renewable energy is viable, identify the merits of your proposed renewable energy project, identify weak points, provide our recommended course of action, as well as our recommendations for products and equipment that need further review or consideration.  Our Feasibility Studies are an excellent "foundation" for building your next renewable energy project.

What is Biomethane?

BioMethane is generated from Anaerobic Digesters, Anaerobic Lagoons, Biomass Gasification, Biomass Gasifiers, Biogas Recovery, BioMethane, Concentrated Animal Feeding Operations Landfill Gas to Energy, and Methane Gas Recovery.  Unlike most companies, we are equipment supplier/vendor neutral. This means we help our clients select the best equipment for their specific application. This approach provides our customers with superior performance, decreased operating expenses and increased return on investment.

The Renewable Energy Institute is leading the engineering and design to develop the world's best Anaerobic Digesters.

Anaerobic Digesters recover Biomethane from organic materials and prevents the Biomethane - which has a Global Warming Potential that is 21 times more harmful to our climate than Carbon Dioxide Emissions - from entering the atmosphere.  

The Biomethane, which we also refer to as "Renewable Natural Gas" is then used as a fuel for our cogeneration and trigeneration power plants. Alternatively, we may sell the Biomethane to a customer and transport it to them from our Anaerobic Digesters via natural gas pipelines.  We believe Anaerobic Digesters are so vital for renewable energy production and preventing climate change, that all wastewater treatment plants as well as most CAFO's (concentrated animal feeding operations) - no matter what country - will be installing Anaerobic Digesters to prevent Biomethane from entering the atmosphere and help reverse climate change.

Thursday, 29 June 2006
Sacramento, California USA and Sweden

In a ceremony held at the Ministry of the Environment in Stockholm, representatives of the Kingdom of Sweden and the State of California signed an agreement pledging the two governments and their related industries to work together to develop bioenergy, with a particular emphasis on Biomethane. 

“Through a strong working relationship between its industry and government, Sweden is showing how bioenergy can be developed in a cost-effective manner that benefits its economy and environment. We are extremely pleased to have signed this Memorandum of Understanding (MOU) that will provide a basis for intensified collaboration between Swedish and California officials to develop a thriving bioenergy industry in California,” said Joe Desmond, Undersecretary for the California Resources Agency.

In particular, Sweden has been a global leader in terms of converting biowaste, largely agricultural material and residues, into usable Biomethane. This gas is then used to either generate electricity, residential heating, or as a transportation fuel.

More than 8,000 vehicles in Sweden are powered by a combination of natural gas and Biomethane. The vehicles include transit buses, refuse trucks, and more than 10 different models of passenger cars. There are more than 25 Biomethane production facilities in Sweden and 65 filling stations. The Swedish Biomethane industry has been growing at an annual rate of about 20 percent over the last five years.

According to the Swedish Gas Association, more than 50 percent of the methane used to power Sweden’s natural gas vehicles now comes from biological sources, up from 45% last year. Natural gas vehicle sales in Sweden are increasing at the rate of 25% per annum. 

Sweden was motivated to develop its Biomethane industry because it has no natural gas reserves, to more efficiently manage its waste, and to meet its obligations under the Kyoto Accord. Since Biomethane is developed from methane sources that would normally release into the atmosphere, it’s considered one of the most climate friendly fuels. Methane (and Biomethane) is 21 times more reactive as a greenhouse gas than carbon dioxide (CO2). Sweden is currently meetings its objectives and schedule as outlined in the Kyoto accord.

Biomethane is developed by heating up and breaking down biomaterials in an (Anaerobic Digester) digester. Among other raw materials, Swedish operators feed their Anaerobic Digesters with slaughterhouse waste, swine manure, and even grassy crops. After the materials breakdown over a 20 day period, technology is then used to remove the impurities and produce Biomethane. Once cleaned-up, Biomethane is 98 percent methane and easily meets the Swedish and California pipeline standards.

The Memorandum of Understanding can be accessed on the California Resources Agency Web site: http://resources.ca.gov/press_documents/CaliforniaSwedenBiofuelsMOU.pdf

We are designing and engineering the world's best Anaerobic Digesters. 

Anaerobic Digesters recover valuable and toxic Biomethane from organic materials and prevents the Biomethane - which has a Global Warming Potential that is 21 times more harmful to our climate than Carbon Dioxide Emissions - from entering the atmosphere.  

Biomethane, which we also refer to as "Renewable Natural Gas" is used as a renewable fuel for our cogeneration and trigeneration power plants. Alternatively, we may sell the Biomethane to a customer and transport it to them from our Anaerobic Digesters via natural gas pipelines.

We believe Anaerobic Digesters and Biomethane represent an exciting opportunity for multiple reasons:

1.  Anaerobic Digesters take an existing liability and waste (Biomethane) and convert it into an asset and profit generator.  

2.  Anaerobic Digesters mitigate and reverse by preventing Biomethane to escape into the atmosphere, which is one of the major causes of global warming and climate change.  Of all Greenhouse Gas Emissions, Biomethane is 21 times more harmful to the atmosphere than are Carbon Dioxide Emissions.

3.  Anaerobic Digesters are vital for renewable energy production and helping our country's drive for energy independence. 

4.  EVERY wastewater treatment plant as well as ALL Concentrated Animal Feeding Operations (CAFO's) - IN EVERY COUNTRY - will soon be installing Anaerobic Digesters to prevent Biomethane from entering the atmosphere and help reverse climate change as well as for use as a renewable fuel.

5.  The country of Sweden is the global leader in Biomethane production.  Sweden has identified the Biomethane opportunities and is converting biowaste derived from agricultural material and residues into usable Biomethane. The Biomethane is used to generate clean, renewable electricity, residential heating, and also as a transportation fuel. Biomass sources make up 45% of Sweden’s Biomethane.  Sweden's Biomethane industry has been growing at an annual rate of around 20% over the last five years.  Biomethane powers more than 8,000 transit buses, garbage trucks, and 10 different models of passenger cars in Sweden. Sweden now has more than 25 Biomethane production facilities and 65 filling stations. The country believes that since Biomethane is developed from natural, organic sources that would have been released into the atmosphere, that Biomethane is considered one of the most climate-friendly fuels. Biomethane is 98% methane and easily meets the Swedish and California pipeline standards.

The electric grid is changing!

The transformation of a very inefficient, "centralized," highly-polluting, costly and "dumb" Electric Grid of today which now resembles:

To the "Smart Grid" of tomorrow - which resembles the slide below - will be very efficient, decentralized or "distributed," non-polluting, low-cost and "smart."

What is BioMethane, BioMethanation and Methanogenesis?

BioMethane is generated from organic materials as they decay.  Sources of BioMethane include; landfills, POTW's/Wastewaster Treatment Systems, and from animal operations where manure can be collected and the BioMethane is generated from anaerobic digesters where the manure decomposes. 

BioMethane, after installation of the requisite equipment, is essentially free, as opposed to buying natural gas, presently costing around $6.00/mmbtu.  

Methanogenesis is the production of CH4 and CO2 by biological processes that are carried out by methanogens.

Again, unlike the price of natural gas, which has been around $6.00/mmbtu for the past year. 

More About Biomass Gasification and BioMethanation Technology 

The process of Biomass Gasification produces BioMethane. BioMethane is also produced in anaerobic digesters, in the process called anaerobic digestion.  BioMethane is a renewable energy resource, as opposed to natural gas (methane), which is a non-renewable energy resource. BioMethane has similar qualities of methane and both are used in interchangeably, and each may be a substitute for the other.  

The production and disposal of large quantities of organic and biodegradable waste without adequate or proper treatment results in widespread environmental pollution. Some waste streams can be treated by conventional methods like aeration. Compared to the aerobic method, the use of anaerobic digesters in processing these waste streams provides greater economic and environmental benefits and advantages.

Interest in BioMethanation as an economic, environmental and energy-saving waste treatment continues to gain greater interest world-wide and has led to the development of a range of anaerobic reactor designs. These high-rate, high-efficiency anaerobic digesters are also referred to as "retained biomass reactors" since they are based on the concept of retaining viable biomass by sludge immobilization.

Biomass Gasification and the Production of BioMethane

Biomass is a renewable energy resource which includes a wide variety if organic resources. A few of these include wood, agricultural residue/waste, and animal manure. 

Biomass Gasification is the process in which BioMethane is produced in the BioMass Gasification process. The BioMethane is then used like any other fuel, such as natural gas, which is not a renewable fuel.

Historically, biomass use has been characterized by low btu and low efficiencies. However, today biomass gasification is gaining world-wide recognition and favor due to the economic and environmental benefits. In terms of economic benefits, the cost of the BioMethane is essentially free, after the cost of the equipment is installed. BioMethane, probably the most important and efficient energy-conversion technology for a wide variety of biomass fuels. The large-scale deployment of efficient technology along with interventions to enhance the sustainable supply of biomass fuels can transform the energy supply situation in rural areas. 
It has the potential to become the growth engine for rural development in the country. 

Principles of Biomass Gasification

Biomass fuels such as firewood and agriculture-generated residues and wastes are generally organic.  They contain carbon, hydrogen, and oxygen along with some moisture. Under controlled conditions, characterized by low oxygen supply and high temperatures, most biomass materials can be converted into a gaseous fuel known as producer gas, which consists of carbon monoxide, hydrogen, carbon dioxide, methane and nitrogen. This thermo-chemical conversion of solid biomass into gaseous fuel is called biomass gasification. The producer gas so produced has low a calorific value (1000-1200 Kcal/Nm3), but can be burnt with a high efficiency and a good degree of control without emitting smoke. Each kilogram of air-dry biomass (10% moisture content) yields about 2.5 Nm3 of producer gas. In energy terms, the conversion efficiency of the gasification process is in the range of 60%-70%.

Multiple Advantages of Biomass Gasification in Methane Production

Conversion of solid biomass into combustible gas has all the advantages associated with using gaseous and liquid fuels such as clean combustion, compact burning equipment, 
high thermal efficiency and a good degree of control. In locations, where biomass is already available at reasonable low prices (e.g. rice mills) or in industries using fuel wood, gasifier systems offer definite economic advantages. Biomass gasification technology is also environment-friendly, because of the firewood savings and reduction in CO2 emissions.
 
Biomass gasification technology has the potential to replace diesel and other petroleum products in several applications, foreign exchange.

Applications for Biomass Gasification

Thermal applications: cooking, water boiling, steam generation, drying etc.
Motive power applications: Using producer gas as a fuel in IC engines for applications such as water pumping Electricity generation: Using producer gas in dual-fuel mode in diesel engines/as the only fuel in spark ignition engines/in gas turbines.

Publicly Owned Treatment Works ("POTW's") or Wastewater Treatment Systems

Our company provides economic and ecological solutions for cities and municipalities and provide a new cash flow simultaneously.  We offer turn-key solutions for cities that includes the preliminary feasibility analysis, engineering and design, project management, permitting and commissioning.  We provide very attractive financing packages for cities that does not add to a city's liability, yet provides a valuable new revenue stream.  And, we are also able to offer a turn-key solution for qualified municipalities that includes our company owning, operating and maintaining the onsite power and energy plant.

For more information, please provide us with the following information about the flare gas or vapor:   

• Type of gas being flared or vented (methane, bio-gas, digester, landfill, etc.).
  

• Chromatograph Fuel/Gas analysis which provides us with the btu's (heating value) and the composition of the gas and its' impurities such as methane (and the percentage of methane), soloxanes, carbon dioxide, hydrogen, hydrogen sulfide, and any other hydrocarbons. 
  

• Total amount of gas available, from all sources, at the facility.  

What is an Anaerobic Digester?

An Anaerobic Digester is a device for optimizing the anaerobic digestion of biomass and/or animal manure, and possibly to recover biogas also referred to as BioMethane for energy production. Digester types include batch, complete mix, continuous flow (horizontal or plug-flow, multiple-tank, and vertical tank), and covered lagoon.

What is Anaerobic Digestion?

The U.S. EPA AgSTAR Program Background

The U.S. EPA AgSTAR is an outreach program designed to reduce methane emissions from livestock waste management operations by promoting the use of biogas recovery systems. A biogas recovery system is an anaerobic digester with biogas capture and combustion to produce electricity, heat or hot water. Biogas recovery systems are effective at confined livestock facilities that handle manure as liquids and slurries, typically swine and dairy farms. Anaerobic digester technologies provide enhanced environmental and financial performance when compared to traditional waste management systems such as manure storages and lagoons. Anaerobic digesters are particularly effective in reducing methane emissions but also provide other air and water pollution control opportunities. AgSTAR provides an array of information and tools designed to assist producers in the evaluation and implementation these systems, including:

• Conducting farm digester extension events and conferences

• Providing “How-To” project development tools and industry listings

• Conducting performance characterizations for digesters and conventional waste management systems

• Operating a toll free hotline

• Providing farm recognition for voluntary environmental initiatives

• Collaborating with federal and state renewable energy, agricultural, and environmental programs

Methane (and Biomethane) Emissions from Animal Waste Management

Methane emissions occur whenever animal waste is managed in anaerobic conditions. Liquid manure management systems, such as ponds, anaerobic lagoons, and holding tanks create oxygen free environments that promote methane production. Manure deposited on fields and pastures, or otherwise handled in a dry form, produces insignificant amounts of methane. Currently, livestock waste contributes about 8 percent of human-related methane emissions in the U.S. Given the trend toward larger farms, liquid manure management is expected to increase. For more information on international emissions, projections, and mitigation costs, see International Analyses.  

Biomethane from Anaerobic Digesters

Methane (and Biomethane) is a gas that contains molecules of methane with one atom of carbon and four atoms of hydrogen (CH4 ). It is the major component of the "natural" gas used in many homes for cooking and heating. It is odorless, colorless, and yields about 1,000 British Thermal Units (Btu) [252 kilocalories (kcal)] of heat energy per cubic foot (0.028 cubic meters) when burned. Natural gas is a fossil fuel that was created eons ago by the anaerobic decomposition of organic materials. It is often found in association with oil and coal.

The same types of anaerobic bacteria that produced natural gas also produce methane today. Anaerobic bacteria are some of the oldest forms of life on earth. They evolved before the photosynthesis of green plants released large quantities of oxygen into the atmosphere. Anaerobic bacteria break down or "digest" organic material in the absence of oxygen and produce "biogas" as a waste product. (Aerobic decomposition, or composting, requires large amounts of oxygen and produces heat.) Anaerobic decomposition occurs naturally in swamps, water-logged soils and rice fields, deep bodies of water, and in the digestive systems of termites and large animals. Anaerobic processes can be managed in a "digester" (an airtight tank) or a covered lagoon (a pond used to store manure) for waste treatment. The primary benefits of anaerobic digestion are nutrient recycling, waste treatment, and odor control. Except in very large systems, biogas production is a highly useful but secondary benefit.

Biogas produced in anaerobic digesters consists of methane (50%-80%), carbon dioxide (20%-50%), and trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide. The relative percentage of these gases in biogas depends on the feed material and management of the process. When burned, a cubic foot (0.028 cubic meters) of biogas yields about 10 Btu (2.52 kcal) of heat energy per percentage of methane composition. For example, biogas composed of 65% methane yields 650 Btu per cubic foot (5,857 kcal/cubic meter).

Anaerobic Digester Designs

Anaerobic digesters are made out of concrete, steel, brick, or plastic. They are shaped like silos, troughs, basins or ponds, and may be placed underground or on the surface. All designs incorporate the same basic components: a pre-mixing area or tank, a digester vessel(s), a system for using the biogas, and a system for distributing or spreading the effluent (the remaining digested material).

There are two basic types of digesters: batch and continuous. Batch-type digesters are the simplest to build. Their operation consists of loading the digester with organic materials and allowing it to digest. The retention time depends on temperature and other factors. Once the digestion is complete, the effluent is removed and the process is repeated.

In a continuous digester, organic material is constantly or regularly fed into the digester. The material moves through the digester either mechanically or by the force of the new feed pushing out digested material. Unlike batch-type digesters, continuous digesters produce biogas without the interruption of loading material and unloading effluent. They may be better suited for large-scale operations. There are three types of continuous digesters: vertical tank systems, horizontal tank or plug-flow systems, and multiple tank systems. Proper design, operation, and maintenance of continuous digesters produce a steady and predictable supply of usable biogas.

Many livestock operations store the manure they produce in waste lagoons, or ponds. A growing number of these operations are placing floating covers on their lagoons to capture the biogas. They use it to run an engine/generator to produce electricity.

The Digestion Process

Anaerobic decomposition is a complex process. It occurs in three basic stages as the result of the activity of a variety of microorganisms. Initially, a group of microorganisms converts organic material to a form that a second group of organisms utilizes to form organic acids. Methane-producing (methanogenic) anaerobic bacteria utilize these acids and complete the decomposition process.

A variety of factors affect the rate of digestion and biogas production. The most important is temperature. Anaerobic bacteria communities can endure temperatures ranging from below freezing to above 135° Fahrenheit (F) (57.2° Centigrade [C]), but they thrive best at temperatures of about 98°F (36.7°C) (mesophilic) and 130°F (54.4°C) (thermophilic). Bacteria activity, and thus biogas production, falls off significantly between about 103° and 125°F (39.4° and 51.7°C) and gradually from 95° to 32°F (35° to 0°C).

In the thermophilic range, decomposition and biogas production occur more rapidly than in the mesophilic range. However, the process is highly sensitive to disturbances such as changes in feed materials or temperature. While all anaerobic digesters reduce the viability of weed seeds and disease-producing (pathogenic) organisms, the higher temperatures of thermophilic digestion result in more complete destruction. Although digesters operated in the mesophilic range must be larger (to accommodate a longer period of decomposition within the tank [residence time]), the process is less sensitive to upset or change in operating regimen.

To optimize the digestion process, the digester must be kept at a consistent temperature, as rapid changes will upset bacterial activity. In most areas of the United States, digestion vessels require some level of insulation and/or heating. Some installations circulate the coolant from their biogas-powered engines in or around the digester to keep it warm, while others burn part of the biogas to heat the digester. In a properly designed system, heating generally results in an increase in biogas production during colder periods. The trade-offs in maintaining optimum digester temperatures to maximize gas production while minimizing expenses are somewhat complex. Studies on digesters in the north-central areas of the country indicate that maximum net biogas production can occur in digesters maintained at temperatures as low as 72°F (22.2°C).

Other factors affect the rate and amount of biogas output. These include pH, water/solids ratio, carbon/nitrogen ratio, mixing of the digesting material, the particle size of the material being digested, and retention time. Pre-sizing and mixing of the feed material for a uniform consistency allows the bacteria to work more quickly. The pH is self-regulating in most cases. Bicarbonate of soda can be added to maintain a consistent pH, for example when too much "green" or material high in nitrogen content is added. It may be necessary to add water to the feed material if it is too dry, or if the nitrogen content is very high. A carbon/nitrogen ratio of 20/1 to 30/1 is best. Occasional mixing or agitation of the digesting material can aid the digestion process. Antibiotics in livestock feed have been known to kill the anaerobic bacteria in digesters. Complete digestion, and retention times, depend on all of the above factors.

Producing and Using Biomethane

As long as proper conditions are present, anaerobic bacteria will continuously produce biogas. Minor fluctuations may occur that reflect the loading routine. Biogas can be used for heating, cooking, and to operate an internal combustion engine for mechanical and electric power. For engine applications, it may be advisable to scrub out hydrogen sulfide (a highly corrosive and toxic gas). Very large-scale systems/producers may be able to sell the gas to natural gas companies, but this may require scrubbing out the carbon dioxide.

Using the Effluent

The material drawn from the digester is called sludge, or effluent. It is rich in nutrients (ammonia, phosphorus, potassium, and more than a dozen trace elements) and is an excellent soil conditioner. It can also be used as a livestock feed additive when dried. Any toxic compounds (pesticides, etc.) that are in the digester feedstock material may become concentrated in the effluent. Therefore, it is important to test the effluent before using it on a large scale.

Economics

Anaerobic digester system costs vary widely. Systems can be put together using off-the-shelf materials. There are also a few companies that build system components. Sophisticated systems have been designed by professionals whose major focus is research, not low cost. Factors to consider when building a digester are cost, size, the local climate, and the availability and type of organic feedstock material.

In the United States, the availability of inexpensive fossil fuels has limited the use of digesters solely for biogas production. However, the waste treatment and odor reduction benefits of controlled anaerobic digestion are receiving increasing interest, especially for large-scale livestock operations such as dairies, feedlots, and slaughterhouses. Where costs are high for sewage, agricultural, or animal waste disposal, and the effluent has economic value, anaerobic digestion and biogas production can reduce overall operating costs. Biogas production for generating cost effective electricity requires manure from more than 150 large animals.

Below-ground, concrete anaerobic digesters have proven to be especially useful to agricultural communities in parts of the world such as China, where fossil fuels and electricity are expensive or unavailable. The primary purpose of these anaerobic digesters is waste (sewage) treatment and fertilizer production. Biogas production is secondary.

Accomplishments

The AgSTAR Program has been very successful in encouraging the development and adoption of anaerobic digestion technology. Since the establishment of the program in 1994, the number of operational digester systems has doubled. This has produced significant environmental and energy benefits, including methane emission reductions of approximately 124,000 metric tons of carbon equivalent and annual energy generation of about 30 million kWh. The graph below shows the historical use of biogas recovery technology for animal waste management.

The development of anaerobic digesters for livestock manure treatment and energy production has accelerated at a very fast pace over the past few years. Factors influencing this market demand include: increased technical reliability of anaerobic digesters through the deployment of successful operating systems over the past five years; growing concern of farm owners about environmental quality; an increasing number of state and federal programs designed to cost share in the development of these systems; and the emergence of new state energy policies (such as net metering legislation) designed to expand growth in reliable renewable energy and green power markets.

In the past 2 years alone, the number of operational digester systems has increased by 30%. For more detailed information on anaerobic digester use in the U.S. , go to the Guide to Operational Systems or see the AgSTAR 2003 Digest

The process of anaerobic digestion consists of three steps. 

The first step is the decomposition (hydrolysis) of plant or animal matter. This step breaks down the organic material to usable-sized molecules such as sugar. The second step is the conversion of decomposed matter to organic acids. And finally, the acids are converted to methane gas. 

Process temperature affects the rate of digestion and should be maintained in the mesophillic range (95 to 105 degrees Fahrenheit) with an optimum of 100 degrees F. It is possible to operate in the thermophillic range (135 to 145 degrees F), but the digestion process is subject to upset if not closely monitored. 

Many anaerobic digestion technologies are commercially available and have been demonstrated for use with agricultural wastes and for treating municipal and industrial wastewater. 

At Royal Farms No. 1 in Tulare, California, hog manure is slurried and sent to a Hypalon-covered lagoon for biogas generation. The collected biogas fuels a 70 kilowatt (kW) engine-generator and a 100 kW engine-generator. The electricity generated on the farm is able to meet monthly electric and heat energy demand.

Given the success of this project, three other swine farms (Sharp Ranch, Fresno and Prison Farm) have also installed floating covers on lagoons. The Knudsen and Sons project in Chico, California, treated wastewater which contained organic matter from fruit crushing and wash down in a covered and lined lagoon. The biogas produce is burned in a boiler. And at Langerwerf Dairy in Durham, California, cow manure is scraped and fed into a plug flow digester. The biogas produced is used to fire an 85 kW gas engine. The engine operates at 35 kW capacity level and drives a generator to produce electricity. Electricity and heat generated is able to offest all dairy energy demand. The system has been in operation since 1982. 

Most anaerobic digestion technologies are commercially available. Where unprocessed wastes cause odor and water pollution such as in large dairies, anaerobic digestion reduces the odor and liquid waste disposal problems and produces a biogas fuel that can be used for process heating and/or electricity generation. 

Technology assessment

This section describes the anaerobic digestion (AD) process, outlines guidelines for assessing the feasibility of AD and biogas usage at a swine facility and provides summary information on AD system performance and reliability.

Anaerobic Digestion Technology Description

AD promotes the bacterial decomposition of the volatile solids (VS) in animal wastes to biogas, thereby reducing lagoon loading rates and odor. The primary component of an AD system is the anaerobic digester, a waste vessel containing bacteria that digest the organic matter in waste streams under controlled conditions to produce biogas. As an effluent, AD yields nearly all of the liquid that is fed to the digester. This remaining fluid consists of mostly water and is allowed to evaporate from a secondary lagoon, land-applied for irrigation and fertilizer value or recycled to flush manure from the swine building to the digester.

The benefits of AD include:

• Odor reduction;

• Reduction in the biological oxygen demand of treated effluent by up to 90 percent, reducing the risk for water contamination;

• Improved nutrient application control, because up to 70 percent of the nitrogen in the waste is converted to ammonia, the primary nitrogen constituent of fertilizer;

• Reduced pathogens, viruses, protozoa and other disease-causing organisms in lagoon water, resulting in improved herd health and possible reduced water requirements; and

• Potential to generate electricity and process heat.

AD takes place in three steps: hydrolysis, acid formation, and methane generation. During the first step, hydrolysis, bacterial enzymes break down proteins, fats and sugars in the waste to simple sugars. During acid formation, bacteria convert the sugars to acetic acid, carbon dioxide and hydrogen. Then the bacteria convert the acetic acid to methane and carbon dioxide, and combine carbon dioxide and hydrogen to form methane and water.

Digester technologies that can be used to collect biogas from swine facilities include:

• Covered anaerobic lagoons,

• Complete mix digesters and

• Sequencing batch reactors.

Although a sequencing batch reactor has been used for AD at one swine facility in the United States , this technology is considered to be experimental, and thus is not included in this report. This report focuses on technologies that have verifiable performance characteristics, namely, covered anaerobic lagoons and complete mix digesters. 

Appendix B provides contact information that can help producers find AD system designers/installers, odor control technologies, generators, heating and cooling equipment, and other information to help manage air and water quality at hog facilities.

Covered lagoon digesters are the simplest AD system. These systems typically consist of an anaerobic combined storage and treatment lagoon, an anaerobic lagoon cover, an evaporative pond for the digester effluent, and a gas treatment and/or energy conversion system. Figure 1 shows a typical schematic for a floating covered anaerobic lagoon.

This section provides guidelines for conducting a preliminary assessment of the feasibility of using AD at a swine facility. Although AD system requirements will vary depending on the application and system design, there are some rule-of-thumb measures that should be noted when assessing the feasibility of AD at a given location. For AD to potentially be technically feasible and cost-effective, a swine facility should:

• Simultaneously house at least 2,000 animals with a total live animal weight of at least 110,000 pounds,

• Have no more than 20 percent variation in animal population throughout the year,

• Collect waste at one central location such as an underfloor pit,

• Collect waste daily or every other day, or can convert to an equivalent collection system,

• Have manure free of large amounts of bedding or other foreign materials, and

• Have some manure storage capability to maintain a steady digester feedstock supply

Facilities that are located south of the line of climate limitation in Figure 3 are usually warm enough for cost-effective energy recovery from covered lagoon digesters. In most cases, facilities north of the climate line in Figure 3 are too cold for cost-effective energy recovery from covered lagoon digesters. Complete mix digesters can be used in cold or warm climates. If odor control is the only objective, either covered lagoon or complete mix digesters may be used, but odor control will be less effective in the winter for covered lagoon digesters south of the line of climate limitation in Figure 3. In general, complete mix digesters are the most appropriate choice for use in Colorado.   

Source: EPA. (July 1997). AgStar Handbook: A Manual for Developing Biogas Systems at Commercial Farms in the United States . EPA 430-B-97-015. pp. 4-12.

Biogas Utilization Systems

Electricity Generation

Ongoing research and development is focusing on the use of microturbines and fuel cells for converting biogas to electricity. Microturbines are high-speed, small-scale (typically less than 100 kW) gas-driven turbine systems that produce electricity efficiently, have low emissions and require little maintenance. Reflective Energies in Viejo , California in partnership with a microturbine manufacturer is working on developing a new microturbine that can use biomethane from animal waste, landfill gas and biomass gasification as its fuel source. Fuel cells are an emerging technology that operate, in principle, like a battery, but do not run out of charge. Instead, fuel cells equipped with a fuel reformer can use any type of hydrocarbon fuel, and run continuously as long as fuel is available. Fuel cells can convert fuel to electricity at efficiencies close to 40 percent, compared to 30 percent for the most efficient engine. In addition, fuel cell emissions include heat, some of which can be recovered for other applications, water, and carbon dioxide.

Direct Combustion

There are several measures of waste management system performance that are relevant for producers considering the use of AD. These include:

• Odor control,

• Water quality protection

• Energy production.