Frequently Asked Questions

We are compiling a growing list of frequently asked questions about anaerobic digesters. We also welcome your questions so we can provide you and others with educated information about biogas systems.

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What is biogas?

When organic material is digested in an anaerobic setting, the process creates biogas, a gas that consists of approximately 60% methane and 40% carbon dioxide. When scrubbed, this gas can be used as a fuel in a motor.

What is a biogas system?

Often referred to as anaerobic digesters (AD), these systems use organic waste streams, ferment or digest the slurry in an anaerobic setting, and produce biogas. In essence a biogas system is a technical replication of the processes that occur in a dairy cow’s stomach. In this case, however, the produced gas is harvested and used energetically.

What are some of the associated revenue streams of an AD system?

Revenue can be realized from tipping fees, the sale of biomethane, the generation of electricity, the production of heat, bedding product and fertilizer. Additionally, the digestate fertilizer has shown to increase crop yield over time, due to improved soil fertility. The weed seeds in the fertilizer are neutralized and there is a subsequent savings from decreased use of herbicides.

What waste products does a biogas system create?

There are no unusable products associated with a biogas system. The anaerobic digestion process produces: a gas that can become fuel in another process; heat that can be used for the digestion process and for adjacent facilities; digestate that can be separated for bedding(solid) and/or used as fertilizer(liquid).

Is biogas explosive?

While in unfortunate situations, explosions can occur, biogas itself is not explosive. Under normal operating conditions, low pressure and low temperature, biogas is an uncompressed, wet gas, and tests have shown that it can simply be burned off (or oxidized with a flare) in a controlled setting.

What are the emissions from a biogas system?

Emissions from a biogas system – actually from the generator motor - generally are the same as any other natural gas motor. The emissions values of our system are below the limits set by regulations.

Is there odor associated with a biogas facility?

A biogas facility will actually reduce odor levels generally associated with organic waste streams by 97%. A well-designed biogas system features containment facilities that store any offensive substrates without odor emissions and before they become part of the digestion process. The retention time of the slurry in the process itself further reduces odor to levels. Even when the digestate is stored in the open lagoon or while being land-applied, any associated odor levels are generally negligible.

How important is a reliable feedstock supply?

Very. The design and performance of the system depends on a reliable feedstock supply.

How do I know if a feedstock is suitable?

It is recommended that feedstocks undergo laboratory testing for certain parameters and then modeling to see how they will perform in your digester. This process is less time-consuming and costly than having to deal with the consequences of an unsuitable feedstock in a digester system.

What can be put into an anaerobic digester?

Typically, carbonaceous feedstocks that are low in lignin; everything digestible except wood. This includes plant matter, waste from food processing and manufacturing facilities, as well as post-consumer organic waste from food preparation (household, restaurants, institutions, etc.).

What should not be put into a digester?

Undesirable materials include those that cannot easily or at all be digested, or those that inhibit gas production. For example, wood has a high lignin content and cannot easily be digested; it would create sedimentation issues and impact digester functioning. Materials containing heavy metals would inhibit the gas-producing bacteria. Inorganic materials (plastics, metals, glass, etc.) would create mechanical issues. Even organic and easily digested feedstocks should be evaluated on their own merit.

Do you procure feedstocks?

Yes. Our expert partners procure a reliable supply of high-value feedstock for digester systems built by CH Four.

Does CH Four consult for digesters designed by others?

Yes. We offer digester rescue and optimization. Contact our offices to discuss how we can help.

What is involved in the operations of an anaerobic digester facility?

During the ongoing operations of a system, it must be visually inspected and certain parameters logged on a daily basis. Depending on the size and complexity of the system, this may take between 15 minutes to a total of 2 hours per day on average.

How long does it take to build a biogas system?

Depending on the size of the facility, the construction phase of the system takes approximately six (6) months. It might take longer if construction is done during winter months or if the system is very complex.

How much does an anaerobic digestion facility cost?

Costs depend on the complexities involved: Terrain characteristics, soil bearing capacity, site logistics, prevalent climate at the site, feedstock qualities and quantities, expansion plans, existing facilities; the list goes on. While development and construction costs for a biogas system vary, typically the cost per kW of installed power is 50% less than other renewable energy facilities. Of course, it is also important to consider the long-term costs and benefits of an anaerobic digestion facility, which has an up-time of greater than 92%.

What is the process, if I want a digester?

The first step would be to undertake a feasibility study that determines whether a digester makes sense for your operations. This is an elaborate process that evaluates the conditions for the development, construction and ongoing operations of a system. When the results reflect that it makes sense, this document becomes the basis for obtaining funding and financing to bring the project to life.

What's the smallest facility you build?

The smallest system we have built is a 500m3 digester with a 100 kW generator.

Where are your digesters located?

CH Four has digesters in Maine and New York; the provinces of Ontario, New Brunswick and Nova Scotia; as well as Chile, South America.

Can I have a tour of your digesters?

Yes, we would be happy to make arrangements for you to see our systems and meet their operators. Please contact our offices.

How are CH Four Biogas systems different?

CH Four designs and builds systems that perform as designed and often exceed expectations. We are proud to be able to say that all of our systems have been continually in operation and our customers are happy. Our systems use proven design, reliable technology, durable equipment, and sustainable operations.

What are the project construction options?

The first is called Design/Build, this is where one organization is in charge of the design and the construction of the project. The second is called General Contract, this is where a contractor who deals in the construction of the project is hired by the owner. The contractor does not do the design of the project, he simply receives the plans and specifications needed to build the digester from the engineers. The third is called Owner Build, this is where the owner heads the construction project and is in charge of all aspects related to the construction of the digester.

Do you warranty your systems?

Yes, we offer performance warranties for our turnkey systems. It is guaranteed that the systems will work as designed.

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