FAQ

What is Biogas?

How is Biogas formed?

What are the characteristics of biogas?

What is a biogas system?

How is an MWK system different?

What are suitable feedstocks for an MWK digester?

How efficient are MWK systems?

Why do your systems have concrete fermentation tanks?

What are potential revenue sources?

What determines system feasibility?

Do you provide operator training?

How much energy can be generated?

What is the potential electric output per cow?

What are the emissions from an MWK Biogas system?

Is biogas explosive?

What are the Environmental Benefits of an MWK Biogas System?

What are the Societal Benefits of an MWK Biogas System?

Does a biogas system require manure?

Do your systems require food crops?

 

What is Biogas?

Biogas is a gas that is created when organic matter is digested or fermented in an anaerobic setting. This is a process that occurs on ocean floors, for example, or during the digestion process.   The gas produced contains mainly methane.

The most efficient producer of biogas is a dairy cow.

 

How is Biogas formed ?

Biogas is a metabolic product of methane-producing bacteria (archae). Biogas is created in an anaerobic environment (that is without light or oxygen) through the transformation of organic substances into metabolic products. Methane bacteria can only exist in an environment that is optimized with sufficient humidity (or dry matter content of less than 50%). The anaerobic decomposition of organic substances is subdivided into four sections: hydrolysis, acidification, acetate formation and methane formation. In the first two stages, the liquefaction and decomposition of the materials takes place. The actual transformation to methane occurs in the last two steps. The individual stages are not only different with regard to the micro organisms involved and the products created, but they are also substantially different with regard to the environmental conditions required.

Hydrolysis

In this first phase of the process, high-molecular substances such as carbohydrates, proteins and fats are decomposed into low-molecular, water-soluble fragments: monomers and oligomers.

Acidification

The monomers and oligomers continue to be consumed by the same bacteria and continue to decompose. In this stage, short-chain carboxyl acids, alcohols, hydrogen and carbon dioxide and/or hydrogen carbonate is formed.

The composition of these products is strongly dependent on the heat and humidity levels in the tank, as well as the pH-value of the slurry. The optimum pH-value for the micro-organisms ranges between 4.5 and 6.3 during the hydrolysis and acidification stages.

Acetate formation

The acetogenic micro-organisms form the link between acidification and methane formation. The metabolic products of the acidifying micro-organisms are transformed to methanogenic usable substances, such as acetic acid, hydrogen carbonate, hydrogen and carbon dioxide. For reaction-kinetic reasons and to prevent being stunted by hydrogen, the micro-organisms must live in symbiosis with the methanogenic micro-organisms. In reaction, the initial substrates for the last step of the anaerobic decomposition, the methanogenic phase, are formed.

Methane formation

Methane bacteria can transform only a few substrates (e.g. acetic acid, formic acid, methanol and carbon dioxide). Hydrogen serves as a universal substrate, whereas carbon dioxide serves as carbon source and electron acceptor. Additionally, the spatial closeness of the micro-organisms of the acetogenic and methanogenic phase has to be ensured by sufficient mixing.

The optimum pH-value for micro-organisms in the acetogenesis and methanogenesis stages ranges between pH 6.8 and pH 7.5. The functional range for methane bacteria is 41°F – 158°F. Mesophilic strains exist at temperatures of 77°F – 100.4°F, and thermophilic strains at temperatures of 113°F – 140°F.

 

What are the characteristics of biogas?

The characteristics of the gas produced depend on the feedstocks used. The following is an example for the use of manure, corn crop and grass. For this mix, the system would be operated at a temperature range of 100.4°F – 131°F for mesophilic fermentation. The “biogas” produced as metabolic product of the methane bacteria has the following physical characteristics.

 

Physical characteristics

CH4

CO2

H2S

Mixture

(65 % CH4)

Volume share (%)

55 - 75

22 - 24

0.1 - 0.7

100

Heat value (kWh/m³)

10

-

6.3

6.6

Fuel value (kWh/m³)

11.1

-

-

7.2

Ignition/ex limit (Vol.-%)

5 - 15

-

4 - 45

6 - 12

Ignition temperature C)

700

-

270

650 - 750

Critical pressure (bar)

47

75

90

75 - 89

Critical temperature C)

- 81.5

31

100

- 82.5

Density normal (kg/m³)

0.72

1.98

1.54

1.2

 

What is a biogas system?

A biogas system - often referred to as "digester" - is basically, the technical reproduction of the processes that occur in the stomach of a dairy cow:

Digestible matter is fed into specially equipped fermentation tanks, and the slurry is heated and mixed. The process is anaerobic and creates a gas that contains mainly methane ("biogas"). The gas is collected and stored and is used to fuel a motor that drives a generator that produces electricity and heat. The residual manure is a high-quality organic fertilizer.

Biogas systems have evolved from manure-only, to manure-and-plants or even manure-free plants. With the today's mixed-substrate technology a long list of digestible matter can be converted into electric and thermal energies.

 

How is an MWK system different?

An MWK system offers many advantages to other systems. Here are just a few:

  • Systems are highly reliable, as they produce at 100% of installed power more than 92% of the time of the year
  • Variety of feedstocks is possible: manure, crops/crop waste, food waste, other organic processing wastes
  • Various and variable combinations of feedstocks possible
  • Depending on available substrates, manure may not be necessary
  • Safety standards that exceed European regulations
  • Can be designed to allow for future expansion with proportionately smaller investment
  • Can offer energy for on- and off-load at production capabilities
  • Remote monitoring capabilities
  • Biological consultation available
  • Effluent has only 4% - 8% solids and is an organic fertilizer that has been proven to be a soil conditioner over time.

 

What are suitable feedstocks for an MWK digester ?

Basically, anything that can be digested or fermented can be a feedstock for our systems: Manure, crops, crop waste, food waste, processing and manufacturing by-products, to name a few.

Input materials vary in terms of gas yield and electricity production, and each feedstock has to be evaluated on its own merits, as well as how it would affect the overall feedstock mix. Its nutrient load, composition, and digestability all play roles.

From the materials available to you, our experts will compose the right mix to meet your specific objectives, and we are also available for consultation when the input materials change.

 

How efficient are MWK systems?

MWK's systems are designed to operate a minimum of 92% of the time of the year - that is 8060 hours annually - at installed power. This is achieved in a number of ways:

  • Our systems are designed so that parasitic load – that is the system's own energy needs - is kept to a minimum. Motors that operate valves, pumps, mixers, etc., will only run when necessary, while at the same time keeping gas production at the desired level.
  • "Flaring" (the oxidizing of abundant methane by burning it) is rarely necessary in our systems; rather, our controls will keep gas production to a level where it is converted to energy, and not wasted.
  • All components and equipment installed have a proven track record in biogas applications.
  • Gas production and collection continues during maintenance and service procedures. Any system downtime is only due to generator service and maintenance.

 

Why do your systems have concrete fermentation tanks ?

MWK Biogas systems are designed with reinforced concrete fermentation tanks because these structures contribute to the overall efficiency, reliability and longevity of our systems.

  • The tanks are more durable than steel tanks.
  • The vessels do not exude traces of gas.
  • The structures have a greater load-bearing capacity.
  • Depending on terrain and groundwater levels, concrete vessels can be placed completely inground.
  • The design allows for components to be easily accessed for maintenance or repair, while the system continues to produce.

 

What are potential revenue sources?

There are many sources of revenue associated with a well-designed biogas system. Depending on your locality, state and federal programs available to you, and type of your operation, you may be able to realize revenues from some or all of the following:

  • Sale of electricity
  • Use of electricity to cut peak prices during main production phases
  • Sale CER’s (carbon credits) through methane reduction
  • Sale of heat or cold
  • Use of heat for production processes, buildings and houses on site
  • Use of cold for all cooling processes, by a connected absorption cooling system
  • Reduced or eliminated fertilizer costs or sale of fertilizer
  • Reduction of own disposal costs
  • Tipping fees from other waste suppliers by putting their waste into the Biogas System
  • Tax depreciations
  • Benefit from subventions from the state or worldwide ecological organisations
  • Marketing advantages in sales and promotion by a ‘green company’ image

 

What determines system feasibility ?

Some of the factors that determine the feasibility of a biogas system are:

  • Electricity wholesale rates
  • Cost off-sets for electric and thermal energies, and/or waste disposal
  • Available renewable energy incentives
  • Available acreage
  • Availability, combination and state of organic feedstocks (manure, crops, food waste, foodprocessing by-products, etc.)
  • Proximity to three-phase power lines
  • Uses for available heat (e.g., for space heating, drying processes)
  • Potential für Einspeisevergütungen

 

Do you provide operator training ?

Yes.

Upon commissioning of the system, MWK will provide training so the owner/operator can become familiar with running the system efficiently. A manual for the system will be furnished that includes checklists with tasks that need to be performed on a regular basis.

The generator manufacturer also provides training, so the operator can efficiently perform routine tasks, such as oil and sparkplug changes.

 

How much energy can be generated?

In a biogas system, the energy that can be generated from a feedstock is dependent on its organic dry matter content. However, it is the overall mix of all feedstocks that determines the actual quantity and quality of the gas that is produced.

Here is a sample calculation for corn silage that has been harvested and compacted in the bunk silo. Typically the corn would have 34% DM (dry matter), of which 96% is organic DM (oDM). This translates to 326 kg oDM. Since one metric ton of oDM produces 595 m3 of biogas,this means that 326 kg results in 194 m3 of biogas. The factor for converting biogas into electricity is 2.4. Thus, 194 m3 equals 466 kW electric output.

 

1000 kg corn silage = 340 kg DM x 96% = 326.40 kg oDM

IF 1000 kg oDM = 595 m3 biogas, THEN 1 m3 = 1.68 kg oDM

THUS 326.40 kg oDM /1.68 kg ODM per m³ = 194.29 m3

194.29 m3 x 2.4 (el factor) = 466.30 kW electric output

 

One metric ton of corn silage has the capacity to produce 466.30 kW of electricity, and slightly more heat (when measured in kW).

In terms of the possible electric output per cow: An MWK system can produce 1.2 - 1.3 kW of electric energy per cow.

That is up to 600% more efficient, when compared to other systems!

 

What is the potential electric output per cow ?

The potential electricity yield per cow is as high as 1.2 - 1.3 kW in a system designed by MWK. This is considerably more than other types of digester systems can produce and is due to our systems' high capacity factors, reliability, efficiency, and low parasitic load.

 

What are the emissions from an MWK Biogas system?

MWK systems are associated with very few - if any - emissions.

Air Quality

In general the biogas cycle is CO2-neutral, because the process does not create additional CO2. Rather, the CO2 levels that are emitted, are the same as those contained in the feedstocks. When the CO2 is used in another process (for example in a greenhouse operation), then the overall process becomes CO2-negative.

For agricultural operations, a biogas system will actually reduce odours associated with conventional farming by up to 90%. This is because the effluent from an MWK biogas system has been fully digested and contains very little odour-causing matter.

Water Quality

The effluent is an organic fertilizer that reduces if not replaces the need for chemical fertilizer. It is more readily uptaken by plants, reduces the phosphor load on the soil, and has a lower BOD-level associated with it.

Soil Quality

The organic fertilizer effluent acts as a soil conditioner, over time improving soil and plant health, and increasing crop yield.

Noise Levels

The loudest component of the biogas system is the generator set. However, the space that houses it can be designed so that normal-level conversations can be held right outside the room.

 

Is biogas explosive?

No.

Biogas itself is not explosive, however, the right mix of oxygen and methane is.

MWK systems are designed with a number of features that ensure that all gas produced is converted into energy; rarely, if ever, would gas actually have to be oxidized. The concrete fermentation vessels do not exude any type of gas, and the equipment used in our systems has been specifically designed to work with biogas.

Additionally, our system is outfitted with sensors throughout that would alert to any type of gas escaping, and life safety measures would be activated.

 

What are the Environmental Benefits of an MWK Biogas System?

Unlike other digesters, MWK Biogas systems offer many environmental benefits:

  • Dramatic Odor Reduction
  • Reduction or Elimination of the Need for Chemical Fertilizers
  • Reduction of Methane Emissions
  • Electricity produced through CO2-neutral process
  • Heat produced through CO2-neutral process
  • Improved Nutrient Management
  • Improved Soil Fertility
  • Reduced Pathogen Levels and BOD (Biological Oxygen Demand) from Manure
  • Visual integration into scenery possible

 

What are the Societal Benefits of MWK Biogas System?

Unlike other digesters, MWK Biogas systems offer the following societal benefits:

  • Farmers experience independence from commodity market prices
  • The community's farmland is protected
  • Young farmers are enticed to stay in farming
  • An opportunity to be a "Gentleman Farmer"
  • Surrounding participating farms or businesses realize a new revenue stream
  • The community may experience an economic multiplier effect due its stable energy supply
  • Contribution to decentralized power production
  • Play a factor in independence on foreign energy

 

Does a biogas system require manure?

Yes and No.

Yes, at the beginning - to start the digestion process dairy cow manure is necessary. Cow manure contains archae bacteria, and these bacteria facilitate the digestion process. Manure is also a stabilizing factor in the biological process, but it doesn't have to be cow manure after the initial "inocculation".

Not all MWK systems require an ongoing supply of manure. Depending on the other substrates that make up the overall mix, cow manure may not be necessary, but it may be necessary to dilute the slurry with another substrate.

 

Do your systems require food crops ?

No.

MWK is a proponent of waste-to-energy digester facilities. Our systems can take all sorts of plant matter, like the corn plant stalks and leaves, or grasses, for example.

 

back to begin


Welche sind die möglichen Einnahmequellen?

 

Es gibt viele Einnahmenquellen in Verbindung mit einer gut geplanten Biogasanlage. Abhängig von Ihrer Lokalität, verfügbaren Programmen auf Landes- und Bundesebene und Art Ihres Betriebes, können Sie Einnahmen aus einigen oder allen der folgenden Punkte erzielen:

 

  • Verkauf von Strom

  • Eigennutzung der elektrischen Energie, um die Spitzenstrompreise in den Hauptproduktionszeiten zu senken

  • Verkauf CER's (Carbon Credits) durch Reduktion von Methan-Emissionen

  • Verkauf von produzierter Wärme oder Kälte

  • Nutzung der Wärme für Produktionsprozesse, Gebäude und Häuser auf dem Gelände

  • Nutzung von Kälte für alle Kühl-Prozesse, mit einem verbundenen Absorptionskälteanlage

  • Geringere oder keinerlei Kosten für Dünger, oder Verkauf von der Düngemittel

  • Reduzierung der eigenen Entsorgungskosten

  • Annahme von Kippgebühren von Abfall-Lieferanten

  • Steuerliche Abschreibungen

  • Subventionen vom Staat oder weltweiten Umweltorganisationen

  • Marketing-Vorteile im Vertrieb und Werbung durch den Ruf eines umweltfreundlichen Unternehmens