Environmental and energy potential

The fermentation of slurry, manure and chicken dung contributes significantly to the reduction of greenhouse gas emissions by utilising the methane for energy production. This avoids emissions which would otherwise be produced during storage in open tanks. What’s more, the utilisation of these raw materials in biogas plants reduces ammonia loss and optimises the nutrient concentration for fertiliser production, which facilitates commercial exploitation in horticulture and other fields. Methane production from these raw materials can be efficiently converted into electricity and heat, which supports industrial customers in particular with their energy supply.

Factors that influence biogas production

1. The species of animal: The composition and properties of slurry and manure vary depending on each species. Cattle manure often has a higher solids content and thus lends itself to gas production, while chicken manure offers advantages for fertiliser production due to its higher nutrient content.
2. Feed quality: The nutrient composition depends heavily on how the animals are fed. A high protein content in the feed increase the nitrogen content of the slurry, while high-fibre feed increase the carbohydrate content – this difference is decisive in industrial fermentation.
3. Storage conditions: Open slurry tanks cause ammonia to be lost, thus altering the concentration of the slurry. Sealed tanks and covered storage facilities help minimise such losses and maintain optimal conditions for fermentation

Economic benefits and profitability

Biogas plants for exploitation of slurry, manure and chicken dung have a long service life and low operating costs, making them a stable, sustainable investment in particular for industrial applications. Thanks to sophisticated fermentation technology, industry and commerce can benefit from energy savings and reduce their environmental impact.

TEWE’s tailored plant concepts take into consideration the specific demands of industrial exploitation of slurry and manure. Factors such as capacity, solids content and material properties are adapted in a targeted manner to ensure efficient and sustainable utilisation of these raw materials and guarantee continuous commercial energy production.

What components are important for fermenting slurry and manure?

Several components are vital for fermenting slurry and manure in biogas plants. These natural raw materials are particularly valuable due to their excellent energy efficiency which helps reduce greenhouse gas emissions. Below is an overview of the most important components and their role in biogas production:

Organic matter in slurry and manure

The organic matter in slurry and manure contains carbohydrates, proteins and fats which are broken down by microorganisms to release the biogas. The organic-matter content directly affects the gas yield: the more there is, the more energy can be extracted. These substrates are ideal for biogas plants because they are relatively easy to ferment.

Microorganisms

Microorganisms such as bacteria and archaea are the driving force of the fermentation process. They break down organic matter in multiple stages:

• Hydrolysis: In this first step, large molecules are broken down into smaller components (e.g. amino acids and sugars).

  • Acidogenesis: Organic acids and alcohol are produced.
  • Acetogenesis: These products are now converted into acetic acid, hydrogen and carbon dioxide.
  • Methanogenesis: Methane bacteria convert the acetic acid and the hydrogen into methane (CH₄) and carbon dioxide (CO₂) – the main components of biogas.

Nutrient ratios and C:N ratio

A balanced carbon-to-nitrogen ratio (C:N ratio) is vital for stable fermentation. Slurry and manure have an ideal C:N ratio, which supports microbiology in the fermenter and promotes efficient gasification. Nitrogen is required for microbial cell building while carbon acts as an energy source.

Moisture content

The moisture content of manure and slurry affects process stability. Ideally, the moisture content should be around 90% to ensure a homogeneous substrate mix and create an ideal environment for the microorganisms. A balanced water ratio improves heat transfer in the fermenter and prevents the fermentation process from stalling.

pH

The pH value is an important control factor in fermentation. Microorganisms in biogas plants work most efficiently at a pH between 6.5 and 7.5. The slurry and manure often naturally have an ideal pH for stable methane production. Regular pH checks in the fermenter ensure smooth operation.

Temperature

The optimal fermentation temperature is in the mesophilic range (35–40 °C) or the thermophilic range (50–55 °C). Slurry and manure respond particularly well to mesophilic temperatures as these promote the activity of the microorganisms and accelerate the formation of methane.

Hydraulic retention time (HRT)

Hydraulic retention time is the period for which slurry and manure must remain in the fermenter in order to fully biodegrade. For slurry and manure, the HRT is usually 15–30 days, which ensures continuous biogas production and efficiently converts the organic components.

Gasification and gas yield

Slurry and manure offer stable, continuous production of gas, especially methane. While the methane yield from slurry alone isn’t especially high, the addition of manure greatly increases the gas yield. Both substrates are ideal for biogas plants that depend on reliable energy production.

Residues and digestate

After the fermentation process, nutrient-rich digestate is left over which can be used as an agricultural fertiliser. These residues improve soil quality and ensure sustainable utilisation of slurry and manure.