The Anatomy of Anaerobic Digesters: Understanding Each Component

Published May 02, 2024

Sustainable waste solutions are a growing concern for businesses, consumers, and investors. The US is currently on track to run out of landfill space by 2036. For some businesses and municipalities, anaerobic digestion is an ideal alternative waste disposal method.

Anaerobic digestion turns organic waste materials into valuable biogas and digestate using microorganisms in the absence of oxygen. This process reduces landfill waste and mitigates greenhouse gas emissions, so it contributes to environmental sustainability.

The biogas is a mixture of methane and carbon dioxide and is a versatile renewable energy source. You can use digestate as a nutrient-rich fertilizer, closing the loop in a sustainable waste-to-energy cycle.

Anaerobic digesting solutions include several components: a pre-treatment unit to prepare the input material, a digester tank where the biological breakdown occurs, a system for capturing and storing the produced biogas, and post-treatment facilities for the digestate.

Feedstock Input System

The process starts with collecting and preparing organic waste to make it suitable for efficient digestion. Organic waste sources, such as agricultural residues, food waste, manure, and sewage sludge, can be digested individually or combined in one digester.

During the pre-treatment phase, waste is sorted to remove inorganic materials and contaminants, then shredded or macerated to increase its surface area, which helps it break down more efficiently.  

Many types of agricultural waste work with anaerobic digestion, including crop residues and animal manure. At EcoRich, we have systems that allow you to use food waste from residential, commercial, and industrial sources. Industrial organic wastes, sewage sludge from wastewater treatment plants, and energy crops specifically grown for bioenergy production all work as well.

Digestion Chamber

The digestion chamber, or digester tank, is where the waste is converted into biogas and digestate. This chamber provides an optimal environment for anaerobic microorganisms to thrive and perform the digestion process. We make sealed, oxygen-free tanks that are constructed from corrosion-resistant materials. Some digesters are equipped with mixers to homogenize the feedstock and heating systems to maintain the ideal temperature for efficient digestion.

Anaerobic digestion only occurs under certain conditions. Digesters have to be kept at specific temperatures — either 50-60°C for thermophilic systems or 35-40°C for mesophilic systems, depending on your microbial community. The pH level of the digester needs to be in a neutral range — around 6.8 to 7.2 —to support microbial life. And you have to maintain an anaerobic environment — without oxygen — to support the organisms that produce biogas.

As long as these conditions are maintained, the microorganisms in the digester break down complex organic compounds through a multi-stage process that produces methane, carbon dioxide, and digestate. This biological process transforms organic waste into renewable energy and valuable by-products for a sustainable waste management solution.

Biogas Collection System

Once you’ve produced biogas, the collection system captures and stores it for later use. Biogas is primarily composed of methane (CH4) and carbon dioxide (CO2). This gas rises to the top of the digester tank, where it is collected through a system of pipes.

The biogas collection system includes gas domes or covers on the digesters that capture the rising biogas, pipelines for transporting the gas, condensate traps and filters to remove impurities and moisture, and gas holders for storage. Our storage units are designed to handle the pressure and composition of biogas so you’ll have a steady supply for energy production or further processing.

The biggest danger of anaerobic digestion systems is fire. Methane is flammable, so our systems include safety measures such as flame arrestors to contain any flames or explosions. They also contain pressure and vacuum relief valves to prevent excess pressure. Our digester meets and exceeds all safety standards.

Biogas Utilization Equipment

The next step is to turn your biogas into energy. Biogas production provides various forms of energy, including electricity, heat, and fuel. This conversion contributes to renewable energy production and reduces reliance on fossil fuels.

Technologies for biogas conversion include combined heat and power (CHP) units, biogas boilers, and upgrading systems for biogas to biomethane. CHP units are highly efficient at using biogas to generate electricity and capture waste heat for heating purposes. This dual-use approach maximizes the energy yield from biogas and can provide sustainable power in industrial, commercial, and residential settings.

Biogas boilers are another effective method. They directly burn biogas to produce heat for space heating, water heating, or industrial processes. Biogas can also be upgraded to biomethane. This process removes CO2, water vapor, and impurities, yielding a higher-quality gas compatible with natural gas standards. Biomethane can be injected into natural gas grids or used as a vehicle fuel, offering a versatile, clean energy source.

Digestate Processing and Storage

Digestate is the other valuable byproduct of anaerobic digestion. It’s a nutrient-rich material composed of undigested organic matter, water, and minerals. It contains nitrogen, phosphorus, and potassium, so it’s an effective fertilizer. To process digestate, the solid is separated from the liquid. The solid matter can be used as a soil conditioner, improving soil structure and water retention, while the liquid part can be directly applied to land as irrigation water. Storage facilities for digestate are designed to prevent leaching and minimize odors for environmental compliance. Proper processing and storage of digestate mitigate potential environmental impacts and maximize its value as a sustainable agricultural resource.

Control and Monitoring Systems

To make sure the anaerobic digestion process runs efficiently and safely, control and monitoring systems track various critical parameters, such as temperature, pH levels, gas composition, and feedstock flow rates. This provides real-time data that helps maintain optimal conditions within the digester.

Monitoring and control systems allow for immediate adjustments to environmental conditions to keep the microbes active and the digestion process stable. They also identify potential issues early, such as leaks or system imbalances, allowing for prompt intervention if necessary.

Maintenance and Safety Considerations

Anaerobic digestion systems are safe and effective, but they have to be maintained correctly to extend the life of the system and protect the operators. Regular inspections and servicing of mechanical components, such as mixers and pumps, will prevent failures that could disrupt the digestion process. Gas collection and storage systems should also be monitored for wear and potential leaks.

The primary safety considerations include managing the risks associated with biogas, a flammable and potentially explosive mixture. This involves installing gas detection systems, ensuring adequate ventilation in enclosed spaces, and implementing emergency shutdown procedures to quickly isolate gas flows in the event of a leak.

Final Thoughts

Anaerobic digestion solutions consist of several essential components. The feedstock input system prepares and introduces organic waste. The digestion tank is where organic material is broken down by microbes to produce biogas and digestate. The biogas collection system captures and stores the biogas. Biogas utilization equipment converts biogas into electricity, heat, or fuel. Digestate processing and storage manage the byproduct for use as a biofertilizer, and control and monitoring systems ensure optimal environmental conditions and system performance.

Understanding each component's function within the anaerobic digester will help you optimize your system's operation and output. At EcoRich, we make on-site composting easy for organizations of every size.  If you’re ready to move to a more sustainable waste management option, reach out to our experts today.