Different technologies can be used to tailor a solution that makes the most of specific feedstocks

Anaerobic digestion is a natural biological process in which bacteria decompose organic matter in an oxygen-free environment. During this process, methanogenic bacteria produce methane as they feed and grow.

The methane-rich biogas produced can be burned to generate electricity or heat, or it can be processed further to produce a valuable source of renewable energy that can be fed into a natural gas pipeline or processed into compressed natural gas (CNG) for use as a clean vehicle fuel.

The process also produces a nutrient-rich slurry that can be used as a soil enhancer or fertilizer.

Classes of Organic Digesters

Anaerobic digesters can be classified based on various factors, including the type of organic waste being treated, the operational mode, and the design configuration. Here are three common classifications:

Type of Organic Waste. Anaerobic digesters can be classified based on the type of organic waste they’re designed to treat. This includes agricultural digesters for livestock manure and crop residues, municipal digesters for sewage sludge and organic solid waste from households, and industrial digesters for specific organic waste streams generated by industries such as food processing or breweries. Different waste types may require specific digester designs and operating parameters.

Several types of biodigesters and technologies can be used to convert organic waste into biogas. They typically fall into one of three main categories:

• Stand-alone digesters, which are used to process food waste or industry-specific wastes, for example, waste from the food and beverage industry.
• Digesters on farms, which help farmers manage manure, reduce odors and nutrients, and generate additional revenue.
• Digesters at wastewater treatment plants, which are incorporated into the wastewater treatment process to treat organic matter and produce biogas.

While the feedstock for anaerobic digestion may vary, the fundamental process remains the same, with some variations in how they operate.

Operational Mode. Anaerobic digesters can be classified based on their operational mode, which refers to the method of loading and unloading the digester. The main operational modes are continuous, semicontinuous, and batch. Continuous digesters receive a steady inflow of waste and simultaneously remove digested material. Semicontinuous digesters operate similarly but allow for periodic loading and unloading. Batch digesters, on the other hand, are filled with waste as a batch or series of batches, and each batch goes through a complete digestion cycle before being emptied.

Design Configuration. Anaerobic digesters can also be classified based on their design configuration. Common ones include continuous stirred tank reactors (CSTR), plug flow digesters, fixed-film digesters, and expanded granular sludge bed (EGSB) reactors. Each configuration has unique characteristics and advantages, such as the level of mixing, retention time, and ability to handle different waste types.

It’s worth noting that these classifications are not mutually exclusive, and digesters can fall into multiple categories depending on their specific characteristics and applications, as well as the type of effluent being processed.

Other Anaerobic Digestion Technologies

Anaerobic digestion can be performed with the use of several types of technologies, depending on factors including the type and concentration of feedstock. In addition to CSTR and ESGB, they include external forced circulation reactor (EFC) and anaerobic granular biomass treatment.

Finding the Best Solution

Fluence has been recognized as a 2023 Top Waste to Energy Solutions Provider by Energy Tech Review. Our team of waste-to-energy experts will carefully analyze your site’s potential to generate biogas in order to design the most efficient solution for your specific needs, whether it’s for a farm, a chemical plant, or a fish-processing plant.

If you want to turn your organic waste into valuable, income-generating products and cut costs, all while improving your environmental and sustainability performance, contact the experts at Fluence to learn more about our waste-to-energy solutions, and how they can add value to your business.