There are many different anaerobic digestion types available in the markets that vary in process configurations and operating conditions. The design considerations and operating conditions of these treatment trains may be suitable for a particular type of feedstock or feedstocks mix but may not be applicable or economical for others. That is why digester type and technology should be selected based on the indented feedstock’s characteristics and availability (the amount to be treated) as well as desired output and process economy in mind.
These different anaerobic digestion types based on their feed type, operating conditions and process configuration can be classified into five different groups:
A brief discussion of these different types are as follows:
Continuous Feed Digester
Continuous feed digesters are either feed continuously or semi-continuously. These are the most common type of digesters.
Batch Feed Digester
In Batch feed digesters, feedstocks are loaded in the digester and left there for a certain period for digestion to take place. Usually the batch digesters need to be bigger in volume due to the long retention time.
Extended Solids Retention (ESR) Digestion
The Extended Solids Retention (ESR) digestion process has greater solids retention time (SRT) than the Hydraulic Retention Time (HRT). This is done by thickening the digestate via thickening equipment and then recycling it back to the digester. This process allows for a longer SRT than the HRT as the solids have been separated from the water and reintroduced to the digester. This extended SRT increases solid reduction and generates more biogas.
An Extended Solids Retention (ESR) Digestion Configuration (Data Source: WEF, 2004)
Some advantages and disadvantages of this process, as listed in the WEF white paper on the anaerobic digestion (2004) are:
Discover more anaerobic digestion technologies and digesters configuration in the following links:
Find more on different Anaerobic digestion types here.
Discover more on Anaerobic Digestion and Biogas
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