How to Choose an Anaerobic Digester

How to Choose an Anaerobic DigesterAlthough the advancement of technology has made production processes very efficient, but still a lot of waste is generated every passing day in industries, farm fields, households, etc. This is the reason why increasing environmental pollution and depleting natural resources demand recycling.

Organic waste can be recycled in many ways; an effective and environmentally friendly way is to divert the organic waste to anaerobic digesters. During anaerobic digestion, the organic waste is broken down by micro-organisms, which produce two useful products; one is the biogas which is used to generate electricity, and the other is a liquid that can be used as a fertilizer.

The process of anaerobic digestion takes place in a closed vessel called anaerobic digester. Anaerobic digesters come in a variety of shapes and designs. The choice of anaerobic digester depends on the type and quantity of waste material to be digested.

When selecting an anaerobic digester for your farm or your business, it is important to know the different types of anaerobic digesters and their technical specifications. Following are some basic types of anaerobic digestion systems and their suitability for different types of waste materials.

Types of Anaerobic Digestion Systems

There are four general types of anaerobic digestion systems which are suitable for recycling different types of agri-food waste materials.

1.      Completely Mixed System

This system consists of a large tank in which the manure is mixed and heated. It is suitable for handling organic waste with 4% to 10% dry matter content. This is the most expensive system among all the digesters available.

2.      Plug Flow System

This type of digester is most commonly used in the United States. It comprises of long channels; the manure is pushed in from one end and the biogas and by-products are pushed out through the other end. It is suitable for liquid manure that has 11% to 13% of solid content.

3.      Covered Lagoon System

This is the least expensive of all the anaerobic digestion systems, and it is suitable to handle 2% or less solid content. In this system, the liquid manure is heated in a vessel which is covered with seal plates to prevent exposure to the environment.

4.      Fixed Film System

This system is made up of a tank with a plastic medium. It is best-suited to handle liquid manure with solid content of 1% to 2%.

Temperature Range

Temperature inside the digester affects the gas production and pathogen removal. There are three temperature ranges at which the process of anaerobic digestion can occur.

1.      Thermophilic (120ºF – 140ºF)

Digesters which operate at this temperature range are more efficient in killing pathogens, but are also more expensive. Retention time is shorter, about 3 to 5 days.

2.      Mesophilic (90ºF to 110ºF)

These systems require a longer retention time, about 20 days or even more.

3.      Psychrophilic (Below 90ºF)

The covered lagoon digester operates at this temperature. This type of anaerobic digester is less expensive, but on the other hand, it is less efficient in pathogen removal and biogas production.

There are many other important considerations for the selection of an anaerobic digester like loading rate, performance, safety, etc. If you want to know that which anaerobic digester will best suit your business, you can contact Energy Recyclers. We provide you with the best recycling solution for your organic waste in Pennsylvania.


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