Complete mix anaerobic digester

Anaerobic Digester Technology

Anaerobic methane digester technology comes in a variety of technical approaches and designs generating biogas from organic materials such as manure, food waste, thin stillage or other organic material. 

 

Systems range from covered lagoons and plug flow digesters to complete mix AD systems working under mesophilic or thermophilic conditions. All systems are continuously fed with organic material.

 

Continuous flow of organic matter to the anaerobic digester system is an important factor to maximize biogas yield. To ensure this, pump systems and buffer tanks collecting liquid substrates are installed, providing a well mixed substrate to the digester.

 

Feeder systems are managing the substrate flow, if materials are getting more solid. Stationary mixer feeder with augers or push floors are used for this purpose. The conveying system feeding the digester needs to be adjusted, depending on the amount, the type or the consistency of the substrates entering the digester.

 

Substrates entering the digester lead to rising substrate levels with digested material overflowing into the next digester stage or storage. Gravity fed or pump driven systems are possible.

To ensure that microorganisms find a sufficient nutrient supply digesters are equipped with mixers helping bringing fresh organic matter to the microbes breaking it down.

Besides making sure that nutrients are available mixers homogenize the digester content and minimize crust building in order to have biogas exiting the liquid phase. 

 

Flexible double-membrane roofs or concrete roofs are most common covering anaerobic digesters. Double membrane roof consist of an outer air-inflated protection foil and an inner flexible gas holder.

 

To keep the process temperature stable tank walls are equipped with heating coils. Coils can be mounted onto the wall or are sometimes build as an in-wall heating. Digester walls and floor are insulated in order to minimize temperature losses to the outside.

 

Gas quality is continuously measured. The H2S content of the produced biogas is kept low by biological desulfurization inside the gasholder. If H2S levels are very high due to e.g. protein rich substrates chemical precipitation is need to adjust gas quality.

 

After water and hydrogensulfide are taken out the biogas there are multiple ways to produce energy. Internal combution engines can generate heat and power, biogas upgrading through water wash scrubbers or PSA technology can deliver a biogas ready to go to public grid or further compression provides CNG and mobility to cars and engines. 

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Video: Anaerobic Digester



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