Classification of biodigesters

We are talking about the different types of biodigesters that we can find. The purpose of a domestic biodigester consists in carrying out the process by which the bacteria present in the sludge naturally transform organic matter into biogas and fertilizer.

Discontinuous biodigesters

In batches.

The biodigesters batch or batch are closed containers which, when loaded, do not allow more substrate to be extracted or added until the full process of biodegradation and biogas production is complete. In other words, the process ends when there is no more biogas production.

These types of digesters admit a higher load of slightly diluted materials, therefore water needs are lower than in continuous systems. Another aspect in favor is that they are not affected by the presence of heavy materials such as earth or sand.

At the start and at the end of the process, biogas production is significantly lower; This is due to the lack of optimal conditions for anaerobic microorganisms at the start and subsequently to the depletion of their nutrients.

Semi-continuous biodigesters

These biodigesters are fed Daily with a relatively low load compared to the total content; This is deposited in the loading chamber, and an equal volume of liquid effluent must also be withdrawn from the discharge chamber in order to keep the volume constant. They generally produce biogas almost permanently, thanks to the constant supply of new nutrients for the bacterial communities.

An important limitation is the availability of water, since the feed should be a mixture of one part organic matter and four parts water (ratio 1: 4).

Full Mix Biodigesters

The defining characteristic of this type of biodigester is that the load added periodically is mixed almost completely with the content already present in the digestion chamber. As a result, part of the non-biodegraded material exits in the effluent, which makes it impossible to guarantee the total elimination of pathogens in plants and animals as well as the seeds of weeds (weeds).

Chinese model.

It originates from China and consists of a closed structure with loading and unloading chambers which can be constructed of reinforced concrete or bricks. They have one Long life expectancy (over 15 years) with good maintenance. However, the relative high or high The cost of building this model means that it has not become as popular in Latin American countries as other models.

Chinese biodigester

The digester only stores a small volume of gas generated inside, so it requires a different container built for this purpose (gasometer).

Indian model.

Also called de floating dome, In its upper part, it has a bell or dome which remains floating in the liquid due to the biogas it retains inside. The dome can be made of metal or preferably of a corrosion resistant material such as reinforced plastics. This Bell it goes up and down depending on the volume of gas it contains and therefore requires a central guide rod or side rails which prevent friction against the walls of the structure.

Floating dome model

They have the advantage that you do not need an external container to store the generated gas. This is maintained at a relatively constant pressure inside the dome, which is very advantageous.

A variant of this model consists of biodigesters which have a flexible polyethylene film at the top to replace the floating dome. Make them more economical and socially accessible.

Plug-in flow biogesters

These are the ones in which the digestion chamber is located elongate and therefore the degradation of the waste occurs as it passes through the digester. In this category are inexpensive family digesters.

Horizontal model.

It is essentially a horizontal tubular digester with the system loading and unloading chambers at its ends. Its elongated configuration prevents the initial liquid charge and the effluent from mixing; This makes it useful in the use of wastes requiring prolonged treatment, such as human excreta and certain wastes from animal slaughter.

Low cost horizontal model

The low cost family biodigestersPopular in developing countries, they are easy to process as they are made from large tubular polyethylene bags. They are usually located in some sort of trench, and their useful life is about five years.

In addition to the common models described in this document, there are others with variations of all kinds; Variations in shape, size, continuity of tributary and construction materials.