Working of a Biogas Plant - Wet AD Biodigesters Features Advantages and ...

Wet Process Biodigesters Explained with Pros and Cons

We went back to basics to explain how biodigesters work and their benefits and problems in this video and in the article below. We hope you find it a useful combination of video presentation and reading material.

Introduction

 Biodigesters use the decomposition of organic matter in anaerobic conditions to facilitate the extraction of the resulting biogas for use as energy.

The biodigester has an entrance for the organic material, a space for its decomposition, an outlet with control valve for the gas (biogas), and an outlet for the material already processed (digestate).

Necessary conditions for biodigestion 

Temperature is very important for the production of biogas, since the microorganisms that carry out biodigestion reduce their activity outside these temperatures.

The temperature in the digestive chamber must be between 20º C and 60º C. To optimize the production time it is desirable to maintain a temperature between 30º C and 35º C.

The level of acidity determines how the fermentation of the organic material unfolds.

The pH of the material must have a value between 6.5 and 7.5.

Being outside this neutral range, organic matter runs the risk of rotting, as the relative activity of the wrong microorganisms increases. This usually produces a very unpleasant odor.

The container must be perfectly sealed to prevent oxygen from entering and thus have an adequate airtight seal.

The most commonly used materials to produce biogas are  manure, from cows, horses, pigs and human sources.

However, almost all organic materials can also be used.

To achieve efficient decomposition, the organic matter must be in digestible sizes, because as ageneral rule, the faster the production of biogas the smaller the particle size.

The organic matter fed into the biogas plant must at all times have a balance of carbon and nitrogen.

Structure of a biodigester

There are many variations in the design of the biodigester.

Some elements that are commonly incorporated are:

Fermentation Chamber: The space where biomass is stored during the decomposition process.
Gas storage chamber: The space where the biogas accumulates before being extracted.

Loading point for adjusting the particle size and a funnel for adjustment of the water content: This is the entrance where the biomass is added to the digester tank (biodigester).

Pile of discharge: The output, serves to remove waste that is spent and are no longer useful for biogas, but can be used as fertilizer (digestate).

Agitator: Displace the residues that are in the bottom-up of the biodigester to take advantage of all the biomass.

Gas pipe: The output of biogas. It can be connected directly to a stove or it can be transported by means of the same pipe to its place of use.

Advantages of Biodigesters 

The anaerobic digestion process or fermentation process which takes place in all biodigesters is a renewable and sustainable energy source. Taking advantage of the natural production of biogas reduces the need to use non-renewable energy. This in turn helps reduce climate change, by minimizing the output of greenhouse gases.

It is possible to use secondary products as fertilizer or fertilizer. It avoids the use of local firewood, thus reducing the pressure on forest resources. Encourages sustainable development. Redirect and take advantage of the greenhouse gases produced by landfills and industrial farms, which reduces the carbon footprint of these establishments and decreases their contribution to climate change.

It can help governments comply with national and international responsibilities to reduce the emission of carbon into the earth's atmosphere.

It prevents the contamination of aquifers.

Creates specialized jobs.

Creates the possibility of farmers and many other businesses that end-up creating a lot of organic waste matter (biomass) developing a cutting-edge and sustainable "green" project.

Disadvantages, risks and special considerations 

Ideally, the location should be close to where the biomass is collected.

The temperature of the digestion chamber must be maintained between 20º C and 60º C; Creating such temperatures may limit its use in cold places.

Biogas contains a byproduct called hydrogen sulfate, which is a corrosive and toxic gas for humans.

As with any other combustible gas, there is a risk of explosion or fire due to malfunction, maintenance or safety.

Biogas contains varying amounts of a byproduct called hydrogen sulfide, which is a corrosive and toxic gas at even very low concentrations for humans.

As with any other combustible gas, there is a risk of explosion or fire due to malfunction, maintenance or safety.

Source: Aboutespanol

Other names for a biodigester are: Anaerobic digester, anaerobic reactor, biological reactor.

Juan Gonzalo Angel Restrepo www.tvagro.tv

Creative Commons video footage used.