Biodigestor is a reservoir where the mixed biomass is put with water. It is in its interior that the fermentation of the biomass happens, creating the biogas.
With the petroleum crisis, in the 70´s, it was brought to Brazil the technology of the biodigestors; being Chinese and the Indian the main implanted models.
The biogas is obtained from the decomposition of the organic matter (biomass). The biomass is put inside of the biodigestor, where through the digestion and fermentation of the anaerobic bacteria, is transformed in a known gas named as methane. That bacterium type does not need the air to survive, provided that the atmosphere has to be as closed as possible. The biogas can be used:
- in lamp;
- for heating of stoves;
- as fuel for interncombustion motors;
- in refrigerators;
- in brooders;
- in grains dryers or other dryers;
- for electric power generation.
The biogas is inflammable, so it should have some concerns when using that gas.
Biomass is organic remains found in the nature, that can be used in the biogas production, such as:
- excrements (bovine, swine, equine, etc.);
- aquatic plants (aguapé, baroness, etc.);
- remains (of rations, fruits, foods, etc);
- peels of cereals (rice, wheat, etc);
- residential sewers.
After the whole production process of the biogas, there is a surplus inside the biodigestor that is called biofertilizer.
The biofertilizer can be used as organic fertilizer to strengthen the soil and for the development of the plant life.
This way, the use of the biofertilizer presents some advantages, such as:
- it doesn't present any cost if compared to the inorganic fertilizers;
- it doesn't stink;
- it is rich in nitrogen, commom lacking substance in the soil;
- the biomass that is inside of the biodigestor without contact with the air, kills all of the aerobicbacterias and existent germs in the feces and other organic matters;
- it is free from the parasites of the esquistossomose, poliomyelitis virus and bacteria like the typhoid fever and malaria;
- it recovers agricultural lands impoverished in nutrients by the excess or continuous use of inorganic fertilizers, in other words, chemical products;
- it is a combat agent the erosion, because it maintains the ecological balance keeping larger amount of pluvial water;
- the residue of the organic matter presents a capacity of humidity retention for the soil, allowing the plant to grow during the drought period.
On the other hand, it is worth to detach that the only disadvantage of the biofertilizer use is the non elimination of the acidity of the soil, caused by the exaggerating use of inorganic fertilizers hindering, a lot of times, the root absorption of water and nutrients of the soil such as the potassium and the nitrogen that influence in the germination and growth of the plant.
Each biodigestor has a characteristic: The ones of discontinuous production or of continuous production.
In the first type, the biomass is put inside of the biodigestor that is totally closed and it will only be opened after the biogas production, this will take about ninety days. After the fermentation of the biomass, the biodigestor is opened, cleaned and reloaded for a new cycle of biogas production.
However, in the continuous production, it happens for a long period, without the need of opening the equipment. The biomass is put in the biodigestor at the same time that the biofertilizer is removed. Observe the illustration 1 that exemplifies how the loading is done for that type of biodigestor.The most used biodigestors types a re the developed by Navy, the Indian and the Chinese.
Biodigestor of the Navy
It is a horizontal model type, that is larger in width than in the depth, its exposition to sun area is bigger, provided that the production of biogas is higher.
Its dome is made of malleable plastic, of PVC type, that inflates with the production of gas, as a balloon. It can be built buried or not. The load box is made in masonry, so that it can be wider avoiding the blockage. The dome can be removed, what helps in the cleaning. The disadvantage of the model is the dome cost.
It is built in masonry; it is a model of only one piece. Developed in China, where the properties used to be small, provided that it was developed buried, to occupy less space. This model has cheaper cost in relation to the other ones, because the dome is made in masonry. They also suffer little temperature variation.
Its dome is usually done of iron or fiber, and it is movable. It is moved upward and downward according to the biogas production. In this biodigestor type the fermentation process happens faster, because it takes advantage of the temperature of the soil that is little variable, favoring the action of the bacteria. It occupies little space and the buried development spares the use of reinforcements, such as concrete belts. In case the dome is made of metal, it should be concluded using a good painting with a rustproof material.
Once the biodigestor is in the underground, it is necessary to be careful, avoiding infiltration in the water table. Existent biodigestors done in concrete, or metal, covered with hindered canvas. This should have two exits, with two valves, in which organic remains are spilled.
Installing concerns for a biodigestor
The biodigestor should be installed at a quite airy place, to avoid stink when it be being carried.
To avoid the entrance of air and the leak of gas, the biodigestor should be much hindered.
The installation of the biodigestor should be as close as possible to the source of biomass. It is also important to exist a source of water next to the biodigestor.
Operation and loadingt of the biodigestor
Some precautions should be done when loading or cleaning a biodigestor, because the gas produced is inflammable.
The biomass should be prepared before going to the biodigestor, standing one or two weeks out of it, for the elimination of the humidity excess. Afterwards water is mixed in the biomass (in the same proportion of the biomass), what helps in the fermentation process.
The loading and the discharge of gas should be made simultaneously, what avoids the modification in the intern pressure of the gas.
Before doing the cleaning of the biodigestor, it is certified that there is not gas, to avoid accidents.
Fibraeng – Equipamentos Ind. Ltda
Manufacturers of cupolas for biodigestores in fiberlass
Rod. Celso Garcia Cid, 843 – Londrina – PR
Phone: (43) 3338-0110
KOBLITZ - Design and assembly of thermoelectric plants (Equipment for biomass).
Piracicaba - São Paulo
Rua Vitório Laerte Furlani, 890 - Vila Rezende
ZIP CODE 13405-430 - Brazil
Phone: (19) 3421-0223
TIAGO FILHO, G. L e FERREIRA, E.F. "Agroenergia - foundations of the use of energy in the rural way"
Practic Manuals - Life, A GUIDE OF SELF-SUFFICIENCY – "It is easy to build a biodigestor", Text: Santos , João Antônio, Editora TRÊS, SP.