During our work we used a substrate that was cow dung taken directly to the local cattle market in N’Djamena and Dakar and waste water from slaughterhouses in different countries. We present a photograph of the substrate in Figure 1.

The mounting equipment consisted of: A number 13 car air chamber; a 30l can serving as a digester; a garden hose; a fitting adapted to the pipe; two (2) T-fittings; two (2) single fittings; two (2) brass nipple; a sealing ring; a burner or stove; a 6 mm gas pipe; a tap and safety valves.

After assembly we have this.

Figure 2 shows the diagram of the bio-digester used for the production of biogas with these different components.

The assembly of bio-digesters followed the method described by [28] . Once completed, we filled the water digester for safety reasons related to any escape. The lack of flow allowed us to implement our production. The water is then removed from the digester tank by the digestate discharge part. For the implementation of the introduction of the substrate and the production of biogas, the method used consists in producing an intermediate sample which will be used as a base for the production of biogas, the volume/mass of which is conditioned by the type of analysis to achieve. Then we calculated the density.

The formula for calculating the density is as follows:

Density = (Sample mass − Curb weight containing)/Volume of the weighed substrate.

Units:

・ Mass of the sample: in kilograms.

・ Mass of the container: in kilograms.

・ Volume of the substrate: in liter.

Cow dung is weighed for a specific mass. Slaughterhouse waste water is added and the mixture is mixed in a vat to allow the dung and water to form a homogeneous mixture. For our use as a 30l digester, we took a mass of cow dung representing less than 1/3 of the summer and a volume more than 2.5/3 of water. The whole of our mixture is evaluated to 28l in ours was of a capacity of 30l. A water content such as the weight of water represents 90% of the weight of semi-solid raw materials [29] . The upper part was thus left for the gaseous cloud that should pass through the pipe connecting the digester and the air chamber used for storing biogas. Once weighed and mixed, we introduce the substrate into our digester by the part dedicated to this action. For this part we have adopted the methodology of written by [30] and [31] . The volume of our system being known, we made a calculation approach previously described by [32] but our results according to the experience made in Chad are different from that of Senegal. The pH was measured initially on the substrate before introduction and at the outlet of the digestate with a pH-meter of the type “Preciva Pen type PHmeter” Model: PH3200001. The temperature is measured daily with a thermometer type “Infrared thermometer −50˚C - 400˚C”.

Each bio-digester was exposed to receive solar heat that varied between 27˚C to 41˚C in Chad and between 24˚C to 30˚C in Senegal.

The population in rural areas does not benefit from liquefied petroleum gases for cooking, they cut trees for firewood and coal.

This excessive cutting of trees causes deforestation and global warming. But most importantly makes women work harder and affects their health. To produce biogas, it is necessary to have a sufficient temperature capable of influencing the treated substrate and to convert the various stages of production of bio methane into biogas. The results of this article prove that with the ambient temperature of the climate we could produce biogas used for cooking. It is true that during hot weather the production of biogas is accelerated and during cold weather it can be delayed. However we are considering a solution in the cold time interval. Among other things, this solution would be to use sensors capable of transforming solar radiation into warmer temperature in the digesters, thus creating a serf process that prevents radiation and the heat entering from emerging.

A second case of solution would be to use solar radiation to create a stirring mechanism via a sensor that will provide energy capable of rotating a crank that will mix inside the digester. It has been shown that agitation is an important factor for biogas production. Monitoring the impact of agitation on the progress of the biogas production process is comparable to the effect of adding the inoculum from the point of view of the speed of the production process. The considerable effect of agitation in a digester is due to the fact that stirring allows the gas bubbles to be released from the deep layers, to maintain the homogeneity of the temperature at different levels and to avoid the consolidation of the crust on the surface of the digester. It promotes, in addition, the supply of bacteria in nutrients and their transport to fresh substrate, newly introduced. This positively influences the evolution of the productivity of the digester. A third example would be to use a solar water heater to either meter the digester in this water heated by solar radiation, or use this hot water to mix cow dung-slaughterhouse waste composed of blood, belly contents, fat and other. Finally one last solution would be to temporarily heat the digester with the biogas it produces. All these solutions can be the subject of different articles adapted to our context and for the simplicity of use in a rural area.

The time required for digestion in both cases was different. The production of biogas began at the end of seven days with flammability on day 21 for the bio-digester in Chad and after twenty-seven days with a flammability at day 36 for the bio-digester of Senegal. As for the experiment conducted in Chad, it is assumed that the digestion time was 21 days because the volume of the inner tube was observed, so the biogas was burned by period and from the twenty-first day onwards. On the fifth day, when the volume of the air chamber decreased as a result of the use of the biogas, the evacuation valve was opened to extract 80% of the contents and we added a fresh load of 80% in the digester. This process is repeated each weekend and Chad’s bio-digester continues to produce a significant amount of biogas until the end of the experiments. For the bio-digester of Senegal the production began four weeks after the implementation of the bio-digester with a flammability noted on the thirty-sixth day. In this case, we assume that the normal digestion time took place in less than five weeks as in the case of [37] . Despite this, the quantity of biogas produced in the inner tube was lower than that of Chad.

The pH was determined in both cases at the beginning of the introduction of the substrate and at the end of each phase of biogas production on the digestate. We present the details of the different pH measured in Table 1.

PH is a very interesting indicator in the stabilization and the good progress of anaerobic digestion. There are several pH values ranging from 5.5 to 8.5, with an optimum around 7 - 8 [38] see 8.5 [39] . Since the anaerobic digestion processes are strongly influenced by pH, they can however take place optimally in the vicinity of neutral pH = 7 and between 6.5 and 7.5 giving a good yield for certain types of substrate and in better conditions. In our work, the results of the pH measured on the experiment in Chad are similar to the work of [40] and for the experiment carried out in Senegal the result is close to that of [41] .

In both cases of experience we used at the beginning of our activities a simple can of water of capacity of 1.5 L. These cans were considered digesters, so before having the ideal ratio for mounting our bio-digester, several experiments were made to find the right ratio that should allow us to use it in our 30 L digester and produce biogas within an acceptable time interval depending on the climate of the different countries of study. We assume that biogas produces in both cases to respect all the stages of the biological mechanisms of anaerobic digestion described by [42] . A photograph of the different uses of biogas for cooking is given in Figure 5. We did not measure the amount of biogas or these physical characteristics, however, the biogas was of necessary quality cooked throughout our work in different countries and this was our goal.

One of our objectives was also to valorize the digests obtained during the different experiments and to use them for several purposes. Thus among the types of valorization of the digestate we have three axes:

The use of digestate to fertilize the soil [2] [43] : this valuation consisted of directly using the liquid digestate in cultivated plots by following the same watering process of the plants but by preparing the growing soil in advance with the liquid digestate (Figure 6(a)).

The second area of development is the use of the solid part of the digestate in sustainable brick making for house construction in rural areas where the introduction and use of cement is still difficult: the process consists of mixing the digestate solid with black clay and dirty end to mold all in a mold used for cement bricks: for this valuation, the characteristics of the brick are still under study and we have not for the moment build a wall with (Figure 6(b)).

For the third valorization and one of the most efficient in terms of ecology and respect for the environment, we manufactured an ecological coal. The solid digestate and a liquid part were used as a basis for mixing with several other types of household waste to dry. The whole is mixed under a given temperature and exposed to the sun. Once dry, it is still mixed with the digestate and covered under a sun shelter, once the moisture content is acceptable, they are put in a pressure mold to have a shape and exposed to the sun to dry and be ready to use (Figure 6(c)).

In developing countries, and particularly in sub-Saharan Africa and South-East Asia, rural villages and remote areas often lack a direct link to power grids, locking them into a cycle of poverty and underdevelopment. More and more countries are nevertheless helping their fellow citizens to escape this energy trap by exploiting an unexpected and under-appreciated resource: animal dung. Poultry, pigs, sheep, cattle and other domestic animals generate about 85% of animal faecal waste. According to Elevage Mondial, turning this livestock manure into biogas offers a way to make a renewable fuel source available to more than one billion people for their home use, giving them access to sustainable, affordable and reliable energy. Chad and Senegal are both breeding countries par excellence. The graph shown in Figure 7 gives a percentage of the animals that could be used for 90% of their excrement.

This approach has already been widely adopted in India and China. Between 2003 and 2013, China built 42 million small biogas plants (from chicken manure and livestock manure) that provide energy and light and heat, as well as many power plants in the country. Biogas, much larger, with a daily capacity of 18,000 to 60,000 kWh, by 2003, India had already installed nearly 3.4 million family-sized biogas reactors in several remote areas of the country, and by 2015 the number of family-size biogas plants across the country had risen. To four million, other countries in Asia and Africa are now exploring the use of biogas to develop household electricity production [44] .

This figure (Figure 8) summarizes the importance of the use of biogas in a number of important and sustainable approaches. We propose this approach to contribute to the waste management system focused on biogas production of job creation and added value to the environmental protection mechanism in the rural world.