Exposés pour la fête des sciences 2015

dimanche 3 mai 2015
par  Webmaster
popularité : 1%

Les élèves de Seconde, qui ont effectué un voyage au Ghana cette année, ont réalisé pour la fête des sciences quatre exposés présentant de leurs découvertes. En plus des deux premiers qui sont à lire dans l’article ci-dessous, vous pouvez télécharger deux dossiers contenant les deux autres exposés.



I. Akossombo dam

II. Valco :
-the carbon anodes construction
-the electrolysis

III. The sustainable development :
-environnemental pillar
-economical pillar
-social pillar


Valco is the aluminium factory we visited during our trip in ghana. Its mission is to produce hight quality, primary aluminium at competitive cost for the ghanaien and international markets.

Its vision is to become the best aluminium smelter in the world, while contributing to the ghana’s development and including the sustainable development.

I. Akossombo

Akossombo Dam is a really important dam, it was built in order to produce electricity notably for Valco. It produces a big part of the national electricity and also sells it to other contries, principally the bondary one. So Valco earns much money. Because of the lock of electricity coming from akossombo, the aluminium’s production in Valco turns at 20% of its capacity.

800,000 habitants have been removed at its construction but they were rehoused and it creates now a lot of jobs. The nature and biodiversity which was there before the dam have been burst so as to build it. In the one hand it doesn’t respect the environnemental pillar, in the other hand it produces green electricity.

II. Valco

The electricity coming from Akossombo is used in the aluminium’s production processus. The aluminium come from an ore called « bauxite ». First, the bauxite is extracted, then it is transformed in alumina powder bought by Valco to Tema.

Carbon anodes

To make aluminium, they need again carbon anodes which serve for the electrolysis.
The carbon anodes are carbon blocks made on the spot. They heat the carbon to pure it and they put coper bars into them in order to let the electricity pass through.


The electrolysis, what a complicated word. It is an electro-chimical reaction between the alumina powder and the carbon. The alumina and the carbon anoder are closed together in the machine.
An electrical current pass through the anodes breaking the bound between aluminium and oxygen.
The oxygen goes with carbon making Co2 which is driven off as gaz.

Al O + C —> Al + CO2

Now they take the aluminium in liquid form at the botom of the cell and cool it down so as to mold it. After this step, tha aluminium is ready to be sold. The final product can take several forms : soda can, hoses, kitchen paper etc.

III. The sustainable development

environemental aspect :

The CO2 rejected in the air pollutes a lot so they don’t respect the environnemental pillar but they search to reduce their carbon print, there is even actually a departement in charge of that in the factory.

economical pillar :

The factory earns money, different aluminiums and they sell it to different markets (local, international) they export their production.

social aspect :

The security is really hight in the factory. Valco contributes to the ghana’s development. It build schools for the national education, hospitals for their workers and for the ghana’s people. Valco creates associations, organizes visites for students like us, employ local laybour etc. They offer also a social security ans an acess to the medical care to each employer and his family.

As we’ve seen, Valco doesn’t observe all the pillars of the sustainable developpement. They reinvest particulary in the social. We concluede that Valco is not a sustainable project.



Kpong Irrigation Scheme

When we went to Ghana, we visited Kpong Irrigation Scheme, which is a state project of Ghana Irrigation development Authority.
As you can see, the field is really wide : it’s about 3500 acres.
They grow rice and bananas and they do aquaculture too. In fact, rice takes more than the half of the field : 2000 acres

The production of the rice needs an important amount of water. To meet this need, they use water from the Kpong Dam. It produces electricity, then the Kpong scheme produce foods and electricity. So it respects the economic pillar.

After to make the water flow faster they made syphons. It creates a difference of level between the party where the water enters and exits. Then when it restores the level, with the gravity power, the water flows faster. This party shows the environmental pillar : the Kpong administration chose the syphons a machine, which needs only mechanical energy to pump, which needs electric energy.

As you can see here, these lines are in fact waterway used to uniformly distribute because the rice have to be submerged by water to grow.
To be harvest the rice need 5 to 6 month. Three weeks before the harvest, the water is drained.
The panniculus are cut with a sickle and dried by the sun.
Finally, this machine takes out the external rice protection and workers pack the rice into plastic bag.
During this process, we saw lot of workers and farmers. Kpong creates 2500 jobs just for the rice. They give between 0.2 and 0,02 acres to the farmers. Kpong respond to the social pillar : with this job people can feed their family and take their children at school to develop the country.

Kpong Irrigation also produces Bananas. And Banana production is called "golden exotic". In the background of this picture, we can see the plantation, is about 1500 acres for 2000 workers. They export their bananas all over the world for example in Ivory Coast or in Senegal.
As you have understood this project creates jobs.

In this picture, you can see how bananas are transported after their growth. Blue plastic bags cover bananas ; they use them in order to protect bananas from the sun so it doesn’t ripen. One spot and the banana is throw away, they have to be in good state so as to export them

This picture shows men who are washing bananas ; they only use water to wash them. The growth of these bananas is ecological cause they don’t use any pesticides but the treatment is done with chlorine. So its mean that the environment pillar is not totally respected.
And when we were there, we noticed that it smelled like bleach.

Here we can see the garbage they are used as natural fertilizers, in order to respect the environment

Finally this project is totally base in the sustainable development. Because all of the important pillars of it are found. But unfortunaly they are not totally respected, some aspect are and others aren’t.
It’s even the case of all companies, which try to the sustainable development.

Documents joints

GTP Woodin


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