By Ebele Orakpo

“If Nigeria should take up this project, it stands the chance of enjoying the benefits and realising her Vision 20-20 20. We are also recommending this to Nigerians because it serves as an alternative source of cheap renewable energy. In Oakland, California, US today, 700 – 1,300 kw of electricity is generated from this project. It also yields an organic fertiliser which serves as soil conditioner.”  These were the words of three students of Infant Jesus Model Secondary School, Oron, Akwa Ibom State while speaking with Vanguard Learning on their locally made anaerobic digester.
Excerpts:

Materials:
ACCORDING to the students, anaerobic digestion of wastes not only deals with the problem of waste disposal but also land pollution, destruction of soil organisms, aquatic life etc. Speaking on the raw materials, they said they can be obtained at zero or minimal cost depending on the size of the digester.

The locally-made anaerobic digester

“For a small one like ours used for demonstration purpose, it was done at zero cost because the materials are available in our surroundings. They include plastic container, used tricep and tube, poultry/animal wastes, leaves, grasses etc. They are easily sourced and sometimes you may be paid for coming to get these wastes from people.”

Construction:
“Constructing the digester does not require educational or technological skill. Just get your plastic container and convert it to a digester by making it airtight to ensure an anaerobic condition of the system.

“To construct the digester, we made the recombination chamber using a plastic container having three openings – the feed inlet, the gas outlet and the effluent outlet. We also needed a gas delivery tube which we improvised with used tricep from our school’s clinic waste bin and finally, a gas collector which we used a tube collected from a vulcaniser. We patched the places with holes so we could collect our gas more efficiently,” said Hope Henry Ekong.

The process: Explaining the process, Richard Andem said; “Feed in your waste into the digester, allow it to decompose under favourable condition of temperature between 35 and 45 oC and a PH range of 6-8 for a retention period of 20 days after which you collect your gas (methane) and manure. The manure is pathogen-free and does not cause diseases in plants/animals.

“Anaerobic decomposition occurs in four different stages. First is hydrolysis of starch. We all know that organic matter is mainly composed of carbohydrates. Carbohydrate is hydrolysed into sugar, alcohol and aldehyde. The alcohol and aldehyde are acted upon by acetogens in a process known as acidogenesis to form fatty and amino acids. They are further acted upon by the same acetogens to produce acetic acid alongside hydrogen, ammonia and a trace amount of hydrogen sulphide.

“The methanogens act upon these to form methane and carbon dioxide. Carbon dioxide is a gas which does not burn so it is scrubbed off in the scrubbing unit containing sodium hydroxide. Hydrogen sulphide is a very dangerous greenhouse gas but we inhibit its production by adding iron (II) chloride to the medium. The hydrogen sulphide reacts with iron (II) chloride to form iron (II) sulphide which is very essential to the growth of plants.”

From right: Hope Ekong, Richard Andem, Perfect  Enerson.

Advantages:
On the advantages of the products of anaerobic digestion, Perfect Enerson said; “Anaerobic digestion has a lot of advantages and it can be applied in several areas of life for different purposes. It could be applied as a waste management process, a cheap alternative energy source and a soil conditioner as it yields pathogen-free manure which is very friendly to soil organisms and  plants.

“The manure has advantages over chemical fertilizer. One, it prevents leeching because of its high water-holding capacity unlike chemical fertiliser; it is not toxic to plants and soil organisms. The advantage over ordinary livestock waste is that it does not have odour so no handling problems. and it doesn’t contain pathogens.”

Electricity generation:
“The methane gas is used to heat up water to produce steam which turns the turbines for electricity production,” said Richard.

The students recommended the project to governments and individuals saying it will address some of the energy, environment and agricultural issues. “This is a safe way of managing organic waste because currently in countries like the UK, Germany and Denmark, anaerobic digestion has  received great attention because government policies in these countries kick against indiscriminate disposal of organic wastes. As a result, household ownership of anaerobic digesters has increased in these countries.

“Our project is environment, economically and agriculturally-friendly, cost-efficient and leaves no waste as residue. It is interesting to know that the UN Clean Development Mechanism is giving financial assistance to countries that are carrying out this project if only they can show they have reduced carbon emission. Ours has even turned the carbon into a raw material for the soap industry.”