The authors would like to thank the Groupe d’Initiave pour les Energies renouvelables (GIER), The Niger Basin Authority, which is attempting to control the spread of the water hyacinth, and the UNICEF representation in Niger, an organization concerned with the welfare of mothers and children, who participated in the ﬁnancing of the project.
1The presence of the water hyacinth (Eichhornia crassipes) was noted in Niger in 1986 in a hydro-agricultural area in Niamey (Garba, 1986). Ten years later, it carpeted sections of the river running through the cities along the riverbanks. Water hyacinths cause ecological and economic problems by impeding navigation and ﬁshing activities, clogging irrigation systems and by creating a chronic shortage of dissolved oxygen harmful to the fauna and the ﬂora (Seehausen et al., 1997; Malik, 2006). Perna and Burrows (2005) noted that the water hyacinth covers on water bodies reduce the gaseous exchanges that take place at the air/water interface and reduce the photosynthetic activity of submerged plants by hindering the penetration of the sun’s rays.
2The Convention on Biological Diversity, in its article 8 (h), recommends that each contracting party take measures to prevent the introduction of exotic species and to control or to eradicate those that threaten ecosystems, habitats or species. The efforts expended by states and target communities have not succeeded in eradicating the water hyacinth from Sahelian West Africa.
3Experts in the ﬁeld believe that it is difficult to eradicate the water hyacinth, since the conditions that allow it to proliferate are not being controlled (Howard and Matindi, 2003).
4Eutrophication and an average decrease of 40 to 60% in the ﬂow of major rivers in West Africa – a result of global climate change – may be factors that contribute to the proliferation of the water hyacinth (UICN-BRAO et al., 2003).
5In Niger, the actions taken have consisted in periodic hand weeding campaigns organized by municipal authorities and associations. The Groupe d’Initiative pour les Energies Renouvelables (GIER) participates in this initiative. Given the important amount of biomass drop from water during these campaigns, it seems worthwhile to investigate potential ways of valorising that biomass Experiments involving the use of water hyacinth for the production of biogas for cooking seemed to present a viable option in the context of Sahelian countries threatened by desertiﬁcation. Indeed, biogas is an ecological fuel that may replace ﬁrewood.
6The context in which member countries of the West African Monetary Union (WAMU) ﬁnd themselves in is essentially rural and poor. The cost of petroleum products and electricity are very high considering the low level of economic activity. Therefore, the utilization of biomass to produce energy for modern use represents a good opportunity and a credible alternative (Arris et al., 2008).
7The international conference organized in Nairobi in May 2007, which was based on the theme Biogas for Better Life: An African Initiative (www.biogasafrica.org), expects to improve living conditions for women, children and the population in general by installing at least 20 million biogas facilities in the households of sub-Saharan Africa by the year 2020.
8However, regardless of the stated intentions, it still seems necessary to document the issue in the context of Sahelian countries. The objectives of the project, which have been established by a local NGO called Groupe d’Initiative pour les Energies Renouvelables (GIER), are to:
Evaluate the potential for biogas production using a combination of water hyacinth and fresh rumen residue to meet collective needs.
Test the functioning of a discontinuous-type facility (batch reactors) in real-life conditions. The discontinuous procedure is simple: the digester is ﬁlled with solid substrates – usually lignocellulosic – inoculum and water, and then hermetically sealed until the production of biogas has ceased.
9The biogas production pilot unit is located in Niamey (Latitude: 13°31 N, Longitude: 2°26 E), the capital of Niger, in a health facility that specializes in providing support for pregnant women when they give birth (maternity).
10At the peak of the water hyacinth’s invasion, the ministry of environment established a national committee in response to its spread, which raised awareness and rallied both municipal populations and authorities. Riverside populations, ﬁshing associations, NGOs, the army and several other volunteer organizations are invited to participate voluntarily in periodic campaigns of hand weeding. A portion of the hyacinths taken out of the water by people in canoes is loaded into vehicles and transported to the experimentation site.
11Depending on the feeding mode and consistency of the substrate, three main types of digestion systems can be distinguished. Discontinuous digesters (batch), which are used in this case, use solid organic substrates (lignocellulosic) submerged in a slurry of bacteria and are then hermetically sealed until the production of biogas ceases. Continuous reactors are fed with liquid substrates providing a constant output (GRET, 1979). The semi-continuous fermenter (sequencing-batch reactor) falls midway between the ﬁrst two.
12The installation is made up of six discontinuous-type digesters and three storage gasometers (Fig. 1). The digesters, buried tanks made of reinforced concrete, measure 5 m3 and were designed to provide the anaerobic environment essential for the bacterial activity that produces the biogas. The gasometer covers and hoods are built with 20/10 black sheet metal.
Figure 1. View of production digesters.
13The sizing was based on an estimate of the average wood consumption of the maternity facility and on the biogas energy equivalent of the ﬁrewood traditionally used for cooking. Twenty kilograms of ﬁrewood are needed on a daily basis. Considering that 1 cubic meter (1 m3) of biogas under normal pressure is equivalent to 2.5 kg of ﬁrewood (Bil-laud and Varagnat, 1983, N’goran, 2006), 8 m3 of biogas are needed per day to meet the needs of the maternity facility.
14Experiments were carried out during the cool season (20– 30°C) and the warm season (30–40°C) and repeated three times. Three hundred kilograms dry weight of water hyacinth (300 kg), cut into small pieces of 5 to 10 cm pieces, and 1,000 kg dry weight of fresh rumen residue (3/1 ratio) were diluted in 20 m3 of liquid and introduced into the digester. The metal cover that slides into the hydraulic joint hermetically seals the mixture. The gas is collected and stored in the gasometers. The volume of biogas is measured using an ELSTER HANDEL GMBH MAINZ volumetric meter, which has a limit of detection of less than 0.0010 m3. Gas pressure is measured with a hand-crafted pressure gauge made of a 10 cm2 section of plastic tube attached (in a U-shape) to a graduated rectangular plank (Figures. 2 and 3). One extremity of the tube containing water is connected to the digester while the other is left open. Gas pressure causes the column of water to move and its displacement indicates the amount of pressure being created.
Figure 2. Biogas usage equipment.
Figure 3. Hand-crafted pressure gauge.
15The study revealed that it is possible to produce biogas from a mixture of water hyacinth and fresh rumen residue. The simplicity of the operating procedures of discontinuous-type installations (batch reactors) is an advantage for popularizing its use. Biogas is a good quality fuel that can be used as a replacement for ﬁrewood and several other energy sources. The study’s evaluation of production potential over a year revealed marked seasonal variations in biogas outﬂow.
16Figure 4 shows the kinetics of daily biogas production and the change in accumulated volume. Although biogas production began on day 8, the gas became combustible only as of day 11. As of day 48, daily production began to decline steadily. The total volume of biogas produced after 65 days was 151.4 m3, that is, 2.6 m3/ day.
Figure 4. Kinetics and cumulative production of biogas during the warm season (30–40°C).
17Figure 5 shows the daily production and accumulated volume of biogas. The reaction began to take place on day 13. The biogas became combustible on day 18. The total volume of biogas produced was 123.4 m3, that is, 1.48 m3/day. Biogas production varies with time.
Figure 5. Kinetics and cumulative production of biogas during the cool season (20–30°C).
18The basic hypothesis of this study, which consists in exploring the possibility of producing biogas with water hyacinth and using it, instead of ﬁrewood for cooking, has been proven, as conﬁrmed by certain authors (Chanakya et al., 1993; Kivaisi and Mtila, 1998; Singhal and Rai, 2003; Kumar, 2005). In this study, Biogas outﬂow is clearly related to seasonal variations in temperature. For the same retention time, the total volume of biogas obtained during the warm season is 1.8 times greater than that obtained during the cool season. However, the climate in Sahelian countries allows for year-round production of biogas with seasonal variations in ﬂow rate.
19The output of the digesters – which are buried tanks made of reinforced concrete measuring 5 m3 – allows the functioning of the system to be assessed. The output, expressed in m3 of biogas per m3 of digester per day, has been calculated at 0.52 during the warm season and 0.29 during the cool season. The mean annual output of 0.41, obtained in this study, can be compared to the results published by the Groupe de Recherche et d’Echange Technologique (Research and TechnologicalExchange Group) (GRET, 1979), which – despite the different results obtained – estimates the output of discontinuous systems to be 0.6. The output obtained in this study has been satisfactory, but can be improved by applying the appropriate pre-treatments (Ahring et al., 2001; Dearman and Bentham, 2006; Lu et al., 2007).
20The biogas produced is intended to meet the needs of a maternity facility, estimated to be 20 kg of wood per day, or 8 m3 per day of biogas. The output obtained can meet the needs of the maternity whatever the season. Based on a ratio of dry matter content varying between 5 and 7%, 300 kg/dw corresponds to approximately 5 tons of fresh biomass (Ganesh et al., 2005). Although the work involved is certainly exhausting, it will lead to a reduction in the river surface area covered by water hyacinth.
21The products obtained from the anaerobic digestion of lignocellulosic substrates are biogas and the compost that is removed from the digester at the end of the digestion process. The compost is an organic fertilizer having the appearance of farm manure and proven agronomical value.
22In the case of biogas, a loading plan per group of three digesters was implemented during the warm season to reduce the costs of resupplying.
23Revenue-generating activities should be organized to ensure that the expenses involved in operating the facility are covered. Every two months, a workforce has to be set up and canoes and vehicles rented in order to remove the water hyacinth from the river and to transport it to the experiment site. The purpose of the pilot project was also to explore how the facility could fall within the scope of local sustainable development plans. The following activities were chosen:
The selling of compost and its use to establish nurseries for fruit trees and ornamental plants to be sold to provide funding for the water hyacinth supply.
The organization of educational training activities using the facility as a teaching aid for environmental education. To be effective, the environmental education process must be able to bring attention to environmental problems, to explain the facts and to propose solutions.
24It must be noted that this is a one-time experimental pilot project, the results of which can help in the decision-making process. With this project, the main constraint, once the facility was set up, was to ensure that a constant supply of water hyacinth was maintained, as there was a transportation shortage.
25Operation requirements become actual constraints only once they are brought into a given socio-economic environment. In terms of promoting biogas as a source of sustainable energy for small communities, a conscious commitment on the part of populations seems to be a determining factor.
26It is essential that, the community should be directly involved, particularly women who have to carry out this new idea. In fact, women are commonly in charge of ﬁrewood issues in the sahelian community. It is important that they feel that the short, medium and long-term economic, ecological and social beneﬁts will contribute to the reduction of poverty.
27The costs of building and purchasing of peripheral equipment for the experimental pilot unit, which are entirely ﬁnanced by the UNICEF representation in Niger, rose to 7,366,450 Francs CFA (11,230 Euros at the given rates on 15 December 2008). Cost remains a limiting factor in the creation of this type of infrastructure that local artisans have the knowledge to develop.
28In the Sahelian context, it would be sensible to focus on farms and agricultural co-operatives to spread the concept of biogas use for domestic and collective purposes. To promote the use of the water hyacinth, the supply constraints can be resolved by setting up the facility close to the raw material source and by including the project in the promotion of vegetable crops. The cost of ﬁrewood and the subsidies on butane gas – under the WAMU (West African Monetary Union) – which biogas should replace, also bear on the proﬁtability of biogas facilities.
29The use of biogas is an instrument to reduce greenhouse gas emissions. The Kyoto protocol contains international monetary mechanisms to provide an incentive for greenhouse gas reductions. Amongst those mechanisms a semi-column ecological taxes, ﬁnancial incentives, emission quota and tradable permits, allow to reduce CO2 emissions at a lesser cost (Mariéthoz, 2000). In this context, the Clean Development Mechanism (CDM) allows developing countries to sell CO2 credits to industrialised countries subjected to emission targets under the Kyoto protocol. The CDM contributes to the reduction of CO2 emissions and to a ﬁnancial inﬂux and technology transfer to the beneﬁt of developing countries (Mariéthoz, 2000).
30The study has shown that discontinuous-type facilities are able to produce biogas from a mixture of water hyacinth and fresh rumen residue to meet collective needs in cooking energy. The facility’s yield, reported in m3 of biogas per m3 of digester per day, has been 0.52 during the warm season and 0.29 during the cool season. Although the yields have been quite satisfactory, they can be improved by applying the appropriate pretreatments. The facility can save 7.3 tonnes of ﬁrewood per year. Promoting the use of biogas will contribute to the ﬁght against desertiﬁcation.
31Using the water hyacinth as a substrate for the production of biogas is an advantageous control strategy because it permits a “productive ﬁght” against the plant’s invasion. The stock, which is available in a given space and time, is renewable, and all of the harvested plants are replenished within a growing season.
32Issues involving the recovery of biomass energy and the decisions concerning the promotion of biogas technology in order to replace ﬁrewood should be discussed in the general framework of the economy of the sahelian countries. Finding a reliable alternative to the excessive use of ﬁrewood to ﬁght desertiﬁcation and restore soil fertility continues to pose a challenge that the promotion of methane fermentation technology might help resolve.
33The creation of a biogas market, led by private contractors, will most likely contribute to the popularization of biogas technology for domestic purposes. The digester is just a small part of the whole system, which encompasses, on the one hand, the harvesting and processing of the raw material (water hyacinth, plant residues, organic urban waste, etc.) and on the other, the management of the ﬁnished products: biogas and organic fertilizer. Running parallel to this process, an artisan sector for the manufacturing and repairing of the equipment that utilizes biogas will probably emerge.
34Successful popularisation of biogas is more than just a question of technological approaches focused on engineering. It must also be in line with a market dynamic towards which a “Clean Development Mechanism” (CDM) could assist in channelling the ﬁnancial ﬂow of carbon payments and technology transfer towards Africa.