**5. Biogas production**

In recent years, interest in anaerobic digestion as a management option for the disposal of organic wastes has grown considerably because of its major role in an effort to reduce greenhouse gas emission and protect the environment. The continuing use of fossil fuels is universally regarded as the principal contributor to global anthropogenic emission of GHG. It also anticipated that the fossil fuel reserves, which provide the bulk of world energy need, will be depleted in foreseeable future. In addition, the challenge of unstable fuel prices and security of the energy supply makes the call for alternative source of energy imperative. Anaerobic digestion, a proven technology for conversion of various organic wastes to biogas, is widely regarded as a source of renewable energy and technology for achieving pollution reduction.

For any nation to be self-sufficient in food production, there is the need to encourage the stakeholders to go from subsistence level where they are to intensive farming. This however has the challenge of high waste generation, particularly organic waste. The farmer/processor, etc. are therefore faced with the challenge of proper disposal of waste. However, proper management of these wastes through anaerobic digestion process could serve as an income generation venture for the stakeholders as well as cheap source of methane gas for cooking and biofertilizer from the slurry. This will save the women long hours previously spent in search of fire wood, hence, more time for their husbands and to breastfeed their children. With appropriate biogas digester for household use, agricultural and other wastes could be channeled towards generating biogas and other by-products that could be used for other purposes.

**95**

**Figure 5.**

to 20 m3

accepted not to exceed 20 m3

*(5) Gas pipe. Source: Arthur et al. [40].*

which could be between 6 and 124 m3

*The Use of Waste Management Techniques to Enhance Household Income and Reduce Urban…*

to about half a liter of diesel oil), and the solid residue (effluent) can be used as organic compost. The impurities (CO2 and H2S) should be eliminated so as to get

Biogas yields from substrates largely depend on the substrates' composition and biodigester conditions. For biodigestion of horticultural wastes on individual farm, the available designs of biodigesters that have been widely disseminated in developing countries could be employed. The available designs of biodigester unit include fixed-domed digester, floating-drum digester and low-cost bag/balloon biodigester. A fixed dome biodigester consists of a closed, dome-shaped digesting unit with a non-movable, rigid gasholder and a "compensation tank" which serves as a reservoir for displaced slurry (**Figure 5**). The gas is stored in the upper part of the digester, and the gas pressure is determined by the difference between the levels of the slurry in the digester and compensating tank. Given the high rates of biogas production from some horticultural wastes, fixed dome digesters could be an ideal option for internal storage of large volume of biogas (estimated to store up

). It also requires less space for construction and less maintenance, offers

) [41] (**Figure 6**).

A balloon biodigester consists of a digester bag with the upper part of the bag serving as gas holder. The inlet and outlet are attached to the skin of the balloon. The desired gas pressure is achieved by the elasticity of the bag or by placing a

*Fixed dome digester. (1) Mixing tank with inlet pipe. (2) Gasholder. (3) Digester. (4) Compensation tank.* 

as compared with the volume of fixed dome digester

self-agitation of slurry and is durable. Some of its demerits include special skills required for its construction and challenge of maintaining a stable gas pressures. Floating-drum digester consists of an underground digester and a moving gasholder. The gasholder floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in the gas drum, which rises or moves down, according to the amount of gas stored. Though it is durable, easy to maintain and offers steady gas pressure, floating-drum digester may not be an ideal option for large farms where the rate of waste generation may inappropriately be higher than the handling capacity of floating dome digester (the digester volume is generally

Properly designed biogas digester will accept highly digestible organic materials such as kitchen waste and other starchy/sugary feedstock (waste/spoilt grain, overripe/rotten fruits and vegetables, nonedible seeds, fruits and rhizomes, etc.). Biogas digester takes organic material (feedstock), with animal waste as an inoculant, into an air-tight tank carefully designed container where bacteria break down the material and release biogas—a mixture of mainly methane (CH4) (50–70%) and carbon dioxide (CO2) (30–40%) with low amount of hydrogen sulphide (H2S). The biogas can be burned as a fuel, for cooking or other purposes (the calorific value of biogas

(20 mega joule), which corresponds

*DOI: http://dx.doi.org/10.5772/intechopen.85580*

has been estimated to be about 6 kWh/m3

good quality methane gas for cooking.

#### *The Use of Waste Management Techniques to Enhance Household Income and Reduce Urban… DOI: http://dx.doi.org/10.5772/intechopen.85580*

Properly designed biogas digester will accept highly digestible organic materials such as kitchen waste and other starchy/sugary feedstock (waste/spoilt grain, overripe/rotten fruits and vegetables, nonedible seeds, fruits and rhizomes, etc.). Biogas digester takes organic material (feedstock), with animal waste as an inoculant, into an air-tight tank carefully designed container where bacteria break down the material and release biogas—a mixture of mainly methane (CH4) (50–70%) and carbon dioxide (CO2) (30–40%) with low amount of hydrogen sulphide (H2S). The biogas can be burned as a fuel, for cooking or other purposes (the calorific value of biogas has been estimated to be about 6 kWh/m3 (20 mega joule), which corresponds to about half a liter of diesel oil), and the solid residue (effluent) can be used as organic compost. The impurities (CO2 and H2S) should be eliminated so as to get good quality methane gas for cooking.

Biogas yields from substrates largely depend on the substrates' composition and biodigester conditions. For biodigestion of horticultural wastes on individual farm, the available designs of biodigesters that have been widely disseminated in developing countries could be employed. The available designs of biodigester unit include fixed-domed digester, floating-drum digester and low-cost bag/balloon biodigester. A fixed dome biodigester consists of a closed, dome-shaped digesting unit with a non-movable, rigid gasholder and a "compensation tank" which serves as a reservoir for displaced slurry (**Figure 5**). The gas is stored in the upper part of the digester, and the gas pressure is determined by the difference between the levels of the slurry in the digester and compensating tank. Given the high rates of biogas production from some horticultural wastes, fixed dome digesters could be an ideal option for internal storage of large volume of biogas (estimated to store up to 20 m3 ). It also requires less space for construction and less maintenance, offers self-agitation of slurry and is durable. Some of its demerits include special skills required for its construction and challenge of maintaining a stable gas pressures.

Floating-drum digester consists of an underground digester and a moving gasholder. The gasholder floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in the gas drum, which rises or moves down, according to the amount of gas stored. Though it is durable, easy to maintain and offers steady gas pressure, floating-drum digester may not be an ideal option for large farms where the rate of waste generation may inappropriately be higher than the handling capacity of floating dome digester (the digester volume is generally accepted not to exceed 20 m3 as compared with the volume of fixed dome digester which could be between 6 and 124 m3 ) [41] (**Figure 6**).

A balloon biodigester consists of a digester bag with the upper part of the bag serving as gas holder. The inlet and outlet are attached to the skin of the balloon. The desired gas pressure is achieved by the elasticity of the bag or by placing a

#### **Figure 5.**

*Fixed dome digester. (1) Mixing tank with inlet pipe. (2) Gasholder. (3) Digester. (4) Compensation tank. (5) Gas pipe. Source: Arthur et al. [40].*

*Elements of Bioeconomy*

**Figure 4.**

presented in **Figure 4**.

**5. Biogas production**

Biochar application to soil has the potential to positively improve the soil health and increase availability of both macro- and micronutrient elements in the soil. The application of biochar can decrease the Al saturation of acid soils which often is a major constraint for productive cropping in highly weathered soils of the humid tropics. Biomass production to obtain biofuels and biochar for carbon sequestration in the sol is a carbon-negative process, i.e. more CO2 is moved from the atmosphere than released, thus enabling long-term sequestration. A recent study indicated that appropriate combinations of these feed stalks will produce good fertilizer blends with optimum nutrient availability. For example, a feed stalk with plantain peels/wastes contains high content of potassium [39], while citrus waste-based biochar has higher N and P content. Biochar made from sawdust is

*Biochar made from sawdust; a and b represent milled biochar and biochar in granular form respectively.*

In recent years, interest in anaerobic digestion as a management option for the disposal of organic wastes has grown considerably because of its major role in an effort to reduce greenhouse gas emission and protect the environment. The continuing use of fossil fuels is universally regarded as the principal contributor to global anthropogenic emission of GHG. It also anticipated that the fossil fuel reserves, which provide the bulk of world energy need, will be depleted in foreseeable future. In addition, the challenge of unstable fuel prices and security of the energy supply makes the call for alternative source of energy imperative. Anaerobic digestion, a proven technology for conversion of various organic wastes to biogas, is widely regarded as a source of

renewable energy and technology for achieving pollution reduction.

For any nation to be self-sufficient in food production, there is the need to encourage the stakeholders to go from subsistence level where they are to intensive farming. This however has the challenge of high waste generation, particularly organic waste. The farmer/processor, etc. are therefore faced with the challenge of proper disposal of waste. However, proper management of these wastes through anaerobic digestion process could serve as an income generation venture for the stakeholders as well as cheap source of methane gas for cooking and biofertilizer from the slurry. This will save the women long hours previously spent in search of fire wood, hence, more time for their husbands and to breastfeed their children. With appropriate biogas digester for household use, agricultural and other wastes could be channeled towards generating biogas and other by-products that could be

**94**

used for other purposes.

#### **Figure 6.**

*Floating-drum digester. (1) Mixing tank with inlet pipe. (2) Digester. (3) Compensation tank. (4) Gasholder. (5) Water jacket. (6) Gas pipe. Source: Arthur et al. [40].*

weight on the balloon. The useful life span of balloon digester is usually between 2 and 5 years. This type of digester seems to be ideal for farm-based management of horticultural wastes due to its low installation and operational costs, low construction sophistication and versatility in treating different waste materials.

Biogas digesters described above are simple and easy to construct from locally available materials, and their operations do not require special skills. Therefore, these reasons provide technical justification for adoption of anaerobic digestion for farm-based management of horticultural wastes. The construction of biogas digesters can also help to create new jobs and help stimulate the rural economy. Biogas technology in developing countries has been based on animal dung as the only viable biogas digester feedstock. Given the higher biogas potentials of various horticultural wastes, animal dung could be co-digested with horticultural wastes, thereby promoting the paradigm shift from mono-feedstock digestion to multifeedstock digestion. This will also improve the economics of biodigester operation.

The biodigester could be operated as a batch-fed or continually fed system. For batch-fed digesters, the digesters are usually filled with substrate and left to digest over a period of time (which can be considered to be their retention) until gas production ceased. Thereafter, the digesters are emptied and fresh substrate added. Though simple in operation, the major drawback is that the process of emptying and filling is laborious. Alternatively, the digesters could be operated as continually fed system. Effluent from an existing biogas plant mixed with carefully prepared substrate can be used. The feeding of the biogas digester should be built up over a few weeks until it provides a steady supply of gas, and thereafter fresh substrate is added and digested slurry added at interval. For greater efficiency, feedstock with large lumps (more than 20 mm) should be broken up or cut to pieces to produce large surface area for bacteria to act on.

A common challenge with biogas digester that uses highly digestible organic materials is that it can become acidic and fail if it is overfed. This however can be recovered by causing feeding to cease and then start building up the feed rate slowly. An important design parameter for biogas digester is the overall loading rate. These are commonly expressed as the number of days of retention time or the quantity of organic matter applied to a given tank volume. This largely depends on the type of feedstock and digester system. Common detention times for farm-based manure digesters are roughly 20–30 days. More complex wastes that include fats and proteins will usually have retention times higher than 30 days.

**97**

*The Use of Waste Management Techniques to Enhance Household Income and Reduce Urban…*

species of bacteria that thrives at their given temperatures. The choice of appropriate temperature zone to operate is a function of the available feedstock, project site logistics, costs for heating and intended use of the digestate. Although, higher temperature systems will achieve additional pathogen destruction, more energy will be required to provide the required temperature. Lower-temperature, mesophilic systems, on the other hand, can provide the benefit of a faster-growing, more robust bacteria population than thermophilic which have slower-growing bacteria. Nigeria annual temperature is forecast to be in the range of 16–25°C in Jos Plateau area and can be as high as 44°C in the far north [42]; this indicates that most biogas digesters in Nigeria will operate well within mesophilic temperature conditions. Methane, the major constituent of biogas, is an environmentally friendly cooking system that burns with a blue flame, without producing any smoke or soot. Hence, the introduction of simple, efficient and low-cost biogas system would not only help households in finding alternative use for agricultural and other wastes but also help in preventing the hazards caused due to indoor air pollution as a result of smoke and soot from burning fuelwood in traditional cooking methods (firewood, kerosene stove, etc.), especially by women and children in rural households. The replacement of fossil fuels with environmentally friendly alternative presented by promoting biogas use will reduce the emission of greenhouse gases. The adoption of biogas production from horticultural waste will also help to promote sanitation by turning wastes that are potential public nuisances and threats to public health into

Plantain/banana is a major staple food in sub-Saharan Africa [43]. It is majorly planted in the southern part of Nigeria due to the favorable growing condition of the area. It has numerous economic values. It can be eaten raw, cooked/fried/baked or processed into other secondary products such as plantain/banana flour. It is reported to have several health benefits. Hence, there is the need to encourage its

In order to maximize the potential of plantain/banana in meeting the need of farmers and also take them beyond subsistence to commercial level of production, cultivation of large hectarage is required. In the alternative, farmers could be encouraged to form clusters (growers and processors). One of the "disadvantages" of mass production of plantain/banana is the enormous waste generation (the peels, stalk and the pseudo stem). Plantain/banana peels could be fed to livestock. However, in places where it is produced in large quantities, the "supply" is usually greater than the "demand". Hence, they are usually piled up at dumpsites where they serve as menace to the society. Apart from odor generation, it could also serve as breeding ground for vectors. These "wastes" are also very rich in potash; hence they could be

Soap is a new substance produced by the interaction of oils and alkali solution through a process known as saponification. Care must be taken to ensure that no free alkali or excessive, free oil remains in the finished product. Virtually, all wastes that are rich in potash can be used for local bath soap production. In cocoaproducing area (e.g. south-western part of Nigeria) where cocoa pods are generated in large quantities, they constitute nuisance to the environment. These can also be

Waste from different cultivars of plantain/banana, viz. peels and stalks, as well as cocoa pods could be collected, shredded and dried. Potassium hydroxide can be

C). Each of these temperature zones relies on a different

*DOI: http://dx.doi.org/10.5772/intechopen.85580*

useful organic fertilizer and feed material.

**6. Local soap production**

production in large quantity.

used in local soap production.

used for local soap production.

thermophilic (50–60°

The digestion process is commonly designed at one of the three different temperature zones, i.e. phsychrophilic (15–20°C), mesophilic (30–40° C) and *The Use of Waste Management Techniques to Enhance Household Income and Reduce Urban… DOI: http://dx.doi.org/10.5772/intechopen.85580*

thermophilic (50–60° C). Each of these temperature zones relies on a different species of bacteria that thrives at their given temperatures. The choice of appropriate temperature zone to operate is a function of the available feedstock, project site logistics, costs for heating and intended use of the digestate. Although, higher temperature systems will achieve additional pathogen destruction, more energy will be required to provide the required temperature. Lower-temperature, mesophilic systems, on the other hand, can provide the benefit of a faster-growing, more robust bacteria population than thermophilic which have slower-growing bacteria. Nigeria annual temperature is forecast to be in the range of 16–25°C in Jos Plateau area and can be as high as 44°C in the far north [42]; this indicates that most biogas digesters in Nigeria will operate well within mesophilic temperature conditions.

Methane, the major constituent of biogas, is an environmentally friendly cooking system that burns with a blue flame, without producing any smoke or soot. Hence, the introduction of simple, efficient and low-cost biogas system would not only help households in finding alternative use for agricultural and other wastes but also help in preventing the hazards caused due to indoor air pollution as a result of smoke and soot from burning fuelwood in traditional cooking methods (firewood, kerosene stove, etc.), especially by women and children in rural households. The replacement of fossil fuels with environmentally friendly alternative presented by promoting biogas use will reduce the emission of greenhouse gases. The adoption of biogas production from horticultural waste will also help to promote sanitation by turning wastes that are potential public nuisances and threats to public health into useful organic fertilizer and feed material.
