**6. Local soap production**

*Elements of Bioeconomy*

**Figure 6.**

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 construc-

*Floating-drum digester. (1) Mixing tank with inlet pipe. (2) Digester. (3) Compensation tank. (4) Gasholder.* 

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

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

The digestion process is commonly designed at one of the three different

C) and

and proteins will usually have retention times higher than 30 days.

temperature zones, i.e. phsychrophilic (15–20°C), mesophilic (30–40°

tion sophistication and versatility in treating different waste materials.

*(5) Water jacket. (6) Gas pipe. Source: Arthur et al. [40].*

**96**

large surface area for bacteria to act on.

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 production in large quantity.

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 used in local soap production.

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 used for local soap production.

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

#### **Figure 7.**

*Stages in local soap production from agricultural waste. (a)–(d) represent ashing of dried cocoa pods/plantain waste in a carefully constructed metal drum, the soap production process, finished product in solid form and finished product in liquid form, respectively.*

extracted from the dried waste via ashing, i.e. burning in a partially closed environment (e.g. in a drum) so as to minimize oxygen (**Figure 7**). Clean water is used to extract potassium hydroxide from the ash. It is then concentrated and used for local soap production.

Most people prefer to make single oil soaps. Due to its relatively cheaper cost, palm kernel oil is commonly used. However, it is possible to mix two or more oils, e.g. blending 80% palm oil and 20% palm kernel oil or using 75% palm oil, 20% palm kernel oil and 5% vegetable oil so as to improve the soap quality. It is believed that the higher the ratio of palm oil and vegetable oil to that of palm kernel oil, the better the quality of the soap. The oil is poured into a steel drum and placed on a gentle fire, starting towards a slow boil. Potassium hydroxide solution is to be added gradually while keeping the heat steady for about 2–6 hours (depending on the quantity and the intensity of the applied heat). The mixture is to be stirred continually in a predetermined direction (depending on the convenience of the one doing the stirring), until it begins to solidify. At this point, the intensity of the heat should be reduced and the content removed from the fire to finish off slowly. Essential oils and/or colorant could be added as desired once the soap is finished cooking. The soap could be "picked" to release the air trapped in it from stirring. It can then be taken out and spread on a flat wooden board to dry in a cool, well-ventilated place for up to 8 hours.

The process of local soap making is very simple, straightforward and easy to understand by stakeholders (unemployed youths, women, etc.). It does not require technical details, and the method could be mastered by people who do not have formal education. More so, it could serve as a means of enhancing their livelihood and improving household income. It is generally believed to be eco-friendly, being a natural product and also friendly to the skin. Hence, the demand for the product is very high.
