Discover five ways agricultural plant waste is sustainably recycled into usable products that are less harmful to the environment.
By Oyewole Okewole
Sustainable practices in agricultural processes and operations are poised to improve the socio-economic and environmental conditions of the stakeholders involved. It is the display of these practices that determines the true indices of agricultural developments, as sustainability guarantees the renewal of resources required for production.
One determinant of sustainability is stability in environmental conditions. Environmental resources, including climatic conditions, soil, and water, must remain constantly refreshed to operate at the needed parameters for agricultural productivity. Sadly, intensified agricultural practices since the Industrial Revolution have negatively impacted the environment. Today, agriculture contributes 11% to global greenhouse gas emissions which cause global warming. The current worldwide generation of bio-wastes from agricultural practices and forestry residues is estimated to be 140Gtyr-1 (Giga tons per year). A major factor which contributes to this is the production of waste during agricultural processes. Waste, if not properly disposed of, poses environmental threats, and in multiple folds constitutes noticeable environmental degradation.
However, through research, several ways have been provided to sustainably dispose of agricultural waste without causing any form of environmental harm. Furthermore, researchers have also indicated alternative forms that agricultural by-products can be of use again through their conversion into value-added products. Being rich in bioactive compounds, agricultural waste can be utilised as alternative feedstock sources for various production processes. They have been increasingly converted to very useful products for human utilisation that are healthy and environmentally friendly such as biogas, biofuel, biofertilisers, biodegradable packaging materials, and raw materials in various research and industries.
The once useless, environmentally degrading, unwanted materials become useful, environmentally friendly, and highly demanded products that are solving even more devastating societal challenges. They are referred to as “Wastes to Wealth” materials. This article highlights plant biomaterials and agricultural waste generated on farms. Some of the examples that fall into this category include husks, bagasse, leaves, seeds, stem, straw, stalk, shell, peels, pods, roots, etc. and they are technologically converted into eco-friendly substances.
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COCOA POD HUSKS
These are the leftover parts from harvested cocoa beans. It is the main cocoa residue after harvest. Each tonne of cocoa beans produces 10 tonnes of cocoa pod husks discarded as waste. The husks make up to three-quarters of the weight of the fruit. Cocoa pod husk can be made into flour and can be used as an ingredient in poultry, sheep and pig feed production. The flour is made by slicing the pod husks into small flakes, mincing/chipping, drying, and then milling into flour. In other processes, they can be pelletised and subsequently dried and cooled for pelletised feed.
In a study reported in 2021, cocoa pod husk flour was used as a starch replacement in Frankfurter sausage. It was revealed that the husks could be used as an additional ingredient that reduces the technological constraints and increases the stability of meat products like sausage.
In addition, the husk contains 3-4% potassium on a dry matter basis. The cocoa pod ash has been commonly used in West African countries to produce African Black soap with a global market reach. This system usually involves sun-drying and burning the husk to produce ash, which comprises 40% potassium hydroxide (potash). It therefore serves as the catalyst during the saponification process in soap making.
Husks can also be burned to generate electricity through the use of a biomass electricity plant. This is particularly useful as most of those cocoa pod-producing communities are not connected to the national grid for the supply of electricity.
BANANA TREES/PLANTS
It has been researched that almost all parts of a banana plant are beneficial including the most common part for food, the fruits. From banana peels, stems, leaves, flowers, and others the plant boasts as an extremely useful plant. While some of the processes required to convert them into other useful products might be as simple as drying, or heating, others might involve more intensified processes and technologies to convert them into more useful products.
Banana peels are used as animal feed because of their nutrient composition which is rich in energy, fibre, and other nutrients for feeding cattle. In addition, the nutrient-rich peels can be used as natural fertiliser. Stem fibres are used as natural craft materials like baskets, the use of the fine threads are blended with cotton to produce fabrics for making garments. Banana leaves are used to wrap desserts, for packing lunch and as natural leaf platters.
Banana trees’ trunks also referred to as pseudo-stems can be used to produce wooden panels and veneer rolls. One of their prominent uses is the production of specialised, high-quality sanitary products such as baby pampers, papers such as banknotes, ropes, placemats, paper cardboard, string thread, tea bags, absorbent, polymer/fibre composites and others.
The extracted fibre is another alternative material that can be used in producing sanitary pads and baby pampers. According to a report by NTVUganda, the fibre is chopped and soaked in water with recommended quantities of sodium hydroxide to soften the fibre material. Usually, white recycled paper is soaked, pounded and added to the mix and all heated to give it a bright colour. The heated mixture is poured into a measured quantity of water where sieves or nets are dipped into the mixture. The mix is then stuck to the surface of the nets and dried appropriately. The dried parts are scraped out and then softened using a roller machine. The softened paper is then mixed with other materials including cotton wool to make the biodegradable sanitary pads.
In producing ropes, especially marine ropes because the fibre exhibits good resistance to seawater, the fibres are extracted from the pseudo-stem leaves by a decorticator. A decorticator is a machine used to strip bark, skin, wood, etc. The loosening of the fiber bundles as reported is followed by the retting and tuxing process. The fibres are subsequently washed and dried while the degumming process removes the foreign matter. They are afterwards manually weaved into ropes or through mechanised equipment.
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SUGARCANE AND SORGHUM BAGASSE
Various value-added bio-products through technologies have been developed for the utilisation of sugarcane bagasse wastes. They have been used in the production of fuels and energy, biodegradable material, construction and bio adsorbents. The sugarcane bagasse ash is used as a cement replacement for the production of sustainable concrete. The ash is used to replace cement which is the most energy-intensive material produced in the world, next only to steel and aluminium, which heavily contributes to the emission of greenhouse gases. The concept of supplementary cementations as reported is used in order to minimise the carbon dioxide emissions from cement production. Agricultural wastes like sugar cane bagasse ash are being used as a partial replacement for cement. They enhance the durability and strength properties of the concrete when used in high-performance concrete.
On the part of Sorghum bagasse, due to its high cellulose content, it is utilised for bioethanol production. The process technology involves milling, gelatinisation, saccharification, fermentation and distillation. It was also reported that it can also be used for paper production. Usually, cellulolytic materials are used for paper production, however, the properties of the paper products vary depending on the morphological characteristics of the fibres used. Sorghum bagasse usage in paper production is beneficial as it reduces greenhouse gas emissions as less energy is demanded and utilised for pulping. It is also eco-friendly, as fewer trees are fell for paper production. The technological process involves the removal of the soft inner portion, of the bagasse and then slicing to about an inch in length. The sliced material is treated with sodium hydroxide solution, cooked for about four hours, and subsequently washed to remove the slippery texture. This treated bagasse is pounded and then bleached to produce different colours of paper and pulp being prepared. The slurry is then moulded into form while water is drained gradually until the sheets are formed.
PINEAPPLE CROWNS AND PEELS
Research indicated that the pineapple industry produces a substantial quantity of solid waste which constitutes about 75-80% of the fruit. They include peels, the core, and the crown. The pineapple peel is very rich in hemicelluloses cellulose, and other carbohydrates and can be utilised effectively in the production of paper. Pineapple wastes discarded in landfills can be used as an excellent bioresource, especially in the production of enzymes like bromelain, used extensively in food processing for tenderising meat, brewing, and preventing browning in baking. They are also used for making antioxidants, ethanol, vinegar, organic acids, and many more.
Piñatex is a sustainable textile material made from pineapple waste used for fashion and manufacturing furnishings made from pineapple leaves. It was discovered by London-based design studio, Ananas Anam. The leaves are processed to extract the fibre and subsequently transformed into the substrate. Piñatex is composed of 80% pineapple leaf fibre and 20% polylactic acid- a thermoplastic polymer.
COCONUT HUSKS
Improper disposal of coconut husks results in soil and water pollution, they become environmental nuisance and produce greenhouse gas emissions. Coir is a natural fibre extracted from the husk of coconut. It possesses a golden colour when cleaned. after removing from the coconut husks. It is also known as “The Golden Fibre”. They are immensely useful in making, floor and outdoor mats, aquarium filters, water prurification, twine, rope, erosion control products, and for garden mulch and horticulture. In addition, pads of brown coir fibre can be sprayed with rubber latex. The latex bonds the fibres together to be used as upholstery padding for the automobile industry especially in Europe, also used for insulation against temperature and sound and for packaging.
It is also used as a flame retardant as it is not easily combustible. It is usually unaffected by moisture and dampness and so becomes an excellent insulator. Coconut husks are increasingly becoming exceptionally useful in various industries including aesthetics, gardening, and automobile.
In summary, many other on-farm wastes including rice and wheat straws, maize stalk and others are increasingly been adapted to environmentally friendly products. Further research is on-going at different research institutes on many on-farm agricultural wastes, their extensive use and applications.
Cover Image: Jircas
