There are many advantages to farming, but as in life in general, there are also some drawbacks. Farm waste, including techniques, such as recycling, reusing, composting, and energy recovery, can be used to help farmers get the best out of their farm waste.
Brian Beseni, a PhD candidate at the University of KwaZulu-Natal (KZN) specialising in nutraceuticals into medicinal, nutritional, and cosmetic marketable products, gives more insight into how waste can be managed on a farm. He is a researcher at heart with several publications focused on pharmacognosy.
Beseni shares his expertise on secondary waste management, strategies and processes that are aimed at managing farm waste that has undergone some form of treatment or processing.
Turning agricultural waste into biogas
According to Beseni, a sustainable and environmentally beneficial method of producing biogas from agricultural waste is anaerobic digestion, which transforms organic materials like animal manure, crop leftovers, and food waste into biogas
It can be done in the following ways:
- Feedstock collection: Farm waste, including animal manure, leftover crops, and agricultural residues, is collected, and stored in a designated area.
- Pre-treatment: Depending on the type of feedstock, pre-treatment may be necessary to enhance the efficiency of the digestion process. This can include shredding or grinding the waste materials to increase their surface area and improve biodegradation.
- Anaerobic digestion: The pre-treated feedstock is then loaded into an anaerobic digester, which is a sealed container or system where the decomposition of organic matter occurs in the absence of oxygen. The digester can be a simple batch system or a continuous flow system.
- Biogas production: Inside the digester, microorganisms break down the organic matter through a series of biochemical reactions. This process releases methane (CH4), carbon dioxide (CO2), and small amounts of other gases collectively known as biogas. Methane is the primary component of biogas and is a valuable energy source.
- Biogas collection: The biogas produced during the anaerobic digestion process is collected and stored in a gas holder or storage tank. It can be used directly as a fuel for heating or electricity generation, or it can be upgraded and purified to produce biomethane, which is a renewable natural gas suitable for injection into the natural gas grid or use as a vehicle fuel.
- Digestate handling: After the anaerobic digestion process, the remaining material, called digestate, is rich in nutrients and can be used as a high-quality fertiliser for agricultural purposes. It is often separated into solid and liquid fractions, with the liquid fraction being used as a liquid fertiliser and the solid fraction used as a soil conditioner or compost.
How can farmers use biogas fertiliser?
Beseni further explains that there is no doubt that secondary waste management can be used by various kinds of farmers in the industry.
Crop farmers: Biogas fertiliser can be beneficial for crop farmers who grow a wide range of crops, including vegetables, grains, fruits, and oilseeds. The nutrients in digestate, such as nitrogen, phosphorus, and potassium, along with other micronutrients, can improve soil fertility, enhance plant growth, and increase crop yields.
Organic farmers: Organic farmers, who follow sustainable and chemical-free farming practices, can utilise biogas fertiliser as an organic alternative to synthetic fertilisers. Digestate helps meet the nutrient requirements of organic crops and contributes to maintaining soil health and long-term sustainability.
Livestock farmers: Farmers who rear livestock, such as dairy farmers, poultry farmers, or pig farmers, can benefit from using biogas fertiliser. The feedstock for biogas production often includes animal manure, which is a significant source of nutrients. The digestion process not only generates biogas but also converts the manure into a stable and nutrient-rich digestate that can be used to fertilise their fields or pastures.
Horticultural farmers: Farmers engaged in horticultural activities, including those growing fruits, vegetables, flowers, or ornamental plants, can utilise biogas fertiliser to enhance the nutrient content of their soil and improve plant growth. The balanced nutrient composition of digestate can promote healthier plants, increase yields, and improve the quality of horticultural produce.
Agroforestry farmers: Agroforestry combines agricultural crops with trees, providing a multi-functional farming system. Farmers practising agroforestry can benefit from the use of biogas fertiliser to support the growth of both agricultural crops and trees. The organic nutrients in digestate contribute to the development of a healthy agroforestry system, promoting tree growth, soil fertility, and overall ecosystem health.
Benefits of secondary waste management
According to Beseni, there is a plethora of benefits when it comes to renewable energy, waste management, and nutrient recycling, all in ways that help mitigate climate change.
“Biogas production from farm waste helps to mitigate climate change by capturing and utilising methane, a potent greenhouse gas that would otherwise be released into the atmosphere,” he says.
- Renewable energy: Biogas is a renewable energy source that can be used to generate heat and electricity, or even replace fossil fuels in vehicles.
- Waste management: Anaerobic digestion helps to effectively manage farm waste, reducing odours, pathogens, and greenhouse gas emissions associated with traditional waste disposal methods.
- Nutrient recycling: The digestate produced from the process can be used as a nutrient-rich fertiliser, closing the nutrient loop, and reducing the need for synthetic fertilisers.
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