**7. Conclusion**

Resource overuse, climate change, and energy autonomy are challenges facing the volatile world. Biogas production and use represents a model example of the circular economy, which is an economy that *offers a path for sustainable growth amid growing energy demand and production requirements.* Anaerobic digestion is a biological process where biodegradable matter is degraded by the action of microorganisms in absence of oxygen to produce biogas, which is a clean fuel from renewable feedstocks with potential use in heat and electricity generation. Factors affecting bio digestion include type of raw materials, temperature, pH, mixing, level preparation and pretreatment, residence time, redox effect, and hydraulic pressure etc. The efficiency of anaerobic digestion can be evaluated in terms of bio-methane potential, gross energy yields, process energy demand, net energy yield, and energy efficiency. Energy crops are the most used substrate for biogas production.

Concerns about greenhouse gas emissions and depletion of fossil fuels have increased demand for sustainable renewable sources. Biogas production is one of the innovative and viable methods for production of energy from biowastes and biomaterials, with an extra benefit of producing biofertilizer to support sustainable agriculture. Huge quantities of biodegradable waste are generated by humanity globally, which can pose a serious threat to human and animal health and their environment. There are many wastes disposal and treatment methods employed to avoid environmental pollution. Among the many options, anaerobic digestion is a popular nonconventional energy source used to produce renewable energy from biodegradable biomass.

Biogas is a product of the anaerobic digestion process with many applications as in generation of renewable energy. The main component of biogas with energy value is methane, but it has impurities like moisture, carbon dioxide, siloxanes, hydrogen sulfide, siloxanes, hydrocarbons, oxygen, ammonia, oxygen, carbon monoxide, and nitrogen whose presence is undesirable as they reduce the calorific value of biogas and create operational problems in the energy systems. This necessitates biogas cleaning and application of multi-stage technologies to produce upgraded biogas called biomethane. Biomethane gas is a flexible and easy to store fuel with similar properties and applications to natural gas with no need to modify any equipment settings for natural gas devices and equipment.

The factors influencing the process and quality of biogas produces include the C/N (carbon nitrogen ratio, the pH, dilution of feedstock, composition and nutritive value of feedstock, residence period, mixing and stirring, temperature, presence of toxicants, loading time, and redox conditions. The main challenges facing biogas production and use include lack of technical training on biogas production and use and lack of subsidies and incentives. Therefore, besides easy access to appropriate and affordable biogas technologies, there is a need for developing a comprehensive policy on construction and operation of biodigesters as well as utilization of biogas and sale of biogas energy products and services. Biogas education and exposure, availability of simple and affordable biodigesters, and facilitating legal and policy environment are key tools needed to increase the adoption of biogas technology and its sustainable use.

Raw or cleaned biogas that is free from harmful contaminants has significant energy value and applications. The multifunctional uses of biogas produce include the production of biofuels and renewable energies, reduction in greenhouse gas

emissions mainly methane and carbon dioxide, reduction in nuisances resulting from odors and flies associated with uncontrolled biodegrading of biomass, economic or financial savings for farmers, sustainable waste treatment and recycling of organic waste, minimization of water and air pollution, rural poverty alleviation, and better social conditions of rural or remote settlements like gender balance, as women who bear the responsibility of looking for firewood are relieved of the struggle, and conservation of forests and vegetation cover due to reduced use of firewood and charcoal.
