1. F. Fao, 2015. World fertilizer trends and outlook to 2018. Food and Agriculture Organization of the United Nations. Reporte. pp 53.
2. Mitigation of global warming through renewable biomass
3. Review on research achievements of biogas from anaerobic digestion
4. Potential of biogas production from farm animal waste in Malaysia
5. N. H. S. Ray, M. K. Mohanty, and R. C. Mohanty, Anaerobic digestion of kitchen wastes: biogas production and pretreatment of wastes, a review. International Journal of Scientific and Research Publications, 3–11. (2013).