This book describes the method adapted in order to develop governing equations of bio-digester performance in classical mechanics and macro thermodynamics. Other aspect of this project is to study climatic and atmospheric effects on the plant by using case studies. Equations are developed by direct method of proof and logical deduction method on basis of experimental data. Assuming Biological process is to be correct and case studies are performed in due respect to considerable thermodynamic properties. Comparison and interpolation of experimental data and mathematical analysis at each stage appropriate corrections are suggested. We accept any sort of suggestions and criticism from readers to improve our research.