naerobic digestion (AD) of biowastes is one of the most common ways to produce methane-rich biogas, which has considerable potential to replace the fossil fuel used in multiple applications, such as vehicular transportation, internal combustion engines, cogenera tion of heat and power systems and many other sys-tems. Many companies are involved in the design and construction of anaerobic digestion systems. Empiri- cal methods have been used to improve AD facilities, but these have needed time-consuming studies and construction of expensive prototype systems. On th e other hand, design and optimization of AD processes for biogas production can be enhanced via validated mathematical models. In this paper a dynamic mathe- matical model has been developed to a pilot anaerobic reactor fed dairy cow / cattle manure. The model is based upon material balances and comprises four state variables, namely biodegradable volatile solids, acid generating microbes (acidogens), methane generating microbes (methanogens) and volatile fatty acids. The model predicts the methane gas flow produced in the reactor. At the end, a sensitivity analysis is done to show how the gas flow rate, maximum reaction rate of acidogens, maximum reaction rate of methanogens, reaction rate of acidogens and reaction rate of methanogens and solid retention time, would change due to changes of some key parameters such as: reactor temperature and also reactor volume.

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