| Popis: |
One of the most promising technologies for production of biogas from organic waste is anaerobic digestion (AD). As the experiments related to AD are time-consuming, labour intensive, and expensive, numerical simulations are important, because they provide a useful tool towards developing optimized and stable AD processes. This paper focuses on the optimization of the AD process in order to maximize biogas production from cattle manure by determining optimal values of process parameters. For this purpose, a modified mathematical model has been developed to simulate AD at various temperatures and pH values by considering appropriate inhibitions, detailed pH and temperature effects on microbial growth, and temperature dependencies of liquid-gas mass transfer coefficients, dissociation constants, and Henry’s law coefficients. This model was applied for the simulation of AD in a batch reactor and verified with experimental data. By using this model in an optimization procedure, the optimal values of pH and temperature, both acting as design variables, were determined. By engaging a gradient-based optimizer, based on an adaptive approximation method, it was shown that a reliable AD model can be used very efficiently in gradient-based optimization. The optimization process proved to be efficient, stable, and starting-point-independent; the engagement of numerical differentiation did not cause any problems. The results show that at optimal process conditions the production of CH4 is significantly improved in comparison to conditions often given in the literature. The results obtained confirm the usefulness of the proposed approach, which can easily be adapted or upgraded for complex substrates and other reactor types. |
