Time-Lag Models for Continuous Stirred Tank and Plug Flow Digesters for Biogas Production

This work presents time-lag models for biogas production from anaerobic digestion of organic wastes in continuous stirred tank and plug flow digesters. The models have the ability of predicting the sigmoid nature of the volumetric rate of production of biogas with process time that is observed experimentally. The models are calibrated against experimental data on biogas production by anaerobic digestion of mixed vegetable wastes in a compartmental digester. The quality of fit of the models to these data is satisfactory (average root-mean-square error = 9.2%). However, the PFR time-lag model is a better representative of the compartmental digester than the CSTR lag model. The time-lag models have a simple mathematical form whose parameters can be estimated easily and they should be useful for correlating biogas yield with process time, and hence in formulating control schemes for an existing anaerobic digester.