Modelling Biogas Production Kinetics of Various Heavy Metals Exposed Anaerobic Fermentation Process Using Sigmoidal Growth Functions

The kinetic evaluation of the biogas potential from heavy metal stressed anaerobic fermentation process was performed using modified sigmoidal bacterial growth curve equations (modified Gompertz and Logistic) in order to investigate their suitability to describe the degradation patterns associated with varied heavy metal species and concentration. The anaerobic co-fermentation experiments were performed at mesophilic conditions with mixed cow dung andPhragmitesstraw as feedstocks. The results show that appropriate concentration of heavy metals brought forward the biogas peaks, shorten the lag-phase (lambda) and promoted the efficiency of co-fermentation. In this way, the cumulative biogas yields expressed the one-phase process and fitted the sigmoidal bacterial growth curve equations better. Both the modified Gompertz model and Logistic model were able to represent the experimental data in the presence of heavy metals as shown by the no significant different correlation coefficients (R-2). However, the discrepancies between the experimental and fitting results of the modified Gompertz model were smaller than the Logistic model which suggested that the earlier was more suitable for describing the degradation patterns under heavy metal stress. The results of this research are expected to provide theoretical guidance for studying the impact of heavy metals and modelling research of anaerobic fermentation process. Graphic abstract