Linkage of kinetic parameters with process parameters and operational conditions during anaerobic digestion

Kinetic characteristics play an important role in anaerobic digestion system for representing biogas production performance, however, its relationship with anaerobic digestion process parameters (i. e., volatile fatty acids, total ammonia nitrogen, pH and total alkalinity) and operational conditions remains poorly understood. To illustrate the linkage of kinetic parameters with process parameters and swine manure content and initial pH, and the effects of swine manure content and initial pH on anaerobic digestion performance, substrate properties, accumulative biogas production, specific biogas production rate and process parameters were analyzed under different treatments. Additionally, the effects of swine manure and initial pH on hydrolysis constant, lag phase, biogas production potential and the maximum biogas production rate were investigated. The results revealed that volatile solid and C:N ratio were significantly decreased with swine manure content increased which were considered as operational conditions with initial pH following the linkage illustration. Furthermore, accumulative biogas production, biogas production rate, final pH, total ammonia nitrogen and hydrolysis constant were increased with swine manure content and initial pH increased, while volatile fatty acids and lag phase showed the opposite trend. The results showed that these operational conditions significantly influenced process parameters and kinetic parameters, with close correlations were observed. Lag phase closely correlated with VFA which was closely correlated with C:N ratio. Therefore, C:N ratio impacted kinetic parameters via effecting VFA, while initial pH directly influenced kinetic parameters. Meanwhile, the correlation of kinetic parameters with C:N ratio was stronger than initial pH. Therefore, C:N ratio should be an indicator for estimating process performance, time the bacteria's acclimatization to the new environment and biogas production. Taken together, these findings provide a scientific theory for estimating anaerobic digestion performance.