Modelling the perturbation effects of the chicken litter overloading shocks on long-term semicontinuous anaerobic digesters

Abstract

Chemical composition and mass flow inlet play a vital role in a successful anaerobic digestion process; if both are kept constant in a continuous process, methane production can be achieved. Thus, one of the main concerns in full-scale processes is the overloading shock. That can unbalance trophic pathways, resulting in the accumulation of volatile fatty acids (VFA). Depending on the disturbance severity, it can lead to digester failure. Mathematical modelling applied to biological systems provides insights and alternatives for overcoming these hurdles. In this context, the Anaerobic Digestion Model number 1 was implemented in the present work to simulate organic overloading shocks. The objective was to propose kinetic parameter values which allow description and understanding of a perturbed system. Two 10 L mesophilic anaerobic digesters working in a semi continuous mode, A and B, were treated under the same operational conditions for data collection. The digesters were submitted to two organic overloading pulses with a long time in between for recovery. VFAs, pH, and specific methanogenic activity (SMA) were used to monitor the digesters’ performance. A standard differential evolution algorithm (DEA) was used for calibrating 28 biochemical parameters. Calibration was obtained using just the data of the first perturbation of digester A. Biochemical parameters related to the degradation of VFAs showed the most significant changes (i.e., Km,c4 from 20 to 4.92; Km,pro from 30 to 2.17; km,ac from 8 to 5.24; km,h2 from 35 to 10.60 kgCOD●m-3 ). After calibration, the model outputs showed a better fit with experimental data regarding modeling efficiency (EF) and the agreement index (index) than standard biochemical parameters. The result showed that DEA provides a robust calibration method for simulating the response of chicken litter overloading shocks in continuous methane production processes.