Investigation of stability of anaerobic digestion of food waste in a plug flow reactor using mathematical modeling and simulation

Abstract

Anaerobic treatment has gained wide acceptance as a sustainable technology for treatment of solid wastes and waste water. Recently, novel plug flow reactor system has been installed at few local institutions to treat semi solid wastes with improved efficiency. However lack of understanding of operational parameters and functional units of this reactor system has led to suboptimal operation and thereby low gas production and methane yield. In this study, plug flow anaerobic reactor is modeled using two modeling scenarios. For this task, Anaerobic Digestion Model No. I (ADM1) implemented in the simulation software package called AQUASIM 2. If is used. Under first scenario, advective diffusive reactor compartment followed by two continuous stirred tank reactors for collection of slurry and gas used to model the plug flow reactor. Under second was scenario, series of CSTR reactors were used to model plug flow reactor and biogas was collected into a common head space via diffusive link. Simulation was performed for the different hydraulic retention times and feed flow rates for the substrate of food waste. Simulation results from advective-diffusive reactor model revealed that accumulation of gasses in the slurry causes an inhibition in methane production. In series of CSTR model, when the food waste alone was used at low hydraulic retention times, pH decreases drastically and causes to process inhibition in the first reactor. This inhibition propagates towards the other connected CSTR reactors and after a certain periods of time total methane production ceases.