A Review on the Rheological Behavior of Organic Waste for CFD Modeling of Flows in Anaerobic Reactors

Abstract

Anaerobic digestion is a widely used process for organic waste treatment and renewable energy production. This is a complex natural biodegradation of organic matter involving four main biochemical reactions through the action of four microbial groups. The performances of anaerobic digestion (biodegradation and biogas production) depend on the contact between the biodegradable materials and the micro-organisms. Consequently, hydrodynamics phenomena have a significant impact on the anaerobic digestion. Computational Fluid Dynamics (CFD) simulations allow to simulate the flow field within anaerobic digesters. In these models, the waste are characterized by their physical properties, specifically their rheological properties. Rheology consists in the study of the flow of liquids or viscous materials. In this respect, it involves the properties related to the flow behavior of liquids and the temporary and/or permanent deformation of materials. The knowledge on the rheological properties of the biowaste is crucial in order to describe the flows using CFD models. The aim of this review is to present the physical properties of different type of waste, as well as the rheological models. In conclusion, the rheological behaviors of wastewater, manure, and sludge are described in literature. However the rheological behaviors of a mix of biowaste and solid food waste are poorly known. Research should focus on the experimental measurements of these biowaste. These data are necessary for CFD modeling of flows in anaerobic reactors treating this type of waste. Graphical Abstract