Transport and retention modeling of the liquid phase through a stratified porous leach-bed. Application for solid-state anaerobic co-digestion of cattle manure and roadside grass

Abstract

The recirculation flow inside the leach-bed during solid-state anaerobic co-digestion of layered cattle manure and roadside grass was characterized using three different methods on lab scale reactors. Tracing experiments and method of moments were used to characterize percolation flow properties with different leach-bed compositions and a new criterion was proposed to quantitatively evaluate the ratio between preferential pathways and dead volumes for each experiment. The impact of recirculation flow on leach-bed complexity for different moments of SS-AD and substrate layering was characterized using steady-state reactor modeling and the impact of recirculation flow on microporosity and macroporosity evolutions all along SS-AD was determined using modeling of hydrodispersive parameters. It appeared that layering and time could significantly impact percolation flow and leach-bed complexity, until 36 % of residence time variation and 110 % of leach-bed complexity. Moreover, layering could impose a different percolation flow for each layer and cause a preferential pathways disruption.