Flow sculpting enabled anaerobic digester for energy recovery from low-solid content waste

Abstract

Traditionally, energy recovery from low-solid-content wastes occurs in Continuously Stirred Tank Reactors, whereas Plug Flow Reactors (PFR) are used to treat high-solid-content wastes. In comparison, this study uses a special configuration of anaerobic PFR (AnPFR), consisting of a coiled tubular structure, for energy recovery from a mixture of Food Waste and Wastewater, fed at a loading rate of 3 gVS.L−1.d−1 and a solids content of 2.5%. The AnPFR was upgraded into a Flow Sculpting enabled Anaerobic Digester (FSAD), an innovative plug flow design relying on flow sculpting via a sequence of pillars to provide passive mixing. The purpose of the FSAD design is to optimize operational performance while maintaining minimum mixing energy requirements. Computational fluid dynamics simulations revealed that pillars induce local vorticity in the fluid and contribute to the inertial deformation of the flow to enhance mixing. Coherently, experimental results proved that upgrading the AnPFR to FSAD resulted in a better stability (VFA dropped from 4433 to 2034 mg L−1) and a higher efficiency (removal efficiencies of COD and volatile solids increased from 75% to 77%–88% and 91%, respectively). Equally important, the methane yield, indicative of energy generation potential, increased from 181 L kg VSfed−1 to 291 L kg VSfed−1.