Identification of Granular Sludge Wash-out Origin Inside an Upflow Industrial-scale Biogas Reactor by the Three-phase Flow Model

Up-flow anaerobic wastewater treatment systems are popular in food and agro-industries due to their energy production potential. In order to achieve the maximum biogas production, factors of operation and design need to be concerned. The biogas plant of a cassava starch factory in Eastern Thailand is facing the problems of granular sludge wash-out and insufficient mixing. This work aimed to identify the cause of granular sludge wash-out inside an industrial-scale biogas reactor using computational fluid dynamics (CFD) model. The 3-phase flow model was validated with experiments. Simulations were performed under the wastewater feeding rate of 1,200 m3/d, representing the peak load. Simulation results showed the possibility of sludge accumulation within the distribution pipe. The inlet orifices adjacent to the reactor wall caused the excess axial-momentum transfer. It accelerated the liquid up-flow velocity overcoming 0.0315 m/s of the granular sludge's terminal velocity. The granular sludge wash-out was promoted.