Optimizing anaerobic digestion performance with silo-shaped reactor configurations

This paper emphasizes the positive attributes of egg-shaped and silo-shaped digester with a roughly 1:1 height:diameter aspect ratio. This tank configuration has the positive attributes of an egg-shaped digester but typically costs less to construct, and has a relatively large liquid/gas surface area as compared to egg-shapes. As compared to pancake shape digesters, other potential benefits associated with a silo-shaped digester are:Decreases required mixing energy.The smaller diameter of a silo-shaped digester allows for a steep cone bottom with a 1:1 slope. A steep cone bottom and lower mixing energy allow high density material, such as grit, to settle to the bottom where it can be transferred out of the process. This results in a mixing system design that is optimized for digestion process requirements, and inherently more energy efficient.Minimizes potential foaming as compared to pancake digesters; pancake shaped digesters require excessive mixing energy to suspend and move grit from the tank; over-mixing has been shown to cause digester foaming.Minimal liquid/gas surface area (as compared to pancakes) allows transfer of low density material from the surface, which mitigates biogas hold-up; while regular grit removal from the steep bottom cone eliminates grit accumulation in digesters.Since the tank only needs to be taken out of service infrequently for inspection, process sizing and redundancy approach can be more aggressive.Silos have more construction material options, which can further reduce system capital cost.