A tubular plug flow digester system assembled from manufactured components, including a holding/heating tank (15) connected to a manifold (14) that feeds a single or multiple parallel injection pumps (12). These pumps force feedstock though check valves (13) and into single or parallel digester hulls. This hulls are composed of manufactured parts including tapered end sections (11) and hull sections (10) that can be assembled onsite to a configuration that accommodates operational needs. Biogas produced by this digester is pressurized due to a liquid column created by an elevated effluent outlet (25). Feedstock is inoculated with relevant microorganisms that promote the generation of methane-rich biogas. Inoculation members (26) positioned within the hulls shelter biofilms containing these microbes while allowing regions of the biofilm to slough or naturally release microbes into the flowing feedstock stream. Biogas is collected through a manifold (22) and its release is controlled by a regulator or a valve.