A modular biomass treatment unit includes a first module having a pretreater and a first frame for transportation to and operation at a site adjacent to a solid biomass growth source. The pretreater is operable to process solid biomass to produce a plurality of solid biomass particles for conversion into a fuel or specialty chemical. The first frame supports the pretreater during transportation to and operation at the site adjacent to the solid biomass growth source. The modular biomass treatment unit can also include additional modules each comprising a reactor, a separator, and a frame for transportation to and operation at a site such as the site adjacent to the solid biomass growth source.