The presently disclosed subject matter relates to an industrial system for processing various plant materials to produce marketable materials. Particularly, the system integrates subcritical water extraction technology and includes a pre-processing module and a two-stage extractor (processing module) with constant control of temperature, pressure, and/or residence time. In some embodiments, the final product of the disclosed system can include feedstock constituents for biofuel production (sugars and/or oil), biochar, raw materials for various industries (such as pulp for manufacturing paper or cellulose for use in various industries). The disclosed system can be modular or non-modular, stationary or mobile, and can include prefabricated elements with programmed automatic or manual operation so that it can be easily moved and/or assembled on site.