Process for preparing fiber boards

A process for manufacturing fiber boards and similar wood-based products from a lignocellulosic raw material having a moisture content of at least 10 wt-%. According to the process, an aqueous fraction is separated from the fibers of the raw material, which fraction later is recycled to the process in order to form at least a part of the agent used for binding the fibers. Before mixing with the fibers, the aqueous effluent is concentrated and enzymatically oxidized in the presence of oxygen in order to polymerize the solubilized wood material and in order to increase its concentration. Lignin can be added to the water solubilized wood material or the solubilized wood material can be added to the fibers together with another binder. Eventually, the mixture is formed into a board and hardened.