One of the most significant birch wood processing with a high added value is plywood production. If not taking into account the last year’s economic situation in the world, production and demand of plywood is increasing in Latvia and EU every year. The reaģent method of wastewater purification after wood hydrothermal hydrolysis in veneer manufacture from the released biomass (lignin, hemicelluloses and extractive substances) is one of the most perspective methods, which allows to recycle purified wastewater in technological cycle. The aim of the study was to compare the effectiveness of the biomass (BM) removal from the modei wastewater of the wood hydrothermal treatment, using separately polymer cation and inorganic salts as coagulants.