One of the stages of raw material preparation for plywood producing is hydrothermal treatment of birch wood. Wastewater of hydrothermal basins are characterized by the high degree of contamination, because they contain lignin and extractive substances (LES), which are responsible for the high chemical oxygen demand (COD) and the degree of water color. It is know, that reagent method for wastewater purification from difficulty oxidized organic products of wood delignification, is the most perspective direction of the wastewater treatment, because purified wastewater can be used back in basic technological cycle. Nowadays it is very important to regenerate industrial wastes with the purpose of getting the products which can be used for the second time, providing a non-waste production. Lignin isolated from wastewater of plywood plant can be of interest as a binder ingredient or surface active substance (Shulga, 2008). Chemical coagulation followed by sedimentation is probed technique for the treatment of high suspended solids wastewater especially those formed by colloidal matters. The mechanism of coagulation method is founded on the release of wastewater from dispersible admixtures by destabilization of the negatively charged colloid particles. In pursuing these aims the chemical reagents – coagulants are used. In water, these coagulants are hydrolysed with formation of slightly soluble bases, which settle LES. The main objective of the present study is to investigate the coagulation efficiencies of polyaluminium chloride (PACl) in LES removal from model solution of hydrothermal wood treatment, analyzing the change of LES content, COD and color of the initial model solution.