Latvia is the biggest producer of plywood in Eastern Europe. One of the stages of raw material preparation for plywood producing is hydrothermal treatment of birch wood. Wastewater from plywood hydrothermal basin is characterized by the high degree of contamination. The basic contaminating component of this wastewater is lignin, which is the main reason of a high level of chemical oxygen demand (COD) and color of water. Insufficient efficiency of purification of lignin wastewater requires the development of advanced coagulation methods. It is known that the coagulation process is affected by its conditions, among which a temperature of wastewater plays a significant role. It has been assumed that the correct choice of this parameter can considerably improve the process of purification of lignin wastewater from hydrothermal basin, using chemical coagulants.