One of the most significant sectors of forest industry in Latvia is the production of wood boards, especially plywood. Latvia is the biggest producer of plywood in Eastern Europe. One of the plywood production steps is a hydrothermal treatment of birch wood. Wastewater from plywood hydrothermal pools is characterized by the high contamination level. One of the main contaminants is birch lignin, which are accountable for a color of water and high chemical oxyden demand (COD). The existent methods of biological purification of wastewater do not remove it completely. Insufficient efficiency of purification from high molecular components requires application and development of physical-chemical methods (coagulation method). Coagulation processes are used in wastewater purification and removal of colloidal admixtures and discoloration of waters containing high-molecular-weight colored compounds. The aim of this work is find optimal conditions for lignin compounds coagulation in hydrolysate of model birch wood hydrolysis in presence of aluminum salts. The received model hydrolysate imitated the wastewater from plywood hydrothermal basin. Optimal conditions of lignin compounds recovery by aluminum salts were studied by varying the dose of coagulant, pH and the temperature of model hydrolysate which are important technological parameters. The coagulation process was produced by mixing equal volumes of coagulant and model hydrolysate. The general volume of the system was 100 ml. The sample was rapidly mixed for 1 min and slowly mixed for 1 min. The aggregation stability and coagulation of lignin compounds in the presence of aluminum salts was studied by spectrophotometry. The efficiency of the coagulation in wide ranges of pH and coagulant dose was determined after 2 h of settling and filtration of the system. The method of spectrophotometry determined the remaining concentration of dissolved solids in a filtrate. COD and permanganate index were determined by total chemical oxidation of the received filtrate by adding potassium dichromate (LVS ISO 6060:1989) and potassium permanganate (LVS ISO 8467:1995), respectively. The color of the filtrate was determined by the method of photometry at the wavelength 436 nm. The results were related to Pt – Co reference solutions (ISO 7887:1994). It was established that using aluminum sulfate with the optimal dose of 340 mg/l at pH 5.0 and with the temperature of model 22°C, COD reduction is 40.1%, the dissolved solids removal 80.2% and color reduction is about 87.3%. The optimum dose and pH for aluminum chloride are 130 mg/l and 6.0, respectively, and here the decrease of COD is 45.1%, the dissolved solids removal 82.1% and 62.7% of color reduction. The recovery of lignin compounds in presence of aluminum chloride takes place at the much less doses of adding coagulant comparing the use of aluminum sulfate. Experiments at varying temperatures showed that better contaminant removal and settling were achieved at the higher temperature of models hydrolysate. The conducted experiments give the possibility to get the complete information about the efficiency of lignin compounds coagulation, and to define the more optimal parameters for purification of wastewater from hydrothermal basin of the plywood industry.