The Doctoral thesis presents a new hybrid composite coagulant and a technological method of its application that increases the efficiency of the biomass removal, especially the low molecular weight lignin fragments, from birch wood hydrothermal treatment wastewater. The biomass extracted with hybrid composite coagulant has been investigated to be able to structure dusty soils and can be used in gravel covering road dust control. Information on the wastewaters of veneer production hydrothermal treatment and the use of the coagulation/flocculation method for the separation of biomass from these wastewaters is summarized in the review of scientific literature. Currently, the most widely used coagulants/flocculants are reviewed and the right selection of composite coagulant for the separation of biomass from wood processing wastewater is justified. The information on current areas of application of wastewater sludge is summarized and, in the context of thinking about the new potential use of biomass, the methods of dust control of gravel covering roads are reviewed. Aim and tasks of the studies are formulated. The methodological part of the thesis contains description of the coagulation/flocculation process. The analysis used and testing methods are described in detail: methods for the determination and characterization of component compositon of wastewater biomass and obtained coagulates, methodology of research on coagulant/flocculant biomass removal efficiency, soil structuring research methodology. In the experimental part of the thesis, the component composition of model wastewater biomass is determined and described. Using polyelectrolyte flocculants - polidiallildimethylammonium chloride (PDADMAC), chitosan and polyethyleneimine (PEI), biomass separation regularities have been studied. The influence of the flocculation process parameters (molecular weight of the polymer, dosage, pH of the environment, temperature) on the biomass removal efficiency was determined. Based on the results obtained, PEI of a high molecular weight is selected as a base cationic polymer together with a polyvalent metal salt for the development of a new hybrid composite coagulant. The optimum mass ratio of the PEI/polyvalent metal salt in the hybrid composite coagulant, as well as the effects of hybrid coagulant dosage, environmental pH and temperature on biomass removal efficiency have been determined. The aqueous suspension of biomass coagulate has been found to be capable of structuring dusty soils and to form mechanically durable aggregates against wind erosion. An alternative of the technological solution for the separation and use of biomass from veneer production hydrothermal treatment wastewater is characterized. The Doctoral thesis is written in Latvian. Its volume is 124 pages. The work contains 82 figures, 16 tables and a list with 202 references.