The objective of the current research is to study and develop a process where forest industry wastes are used for production of carboxylic acids. These chemicals are currently produced from fossil sources increasing the consumption of fossil raw materials. The conversion of organic matters to valuable chemicals can be done by partial oxidation of the organic molecules in wet oxidation process at elevated temperature and pressure. The produced carboxylic acids are then separated from the aqueous stream and purified to products. Separation might be based on extraction and solvent recovery, or possibly on membrane technology. From scientific viewpoint, the goal is to generate new knowledge and novel technology: (i) chemistry and kinetics of wet oxidation of organic matter, including catalysis (ii) development of novel hybrid separation methods, such as reactive extraction, membrane extraction and combined oxidation and membrane separation. From practical viewpoint, the study has both social and environmental benefits since it reduces the waste discharges to the environment, increases the efficiency of the usage of biomass in pulp and paper industry and increases the energy efficiency of chemical industry in global terms by reducing the amount of fossil raw materials used for chemical production.