Oil shale ash as a catalyst in wastewater treatment in the pulp and paper industry

Abstract

The pulp and paper industry is one of the largest and most polluting industries in the world, mainly due to coloration and toxicity problems in wastewaters. Wood debarking, a primary wood treatment process, produces an aqueous effluent that is currently considered as one of the most toxic wastewaters in the papermaking industry. Due to the biological toxicity of the stream debarking wastewater, which contains hardly any biodegradable lignin, is the unsolved problem for wastewater biological treatment. Wet oxidation (WO), water treatment in elevated temperatures and pressures, is an effective process for lignin destruction in debarking water. The main problems in process realization are temperature that is too high (close to 200°C), pressure that is too high and the long duration time of treatment (1.5-2 hours) for lignin degradation. The way to decrease the process temperature and pressure is to use catalytic wet oxidation (CWO). The catalytic effect of an Estonian oil shale alkaline ash (waste material of multicomponent composition forming in high quantities at heat and power production based on firing of local low-grade carbonaceous fossil fuel) in WO of lignin containing waters has been established. The composition of ash is presented. The results of CWO are compared with WO results without ash. Catalytic wet oxidation of lignin water using platinum (Pt) as the catalyst is also briefly presented. It is demonstrated that a certain amount of ash accelerates the oxidation process of organics in water; it degrades the lignins content more quickly, as well as the values of COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) in lower reaction temperatures and pressures, such as those in WO. © 2010 WIT Press.