Combined methods for the treatment of a typical hardwood soaking basin wastewater from plywood industry

In this research, various combinations of physicochemical (coagulation, Fenton process and ozonation) and biological (aerobic oxidation) treatment methods were used to purify wastewater originating from wood soaking basins in plywood production industry. Although the wastewater has good biodegradability (92 %), there is a high fraction of organic material expressed as recalcitrant chemical oxygen demand (COD) of approximately 360 mg L-1. High fraction of organics is caused by woodoriginating water-soluble material, i.e. extractives, including lignin and tannins. It was found that optimal treatment method for hardwood soaking basin wastewater is the combination of biological pre-treatment, chemical treatment with Fenton reagent and biological post-treatment. Under optimal conditions of combined process performance, up to 99 % removal of the organic loads, nitrogen and phenols was achieved. Besides achieving target discharge limits stated for industrial wastewater, the effluent met the requirements set for municipal wastewater treatment plants, making the treated water acceptable for subsequent discharge into natural water bodies: treated water COD = 90 ± 3 mg L-1; BOD7 = 10 ± 1 mg L-1. The main result of the present work was the establishment of sustainable, efficient and economically feasible process to treat the wastewater with minimised chemicals consumption. This differs considerably from approaches such as coagulation or wet oxidation, used to treat similar water types according to the literature, and is readily applicable for the production facilities of various scales, including small and medium enterprises, without the need to make changes in existing technological schemes.