Abstract
The wastewater from a wood‐processing factory is characterized by a high COD, chlorides and nitrogen content. Various treatment processes were applied to treat this wastewater in pilot‐scale units. By applying one‐stage denitrification–activated sludge biological treatment it was not possible to remove nitrogen. Nitrification was inhibited by wastewater compounds. By applying a second stage of a nitrification biofilter it was possible to have a high degree of nitrification. The denitrification was complete. With biological methods the reduction of COD, and ${\bf NO_{3}^{-}}$‐N and ${\bf NH_{4}^{+}}$‐N concentrations to acceptable values was not achievable. Physical–Chemical methods as H~2~O~2~/UV, electrolysis and ozonation were used as post‐treatment of effluents from the biological system. Radical degradation, initiated by the powerful hydroxyl radicals which are generated from H~2~O~2~ by UV activation, is used for wastewater post‐treatment. The combination of H~2~O~2~/UV was not suitable for post‐treatment of this wastewater. With electrolysis, ${\bf NH_{4}^{+}}$‐N and COD removal can be complete. The total amount of ammonia and organic nitrogen converted to nitrate nitrogen for current density of 1.15 Adm^−2^ and energy consumption of 71.6 kWhm^−3^ was 0.35 gdm^−3^. Further biological denitrification is required for ${\bf NO_{3}^{-}}$‐N removal to permitted values. Energy consumption for the elimination of 1 kg COD was 40.4 kWh and 35.8 kWh for current densities of 0.7 Adm^−2^ and 1.15 Adm^−2^ respectively. The energy required to reach the limit value of COD equal to 150 mgdm^−3^ for current density of 1.15 Adm^−2^ was 71.6 kWhm^−3^. With ozonation, the COD removal can be complete. Further biological nitrification–denitrification is required to remove ${\bf NH_{4}^{+}}$‐N and ${\bf NO_{3}^{-}}$‐N to permitted values. At pH 7.0, in order to reach the limit value of COD equal to 150 mgdm^−3^, specific ozone dose was 6.0 g per g of COD removed and the total amount of ammonia and organic nitrogen converted to nitrate nitrogen was 0.25 gdm^−3^. The total equivalent energy required is estimated to be 75.0 kWhm^−3^.
© 2001 Society of Chemical Industry