Chemical industrial wastewater treated by combined biological and chemical oxidation process

Wastewaters from phenol and rubber synthesis were treated by the activated sludge process in a large-scale chemical factory in Shanghai, but the final effluent quality cannot conform with the local discharge limit without using river water for dilution. Therefore, this chemical factory had to upgrade its wastewater treatment plant. To fully use the present buildings and equipment during upgrading of the chemical factory's wastewater treatment plant and to save operation costs, a sequential biological pre-treatement, chemical oxidation, and biological post-treatment (or BCB for short) process had been proposed and investigated in a pilot trial. The pilot trial results showed that about 80% COD in the chemical wastewater could be removed through anoxic and aerobic degradation in the biological pre-treatement section, and the residual COD in the effluent of the biological pre-treatment section belongs to refractory chemicals which cannot be removed by the normal biological process. The refractory chemicals were partial oxidized using Fenton's reagent in the chemical oxidation section to improve their biodegradability; subsequently the wastewater was treated by the SBR process in the biological post-treatment section. The final effluent COD reached the first grade discharge limit (<100 mg l⁻¹) of Chinese Notational Integrated Wastewater Discharge Standard (GB8978-1996) even if without using any dilution water. Compared with the original dilution and biological process, the operation cost of the BCB process increased by about 0.5 yuan (RMB) per cubic metre wastewater, but about 1,240,000 m³ a⁻¹ dilution water could be saved and the COD emission could be cut down by 112 tonne each year.