(91h) Biodegradability of Alkaline Wastewater in Refinery

Alkaline wastewater containing high concentrations of COD, phenol, sulfides and salts, etc. in oil refinery is difficult to biodegrade and a great harm to environment. Main methods of alkaline wastewater treatment such as direct method due to prone to transferring pollution to atmospheric or elsewhere and chemical method due to high equipment investment and operating costs are restricted to a certain extent. Biological oxidation is concerned widely due to having good technical and economic value, but alkaline wastewater contains a large number of poorly biodegradable organics, or the substances of inhibiting and poisoning microbial growth, or the lack of certain nutrients required and environmental conditions etc. for microbial growth, which need a lot of experiments to examine the feasibility of biological treatment to ensure rationality and reliability of wastewater treatment options, so the treatment of alkaline wastewater has become a difficult problem in petrochemical industry and been also puzzling the development of enterprises for a long time. In this study, alkaline wastewater was pretreated by extraction of byproduct toluene from refinery, and adding nutrients (N, P elements and K⁺, Mg²⁺, Ca²⁺, Zn²⁺ salts) to wastewater after extraction, then the biodegradability of alkaline wastewater before and after pretreatment was evaluated by the methods of static (BOD₅/COD_Cr ratio method) and dynamic (Warburg breathing equipment method) determination. The results showed that the biodegradability of alkaline wastewater after pretreatment was improved significantly, and the result of static and dynamic determination was consistent, which provides a theoretical basis for biological treatment of alkaline wastewater.