Design concepts for biological treatment of industrial wastewater



Wastewater treatment systems have an operating envelope bounded by upper and lower operating limits. The design criteria should therefore include upper and lower operating limits. Upper limits are generally dictated by the effluent permit, whereas lower limits are the result of design. The design challenge for an industrial wastewater treatment system is to create a process which is capable of responding to extreme variations in flow and pollutant concentration, yet maintain the effluent within permit limitations. Industrial wastewater is contaminated with oil, aromatics, ammonia, phenols, sulfide, and heavy metals. Because the operating loads (flow, pollutant concentration, toxics, pH, and salinity) are largely unpredictable, maximum flexibility and controllability should be incorporated into the design. Since the heart of the wastewater treating system is the biological oxidation process, particular attention should be given to its specifications. A biological oxidation system that is too large can cause as many problems as one that is too small. This paper focuses on design considerations for the activated sludge process for industrial wastewater.

Case Study 1 is an example of how to design a grass roots wastewater treatment plant for a new refinery. This design provides for the maximum efficiency and operability within permit limits. However, Case Study 2 is an example of how not to design an industrial wastewater treatment plant. Typically wastewater treatment systems like Case Study 2 are over-designed, which causes many operability problems that lead to permit excursions.