Stringent effluent guidelines relating to volatile organic carbon (VOC), effluent toxicity and priority pollutants require a reappraisal of design criteria for wastewater treatment plants in the chemical and petrochemical industry. In the case of volatiles, the biodegradability of the VOC as well as the type of aeration equipment needs to be considered. High temperatures in covered aeration basins can create serious sludge settling problems. Priority pollutant removal requires careful consideration of adequate sludge age. Temperature is particularly significant in reducing priority pollutants to acceptable levels.

The generation of non-degradable by-products, SMP, can create effluent toxicity problems. This may require tertiary treatment with activated carbon.