In the past, biological treatability studies were directed toward defining effluent BOD and TSS. Recent regulations now require effluent limitations on volatile organic carbon, specific priority pollutants, aquatic toxicity and in many cases nitrogen for complex wastewaters. This, in turn, has changed the focus of biological treatability studies. It is assumed that a screening protocol has been employed to define biological treatment as a candidate process [1]. (a) Priority Pollutants-If on or more priority pollutants are a permit issue, a fed batch reactor (FBR) is run using acclimated biosolids to determine the maximum degradation rate, q(m), and the half velocity constant, K-s. From these data, the required SRT to meet effluent limitations can be computed. (b) Aquatic Toxicity-If the wastewater exhibits aquatic toxicity in addition to priority pollutant requirements, bioassays are run on the biological units. Effluent toxicity and COD are tracked with time. Since effluent toxicity is frequently associated with soluble microbial products (SMP), the SMP is estimated from the effluent COD over time of aeration. (c) Nitrogen-Many organics including SMP are inhibitory to nitrification. The nitrification. rate should be determined on the effluents using seeded NH4Cl as a control. From these data, the required SRT can be computed. This paper reviews the required protocols and presents several case histories from the chemical and pharmaceutical industry.
