Does the semi-continuous activated sludge (SCAS) test predict removal in secondary treatment?

The semi-continuous activated sludge (SCAS) test was formalized by the U.S. Soap and Detergent Association in 1965. The SCAS procedure has also been adopted by the Organization for Economic Cooperation and Development (OECD) as a test for inherent biodegradability and by the U.S. EPA as a test guideline (40CFR 835.3120) under the Toxic Substances Control Act. To investigate whether the SCAS test may be used to predict removal in full-scale activated sludge treatment systems, we first collected all available SCAS data for organic chemicals, and then retrieved data from full-, pilot- or bench-scale continuous-feed activated sludge (CAS) studies for the chemicals that had SCAS data. The intersected file was subjected to statistical analysis. Conclusions were as follows: (i) SCAS data were strongly clustered at high (> 90 %) removal; (ii) for SCAS removal > 90 %, it is probable that removal in the field will be > 50 %; (iii) however, for SCAS removal < 90 % adequate treatability cannot be predicted with confidence.