A biological and chemical characterization strategy for small and medium-sized industries connected to municipal sewage treatment plants

A cost‐effectives strategy for the characterization of wastewater from small and medium‐sized industries is described. A mobile laboratory, equipped for performing on‐site biological tests, was established near wastewater treatment facilities in two cities in Sweden for 1 week each in November 1992 and November 1993. The biological and chemical characterization was done on 24‐h samples from 29 industries representing 12 types of activity with a bias toward the surface treatment and graphics industries. The biological testing program included a modified nitrification test, the Microtox® test, and a modified growth inhibition test using Selenastrum capricornutum (an alga test). A Ceriodaphnia dubia (crustacean) test was also used for some industries. Different chemical assessments, aimed at indicating toxic, persistent, and bioaccumulating substances, were chosen for each industry on the basis of information they provided. Results show that sampling period and time are important factors to consider when designing a characterization strategy. Twenty‐four‐hour sampling is preferred to weekly sampling because highly toxic emissions of short duration that are detrimental to the biological treatment plant may occur. Variability in emissions was shown in this study but would not have been detected by a study based on weekly sampling. The strategy developed in this study was shown to be both a cost‐effective and efficient tool for characterizing effluents from small and medium‐sized industries.