The variability of toxic trace contaminants in influents and effluents at three full-scale municipal sewage treatment plants was measured by collecting grab samples of degritted raw wastewater and non-chlorinated secondary effluent at two hour intervals over eight consecutive days. The samples were analyzed for metals, conventional contaminants and a range of organic trace contaminants.
The metals and volatile organic compounds were the dominant contaminants found in the influents. In the effluents, organic concentrations were close to detectable levels and polyaromatic hydrocarbons were almost never detected. Some influent metal and organic contaminants varied diurnally while others appeared to fluctuate randomly with periodic spike inputs. The variability of most effluent trace contaminant concentrations was considerably attenuated in comparison to influent concentrations.