Published online by Cambridge University Press: 03 April 2007
It is crucial to understand the response reproducibility of on-line continuous-flow respirometers applied as biological toxicity monitors to alert plant operators to contamination in wastewater influent. Used as upset early warning systems, on-line respirometers could identify toxic waste streams that should be diverted from activated sludge treatment systems. This study used a continuous flow-through respirometer (Bioscan™) to examine the reproducibility in the respiration response of activated sludge biomass from a local wastewater treatment plant and a commercially available seed (POLYTOX®), when each was exposed to a toxic pH 3.0 buffer solution. Respiration response is characterized in this study as a change in dissolved oxygen concentration over time in the respirometer effluent. This response was segregated into groups, including within an inoculated population of a given seed source (activated sludge biomass or POLYTOX®), between different inoculations of the same seed source, and by the two different seed sources. Reproducibility in the response of the Bioscan™ respirometer was as high as 22% within populations, 23% between populations, and 29% for the same population over time. In addition, time dependency in the respirometer response to the toxin was examined. It was demonstrated that response to the same toxic pulse varies between and within populations and that reduced sensitivity of the microorganisms can occur if repeatedly exposed to an individual toxin. A genetic DGGE analysis for one population suggests that the observed reduction in sensitivity may be caused by changes in species composition.