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 TM ) to examine the reproducibility in the respiration response of activated sludge biomass from a local wastewater treatment plant and a commercially available seed (POLYTOXா), 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 POLYTOXா), between different inoculations of the same seed source, and by the two different seed sources. Reproducibility in the response of the Bioscan TM 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. Environmental Practice 9:42-53 (2007)
There is the potential to use continuous sampling whole effluent toxicity monitors, based on respirometry, as early warning systems for water contamination. in order to apply these monitors, however, many issues influencing system response and data analysis must be addressed. This study examines the use of a continuous flow-through toxicity monitor (Bioscan@) to (1) determine the sensitivity, accuracy, and precision of the toxicity monitor to different concentrations of a stressing agent (in this case pH), (2) establish operational and maintenance procedures, and (3) examine the consistency in the measured response to a single perturbation. The system precision was sensitive to all the pH pulse perturbations, with stable background variability (1 O/O to 6%); however, replicated pulse applications demonstrated that the system has lower accuracy (31 o/ o to 38%). The response consistency was limited, with notable differences in maximum dissolved oxygen and recovery time. The initial response time (inclining slope) was relatively consistent. Although this examination should be repeated with other contaminants used to stress the toxicity monitor, it appears that continuous flow-through toxicity monitors like the Bioscan@ are well suited for qualitative early alert warning systems for water contamination. Environmental Practice 6:306-315 (2004) atural waterways, wastewater treatment facilities, and
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