DISCUSSION
A healthy population was established three days after inoculation of the Biofilter with Polytox microbial seed. The population survived the one-month duration of the study. Nutrient and sample levels were checked daily and the system was cleaned of slime formation every three days. The flowthrough chamber was not used in this study because its use, which requires the purchase of additional equipment, is not necessary. Water sample was pulled directly from polyethylene containers. Water was used as sample during background data collection and pH 4 buffer solution used to measure system response to toxicity. Following each pulse of pH 4 buffer solution, the system was allowed to recover and maintain baseline DO for approximately 24 hours before another pulse was introduced.
The Bioscan provided precise dissolved oxygen readings. System response to pH 4 solution was rapid (see below). System sensitivity to the length of toxic exposure was measured by running pulses of decreasing length through the system. Recovery time to baseline DO following each pulse of pH 4 solution was proportional to the length of the pulse.
--Background variablity in measured dissolved oxygen was less than 6%
--The system responded to each pulse within 15 minutes of introduction to the system
--Recovery time was 50 minutes following the one hour pulse, 20 minutes following the thirty minute pulse, and 10 minutes following the ten minute pulse.
Variables that affect system response and recovery need further investigation. These variables include sample fluctuations in pH, system exposure to toxins such as metals and organics, the use of activated sludge vs. Polytox seed, and the use of LLNL wastewater as sample.
CONCLUSION
The Bioscan provided precise and consistent dissolved oxygen measurements. System response time and recovery from multiple pulses of a pH 4 solution were rapid. Given these results, the Bioscan has the potential to provide precise, real-time measurements of wastewater toxicity. Variables that affect system response and recovery need further investigation.
For more information, please send an email to Rob Vellingeror or Chris Campbell with LLNL.
This page was last updated on November 7, 2007