Detecting wastewater toxicity in due time is essential for protection of a sewage works and the receiving waters. A respirometric method is presented that performs short batch experiments, so-called In-Sensor-Experiments for toxicity detection. Two types of wastewater samples can be added to the reactor in the device: either the potentially toxic wastewater entering the plant, or, a defined mixture of acetate and ammonia. From the latter experiments models are identified that describe the heterotrophic and autotrophic activity of the sludge. Since these ‘calibration’ experiments are alternated with experiments in which wastewater is injected, the effect of the wastewater on the sludge can be quantified unequivocally. Full-scale toxicity detection (and the corresponding effluent quality) results are reported for a plant treating a mixture of hospital and municipal wastewaters. The respirometer was installed at the influent line of the plant. It was evaluated during a 6-month period for its on-line toxicity detection capacity. Both deliberate and accidental intoxications were recorded and compared with off-line toxicity measurements. Inhibitory wastewaters affected the nitrification activity of the sludge. This was confirmed by the concomitant increase in NH4+ discharge of the treatment plant. To evaluate the efficiency of control actions, the deliberate addition of toxicant was interrupted at the time a toxicity alarm was triggered by the respirometer. It was observed that plant performance then remained unaffected for all monitored criteria.
A respirographic biosensor is presented that is capable of monitoring the waste load and potential toxicity of wastewaters, both off‐line in a laboratory or on‐line at the wastewater treatment plant. The principles of the sensors' operation have been developed and implications of the design choices evaluated. Short term BOD values were obtained every 30 min. The linear dynamic range spanned concentrations differing by a factor of 5000. This range could be expanded by a factor of 10 by adjusting the aeration rate of the bioreactor in the sensor. The response time for toxicity detection was approximately 1 h. The use in the sensor of activated sludge from the plant concerned ensured relevant toxicity information was obtained. To check the condition of the sludge, an independent respiration measurement is proposed. When a siginificant activity change is observed, the sludge in the sensor must be replaced. The presence of oxidoreduction chemicals can cause interferences that may lead to measurement errors. Based on a difference in reaction kinetics, their presence can be assessed and the effect eliminated. Both on‐line and laboratory applications in the chemical industry are presented. Special emphasis is given to the usefulness of the sensor data for waste management of production divisions. On‐line assessment of load variations and hydrogen peroxide spills are given as illustrations of the implementation of the sensor on the treatment plant. Attention is drawn to the potential application of the data for process control and improved performance of the treatment plant.
The objectives of this research were to investigate the potential to biologically treat volatile organic compounds emitted by the forest products industry at thermophilic conditions and to examine the microbial community developed at high temperatures. Three biotrickling filters were run in parallel at temperatures ranging from 40 degrees C (mesophilic control) to 70 degrees C. The first phase involved treatment of methanol, for a 3-month run, and the second phase involved a 260-day run on the treatment of alpha-pinene. Methanol removal rates over 100 g m(-3) h(-1) where achieved at temperatures up to 70 degrees C. Alpha-pinene removal was achieved at temperatures up to 60 degrees C with optimal treatment occurring at 55 degrees C at rates up to 60 g m(-3) h(-1). The time for acclimation increased with increasing temperature and was longer for pinene than for methanol. Filter performance was also able to quickly recover from a shutdown period of up to 2 weeks due to the robustness of the microbial communities as determined by DNA fingerprinting analysis. The high-temperature communities treating methanol or pinene were more similar to each other than the mesophilic communities (i.e., 40 degrees C). The mesophilic methanol community had a high degree of functional redundancy, while the mesophilic pinene community was more unique and very distinct from the others. These results show that biofiltration at high temperatures is achievable and opens up a range of possibilities for applying biofiltration to hot gas streams.
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