In many countries, there are water quality standards for the effluent of the sewerage treatment plants. In these standards, the different parameters like pH, conductivity besides organic load expressed as COD or BOD should be monitored. Further, in addition to these parameters, the quality of the water is important for the environment and living organisms anyhow. All wastewater treatment plants aim to remove different pollutants based on the process they are designed for. Indeed the important issue is to be sure that the treated water is not toxic at all. Only the bio-monitoring method can do this task. With bio-monitoring, the behaviour of living organisms like daphnia (water flea), algae, or fish is used to detect the toxins in the water. Therefore the wastewater treatment plants are another application of the established bbe Toximeters.
In this case study, some information about the Daphnia Toximeter, installed in the Kiel City wastewater treatment plant has been described.
The bbe DaphniaToximeter is approved for quality control of wastewater treatment (mixed water from households and industry). It provides excellent sensitivity for a wide range of toxic substances harmful to humans.
The bbe DaphniaToximeter is an instrument for continuous and reliable monitoring of contaminants in water systems and is at the same time easy to operate.
Living water fleas (Daphnia magna) are permanently exposed to a sample water flow and are continuously monitored by a camera inside of the toximeter.
If acute poisoning occurs (i. e caused by pesticides or heavy metals), the swimming behaviour of daphnia changes considerably, and an alarm is triggered. Online Bio-monitors are more sensitive than static tests and on the other hand, their results are in real-time.
This application runs in the effluent of the WWTP in Bülk (North Germany).
Bülk, the second-largest sewage treatment plant in Schleswig-Holstein, treats the sewage of approximately 310,000 inhabitants and 65,000 inhabitant equivalents (industry and trade) in the Kiel and its 21 neighbouring communities.
The sewage treatment plant receives approximately 20 million cubic meters of effluent per year or 50,000 to 60,000 cubic meters per day. Contamination of the facilities with germs is unavoidable depending on the weather and wind conditions, despite intensive hygiene measures, as bacteria are indispensable both for biological purification and sludge treatment.
Toxicity index (sum of toxicity indices; top left window), number of live organisms (bottom left), average velocity (top right), and height class index (bottom right) are shown here for the corresponding date.
Toxicity points are indices used to record variations in typical swimming behavior and Daphnia mortality in the water. Thus, they provide a measure of water pollution.
The top figure shows data from a week with no toxic pollution in the plant's treated effluent. The number of living organisms was stable and the swimming behavior of the daphnia showed only the typical fluctuations.
As shown in the figure below, the toxicity points suddenly spiked in the second week and the swimming behavior and mortality of the Daphnia changed significantly. When 10 toxicity points were exceeded, an alarm was triggered (red line on the toxicity index).
Increased use of ferrous sulfate as a flocking agent for phosphate is suspected as the cause for the rising toxicity index of the Daphnia Toximeter (s. left diagram).
The toxicity index correlates fairly with the used amount of ferrous sulfate (see the right diagram).
Below video shows application of bbe Daphnia Toximeter and AlgaeToximeter in a wastewater treatment plans in the Switzerland