The biological online monitoring of surface waters commonly involves the use of invertebrate organisms, bacteria and algae as indicator species. LimCo International GmbH’s technology relies primarily on aquatic organisms as they are able take up dissolved as well as particle-bound pollutants. “These organisms enable us to assess and evaluate the overall level of pollution,” says Dr. Gerhardt. In addition, discharge from sewage plants usually contains a large quantity of particles consisting of bacterial biomass and the pollutants and nutrients bound to it. This is why so-called particle feeders - filterers (e.g. net-spinning caddisflies), fine-particle feeders (e.g. non-biting midges) and coarse-particle feeders/shredders (e.g. gammarids, if the pollutant level is not too high) - are frequently found in waterways into which treated water is discharged. 

Gammarids primarily feed on coarse organic material, but do also feed on other food sources such as algae and invertebrate organisms. Gammarids play a crucial role in the substance cycle of flowing waters and are important prey organisms of fish and aquatic birds. Gammarids are used as water quality grade II indicators, which is the level of water quality the EU Water Framework Directive is seeking to achieve for flowing waters. “The organisms’ lifespan of approximately one year is long enough for them to develop and indicate chronic effects at even low pollutant levels,” Dr. Gerhardt explains.

The biological early warning system was used in the state-of-the-art Limmattal wastewater treatment plant near Zurich, Switzerland, and the continuous biological and ecotoxicological monitoring of water quality was successfully tested and installed. A total of seven test runs of between two and three weeks each were carried out using wastewater from the Limmattal wastewater treatment plant. The gammarids and hydropsychids survived for a period of between one and three weeks. The initial low oxygen content in the wastewater was subsequently optimised. “The abrupt death of the animals within only a few weeks suggests that the wastewater was highly polluted,” Dr. Gerhardt says, assuming that compounds such as polyacrylamide and diclofenac were responsible for the death of the animals. Road salts with peak conductivity values and unknown pollutants might also account for the deaths. When a warning is issued, it is crucial to make a detailed comparison of the data with online analytics data in order to identify the concrete cause of death. The company therefore plans to combine biological early-warning systems with chemical analytics.