Campylobacter in afvalwater : Het effect van de zuiveringsprocessen op de hoeveelheid Campylobacter in afvalwater op een pluimveeslachterij en de ontvangende rioolwaterzuiveringsinstallatie

Summary

Research was conducted on the concentrations of Campylobacter in wastewater from a Dutch broiler slaughterhouse and the effects of the treatment steps performed at the slaughterhouse before the wastewater was discharged to the municipal sewer system. Subsequently, samples were collected at the regional sewage treatment plant (WWTP) that processes wastewater including that from the poultry slaughterhouse. Both incoming (influent) and treated water was sampled before it was discharged to surface water. The raw wastewater from the poultry slaughterhouse was found to contain very high numbers of Campylobacter throughout the study period, from September 2022 through January 2023, with an average of 6.6 log10 Campylobacter per Liter. The slaughterhouse purification process consisting of coagulation/flocculation followed by a flotation step gave a limited reduction in Campylobacter count of about 0.7 log10. Discharge of the water to the public sewer system accounts for a dilution due to mixing with other wastewater streams. The dilution based on the measured volumes from the slaughterhouse to the WWTP was found to fairly match the measured concentrations of Campylobacter in the influent of the WWTP averaging 4.4 log10/Liter. Subsequently, a strong reduction occurred as a result of the WWTP's treatment processes by an average of 2.6 log10. Despite this reduction, Campylobacter was also still found in much of the sampled volumes of WWTP effluent, with concentrations ranging from <0.5 log10 to 2.5 log10/Liter of water. In addition to the amount of culturable Campylobacter, wastewater was also examined for the presence of viable but non-culturable (VBNC) Campylobacter. VBNC Campylobacter bacteria may still be infectious and potentially form an underrated source of infection for humans or animals. In this study however, no significant amounts of VBNC Campylobacter were found in any of the samples examined. It is plausible that the transformation to this non-culturable form occurs following Campylobacter's exposure to surface water, as this process may require a few days to complete. While the poultry slaughterhouse is just one of several possible sources of Campylobacter in sewage, the relative contributions from other sources and sectors are unknown. It can be noted that, despite significant reductions in Campylobacter counts during the treatment of poultry slaughterhouse wastewater, there is still a likelihood of this water contributing to surface water contamination. The implications for public health are complex and challenging to evaluate.