Abstract
Within the framework of a one-year study the treatment capacity of a municipal wastewater treatment plant (WWTP) was evaluated, with regard to fecal indicator bacteria (FIB) and to their influence on the recipient. The logarithmic reduction rates for fecal coliforms (FC), Escherichia coli (EC) and intestinal enterococci (IE) were 2.84, 2.90 and 2.93. In the investigated period of time, the tested treatment plant released 4.3% of the total annual load flow volume as combined sewer overflow (CSO), that is, when the influent into the combined sewer exceeds the capacity of the treatment plant and coarsely cleaned wastewater arrives at the recipient. This CSO discharge increased the number of FIB significantly by 1.2 × 102 MPN/100 mL for EC, and by 1.8 × 101 MPN/100 mL for IE. For the Styrian part of the Mur River (1.6 million inhabitants), a calculation of FIB of all sewage treatment plants estimating the same ratio of CSO (4.3%) and a given mean flow rate (QM) results in a significant increase of the FIB load in the recipient: 3.8 × 103 MPN/100 mL for EC and 5.8 × 102 MPN/100 mL for IE. On the basis of these values the standards of water quality for recreational purposes cannot be met.
Highlights
Continual efforts in improving the water quality over the last decades and the national implementation of European Directives have been successful
A previous study carried out by Kittinger et al investigated the Mur River concerning its burden of fecal bacteria-like fecal coliforms (FC), Escherichia coli (EC), intestinal enterococci (IE) and Salmonella spp. [4]
When we investigated fecal indicator bacteria (FIB) of combined sewer overflow (CSO) samples in our study, the FIB number did not differ from untreated wastewater
Summary
Continual efforts in improving the water quality over the last decades and the national implementation of European Directives have been successful. The quality of the Mur River has improved and risen from IV to II according to the saprobic system [1,2], most effectively through the implementation of wastewater treatment plants in the catchment area. 85% of the population within the catchment area are connected to central sewage treatment plants, and this was the main reason for the improvement of the river water quality. The microbiological data showed a massive burden of FIB, with an increasing load of bacteria in the flow direction and seasonal fluctuation. Interpreting these values on the basis of the European bathing water regulation [5], the Mur River is not suitable for recreation or water sports. Outbreak sof zoonosis among sporting events in rivers and the evidence of multiresistant bacteria underline the improper quality of river water for recreational purposes [9,10,11]
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