Kirchbach Wastewater Treatment Plant, Kirchbach-Zerlach, Steiermark

The Kirchbach wastewater treatment plant is located in Kirchbach-Zerlach, a municipality in the district of Südoststeiermark, Steiermark, Austria. It serves a population of approximately 4,505 residents, classifying it as a small to medium agglomeration under Austrian and EU regulations. The plant employs advanced treatment processes, which go beyond the secondary treatment standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. With a designed capacity of 4,700 m³/day and an average discharge volume of 574.47 m³/day, the facility operates well below its capacity, indicating room for future growth or seasonal variations. The treated effluent is discharged into local watercourses that ultimately drain into the Mur River, a major tributary of the Drava River, which flows into the Danube and then the Black Sea. The plant's advanced treatment helps protect the sensitive aquatic ecosystems of the Mur-Drava-Danube basin, supporting biodiversity and water quality downstream.

The plant's discharge enters small streams in the Raab basin, which flow into the Mur River near the Austrian-Slovenian border. The Mur River is part of the Danube catchment, ultimately reaching the Black Sea. The region supports diverse aquatic life, including fish species such as grayling and brown trout, and the advanced treatment helps maintain ecological balance in these sensitive water bodies.