Hohenahr Erda Wastewater Treatment Plant, Erda, Hessen, Germany

The Hohenahr Erda wastewater treatment plant is located in Erda, a district of Hohenahr in the Lahn-Dill-Kreis region of Hessen, Germany. It serves a population of approximately 2,100 residents, classifying it as a small agglomeration under German and EU regulations. The plant operates under the framework of the EU Urban Waste Water Treatment Directive (91/271/EEC), which requires secondary treatment for agglomerations of this size discharging into freshwater. The plant provides secondary treatment, which typically involves biological processes to remove organic matter and suspended solids. With a designed capacity of 2,300 m³/day and an average daily discharge of 345 m³/day, the plant operates well below its capacity, indicating room for future growth or seasonal variations. As a German facility, it is subject to the national Wasserhaushaltsgesetz (Water Resources Act) and must comply with strict effluent standards set by the state of Hessen. The treated effluent is discharged into local watercourses that ultimately drain into the Lahn River, a tributary of the Rhine. The Rhine basin is a major European watershed supporting diverse aquatic life and providing drinking water for millions. The plant's secondary treatment helps protect the Lahn and Rhine ecosystems from nutrient pollution and organic loading.

The plant discharges into small streams in the Lahn-Dill-Kreis area, which flow into the Lahn River. The Lahn joins the Rhine near Koblenz, contributing to the Rhine basin, a critical waterway for Europe. The region is characterized by mixed agricultural and forested landscapes, and the receiving waters support fish populations and aquatic invertebrates. Secondary treatment reduces biochemical oxygen demand and suspended solids, mitigating eutrophication risks downstream.