Zagreb Wastewater Treatment Plant, Općina Rugvica, Croatia

The Zagreb wastewater treatment plant is located in Hrušćica, Općina Rugvica, within the Zagreb County of Croatia. It serves the greater Zagreb metropolitan area, one of the largest urban agglomerations in the country. The plant has a designed capacity of 1,200,000 cubic meters per day, indicating it is a major facility for the region. The plant provides secondary treatment, which is the standard biological treatment stage required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for large agglomerations. As Croatia is an EU member state, the plant operates within this regulatory framework, which mandates secondary treatment for discharges to freshwater and estuaries, and more advanced treatment in sensitive areas. The treated effluent is discharged into the Sava River basin, which flows through Zagreb and eventually into the Danube River and the Black Sea. The plant plays a critical role in protecting the Sava River and downstream ecosystems from untreated wastewater, supporting water quality and aquatic life in this major European waterway.

The plant discharges into the Sava River, a tributary of the Danube, which ultimately drains into the Black Sea. The Sava River supports diverse aquatic ecosystems and is an important migratory corridor for fish species. The plant's secondary treatment helps reduce organic pollution and nutrient loads, protecting downstream water quality and the ecological health of the Danube basin.