Realization: 2011 – 2013 Number of PE: 17 400 Client: Bratislava water company, joint-stock company Cost of electromechanical part: 3 956 595,– EUR WWTP Holíč was under total reconstruction because insufficient structure and capacity for the needs of the agglomeration of Holíč. After the reconstruction and intensification is WWTP Holíč working as a mechanical-biological plant with nutrients removal, with enhanced biological phosphorus removal. Sludge management consists of anaerobic sludge stabilization and utilization of produced biogas for the needs of the plant WWTP Holíč works as a mechanical-biological treatment plant with nutrients removal and with a chemical precipitation of phosphorus by ferric sulfate solution. Sludge management consists of anaerobic sludge stabilization and of utilization of produced biogas for the needs of the plant. The mechanical step consists of mechanical coarse screens, mechanical fine screens and sand traps, sand separator and primary sedimentation tank. Storm waters are relieved to recipient after the mechanical step. The biological step (3 400 m3) consists of two parallel lines of anaerobic tank for enhanced biological phosphorus removal, pre- denitrification and nitrification. Additional phosphorus removal is provided by chemical precipitation with ferric sulfate solution. Return sludge is regenerated under the aerobic conditions in the regeneration tanks of volume 580 m3. The air for nitrification and regeneration is delivered by rotary blowers (nitrification 3 600 m3/h, regeneration 390 m3/h) in dependency of on line measurement of dissolved oxygen or ammonium nitrogen concentration. After the nitrification sections biologically treated water with activated sludge flows to two radial secondary clarifiers (350 m3) for separation. After secondary clarifiers the treated water goes through tertiary treatment – two micro drum filters and then flows to pumping station. From where it is pumped approx. 3,1 km to recipient. The sludge management consists of anaerobic stabilization tank operated under mesophilic conditions, mechanical thickening of biological excess sludge and dewatering of anaerobically stabilized sludge. The anaerobic stabilization tank is mixed by pneumatic mixing with produced biogas by rotary compressors or alternatively by hydraulic mixing with a pump. A biogas produced in anaerobic stabilization tank is stored in dry two membrane gasholder (270 m3). These membranes are made of high resistant polyester fabric coated with PVC. The biogas is preferably used as a fuel to produce electricity in cogeneration unit for the needs of WWTP and created heat is used for the heating of sludge in anaerobic stabilization tank. In the boiler room is produced heat from the biogas to heat buildings in winter time. The excess biogas is burned in a gas burner. The measurement and control of the main technological processes is ensured by on-line measurement of ammonium nitrogen, nitrate nitrogen, dissolved oxygen and phosphate phosphorus in biological step or at the outlet of WWTP.