The Wastewater Treatment Plant at Subotica has been built in the 1970’s and is operational since 1977 with a design capacity of 15,400 m³/day and the capacity was increased in 1989 to 27,000 m³/day. In 2003 the aeration system was changed and two settlement tanks refurbished. In September 2004 more than 61,000 inhabitants were connected to the sewer system while the number of industries connected to the system was decreased over past recent years. To cater for the year 2020 needs (project horizon), the capacity of the plant had to be increased to 36,000 m³/day what would cover the treatment load of 150,000 population equivalent and includes 8,000 m³/day for industrial waste water and 4,300 m³/day for groundwater inflow.
The Municipal Infrastructure Agency of Serbia prepared a preliminary assessment of the WWTP requirements necessary to comply with the EU standards (directive 91/271/EEC) and the resulting cost of the project, between 12 and 15 Million €. The project was financed through a combination of sources (EBRD / EAR and City of Subotica) and consisted in the upgrading of the wastewater treatment plant, increasing its hydraulic and biological capacity and adjusting its treatment process in order to:
- Extend its catering capacity for future 2020 loads;
- Meet in particular the nutrient standard, for the effluent;
- Substantially reduce or inhibit, if possible, algal growth in the Lake Palic system;
- Minimally meet EU standards and year 2020 anticipative capacity.
The treatment of the wastewater was carried out using an activated sludge treatment with biological nitrogen removal. The treatment of excess sludge (primary and secondary) included thickening before mesophilic sludge digestion and mechanical dewatering after mesophilic sludge digestion.
IRD undertook all the duties of “the Engineer” as per FIDIC Yellow Book Conditions of Contract.