In this paper carbon footprint is estimated for wastewater treatment plant Constanta South, Romania, by using a combined model from the available protocols for carbon footprint calculation. Off-site and on-site emissions were taken into account. The carbon footprint calculations were based on the operational data regarding power consumptions, sludge, chemicals and biogas production. A prediction for carbon footprint is done for upgrading wastewater treatment plant. For the current plant technology it is found that 0.44-0.54 kg CO2 eq have been released per cubic meter of treated wastewater for 2010-2013 years or 33.08-37.68 [kg CO2eq/PE and year]. For the upgraded plant, taking into account design data and the credit for biogas usage, it is found that the GHG emissions will be reduced at 0.17 kg CO2 eq per m3 treated wastewater or 32.33 [kg CO2eq/PE and year].