After the Industrial Revolution, human activities within sectors such as transport, industry and energy are becoming more enhanced. Sectors as such are recording significant increase in emissions of harmful gases into the atmosphere. An increase in the concentration and total amount of greenhouse gases in the atmosphere leads to an increase in the average temperature of the Earth and the phenomenon called global warming, which has the greenhouse effect as its main cause. Enhanced greenhouse effect is characterized by an increased concentration of greenhouse gases in the atmosphere, i.e. gases that have the ability to absorb and reflect the Sun's infrared radiation. In addition to pronounced and frequent climate changes, there is a decrease in the quality of air, water and soil in the world, which has a harmful effect on human life, the environment and nature. To protect the planet, human health and preserve biodiversity, leaders around the world are adopting strategies, actions and laws that regulate human activities and strive to reduce emissions of harmful substances. The construction sector is considered as one of the sectors whose activities generate significant amounts of greenhouse gas emissions and thereby contribute to the greenhouse effect. Following the guidelines and methodologies of the European Investment Bank (EIB) for determining the impact of interventions on the environment and climate change, this paper explains the application of the methodology for calculating the carbon footprint, i.e. total greenhouse gas emissions, on the example of a wastewater treatment plant that uses different wastewater treatment and sludge disposal technologies. The obtained results were used to select the optimal solution in relation to potential impacts on the environment, that is, the solution with the lowest greenhouse gas emissions and the lowest impact on the environment. After the calculation, different variant solutions count different amounts of total greenhouse gas emissions expressed in tons of CO2 equivalent per year (t CO2e/year). The obtained values range from 717,30 t CO2e/year to as much as 4 060,20 t CO2e/year. The lowest emission of greenhouse gases was generated by the tertiary treatment of wastewater with anaerobic digestion with disposal of sludge by incineration, so this variant solution was chosen as optimal.