Wastewater treatment is responsible for removing organic pollutants from wastewater producing sewage sludge as by-product that cannot be directly disposed into ecosystems due to its high presence of organic pollutants. To solve this problem, anaerobic digestion (AD) is commonly used to treat the sewage sludge, generating biogas that is converted into energy used on site by the wastewater treatment plants (WWTPs). However, the energy efficiency of biogas is not optimal due to the presence of CO2. By removing CO2, the methane content is higher, and its energy efficiency has been increased. This technological improvement is called biogas upgrading (BU), where biomethane is produced and used as renewable gas. Biomethane uses sewage sludge as raw material helping both the WWTPs to reduce wastewater treatments costs and reducing energy consumption of production processes. Specifically, biomethane has higher calorific value than biogas due to its percentage of methane (90%). This value makes biomethane as an energy source comparable to conventional natural gas, opening a wide range of possibilities to implement it in different areas. This chapter assesses the benefits of producing biomethane under different points of view, according to the economic sectors, the conservation degree of ecosystems and the human well-being. Throughout the identification of this benefits, the advantages of BU in WWTPs can be highlighted. Results obtained highlight the importance of biomethane for the decarbonization of societies through promoting high-quality renewable energies and ensuring the short-, medium-, and long-term environmental conservation thanks to the circular economy approach.