Achieving energy self-sufficiency in wastewater treatment plants by integrating municipal solid waste treatment: A process design study in Spain

Water-energy nexus is a highlighted topic nowadays, particularly, the energy consumption in wastewater treatment plants (WWTPs) is becoming an important issue. WWTPs typically consume more energy than the one that can be obtained from the biogas produced from sludge anaerobic digestion. In this work, a process-level analysis is presented to study the feasibility of integrating wastewater and municipal solid waste (MSW) treatment to achieve the energetically self-sustainable operation of a WWTP. The influence of the climate of different regions across the Iberian Peninsula on the energy requirements has also been evaluated. Mesophilic and thermophilic digestion is compared in Salamanca as a case base, and the optimal digestion temperature is also evaluated, finding a value of 30∘C. Moreover, in all cities considered, it is necessary for MSW to provide between 37–40% of the facility energy consumption corresponding to around 0.19 kg of MSW per kg of sludge, with a small difference between cities. From an economic point of view, an investment between 0.09–0.16 €/kg of sewage sludge is required for the integrated process. Therefore, this techno-economic assessment demonstrates the feasibility of integrating these two treatments for a fully self-sufficient and sustainable process.