Development must balance social, economic, and environmental sustainability; it is for this reason that the Sustainable Development Goals (SDGs) are integrated, in fact, action in one of them will affect outcomes in others. In consequence, research on the SDGs is broad, complex, and fragmented due to the great diversity of disciplines and approaches involved, making it difficult to obtain valuable and unbiased information for future studies. As a result, a comprehensive review of contributions could provide a comprehensive critical perspective. This article applies SciMAT software to analyze the evolution of this field of research through a systematic literature review of bibliographic records on the SDGs and a review based on bibliometric analysis of 10,272 selected records. Additionally, hidden themes and their development in this field from 1990 to 2020 have been identified to produce strategic diagrams, graphs of thematic evolution and performance indicators of the research field in different periods. The results obtained show a constantly evolving scientific field, from its initial focus on the millennium goals to the gradual inclusion of the current SDGs. They provide field experts with a comprehensive overview of the status quo and predict the dynamic directions of future research, serving as a basis for the development of new strategies for the implementation of the SDGs.

Energy recovery, according to circular economy and sustainable principles, has established itself as an inevitable field of action in wastewater treatment plants (WWTPs). Energy costs are forcing the optimization of processes and increases in the development of applicable waste-to-energy (WtE) technologies. This study aims to analyze the existing knowledge on WtE research in municipal WWTPs using a systematic literature review and a bibliometric analysis from 1979 to 2021. For this purpose, Science Mapping Analysis Tool (SciMAT) and VosViewer, two softwares for analyzing performance indicators and visualizing scientific maps, were used to identify the most relevant figures in the research. The results show an exponential increase in the number of publications over time, which has yet to reach a stage of maturity. The analysis of the evolution of the topics exposes variability in the keywords over the years. The main field of WtE research has focused on sludge treatment, with technologies ranging from anaerobic digestion to more recently-emerging ones such as microalgae or membrane technologies. The analysis also identified the need for more publications on other wastes in WWTPs, which are necessary to achieve zero waste.

The development in wastewater management has caused a shift towards a circular model that prioritises energy generation and waste reduction. Traditional unitary processes in wastewater treatment, such as screening, only allow for landfill disposal without energy recovery. However, producing solid recovered fuel (SRF) from waste screening may be a possibility. The economic and environmental viability of this alternative, as a fundamental requirement for its implementation at industrial level, was assessed through a multi-scenario analysis using Monte Carlo simulation. The cost and benefit streams were determined based on the financial net present value (NPV_f) and the social net present value (NPV_s), including monetised CO₂ emissions generated. The results showed that waste drying costs were found to be the most significant ones, with thermal drying being more financially advantageous than solar drying. The densification of SRF raises the costs by 7.88 to 8.48%, but its use as fuel would likely be profitable due to the economic benefits it provides. Current landfill disposal practices, which have an NPV_s of −1052.60 EUR/t, are not a feasible, particularly when compared to the other SRF production scenarios, with maximum NPV_s of −53.91 EUR/t. SRF production without densification using solar drying is the most acceptable scenario with the lowest NPV_s (38.39 EUR/t).

The circular economy, as a new model of waste management through energy self-sufficiency and valorisation, can be applied to wastewater treatment plants (WWTPs). Screening waste from WWTP pretreatment is the only waste that is not energetically recovered and thus constrains the achievement of zero waste. Previous studies demonstrated the technical feasibility of producing solid recovered fuel (SRF) from this waste. Environmental benefits, including waste reduction, resource conservation, or reduced greenhouse gas emissions are analysed in this work. Environmental impact is quantified using the life cycle assessment (LCA) methodology through the SimaPro 9.2. software and the CML-IA baseline v3.08 impact methodology, that propose 11 impact categories. Five scenarios were established to compare current landfill disposal with the production of densified and non-densified SRF using solar and thermal drying. Within the system boundaries studied, from waste generation to SRF production, results show that landfill is the most environmentally damaging option while producing non-densified SRF using solar drying is the most environmentally viable scenario.

Within the context of the new circular model for wastewater treatment aimed at achieving zero waste, this research seeks an alternative to landfill disposal of waste screenings. It examines the feasibility of thermochemical processes—combustion and gasification—for the valorisation of solid recovered fuel (SRF) derived from screening wastes, which are the only waste in wastewater treatment plants (WWTPs) that typically have an absence of existing recycling or valorisation processes. Laboratory-scale experiments assessed the technical viability of gasification, and energy balances were calculated for both combustion and the syngas obtained from gasification experiments. Results indicate that both processes are feasible for SRF valorisation. Combustion demonstrated the highest energy efficiency, yielding up to 1.6 MJ per kg of raw SRF, compared to gasification’s maximum of 1.4 MJ. The moisture content in SRF feedstock influences both processes, underscoring the need to optimise moisture levels. Additionally, combustion showed a higher conversion efficiency due to the complete oxidation of the feedstock, whereas gasification produced valuable syngas that can be further utilised for energy production or as a chemical feedstock. The study concludes that, from a purely energetic perspective, combustion is the most efficient process for SRF valorisation. However, gasification offers significant environmental and sustainability advantages, including lower greenhouse gas emissions and the potential for integrating with renewable energy systems, making it a more attractive option for long-term sustainability goals.