The performance of integrating solar-biomass energy in wastewater treatment plants (WWTPs): A review paper

Integrating renewable energy into wastewater treatment is increasingly recognized as a key strategy for achieving energy self-sufficiency and environmental sustainability. Among the emerging approaches, hybrid systems that combine solar and biomass energy offer promising potential by enhancing treatment efficiency while supporting circular economy principles. This review synthesizes recent advancements in solar-assisted anaerobic digestion, algae-based systems, biochar-enhanced processes, and hybrid photobioreactors. Drawing on experimental data, pilot-scale trials, and field implementations, the findings demonstrate notable performance improvements: methane yield enhancements of up to 30%, pollutant removal efficiencies reaching 95% in solar-assisted AOPs, significant nutrient recovery, and measurable reductions in CO₂ emissions and fossil energy consumption. The comparative analysis highlights technology-specific strengths, regional applicability, and operational trade-offs. However, limitations persist including high capital costs, system complexity, limited technical capacity, and the absence of supportive policy frameworks which continue to hinder widespread adoption. Overall, solar–biomass hybrid systems represent a viable pathway for transforming wastewater treatment into a low-carbon, resource-efficient process. Addressing current barriers through modular design, capacity building, and policy innovation is essential to unlocking their full potential. • Recent advancements in solar-biomass systems for wastewater treatment are comprehensively reviewed. • Integrating solar energy and biomass enhances nutrient recovery and pollutant removal. • Microalgae-based systems offer sustainable solutions for bioproducts and CO₂ emissions reduction. • Hybrid solar-biomass systems optimize anaerobic digestion for methane production. • Renewable energy applications reduce wastewater treatment costs and environmental impact