GHG emission reduction and energy production through sewage treatment plants

Sewage Treatment Plants (STPs) are essential infrastructure for addressing climate change, preserving aquatic ecosystems, and enabling sustainable energy transitions. Traditionally focused on meeting regulatory standards by removing pollutants, modern STPs have transformed into multifaceted systems capable of tackling environmental challenges through resource recovery, energy generation, and emissions reduction. This evolution positions STPs as integral components of the circular economy and broader climate action strategies. Untreated wastewater is rich in organic matter, which decomposes and releases greenhouse gases, primarily methane (CH₄) and nitrous oxide (N₂O), with emissions ranging between 75–175 CO₂eq/m³ and approximately 0.625 kg/m³ of solid dry waste. By efficiently separating and processing organic matter, STPs can reduce these emissions by about 35% and solid dry waste by nearly 70%. Advanced sludge treatment technologies, such as anaerobic digestion and gasification, enhance STP efficiency by enabling resource recovery and energy generation. Adopting energy system modelling and assessment frameworks can significantly improve the operational and environmental performance of STPs. These tools comprehensively evaluate energy flows, emissions, and resource recovery processes, offering insights into system retrofitting and renewable energy integration. Such analysis also reveals opportunities for producing renewable energy sources, including biogas and syngas, which can be processed into hydrogen, a clean energy carrier with significant potential for decarbonizing energy systems. Reforming these gases to produce hydrogen reduces reliance on fossil fuels and supports a net-zero emissions framework. Scenario modelling enables stakeholders to assess the impacts of policy interventions, renewable energy synergies, and small-scale energy generation technologies. Additionally, STPs contribute to nutrient recycling by recovering essential elements like nitrogen and phosphorus from wastewater, reducing dependence on energy-intensive synthetic fertilizers and their associated greenhouse gas emissions. Advanced technologies like sludge-to-fertilizer conversion or biochar production further reinforce the circular economy by generating valuable outputs from waste streams. The study reveals that incorporating advanced sludge treatment technologies and hydrogen production pathways can reduce greenhouse gas emissions by up to 98% and solid waste by approximately 95%. Furthermore, these systems have the potential to produce 2.2 g/m³ of hydrogen and 54.3 g/m³ of methane from syngas and biogas, respectively. Through this holistic approach, STPs can drive progress toward achieving circular economy objectives and addressing the urgent challenges of climate change.