Towards enhancing wastewater treatment in Integrated Assessment and Computable General Equilibrium models

Sustainable water management is essential to increase water availability and decrease pollution in surface and ground water. The expanding wastewater sector plays a pivotal and growing role in managing wastewater globally. Furthermore, technology in use at wastewater treatment plants is evolving to recover nutrients, which increases energy consumption. This technology, however, may reduce demand to produce nutrients from virgin sources. To capture these trends in the wastewater sector and its interlinkages with the fertilizer and agricultural sectors, it is essential for integrated assessment and computable general equilibrium models that address the energy-water nexus to evolve. We estimate how much energy consumption (1,100 million GJ) and greenhouse gas emissions (84 million t CO2e) may increase globally until 2030. We also estimate that the share of national fertilizer demand that could be recovered from wastewater could be nearly 100% for some African nations, but is much lower for large, agriculturally dominant nations like China and the United States. We then review sixteen models integrated assessment and computable general equilibrium models to assess how well they capture wastewater treatment plant energy consumption and GHG emissions. Only three models included biogas production from wastewater organic content. Four models explicitly included representations of energy demand for wastewater treatment, and eight models included explicit representation of the greenhouse gas emissions produced by wastewater treatment. Of the eight models including representation of greenhouse gas emissions from wastewater treatment, six models include representation of methane emissions from treatment, five models include representation of emissions of nitrous oxide, and two models include representation of emissions of carbon dioxide. Our review concludes with proposals to improve integrated assessment and computable general equilibrium models to better capture the energy-water nexus associated with the evolving wastewater treatment sector.