Method for Estimating and Predicting CO_2e Emissions: Case Study of an Urban Wastewater System in Suzhou, China

As a fundamental infrastructure to sustain human activities and development, urban wastewater systems are becoming more and more important in the context of population growth and business expansion. It is important to analyze and assess environmental impacts of these systems to community development. This paper presents a model developed for estimating carbon dioxide equivalent (CO2e) emissions resulting from urban wastewater systems addressing both construction and operational activities. Construction emissions are divided into three categories: material manufacture, material transportation, and pipe installation. Operational emissions include the following: energy consumption-related emissions and wastewater treatment-related emissions. Emission factors of gasoline, diesel oil, and electricity were calculated. The model was demonstrated by applying it to the wastewater system in the city of Suzhou, China, to quantify CO2e emissions for the period of 2005-2010. The results highlight the high proportion of emissions from material manufacturing during the construction stage and electricity usage during the operational stage. The CO2e emissions in the construction and operational phases were 517.52 t CO2e/km of pipe construction and 0.53 kgCO_2e/t for wastewater treatment, respectively. Finally, a forecasting model was developed to predict future CO2e emissions over a 5-year horizon, which is a contribution to the overall body of knowledge in environmental sustainability.