Integration of life cycle assessment and statistical analysis to understand the influence of rainfall on WWTPs with combined sewer systems

Abstract

Rainfall plays a vital role in the operation phase of wastewater treatment plants (WWTPs) when receiving wastewater from combined sewers in rainy days. The aim of this study is to investigate how, and to what extent, the life cycle assessment (LCA) impacts of the WWTP with a combined sewer system could be influenced by the rainfall. Comprehensive correlation and regression analyses were preliminarily conducted to understand the statistical correlation among monthly rainfall precipitation, wastewater indicators (wastewater quality and quantity) and environmental burden contributors (resource consumptions and pollution emissions) in a case-study WWTP in eastern China. A dynamic LCA was then performed to quantify monthly CML2001 environmental impacts (including Abiotic Depletion Potential (ADP), Acidification Potential (AP), Eutrophication Potential (EP), Global Warming Potential (GWP), and Photochemical Ozone Creation Potential (POCP)) under different monthly rainfall precipitations. Finally, a regression analysis based on the preceding work was performed and five best fitting curves were obtained to model the relationship between monthly rainfall precipitations and CML2001 environmental impacts. It was found that monthly inflow rate had a linear relation with monthly rainfall precipitation below 193.2 mm and both of them had a moderate to strong correlation (|r| > 0.5) with all wastewater indicators. Most of the variations in environmental burden contributors can be interpreted by wastewater quality and quantity variations except for the discharge of effluent NH3-N. All environmental impacts show a rising trend with monthly rainfall precipitation below the threshold value for different reasons and then remain stable. The result indicates that the total environmental impacts of the WWTPs might be highly dependent on the capabilities of sewer systems and the WWTP.