Assessing entropy changes in urban sewer systems during pollutant degradation

Human activities are intricately linked to entropy changes, inevitably impacting the ecological environment. The initial transportation of urban pipe network systems plays a critical role in this process. These systems involve processes such as fermentation, hydrogen production, acetic acid production, and methane production, generating gases, such as methane and carbon dioxide. Despite their importance, the mechanisms underlying entropy changes during organic matter degradation remain underexplored. This study establishes a 1,200-m-long urban sewer pilot system to analyze pollutant degradation through reaction equations. A novel method, based on standard molar reaction enthalpy changes, is developed to calculate entropy changes, revealing distinct stages of entropy increase. Results indicate that environmental entropy rises primarily during sugar degradation and acetic acid production, while entropy decreases during glucose degradation and methanogenesis. During sewage transport, the heat released from pollutant degradation exceeds that associated with greenhouse gas emissions, leading to a general increase in entropy in the external environment. The findings of this study could help to predict the actual influent quality of wastewater treatment plants and facilitate the optimization of wastewater treatment.