Establishment of a Carbon Emission Balance Model and Analysis of Carbon Neutrality Pathways for Urban Reclaimed Water Plants
In the context of carbon peaking and carbon neutrality, urban reclaimed water plants must adopt measures such as energy conservation, consumption reduction, and enhanced resource and energy utilization to achieve carbon neutrality. This study developed a carbon emission balance model and accounting method for such plants, incorporating strategies of carbon emission reduction, carbon substitution, and carbon sink. The optimal pathway towards carbon neutrality was evaluated based on the carbon emission balance ratio. Using a 1×10⁵ m³/d urban reclaimed water plant as a case study, the results showed total carbon emissions of 20,934 t CO2e. The carbon emission reduction from reclaimed water source heat pumps for heating and cooling was 21,701 t CO2e, yielding a carbon emission balance ratio of 103.7%. In contrast, other carbon reduction measures contributed 15,424 t CO2e, with a balance ratio of 73.7%, highlighting the pivotal role of reclaimed water source heat pumps. When the heat pump extracted 27% and 36% of residual thermal energy, coupled with reclaimed water reuse or sludge anaerobic digestion-cogeneration, respectively, both pathways achieved a 100% balance ratio. Assuming year-round extraction, the balance ratio reached 213%. The carbon reduction ratio between utilizing residual thermal energy and chemical energy was 8.76:1. This study demonstrates that urban reclaimed water plants can achieve carbon neutrality through multiple pathways, with residual thermal energy recovery exhibiting significant potential.