Carbon neutral and techno-economic analysis for sewage treatment plants

Sewage treatment plants consume great lots of power and result in a large amount of indirect carbon dioxide emissions. Four typical energy conservation and emission reduction technologies were selected for sewage treatment plants, included reclaimed water source heat pump for heating, reclaimed water source heat pump for sludge drying, sludge anaerobic digestion technology with a biogas cogeneration system and photovoltaic power generation. The carbon neutral, energy and economic analysis model were established for the four typical technologies. The results show that reclaimed water source heat pump can achieve a higher carbon neutrality effect than sludge anaerobic digestion technology with a biogas cogeneration system. The reclaimed water source heat pump for sludge drying can recover a large amount of waste heat. The payback period of photovoltaic power generation is more sensitive to the electricity price changes, while reclaimed water source heat pump for heating is more sensitive to the heat price changes. From the discussion, Z-value have a greater effect on the reclaimed water source heat pump for heating. With the treatment load of the sewage plants increases, the reclaimed water source heat pump can achieve a higher carbon neutrality effect. The application of photovoltaic power generation needs to consider the geographical location, and it can achieve higher carbon neutral efficiency in rich solar energy resources areas. A combined district heating method with reclaimed water source heat pump is proposed to expand the district heating radius of the reclaimed water source heat pump, and improve waste heat recovery efficiency in sewage.