Improving Anaerobic Digestion Process of Sewage Sludge in Terms of Energy Efficiency and Carbon Emission: Pre- or Post-Thermal Hydrolysis?

Yawen Ye, Azizi Selemani Msuya, Xiaohu Dai, Xiaoli Chai and Boran Wu ()
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Yawen Ye: State Key Laboratory of Water Pollution Control and Green Resource Recycling, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
Azizi Selemani Msuya: State Key Laboratory of Water Pollution Control and Green Resource Recycling, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
Xiaohu Dai: State Key Laboratory of Water Pollution Control and Green Resource Recycling, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
Xiaoli Chai: State Key Laboratory of Water Pollution Control and Green Resource Recycling, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
Boran Wu: State Key Laboratory of Water Pollution Control and Green Resource Recycling, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China

Sustainability, 2025, vol. 17, issue 13, 1-13

Abstract: Sewage sludge, a by-product of biological wastewater treatment, poses significant environmental and health risks if not properly managed. Anaerobic digestion (AD), widely used as a stabilization technology for sewage sludge, faces challenges such as rate-limiting hydrolysis steps and difficult dewatering of residual digestate. To address these issues, thermal hydrolysis (TH) has been explored as a pretreatment or post-treatment method. This study systematically analyzes the typical sludge treatment pathways incorporating TH either as a pretreatment step to AD or as a post-treatment step, combined with incineration or land application for the final disposal. The mass balance algorithm was applied to evaluate the chemical consumption, and energy input/output calculations were conducted to assess the potential effects of TH on energy recovery. Carbon emissions were estimated using the Intergovernmental Panel on Climate Change (IPCC) methodology, considering direct, indirect, and compensated carbon emissions. The results indicate that applying TH as a post-treatment significantly reduces the carbon emissions by 65.94% compared to conventional AD, primarily due to the enhanced dewaterability and reduced chemical flocculant usage. In contrast, TH as a pretreatment step only moderates the emission reduction. The combination of post-TH with land application results in the lowest carbon emissions among the evaluated pathways, highlighting the environmental benefits of this approach. All the findings here are expected to provide insights into optimizing the technical combination mode of sludge processing pathways in terms of minimizing carbon emission.

Keywords: sewage sludge treatment; anaerobic digestion; thermal hydrolysis; sludge disposal; carbon emission estimation (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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