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Combustion Behavior of Sewage Sludge Hydrochar Obtained in Fast Hydrothermal Carbonization
Guilherme Afonso de Campos Avanzi1, Vinicius Sarracini Santos1, Isabela Carreira Constantino1
1Institute of Biosciences, Humanities and Exact Sciences, Department of Chemistry and Environmental Sciences, São Paulo State University (UNESP), São José do Rio Preto, São Paulo 15054-000, Brazil.
ACS Omega
|June 23, 2025
Summary
Hydrothermal carbonization (HTC) converts sewage sludge into energy-rich hydrochar. Optimizing HTC conditions like temperature, time, and sulfuric acid enhances energy yield and thermal stability for this sustainable material.
Area of Science:
- Environmental Engineering
- Chemical Engineering
- Materials Science
Background:
- Sewage sludge (SS) is a complex biomass byproduct with significant organic and inorganic content.
- Effective management of SS is crucial due to its increasing volumes and disposal challenges.
- Hydrothermal carbonization (HTC) offers a promising route for valorizing SS into a stable, energy-dense material.
Purpose of the Study:
- To investigate the production of energy-dense carbonaceous material from SS via HTC.
- To evaluate the influence of process parameters (temperature, time, acid addition) on hydrochar properties and energy yield.
- To characterize the resulting hydrochar (HC) and assess its combustion behavior.
Main Methods:
- Sewage sludge was subjected to HTC at temperatures of 200-280 °C for 30-120 min, with and without sulfuric acid addition.
- Hydrochar products were analyzed using FTIR spectroscopy, CHNS elemental analysis, and thermogravimetric analysis.
- Higher Heating Value (HHV) was estimated to evaluate energy content and densification.
Main Results:
- Hydrochar yields ranged from 44.4 to 57.8%, with significant organic matter and ash content.
- H/C and O/C atomic ratios confirmed the carbonization of SS, indicating dehydration and decarboxylation.
- Hydrochar HHV ranged from 13.4 to 16.5 MJ kg⁻¹, with energy densification between 0.9 and 1.1.
- Energy yield efficiency varied from 38.2 to 57.2%, correlating with temperature, time, and acid concentration.
- Increased temperature, time, and sulfuric acid enhanced the thermal stabilization of hydrochar.
Conclusions:
- HTC is effective in producing carbonaceous materials from sewage sludge with potential energy applications.
- Process parameters significantly influence hydrochar yield, energy content, and combustion characteristics.
- Optimized HTC conditions, including sulfuric acid addition, can improve the energy efficiency and stability of hydrochar derived from sewage sludge.
