Improved solid/liquid separation performance of hydrochar from sludge via hydrothermal carbonization

Area of Science:

• Biomass Conversion and Bioenergy
• Materials Science and Engineering
• Environmental Science and Technology

Background:

• Solid-liquid separation is critical for hydrochar utilization from biomass via hydrothermal carbonization (HTC).
• Sludge-derived hydrochar presents unique separation challenges due to its composition.

Purpose of the Study:

• To evaluate the solid-liquid separation performance of hydrochar derived from coking sludge (CS) and municipal sludge (MS) using HTC.
• To elucidate the mechanistic insights governing hydrochar separation and dewaterability.

Main Methods:

• Hydrothermal carbonization (HTC) of CS and MS at varying temperatures.
• Analysis of hydrochar dewatering effects and filtration resistance.
• Characterization of hydrochar surface functional groups and organic components.

Main Results:

• HTC significantly enhanced hydrochar separation, with higher temperatures improving dewatering (53.25% in CS, 77.05% in MS) and reducing filtration resistance.
• Bound water release, driven by carbohydrate decomposition (180°C) and protein decomposition (210-300°C), was key to improved dewatering.
• Reduced particle hydrophilicity, due to elimination of hydrophilic groups and formation of aromatic structures, was more critical than particle size for separation efficiency.
• The lower heating value of hydrochar increased significantly, indicating enhanced fuel quality.

Conclusions:

• HTC is an effective method for improving hydrochar solid-liquid separation from sludge.
• Understanding the roles of bound water release and hydrophilicity changes provides mechanistic insights for optimizing HTC processes.
• The findings support enhanced utilization of sludge-derived hydrochar as a valuable energy resource.