Bio- and hydrochars from rice straw and pig manure: Inter-comparison

Area of Science:

• Environmental Science
• Agricultural Chemistry
• Material Science

Background:

• Agricultural waste management presents challenges.
• Valorization of rice straw (RS) and pig manure (PM) into chars is a sustainable disposal and recycling strategy.
• Pyrolysis and hydrothermal carbonization are key thermochemical conversion processes.

Purpose of the Study:

• To investigate the production of chars from RS and PM using pyrolysis and hydrothermal carbonization.
• To compare the characteristics and potential applications of the produced biochars and hydrochars.
• To evaluate the suitability of RS-derived chars for carbon sequestration and PM-derived chars for soil amendment.

Main Methods:

• Pyrolysis and hydrothermal carbonization were employed to convert RS and PM into chars.
• Characterization of chars included analysis of yield, C/N ratio, elemental composition (C, H, O, N), and inorganic fractions.
• Temperature effects on char properties were systematically studied within specified ranges (300-700°C for biochar, 180-300°C for hydrochar).

Main Results:

• Char yield decreased with increasing temperature for both RS and PM.
• RS chars exhibited higher C content and C/N ratios compared to PM chars.
• Increasing temperature led to higher C and ash content, and lower H/C, O/C, and (O+N)/C ratios in the chars. Biochars showed lower H/C ratios, indicating greater stability than hydrochars.
• KCl was the dominant inorganic fraction in RS biochars, while quartz and albite were dominant in PM biochars and hydrochars, respectively.

Conclusions:

• Rice straw chars are more suitable for long-term carbon sequestration due to their higher stability and carbon content.
• Pig manure chars, with their distinct inorganic composition, are better suited as soil amendments.
• Thermochemical conversion offers a viable pathway for waste valorization and resource recovery.