Comparing Physicochemical Properties and Sorption Behaviors of Pyrolysis-Derived and Microwave-Mediated Biochar

Abstract

Biochar’s ability to amend and remediate agricultural soil has been a growing interest, though the energy expenses from high-temperature pyrolysis deter the product’s use. Therefore, it is urgent to improve the pyrolysis efficiency while ensuring the quality of produced biochar. The present study utilized three types of feedstock (i.e., switchgrass, biosolid, and water oak leaves) to produce biochar via conventional slow pyrolysis and microwave pyrolysis at different temperature/energy input. The produced biochar was characterized and comprehensively compared in terms of their physiochemical properties (e.g., surface functionality, elemental composition, and thermal stability). It was discovered that microwave-mediated biochar was more resistant to thermal decomposition, indicated by a higher production yield, yet more diverse surface functional groups were preserved than slow pyrolysis-derived biochar. A nutrient (NO3-N) adsorption isotherm study displayed that microwave-mediated biochar exhibited greater adsorption (13.3 mg g−1) than that of slow pyrolysis-derived biochar (3.1 mg g−1), proving its potential for future applications. Results suggested that microwaves pyrolysis is a promising method for biochar production.

Biochar for Soil Carbon Sequestration: Current Knowledge, Mechanisms, and Future Perspectives

“…A consistent trend of increasing C content was observed across various biochars derived from different waste types when subjected to higher pyrolysis temperatures, as reported in numerous previous studies [33,43,51,53,54]. This rise in C content at elevated pyrolysis temperatures can be attributed to the decomposition of organics and the volatilization of elements such as oxygen (O) and hydrogen (H).…”

“…The H/C atomic ratio serves as an ideal indicator of biochar's C structure, reflecting the degree of unsaturation and the presence of C-C double bonds [48,59]. A H/C atomic ratio below 0.7 signifies aromatic structures and distinguishes biochar from its raw feedstock, while a ratio below 0.4 indicates high biochar stability and enhanced C sequestration potential with reduced biochar deposition rates [53,56] (Figure 1). In addition, the O/C atomic ratio is employed to classify C combustion residues, with graphite representing the most stable C form.…”

Pyrolysis of Biosolids to Produce Biochars: A Review

“…Another approach to sewage sludge pyrolysis is the use of microwave-assisted technology which was explored by several researchers such as [67,80]; their work aimed to test sewage sludge as a feedstock using a continuous microwave-assisted pyrolysis scheme. Furthermore, the influence of the pyrolysis processing temperature on the bio-oil compositions and products yield were investigated.…”

Systemic review for the use of biochar to mitigate soil degradation

“…The pyrolysis process retains more functional groups on its surface because of the insideout heating mode. Brickler et al (2021) reported that microwave pyrolysis biochar has better NO 3 − adsorption capacity than slow-pyrolysis biochar at the same pyrolysis temperature, most likely because the surface of microwave pyrolysis biochar contains more hydrophilic functional groups. Hydrolysis places the feedstocksin a subcritical liquid water environment of 160-350°C and 2-10 MPa (Fang et al, 2018;Mumme et al, 2011).…”