Characterization and Potential Applications of Hydrochars Derived from P- and N-Enriched Agricultural and Antibiotic Residues via Microwave-Assisted Hydrothermal Conversion

The effect of treatment temperature on hydrochars' properties using P- and N-enriched agricultural and antibiotic residues as feedstocks via microwave-assisted hydrothermal conversion (MW-HTC) was investigated in this study. MW-HTC changed the physicochemical properties of hydrochars, nutrient fractions (phosphorus (P) and nitrogen (N)), and surface functional groups which were characterized by various analysis tools. The N contents in hydrochars derived from rapeseed (RS) and lincomycin (LM) residues were 7.26 and 7.76% at 120 degrees C, respectively. At 210 degrees C, those values were reduced to 5.16 and 3.14% accordingly, indicating a higher temperature led to more N release. The speciation of P fractions was affected by temperature, and LM derived hydrochars possessed higher bioavailable P for plants' nutrient uptake. The atomic ratios of H/C and O/C decreased with treatment temperature for both RS and LM derived hydrochars. LM derived hydrochars were thermally more stable than RS derived hydrochars. RS derived hydrochars exhibited better higher heating value (HHV; 22.0-26.8 MJ/kg) while LM derived hydrochars revealed higher fuel ratio (0.47-0.95). MW-HTC offered a viable route for conversion of P- and N-enriched agricultural and antibiotic residues into highly efficient hydrochars for environment-friendly applications.