Paracetamol degradation pathways in soil after biochar addition.

Little is known about the effect of biochar on the degradation of paracetamol in soil, considering the ubiquity of this pollutant in the environment. Given the importance of the electrochemical properties of biochar for contaminant remediation, we investigated the influence of raw and designer redox-active biochars on paracetamol degradation in soil. Metabolite quantification indicated that a minimum of 53% of the spiked paracetamol was transformed in biochar-amended soil, resulting in the accumulation of different degradation products. The identification of these products allowed us to chart paracetamol degradation pathways in soil with and without biochar amendment. Some of the major degradation routes were observed to proceed via catechol and phenol, despite being previously described as having only a minor role in paracetamol metabolism. Additionally, a new transformation route from paracetamol to NAPQI was discovered in anaerobic soil originating from direct redox reactions on the surface of the designer biochars. These results may contribute to change our understanding of the environmental fate of paracetamol in soil and the role of biochar in its biodegradation.

Overcoming biochar limitations to remediate pentachlorophenol in soil by modifying its electrochemical properties.

In this study, we produced modified biochars with enhanced electrochemical properties to increase PCP remediation in soil. Although all biochars enhanced PCP remediation in aerobic conditions, only a few did in anaerobic soil. The most successful modifications were (i) the preloading of biomass with 10% w/w FeCl3, to obtain a biochar rich in redox-active metals (B-Fe); (ii) the oxidation of a conductive biochar pyrolyzed at 1000 ºC with 0.025 M KMnO4, to produce a biochar with both moderate conductivity and redox capacity (B-1000-KMnO4); and (iii) KMnO4 oxidation of an amorphous biochar pyrolyzed at 400 ºC to obtain a biochar with very high redox capacity (B-KMnO4). B-Fe reduced extractable PCP to almost zero after 50 days in both incubations, but showed slow kinetics of remediation in aerobic soil. B-1000-KMnO4 had the highest rate of remediation under aerobic conditions, but no significant effect under anaerobic conditions. B-KMnO4, however, presented high rates of remediation and high removal of extractable PCP under both conditions, which made it the recommended modification strategy for increased PCP remediation. We found that the degree of remediation primarily depends on the redox capacity, while the rate of remediation was determined by both the conductivity and redox capacity of biochar.