Dynamic variations in dissolved organic matter and the precursors of disinfection by-products leached from biochars: Leaching experiments simulating intermittent rain events

Biochar-leached dissolved organic matter may have a substantial impact on the water quality of receiving water surrounded by biochar-amended fields. In this study, we tracked variations in the spectroscopic characteristics and the disinfection by-products formation potentials of dissolved organic matter (DOM) leached during sequential extraction for three different biochars (BCs), which simulates DOM from BC-amended fields during intermittent rain events. The optical properties of DOM were more dependent on the BC types with different origins (sludge, corn, and rice) rather than on the extraction time. A large amount of DOM was released during the initial period of the extraction (1 day), which was equivalent to 52–60% of the total cumulative organic carbon during 17 days of extraction. The relative contribution of the initial extraction to the total cumulative amounts was greater for the formation potential of trihalomethanes (THMs) per BC (71–82%) compared to those of haloacetic acids (HAAs) or dissolved organic carbon (DOC), suggesting that the leaching behaviors of disinfection byproducts (DBP) precursors from BCs may be different from those of DOC (i.e., bulk DOM). Among the three BCs, corn BC-derived DOM exhibited the highest formation potentials of THMs and HAAs per BC for both the initial and the total cumulative extraction. The specific (or DOC-normalized) THMs formation potential was positively correlated with the ratios of terrestrial humic-like to fulvic-like components, implying condensed aromatic structures could operate as a surrogate for THMs formation of BC-derived DOM. This study provided insight into dynamic leaching behaviors of DOM from BCs and the formation potentials for THMs and HAAs in BC-amended fields under intermittent rainfall. Contribution of initial leaching to total amounts of BC-derived DOM was greater for THM precursors than for the bulk DOM (DOC), followed by HAA precursors.