Characteristics and chlorine reactivity of biochar-derived dissolved organic matter: Effects of feedstock type and pyrolysis temperature

Increasing biochar application worldwide may release more biochar-derived dissolved organic matter (BDOM) to the source water for drinking water supply. However, it is unclear how feedstock types and pyrolysis temperatures for biochar production would affect the characteristics and chlorine reactivity of BDOM. Here, we studied the spectroscopic characteristics of BDOM pyrolyzed from pine needle, wheat straw, walnut shells, alfalfa, pig manure, and sludge derived biochars at 300, 500, and 700 degrees C, as well as the formation potential of disinfection byproducts (DBPs) and their bulk toxicity after BDOM chlorination. The N/C ratio of biochar was higher for Nrich than C-rich feedstocks. Optical analyses indicated that BDOM aromaticity was highest at 700 degrees C, while the impact of pyrolysis temperature on the molecular weight of BDOM varied greatly among feedstocks. Increasing pyrolysis temperature caused consistently decreased BDOM reactivity toward haloketone formation but did not show consistent impacts on the other DBPs. Among feedstocks, the N-rich sludge showed the highest specific haloacetonitrile formation potential of BDOM at any given pyrolysis temperature. The DBP formation potential from biochar was consistently highest at 300 degrees C and was higher for N-rich than C-rich feedstocks. The microtoxicity of DBP mixture was highest for the BDOM derived from sludge produced at 300 degrees C. This study highlights the high variations in characteristics and chlorination reactivity of BDOM with varying feedstocks and pyrolysis temperatures, which implies that more attention should be paid to the environmental impacts of the intensive application of low-temperature biochar from N-rich feedstock such as sludge.

Automated summary

This study investigates the impact of different feedstocks and pyrolysis temperatures on the characteristics and chlorine reactivity of biochar-derived dissolved organic matter (BDOM). The results show high variations in BDOM properties and reactivity, suggesting that the intensive application of low-temperature biochar from nitrogen-rich feedstocks, such as sludge, may have significant environmental implications.