[Leaching Behavior of Dissolved Organic Matter in Biochar with Different Extracting Agents]

Biochar is widely used in environmental pollution remediation, soil improvement, and biotransformation of waste. However, the leachable substances within biochar may leach out during the application process, causing detrimental effects to the reaction system and the environment. Here, the simulated solutions (distilled water, buffer salt solution, methanol, and humic acid solution) at different stages of anaerobic digestion were used as the extracting agents, and high-resolution liquid chromatography-mass spectrometry was used to study the dissolved organic composition of biochar leachates. A total of 536 effective substances were detected in the biochar leachates, of which 100 substances were highly matched to the standard substance database. The molecular weights of these 100 substances, which included phenols, aromatic acids, aromatic aldehydes and ketones, aliphatic acids, and other substances, were in the range of 109-458 and averaged 290.2. The buffer salt solution, which is commonly used for anaerobic culturing, extracted three additional aliphatic acids and four additional aromatic substances from biochar than distilled water as used in traditional research methods; the leachate of methanol contained the most diverse compounds-71 in total-including a large number of phenols and organic acids. Some humic acid organic substances are adsorbed by biochar during the leaching by humic acid, including alcohols and aliphatic acids, but humic acid still promoted the leaching of phenolic substances, while the total number of substances that were detected was reduced by 41.7%.