Objective  The surface property, which closely relates to the functionality, of biochar made from discarded mushroom stems under varied pyrolysis temperature and time was studied.

  Method  Waste of edible mushrooms including Hypsizygus marmoreus , Pleurotus geesteranus , and Tremella fuciformis was processed under oxygen-limited pyrolysis at 400℃, 500℃, 600℃ or 700℃ for 1.5 h, 2.0 h, 2.5 h or 3.0 h. The structure property of the resulting biochar samples was analyzed using Fourier transform infrared spectroscopy (FTIR).

  Result  The increasing pyrolysis temperature and time reduced the relative contents of C=O and C-N in the proteins, C-O-C in the celluloses, and C-H functional groups in the benzene rings of the raw material, while raised the relative contents of C-C functional groups in the benzene rings reaching a maximum when processed at 700℃ for 3.0 h. Among the 3 biochar samples obtained under same pyrolysis conditions, the maximum absorption by the oxygen functional groups of H. marmoreus biochar was the highest, and that of T. fuciformis the lowest; whereas, that by the C-C functional groups in the benzene rings of P. geesteranus biochar was the highest, and T. fuciformis biochar the lowest.

  Conclusion  Increased pyrolysis temperature and time decomposed the organic substances such as proteins, polysaccharides, and fatty acids in the raw mushroom material, diminished the alkyls, and formed aromatics in the biochar. Processed under 700℃/3.0 h pyrolysis, the biochar attained a stable structure. As indicated by the analytical results, the H. marmoreus biochar was expected to be most effective among the 3 materials in removing heavy metals or organic pollutants, and the P. geesteranus biochar in carbon-sequestrating in soil.