Fungal fermentation enhances organic pollutant adsorption performance of straw biochar

Abstract:

Background China has abundant waste straw. The incomplete transformation of straw by microbial fermentation causes secondary pollution and resource wastes. The wastes from straw fermentation can be carbonized to prepare the adsorbent for removing organic pollutants from water. Objective To investigate the pollutant removal efficiency of biochar prepared from fermented straw, clarify the effects of fermentation process on the properties of straw biochar, and finally provide a theoretical basis for reusing the wastes from straw fermentation and removing organic pollutants from water. Methods Solid-state fermentation of wheat straw and rice straw was carried out with Trichoderma reesei QM6a and T. asperellum T-1, respectively. The fermentation residues were then pyrolyzed to adsorb methylene blue (MB). Results The fermentation of straw effectively shortened the time to adsorption equilibrium and improved the MB adsorption efficiency of wheat straw biochar. The adsorption efficiency of MB (50 mg/L) by the biochar pyrolyzed at 600 ℃ from wheat straw pre-fermented by T. asperellum T-1 (BaWS 600) was 53.6% higher than that from natural straw (BWS 600). The pseudo-second-order model could well fit the adsorption process, and the MB adsorption capacity of BaWS 600 was 119.4% and 299.4% higher than that of BWS 600 and BWS 800, respectively. Freundlich isothermal adsorption equation could well characterize the isothermal adsorption process, which indicated the multi-molecular layer adsorption of MB by straw biochar. Straw fermentation increased the specific surface area of wheat straw biochar by 47.4% to 245.8% and promoted the exposure of oxygen-containing functional groups, which might be the main reasons for the improvement of MB adsorption efficiency. Conclusion Fermentation can effectively improve the properties of straw biochar for pollutant removal. T. asperellum T-1 was identified to be more suitable for straw fermentation to improve the pollutant adsorption performance of biochar because of its stronger cellulase-secreting ability.