Production of H2 and CNM from biogas decomposition using biosolids-derived biochar and the application of the CNM-coated biochar for PFAS adsorption

Anaerobic digestion is a popular unit operation in wastewater treatment to degrade organic contaminants, thereby generating biogas (methane-rich gas stream). Catalytic decomposition of the biogas could be a promising upcycling approach to produce renewable hydrogen and sequester carbon in the form of carbon nanomaterials (CNMs). Biosolids are solid waste generated during the wastewater treatment process, which can be valorised to biochar via pyrolysis. This work demonstrates the use of biosolids-derived biochar compared with ilmenite as catalysts for biogas decomposition to hydrogen and CNMs. Depending on the reaction time, biosolids-derived biochar achieved a CH4 and CO2 conversion of 50-70 % and 70-90 % at 900 degrees C with a weight hourly space velocity (WHSV) of 1.2 Lg(-1)h(-1). The high conversion rate was attributed to the formation of amorphous carbon on the biochar surface, where the carbon deposits acted as catalysts and substrates for the further decomposition of CH4 and CO2. Morphological characterisation of biochar after biogas decomposition revealed the formation of high-quality carbon nanospheres (200-500 nm) and carbon nanofibres (10-100 nm) on its surface. XRD pattern and Raman spectroscopy also signified the presence of graphitic structures with I-D/I-G ratio of 1.19, a reduction from 1.33 in the pristine biochar. Finally, the produced CNM-loaded biochar was tested for PFAS adsorption from contaminated wastewater. A removal efficiency of 79 % was observed for CNM-coated biochar which was 10-60 % higher than using biochar and ilmenite alone. This work demonstrated an integrated approach for upcycling waste streams generated in wastewater treatment facilities.

Automated summary

Anaerobic digestion is widely used in wastewater treatment to degrade organic contaminants and produce biogas. This study explores the use of biosolids-derived biochar as catalysts for biogas decomposition to generate hydrogen and carbon nanomaterials. The biosolids-derived biochar showed high CH4 and CO2 conversion rates due to the presence of amorphous carbon on its surface. Morphological analysis revealed the formation of carbon nanospheres and carbon nanofibres. Furthermore, the CNM-loaded biochar demonstrated efficient removal of PFAS from contaminated wastewater. This research showcases an integrated approach for upcycling waste streams in wastewater treatment facilities.