Effects of different types and pyrolysis temperature of straw biochar on promoting hydrogen production of sludge fermentation

Biohydrogen production is regarded as a prospective approach for hydrogen production, given its capacity to harness functional microorganisms for the conversion of diverse substrates into hydrogen gas. However, challenges such as low hydrogen production rates and poor stability hinder the large-scale application of dark fermentation. Recent research has shown that biochar is an effective additive in anaerobic fermentation processes. This study investigated the effects of biochar formed from three different kinds of straw at different temperatures on hydrogen production during activated sludge fermentation. The incorporation of rice straw biochar formed at 500 °C (RSBC500) to the fermentation process significantly increased hydrogen production by 27.27 % and improved microbial metabolic pathways. The results of the metabolite analysis indicated a notable increase in the content of both acetate and butyrate, from 16.78 and 15.35 mmol/L, respectively, to 18.50 and 18.26 mmol/L. The characterization of biochar formed at different temperatures and the analysis of the electron transfer capacity of fermentation residues and extracellular polymeric substances revealed that RSBC500 with more redox active functional groups and higher electron transfer capacity enhanced electron transfer between microorganisms. This study presents a strategy for optimizing biochar raw materials and pyrolysis temperatures to promote biohydrogen production, deepening the understanding of biochar promoting hydrogen production from sludge fermentation and providing valuable insights into the resource utilization of crop straw.