Methane production enhancement from anaerobic digestion of waste activated sludge with corn straw-derived biochar: Insights into the roles of tubular and lamellar structures

Biochar derived from corn straw is commonly used to enhance anaerobic digestion (AD) of waste activated sludge (WAS). However, the present strategies mainly use corn straw to produce biochar without regarding the roles of tubular and lamellar structures. Herein, four types of biochar were prepared using corn cob outer shells, cob inner cores, stalk outer shells, and stalk inner cores. The results proved that the tubular porous biochar derived from outer shell of corn cob or outer shell of corn stalk, exhibited promoting effects on methane production due to the rich three-dimensional structure, while the lamellar biochar derived from inner core of corn cob or inner core of corn stalk exhibited inhibitory effects. Also, the tubular porous biochar shortened methanogenesis lag phase. The mechanism analysis indicated that the tubular porous biochar not only promoted the degradation of proteins and polysaccharides, thus providing sufficient substrates for methanogens, but also promoted the activities of enzymes associated with methanation. Moreover, the tubular porous structure and high electrical conductivity benefited to the enrichment of hydrogenotrophic and acetoclastic methanogens. Methanosarcina , Methanothrix , and Clostridium_sensu_stricto_13 promoted the methanogenic activity through the facilitation of direct interspecies electron transfer, thus improving methane production performance. These findings suggested that plant tissue classification could serve as a useful basis for the targeted preparation of functional biochar, as well as for the roles of the structural differences of tubular and lamellar biochar in AD for methane production enhancement.