Maximization of bio-methane gas from anaerobic digestion of black liquor wastewater using a fabricated mesoporous graphene oxide nanosheets: experimental and microbial community shifts

Abstract The global demand for sustainable energy has intensified research into waste-to-energy technologies. The pulp and paper industry generates large volumes of black liquor (BL), a by-product rich in lignin and organic matter, which presents both environmental challenges and energy recovery opportunities. This study explores the enhancement of bio-methane production from paper mill black liquor through the addition of graphene oxide nanosheets (GONSs) synthesized via a modified Hummers method. GONSs was thoroughly characterized using FTIR, XRD, SEM, TEM, zeta potential, BET surface area, and Raman spectroscopy, confirming its high purity, mesoporosity (average pore radius 2.75 nm), and excellent colloidal stability (zeta potential − 36.2 mV). The anaerobic digestion performance of GONSs was tested by treating BL samples with a concentration ranging from 0 to 80 mg/L of GONSs. The high surface area (419.43 m 2 /g) and functional groups of GONSs facilitated better microbial attachment and electron transfer, overcoming the inhibitory effects of black liquor’s complex organics. The results demonstrated an enhancement in the bio-methane production rate compared to the control phase without the GONSs, as the bio-methane yields increased by 2.0 factor using 60 mg/L GONSs compared to the control batch. GONSs effectively promoted the degradation of organic pollutants in the BL, regarding the chemical oxygen demand (COD) by 31.2%. Furthermore, microbial analysis revealed that GONSs enhanced the activity of microbial species responsible for the methanogenic process such as the Chloroflexi phyla that increased from 10.1 to 29.2%. All these findings indicate that GONSs are effective nano-additives for optimizing anaerobic digestion of industrial waste, providing a promising pathway for sustainable waste management and renewable energy generation.