Anaerobic Conversion of Microalgal Biomass to Biomethane in the Presence of Carbon-Based Materials: Additive Type, Concentration, and Impact on Microbial Communities

Today, waste is viewed as a renewable energy source and a potential supplier of new bioproducts. Microalgae are essential in wastewater treatment, and the anaerobic digestion (AD) of the harvested biomass leads to the production of biomethane. However, the process of producing methane from algae requires energy-intensive pretreatment steps. This study investigates the potential of carbon nanotubes (CNTs) and granular activated carbon (GAC) to enhance methane production through AD of untreated Chlorella sorokiniana and Tetradesmus obliquus biomass. Indicators of process stability included organic acid, total ammonia nitrogen concentrations, methane production data, and microbial community structure and dynamics. The results suggest that adding CNTs (2.0 and 4.0 g L–1) and GAC (4.0 g L–1) following the acclimatization stage is an effective strategy to enhance the utilization of produced organic acids and promote long-term methane production from the tested biomass. Additionally, the significance of the bacterial genus Ruminofilibacter in biomass hydrolysis has been emphasized. Among methanogens, there was a decrease in the relative abundance of Methanosarcina, while the relative abundances of Methanothrix and Methanoculleus increased by day 12 in CNTs/GAC-added experiments, during which substantial differences in methane production were observed. This proposed approach has the potential to promote environmentally sound waste management and enhance the production of renewable energy.