Table 2.

Summary of latest studies on biogas production from anaerobic digestion

Research focus	Process	Generated product	Study scale/type	Advantages	Limitations	Source
Production of hydrogen assists with biochar and activated char	Catalytic methane decomposition	Hydrogen	Lab/experimental scale	Increase methane conversion rate	Rapid blockages of active sites and surfaces of biochar and activated char can cause a rapid decline in methane conversion	(Patel et al. 2020)
Increasing anaerobic digestion efficiency using biochar	Anaerobic digestion	Methane	Experimental	Increase the production of digestion gas	Controlled conditions	(Shin et al. 2022)
Optimal technology selection for the biogas upgrading to biomethane	Biogas upgrading to biomethane	Methane	Desk-top modelling	The developed model can determine the optimal technology and operational conditions	Conceptual optimal design	(Martín-Hernández et al. 2020)
Thermal hydrolysis process as pre-treatment for electricity generation	Pre-treatment using thermal hydrolysis process for anaerobic digestion	Biogas	Pilot and demonstration scale	Increase the biogas conversion rate	Anaerobic digestion requires pre-defined feeding schedules	(Lafratta et al. 2020)
Predict anaerobic digestion performance using machine learning algorithms	Model development	Methane	Desk-top modelling	Accurate prediction of digester performance using machine learning algorithms	Small dataset of this study	(Freund et al. 2020)
Improve plant performance and biogas production	Optimisation of nitrogen removal	Biogas	Desk-top modelling/concept study	A range of scenarios are considered with potential	The concept of shifting aerobic to anaerobic sludge stabilisation needs to be tested for the specific case	(Vergara-Araya et al. 2022)
Estimation of biogas production	using data-driven approaches to optimise energy generation	Biogas	Desk-top modelling	The most accurate model was established	Models need to be developed using the specific conditions	(Asadi et al. 2020)
System optimisation for effective hydrogen production	Anaerobic digestion and biogas steam reforming	Hydrogen	Experimental	Increased biogas production	The reforming catalyst with resistance to sintering	(Park et al. 2020)
Energy recovery	Anaerobic digestion of algal biomass from integrated with microalgae/constructed wetland wastewater treatment	Methane	Pilot study	Promising electric energy generation potential	Need to test the proposed technology with different native species from diverse regions	(Silveira et al. 2023)
Estimation of the electrical energy produced by energy recovery	Model development	Biogas	Desk-top modelling	Electrical energy is predicted using only 3 parameters (gas flow, conductivity, and TSS)	Errors in the prediction need to be reduced	(Kerem and Yuce 2023)