Special Issue on Production, Treatment, Utilization, and Future Opportunities of Biogas

1. Introduction

Over recent decades, anaerobic digestion has emerged as a widely adopted approach to address environmental and energy issues [1,2,3], recognized as a valuable tool for mitigating global warming. Annually, humanity produces more than 100 billion tons of organic waste worldwide, which should be viewed as a resource rather than a burden [4,5]. Anaerobic digestion stands out for its adaptability, capable of processing various organic waste types and energy crops, including liquid (e.g., wastewater), solid (e.g., solid waste and crops), and semi-liquid (e.g., slurries) [6,7,8]. Moreover, these systems offer flexibility and scalability, enabling efficient resource recovery from diverse feedstocks. As a renewable energy source, biogas provides multiple benefits as it can be compressed, stored, refined, or even liquefied [9,10,11]. This versatility presents significant opportunities for biogas expansion, allowing it to leverage existing natural gas and liquefied natural gas infrastructure.

Therefore, the general target of the present Special Issue is to contribute to the expansion of knowledge in this field, promoting research focused on biogas production, upgrading, and utilization.

2. Advances in Anaerobic Digestion and Biogas Utilization Through Innovative Technologies and Strategies

In light of the above, this Special Issue was introduced to collect latest research on relevant topics, mature conventional and innovative technologies to address present challenging issues with different strategies to enhance the anaerobic treatment process and the use of biogas. There were 10 papers published in this Special Issue, 8 of them being original research articles, and 2 are review articles. When looking back to the Special Issues, various topics have been addressed—five of them were for enhancing the anaerobic process by using conductive materials, using hybrid reactors, applying a pre-treatment process, or by studying the salinity inhibition in the thermophilic anaerobic digestion of organic wastes.

The researchers behind Contribution 1 investigated how the addition of conductive materials and bioelectrochemical systems (BES) affects the performance of anaerobic digestion processes for sewage sludge. Their findings showed that incorporating BES enhances process reliability and boosts methane yields, achieving a 5–10% increase in methane content within the biogas across the entire operation, even under elevated organic loading conditions, by promoting varied electron transfer mechanisms. In the experiments detailed in Contribution 2, researchers studied how bacterial and archaeal populations respond to high-salinity conditions, determining that specific microbial communities can adapt to hypersaline environments and maintain activity during the anaerobic digestion of high-salt substrates. Additionally, a novel pilot-scale hybrid anaerobic labyrinth-flow bioreactor was designed to optimize anaerobic biodegradation and enhance biogas production efficiency was performed in Contribution 3. Moreover, two other works studied different pre-treatments to enhance the anaerobic process: The authors of Contribution 4 aimed to assess how electromagnetic microwave radiation employed as a heat source influences the anaerobic processing of high-load poultry slaughterhouse wastewater and its efficiency. The authors concluded that microwave reactor heating has a positive effect on high-load poultry slaughterhouse wastewater anaerobic digestion performance. On the other hand, the authors of Contribution 5 studied the combined impact of simultaneous ultrasound heating and disintegration on the technological performance and energy balance of anaerobic digestion for high-load poultry slaughterhouse wastewater. Their findings indicated that integrating heating with ultrasonic disintegration markedly increased the proportion of organic matter in the dissolved phase compared to traditional heating methods, leading to enhanced biogas production, higher methane content, and improved process kinetics.

There were also some more works dealing with different potential benefits from biogas applications. For instance, the work performed in Contribution 6 investigated the transformation of biogas into high-value liquid products through a non-thermal plasma-assisted process in a dielectric barrier discharge reactor, utilizing Ni/Al₂O₃, Fe/Al₂O₃, and Ni-Fe/Al₂O₃ catalysts to enhance the generation of valuable chemicals from biogas. The researchers of Contribution 7 demonstrated how biogases derived from crop residues in the Andean region influence the performance of a medium-sized gas turbine used for electrical power generation.

There is also an interesting study in the Contribution 8 that reported the use of an open photobioreactor for microalgae cultivation to upgrade biogas by removing CO₂.

There is a review article performed by the authors of Contribution 9 that discusses how biogas and biomethane from anaerobic digestion of diverse wastes offer sustainable energy solutions and environmental benefits in a circular economy. To end with the Special Issue, the paper presented by the authors of Contribution 10 make a valuable review of studies focused on biogas production via the treatment of municipal and domestic wastewater with the use of anaerobic membrane bioreactors technology.

3. Perspectives on the Future Use for Biogas

The future of biogas holds immense potential as a sustainable energy source in a circular economy. Derived from anaerobic digestion of organic wastes like agricultural residues, food scraps, and livestock manure, biogas offers a renewable alternative to fossil fuels. Advances in technology will enhance biogas production efficiency, improve biomethane upgrading, and expand its applications in electricity, heating, and transportation. Integrating biogas with smart grids and carbon capture systems could further reduce greenhouse gas emissions. By valorizing waste and promoting energy independence, biogas is poised to play a pivotal role in achieving global climate goals and fostering resilient, eco-friendly energy systems.