Poor management of organic waste is a key environmental and public health issue as it contributes to environmental contamination and the spread of diseases. Anaerobic digestion (AD) presents an efficient method for organic waste management while generating energy and nutrient-rich digestate. However, the AD process is limited by key factors, which include process inefficiencies from substrate-induced instability, poor quality digestate, and poor management of effluent and emissions. Lately, there has been more interest in the use of biochar for improving anaerobic digestion. Biochar can improve methane production by speeding up the methanogenesis stage, protecting microorganisms from toxic shocks, and reducing inhibition from ammonia and volatile fatty acids. It can be applied for in situ cleanup of biogas to remove carbon dioxide. Applying biochar in AD is undergoing intensive research and development; however, there are still unresolved factors and challenges, such as the influence of feedstock source and pyrolysis on the performance of biochar when it is added to the AD process. In light of these considerations, this review sheds more light on various potential uses of biochar to complement or improve the AD process. This review also considers the mechanisms through which biochar enhances methane production rate, biochar’s influence on the resulting digestate, and areas for future research.

Liquefied natural gas (LNG) is regarded as the cleanest among fossil fuels due to its lower environmental impact. In power plants, it emits 50–60% less carbon dioxide into the atmosphere compared to regular oil or coal-fired plants. As the demand for a lower environmental footprint is increasing, fuel cells powered by LNG are starting to appear as a promising technology, especially suitable for off-grid applications, since they can supply both electricity and heating. This article presents a techno-economic assessment for an integrated system consisting of a solid oxide fuel cell (SOFC) stack and a micro gas turbine (MGT) fueled by LNG, that feeds the waste heat to a multi-effect desalination system (MED) on the Greek island of Patmos. The partial or total replacement of the diesel engines on the non-interconnected island of Patmos with SOFC systems is investigated. The optimal system implementation is analyzed through a multi-stage approach that includes dynamic computational analysis, techno-economic evaluation of different scenarios using financial analysis and literature data, and analysis of the environmental and social impact on the island. Specific economic indicators such as payback, net present value, and internal rate of return were used to verify the economic feasibility of this system. Early results indicate that the most sensitive and important design parameter in the system is fuel cell capital cost, which has a significant effect on the balance between investment cost and repayment years. The results of this study also indicate that energy production with an LNG-fueled SOFC system is a promising solution for non-interconnected Greek islands, as an intermediate carrier prior to the long-term target of a CO₂-free economy.