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.

Occupant safety is one of the critical performance criteria established in the aerospace industry. Several composite materials have been developed but the energy absorption properties are not yet satisfactory. This study investigates the energy absorption characteristics of aluminum tubes reinforced with coir-fiber/epoxy system at varying proportions (10-90%) according to the specifications of hybrid tube thickness compositions (10T, 15T, 20T) towards evolving a criterion for optimal performance. Finite element analysis was conducted in ABAQUS to determine the load–displacement response and the crashworthiness properties of the tubes while a representative volume element (RVE) model was formulated to obtain the elastic properties of the reinforcement phase. The results indicated that the incidence of high peak forces P_max is related to tube thickness variations where the 20T tubes were found to give the best performance, while the 15T tubes showed a superior performance under progressive crushing and presented the best responses for specific energy absorption (SEA). A multi-objective optimization plan was implemented and through the Pareto fronts, tube configurations (C20T60F), (C15T70F) and (C20T40F) were found to be most consistent with the design criteria. Results from experimental validation were found to be in close agreement with numerical predictions and satisfied the overall objective of achieving a good balance in lightweight design for crashworthiness applications.