Hydrogen is a clean, flexible, powerful energy vector that can be leveraged as a promising alternative to fossil fuels. Additionally, green hydrogen production has been recognized as one of the most prevalent solutions to decarbonize the energy system. Water electrolysis studies have increased throughout the decade as higher industrial interest comes into play. The catalyst, system design, and configuration act in a congenial manner to deliver high‐performing water electrolysis. Despite performance targets peaking at high current densities, the current status of water electrolyzer technologies would require more research efforts to achieve such goals. This work presents a comprehensive review of how catalysts and electrolyzer designs can be enhanced to attain high current density water electrolysis. Modification strategies of catalysts, advances in characterization and modelling, and optimizing system designs are highlighted. Furthermore, this paper aims to elucidate the future research direction of water electrolysis to bridge the laboratory‐to‐industry gap.

Organic waste has been discharged into the environment by various industries in a global society. Anaerobic digestion has proven its potential as a waste-to-energy (WTE) technology to produce biogas, which can also replace fossil fuels while accommodating these unwanted wastes. However, there are limitations to anaerobic digestion, such as poor biomethane yield due to limited supply and fluctuations in the composition of the substrates, and an inadequate C/N ratio in the feedstocks. This paper aims to discuss possible methods to overcome the constraints in the process, including co-digestion and immobilization of the substrates via a moving bed biofilm reactor. The parameters discussed in this literature were the following: (1) mode of operation; (2) temperature; (3) type of anaerobic digestion; (4) pre-treatment methods; (5) addition of nutrients; and (6) using plastic carriers. An in-depth study highlighting the role of industries in biogas production toward achieving circularity was also examined. Several studies have shown that co-digestion enhances biogas production more than mono-anaerobic digestion. Notably, using plastic carriers for immobilization can improve the metabolic process due to biofilm formation and serve as a niche for microbial culture. In addition, excessive nutrients can be highly toxic as they can inhibit bacterial activity in the methanogenic phase. This review also presented the techno-economic analysis of utilizing distillery wastewater and press mud from sugarcane industries to produce biogas. Therefore, the findings in this article allow the development of optimization designs for industrial scale based on circular economy to address various organic wastes.

Laboratory-scale anaerobic digesters were fabricated and used in the co-digestion of press mud and distillery effluent to investigate the effect of pretreatments (biological/enzymatic and chemical/alkaline) and nutrient supplementation for enhanced biogas production. The findings of this study showed that maximum biogas yield (502.86 mL/g TVSadded) with maximum percentage of methane (55%) was obtained in combined enzymatic and alkaline (calcium hydroxide) pretreatment with addition of nutrients (i.e., B6). Combined alkaline pretreatment and nutrient supplementation resulted to a 55.07% increase in biogas yield compared to the control. Sole nutrient addition enhanced the yield by 64.38%. However, single alkaline pretreatment presented inhibitory effect which resulted to a 22.48% decrease in biogas production. Moreover, the percentage of methane gas in the biogas samples was between 14 and 55%. Samples dosed with enzymes resulted to better methane yields (>50%) than the samples without enzymes. Highest reductions in BOD, COD and TSS were also achieved in sample B6. Thus, enzymes, especially when combined with other methods, have potential for improving biogas production from sugarcane wastes.