The rapid depletion and environmental concerns associated with the use of fossil fuels has led to extensive development of biofuels such as bioethanol from seaweeds. The long-term prospect of seaweed bioethanol production however, depends on the selection of processes in the hydrolysis and fermentation stages due to their limiting effect on ethanol yield. This review explored the factors influencing the hydrolysis and fermentation stages of seaweed bioethanol production with emphasis on process efficiency and sustainable application. Seaweed carbohydrate contents which are most critical for ethanol production substrate selection were 52 ± 6%, 55 ± 12% and 57 ± 13% for green, brown and red seaweeds, respectively. Inhibitor formation and polysaccharide selectivity were found to be the major bottlenecks influencing the efficiency of dilute acid and enzymatic hydrolysis, respectively. Current enzyme preparations used, were developed for starch-based and lignocellulosic biomass but not seaweeds, which differs in polysaccharide composition and structure. Also, the identification of fermenting organisms capable of converting the heterogeneous monomeric sugars in seaweeds is the major factor limiting ethanol yield during the fermentation stage and not the SHF or SSF pathway selection. This has resulted in variations in bioethanol yields, ranging from 0.04 g/g DM to 0.43 g/g DM.

Electrode materials are critical for microbial fuel cells (MFC) since they influence the construction and operational costs. This study introduces a simple and efficient electrode material in the form of palm kernel shell activated carbon (AC) obtained in tropical regions. The novel introduction of this material is also targeted at introducing an inexpensive and durable electrode material, which can be produced in rural communities to improve the viability of MFCs. The maximum voltage and power density obtained (under 1000 Ω load) using an H-shaped MFC with AC as both anode and cathode electrode material was 0.66 V and 1.74 W/m³, respectively. The power generated by AC was as high as 86% of the value obtained with the extensively used carbon paper. Scanning electron microscopy and Denaturing Gradient Gel Electrophoresis (DGGE) analysis of AC anode biofilms confirmed that electrogenic bacteria were present on the electrode surface for substrate oxidation and the formation of nanowires.

Hydrolysis in bioethanol production is one of the most limiting stages in the entire production process since it is the stage where the sugars to be converted to ethanol are obtained. Ulva fasciata, Hydropuntia dentata and Sargassum vulgare seaweeds were examined in this study to determine the most efficient pretreatment, optimal hydrolysis conditions and predictive models with dilute sulphuric acid and cellulase enzyme as catalysts. Dilute acid pretreatment was found to be the most efficient in maximizing the catalytic efficiency of enzymes applied on all the three selected seaweeds. Ulva fasciata, however, was found to be efficiently hydrolysable without any form of pretreatment. The study also found dilute sulphuric acid hydrolysis to be less effective since it released up to 52.4% of reducing sugars in the seaweeds as compared to the 90.9% from hydrolysis with cellulase enzyme. Also, the most efficient regression model between the seaweed species studied was obtained for the enzymatic hydrolysis of U. fasciata with a correlation coefficient of 99.4%. This indicates a high precision in predicting the reducing sugar yields from the species within boundary conditions. Overall, the optimal enzymatic hydrolysis process was influenced most by substrate concentration for all three seaweeds examined.

Pineapple is one of the most popular tropical fruits, enjoyed globally due to its numerous nutritional benefits and unique flavour. However, fruit processing generates substantial underutilized biowaste, highlighting the need for innovative valorization of this waste-stream to produce useful bio-based products. This supports Sustainable Development Goal (SDG) 12 that focuses on Responsible Production and a circular bioeconomy. This study investigated the sequential recovery of soluble and insoluble sugars from Pineapple Processing Residues (PPR) to formulate hexose–pentose syrups as an alternative approach to residue valorization. The recovery process utilised an integrated approach of solid–liquid extraction and chemical catalysts to efficiently hydrolyse complex biomass into fermentable sugars. The study established that all syrup yields from the various PPRs were within the ranges of 11–15% and with high concentrations of glucose (22–55 g/100 g syrup) and fructose (23–49 g/100 g syrup) and no significant variation in their monomeric sugar compositions. A further optimization study revealed that all PPR types can be hydrolysed under the same optimal conditions of 50 min reaction time, 120 °C temperature, and 0.3 M acid concentration. Among the PPRs, the core of the smooth cayenne cultivar (SCC) was identified as the most viable for soluble sugar yield (64.2 g/100 g DM) and insoluble sugar yield (17.74 g/100 g DM). Overall, the analysis revealed that all four PPRs were viable for producing high hexose-pentose syrups. Graphical Abstract