Air pollution is a precursor to many health issues such as difficulty breathing, asthma, lung and heart diseases, and cancer. This study presents a concise view of biodiesel combustion in mitigating pollutant emissions which are generated by the combustion of fossil fuels, thereby eliminating the negative effects on human health and the environment. Gaseous pollutants such as carbon monoxide, unburned hydrocarbons, nitrogen oxides, particulate matter, and carbon dioxide are found to be major exhaust emissions from vehicles running on fossil fuels. Excessive exposure to these pollutants was found to be a precursor to reductions in life expectancy via health complications in humans. Greenhouse gas emissions from the transport sector were found to be 24% of total annual emissions, 74.5% of which came from the combustion of fossil fuel in road vehicles. Biodiesel combustion in vehicular engines is established to be a control technology in reducing gaseous pollutants toward building a sustainable and healthy human–environment scenario. The emissions reduction index from the United States National Biodiesel Board showed that the combustion of biodiesel wholly as a transportation fuel decreased total hydrocarbons, polycyclic aromatic hydrocarbons, carbon, and sulfur emissions by 67%, 80%, 48%, and 100%, respectively. Evaluation of emission results from topical literature strongly suggests that the use of biodiesel is effective in the reduction in pollutants, which is beneficial to human and environmental sustainability.

Anaerobic digestion (AD) processes can face operational challenges or flaws such as substrate structure and characteristics complexity, process complexity, low productivity, inefficient biodegradability, and poor stability, which suppresses or reduces biogas and biomethane production. As a result of the need to overcome these challenges/shortcomings and improve or enhance biogas and biomethane yield, process intensification methods have gained attention. There is some literature review on pretreatment and co-digestion as a means of improving AD performance; however, there is no systematic information on the various strategies required for improving AD performance and, in turn, increasing biogas/biomethane yield. The AD process produces biogas, a valuable renewable biofuel. Biogas is composed primarily of biomethane and other undesirable components such as carbon dioxide, oxygen, hydrogen sulphide, water vapour, ammonia, siloxanes, nitrogen, hydrocarbons, and carbon monoxide, which act as impurities or contaminants and tend to reduce the biogas specific calorific value while also causing various problems with machine operation. As a result, various technologies are used to improve raw biogas quality by removing contaminants during biogas transformation to biomethane. As a result, this paper provides a comprehensive review of the various systematic process intensification strategies used to overcome AD process challenges/shortfalls, improve or enhance biogas and biomethane production, and conventional and emerging or advanced technologies for biogas purification, cleaning, and upgrading.

Conventional production of biodiesel employs the use of alkaline catalysts because they are cheaper and less corrosive, and they use minimal energy when compared to other acidic catalysts. Heterogeneous catalysts have also shown significant effects on biodiesel production with its ease of recovery and reusability. Three reaction variables—temperature, time, and molar ratio of alcohol to oil—were optimized for biodiesel production from milk bush oil using snail shell as a catalyst. The catalyst was prepared by calcinating waste giant African land snail in an electric oven for 3.5 hours at 900°C. Also, a control transesterification experiment was carried out using potassium hydroxide (KOH) as a catalyst. Catalyst concentrations of 3.0 wt % of calcined snail shell (CSS) and KOH were used for the transesterification of the oil. A response surface analysis of biodiesel production using CSS as a catalyst showed that all reaction variables were significant. Biodiesel yield of 81% was recorded experimentally as the highest yield when temperature, reaction time, and alcohol-to-oil ratio were 65°C, 2 hours, and 9:1, respectively. An average yield of 94.33% was obtained at these same reaction conditions when KOH was used as a catalyst.

The continual generation and discharge of waste are currently considered two of the main environmental problems worldwide. There are several waste management options that can be applied, though anaerobic digestion (AD) process technology seems to be one of the best, most reliable, and feasible technological options that have attracted remarkable attention due to its benefits, including the generation of renewable energy in the form of biogas and biomethane. There is a large amount of literature available on AD; however, with the continuous, progressive, and innovative technological development and implementation, as well as the inclusion of increasingly complex systems, it is necessary to update current knowledge on AD process technologies, process variables and their role on AD performance, and the kinetic models that are most commonly used to describe the process-reaction kinetics. This paper, therefore, reviewed the AD process technologies for treating or processing organic biomass waste with regard to its classification, the mechanisms involved in the process, process variables that affect the performance, and the process kinetics. Gazing into the future, research studies on reduced MS-AD operational cost, integrated or hybrid AD-biorefinery technology, integrated or hybrid AD-thermochemical process, novel thermochemical reactor development, nutrient recovery from integrated AD-thermochemical process, and solid and liquid residual disposal techniques are more likely to receive increased attention for AD process technology of biomass wastes.

The use of vegetable oil as feedstock for biodiesel production is controversial as a result of the challenges of a food-fuel crisis associated with the use of edible oils for biodiesel production and use of arable land for energy feedstock generation. This work, therefore, focused on the extraction of oil from non-edible seed such as sandbox seed using a solvent extraction method, evaluation of optimal conditions for oil extraction from sandbox, and testing the fuel properties of extracted sandbox oil. A Box-Behnken design of response surface methodology (RSM) with 17 experimental runs was used to investigate the optimum conditions for the extraction, and the selected variables were effective seed/solvent ratio (0.04, 0.06, 0.08 g/ml), extraction temperature (65, 60, 75ºC), and extraction time (3, 5, 7 h). Selected fuel properties (specific gravity, viscosity, cloud point, pour point, density, and refractive index) of the extracted oil were determined according to American Society for Testing Materials (ASTM) standards. The optimum oil yield (63.4%) was obtained at the seed/solvent ratio, extraction temperature, and extraction time of 0.05 g/ml, 68.13ºC, and 5 h, respectively The viscosity at 30ºC, specific gravity, density, cloud point, pour point, and refractive index of the extracted oil were 4.55 mm²/s, 0.91, 910 kg/m³, 5.9 ºC, –1.0ºC, and 1.4683, respectively. Thus the result from this research work has established the optimal conditions for solvent extraction of oil from sandbox seed. The fuel properties of the sandbox oil show that it is potentially suitable to produce biodiesel that can be used to power internal combustion engines.

The use of biobased heterogeneous catalysts made from agricultural waste for producing biodiesel has gained attention for its potential to create a sustainable and low-cost process. The blending of two or more biomass residues to create more viable biobased catalysts is still in its early stages. In this study, a Biobased Composite Heterogeneous Catalyst (CHC) was made by blending the shells of periwinkle (PWS), melon seed-husk (MSH), and locust bean pod-husk (LBP) at a mixing ratio of 67:17:17 using Simplex Lattice Design Mixture, that was then calcined for 4 h at 800 °C. The chemical, structural, and morphological components of the CHC were characterized via XRF, XRD, SEM-EDX, BET, TGA/DSC, and FTIR to assess its catalytic potential. The CHC was employed to synthesize biodiesel from palm kernel oil, and the process optimization was conducted using the Taguchi approach. The XRF analysis showed that the catalyst had 69.049 of Calcium (Ca) and 9.472 of potassium (K) in their elemental and oxide states as 61.592% calcium oxide and 7.919% potassium oxide. This was also supported by the EDX result, that showed an appreciable value of 58.00% of Ca and 2.30% of magnesium, that perhaps provided the active site in the transesterification reaction to synthesize biodiesel. The morphological and physisorption isotherms via SEM and BET showed mesoporous structures in the CHC that were made up of nanoparticles. A high maximum biodiesel yield of 90.207 wt.% was attained under the optimized process conditions. The catalyst could be reused for up to four cycles, and the biodiesel produced met both ASTM D6751 and EN 14214 standards for biodiesel. This study demonstrates that blending PWS, MSH, and LBP waste materials can produce high-quality biodiesel without the need for additional catalysts.