For the production of biodiesel from waste cooking oil with an acid value of 1.86 mg KOH/g, five heterogeneous catalysts—Ba(OH)₂, CaO, MgO, ZnO, and AlCl₃—were employed. To optimize the reaction parameters of each catalyst, the influence of crucial process variables, such as catalyst loading, methanol-to-oil ratio, and reaction duration, was investigated. In addition, the effect of acetone as a cosolvent toward the progress of biodiesel production and the reusability of the heterogeneous catalysts were also examined, and the data were statistically evaluated with a 95% confidence level. Ba(OH)₂ performed exceptionally well, with a 92 wt.% biodiesel yield, followed by CaO with an 84 wt.% yield. However, none of the results for MgO, ZnO, or AlCl₃ were adequate. In addition, regardless of the type of catalyst utilized, adding 20 vol.% acetone to the biodiesel manufacturing process led to an increase in output. Furthermore, every heterogeneous catalyst was reusable, but only Ba(OH)₂ and CaO produced a significant yield until the third cycle. The other catalysts did not produce yields of any significance.

The crude glycerol produced as a byproduct of transesterification synthesis has very few applications because it comprises of significant amounts of methanol, catalyst, and soap. On the other hand, transesterifications of highly acidic oil in the presence of an alkaline catalyst are problematic due to the presence of high amounts of free fatty acids. In this study, the free fatty acid level of high acid oil, which was initially determined to be 19.25%, was decreased to permit the direct production of biodiesel via glycerolysis with pure glycerol, making direct transesterification feasible. Through a process of purification, crude glycerol was refined to 92.5% purity. It was revealed that the physiochemical parameters of density, moisture content, ash content, matter organic non-glycerol content, pH, and Na/K concentrations of generated purified glycerol are equal to those of commercially available glycerol. In contrast, glycerolysis treatment successfully decreased the free fatty acid level to less than 2% under optimal conditions, which were determined to be 200 °C, a glycerol-to-oil molar ratio of 4:1, and a KOH catalyst concentration of 1.6 wt.% at 350 rpm. The inclusion of hexane as a co-solvent accelerated the glycerolysis process, and the weight ratio of oil-to-hexane was 8:1. Moreover, it was viable to use waste methanol for biodiesel synthesis and purified crude glycerol as a raw material in a variety of industries, including biodiesel production. In addition, compared to acid esterification, the FFA concentration of oil with a high acid value fell significantly.

A growing awareness of global climate change has led to an increased interest in investigating renewable energy sources, such as the anaerobic digestion of biomass. This process utilizes a wide range of microbial communities to degrade biodegradable material in feedstock through a complex series of biochemical interactions. Anaerobic digestion exhibits nonlinear dynamics due to the complex and interacting biochemical processes involved. Due to its dynamic and nonlinear behavior, uncertain feedstock quality, and sensitivity to the process’s environmental conditions, anaerobic digestion is highly susceptible to instabilities. Therefore, in order to model and operate a biogas production unit effectively, it is necessary to understand which parameters are most influential on the model outputs. This also reduces the amount of estimation required. Through a scoping review, the present study analyzes the studies on the application of sensitivity analysis in anaerobic digestion modeling. Both local and global sensitivity analysis approaches were carried out using different mathematical models. The results indicate that anaerobic digestion model no.1 (ADM1) was the most commonly used model for analyzing sensitivity. Both local and global sensitivity analyses are widely employed to investigate the influence of key model parameters such as kinetic, stoichiometric, and mass transfer parameters on model outputs such as biogas production, methane concentration, pH, or economic viability of the plant.

Massively using conventional plastics has led to significant environmental issues, including harm to ecosystems, wildlife, and human health, contributions to greenhouse gas emissions, and resource depletion through their extraction and production. Thus, there is an urgent imperative to seek sustainable alternatives like bio-composites. This research established the viability of banana peels and cassava starch for eco-friendly bio-composite sheets, offering insights into their properties and performance The bio-composite materials, composed of banana peels, cassava starch, banana stem fiber, glycerol, and acetic acid, were prepared in different weight-based proportions. The preparation process involved cleaning, drying, blending, and molding the materials to produce consistent bio-composite samples. The properties and performance of the composite samples were assessed for water absorption, moisture content, and tensile strength. Notably, the combination of banana peels and cassava in a 1:2 ratio, along with banana stem fiber, demonstrated favorable attributes, including reduced water absorption (ranging from 6.42 to 30.91%), desirable moisture content (ranging from 8.06 to 11.27%), and increased tensile strength (ranging from 5.345 to 11.892 MPa). These findings confirm the viability of using banana peels and cassava starch in producing bio-composite sheets, offering a sustainable alternative to conventional plastics. This study contributes to the field of sustainable materials by providing insights into the properties and performance of bio-composites, thereby supporting the development of eco-friendly bio-composite sheets.

Biogas upgrading to biomethane with microbial electrosynthesis (MES) is receiving much attention due to increasing biomethane demands and surplus renewable energy. Research has demonstrated the feasibility of MES to increase methane yield by reducing CO₂ in anaerobic digestion (AD). Such CO₂ reduction occurs at the cathode and requires the supply of both protons and electrons. The most studied sources of protons and electrons are oxidation of organic substances and water, generated at the anode. These anodic reactions, however, also imply the production of CO₂ and O₂, respectively, both with negative implications for the AD process. A source of protons and electrons without CO₂ and O₂ as by-products would be beneficial for MES-enhanced biomethane production. This opinion article discusses the possibility of ammonium to serve as a sustainable proton and electron source.

Textile factory water consumption could be optimized to minimize the generation of wastewater, reduce treatment costs, and promote resource recovery. However, downstream plant operation and management is a prime concern in the textile industry, particularly bringing treated wastewater effluent to an acceptable discharge limit. The aim of the study was to optimize key process control parameters to the observed operational challenges of existing processes and suggest an operational guide to the operators and decision makers to enhance the treatment performance in GPS-X. The formulated troubleshooting and decision support strategy, and the optimization results of waste-activated sludge in the primary and secondary clarifiers, was within the range of 15 ± 5 m³/d and 83 ± 7 m³/d, respectively, with a recycle-activated sludge flow of 150 ± 10 m³/d. The sludge retention time was 5 ± 1 d and 6.7 ± 0.5 d in the secondary and primary clarifiers, respectively. The addition of a carbon source in the form of molasses had a flow of 0.5 ± 0.05 m³/d, and the variation in the influent due to wastewater characteristics and rainfall was optimized to 600 ± 50 m³/d. The optimum air flow into the aeration tank was 550 ± 5 m³/hr and saved 91.5% of energy in the optimized process. Thus, the study is indispensable for the effective and efficient operation of the plant and serves as a good guide to the plant operators and decision makers for the best course of action.