Dependence on fossil fuels for meeting the growing energy demand is damaging the world’s environment. There is a dire need to look for alternative fuels that are less potent to greenhouse gas emissions. Biofuels offer several advantages with less harmful effects on the environment. Biodiesel is synthesized from the organic wastes produced extensively like edible, non-edible, microbial, and waste oils. This study reviews the feasibility of the state-of-the-art feedstocks for sustainable biodiesel synthesis such as availability, and capacity to cover a significant proportion of fossil fuels. Biodiesel synthesized from oil crops, vegetable oils, and animal fats are the potential renewable carbon-neutral substitute to petroleum fuels. This study concludes that waste oils with higher oil content including waste cooking oil, waste palm oil, and algal oil are the most favorable feedstocks. The comparison of biodiesel production and parametric analysis is done critically, which is necessary to come up with the most appropriate feedstock for biodiesel synthesis. Since the critical comparison of feedstocks along with oil extraction and biodiesel production technologies has never been done before, this will help to direct future researchers to use more sustainable feedstocks for biodiesel synthesis. This study concluded that the use of third-generation feedstocks (wastes) is the most appropriate way for sustainable biodiesel production. The use of innovative costless oil extraction technologies including supercritical and microwave-assisted transesterification method is recommended for oil extraction.

The palm biodiesel industry is facing many challenges implementing biodiesel program in Malaysia. This paper addresses the importance of the B10 blend (10% biodiesel, 90% petroleum diesel), global challenges of palm oil import and export, and protective measures for continuous positive growth of the palm oil sector. Palm oil is the backbone of Malaysia’s economy, covering more than 5% of its gross domestic product (GDP). The key steps taken by the Malaysian government for the successful implementation of the B10 program are discussed in this review study. Till now, B5 and B7 biodiesel programs have been successfully implemented in Malaysia. The B10 biodiesel program is attractive because of the developed local palm oil sector. The B10 biodiesel program will increase the use of renewable energy sources, and is expected to increase the productivity of palm oil and biodiesel implementation in the country. Despite successful B5 and B7 programs, Malaysia is facing challenges for the implementation of biodiesel due to fluctuation in crude palm oil prices, low domestic usage of palm oil, and vehicle warranty. The improvement of palm oil and promotion of B10 through targeted agencies in the central region of Malaysia will help to implement the biodiesel program successfully.

Microbubbles with slow rising speed, higher specific area and greater oxygen dissolution are desired to enhance gas/liquid mass transfer rate. Such attributes are very important to tackle challenges on the low efficiency of gas/liquid mass transfer that occurs in aerobic wastewater treatment systems or in the aquaculture industries. Many reports focus on the formation mechanisms of the microbubbles, but with less emphasis on the system optimization and assessment of the aeration efficiency. This work assesses the performance and evaluates the aeration efficiency of a porous venturi-orifice microbubble generator (MBG). The increment of stream velocity along the venturi pathway and orifice ring leads to a pressure drop (P_atm > P_abs) and subsequently to increased cavitation. The experiments were run under three conditions: various liquid velocity (Q_L) of 2.35–2.60 m/s at fixed gas velocity (Q_g) of 3 L/min; various Q_g of 1–5 L/min at fixed Q_L of 2.46 m/s; and free flowing air at variable Q_Ls. Results show that increasing liquid velocities from 2.35 to 2.60 m/s imposes higher vacuum pressure of 0.84 to 2.27 kPa. They correspond to free-flowing air at rates of 3.2–5.6 L/min. When the system was tested at constant air velocity of 3 L/min and under variable liquid velocities, the oxygen dissolution rate peaks at liquid velocity of 2.46 m/s, which also provides the highest volumetric mass transfer coefficient (K_La) of 0.041 min⁻¹ and the highest aeration efficiency of 0.287 kgO₂/kWh. Under free-flowing air, the impact of Q_L is significant at a range of 2.35 to 2.46 m/s until reaching a plateau K_La value of 0.0416 min⁻¹. The pattern of the K_La trend is mirrored by the aeration efficiency that reached the maximum value of 0.424 kgO₂/kWh. The findings on the aeration efficiency reveals that the venturi-orifice MBG can be further optimized by focusing on the trade-off between air bubble size and the air volumetric velocity to balance between the amount of available oxygen to be transferred and the rate of the oxygen transfer.

Increasing global concern on clean water scarcity and environmental sustainability drive invention in water reclamation technology. Laundry wastewater reclamation via membrane technology faces the challenge of membrane fouling. This paper assesses a tilting-the-filtration-panel filtration system for the treatment of real laundry wastewater filtration aimed for water and detergent reuse. Results showed that the panel tilting significantly improved fouling control and enhanced permeability due to enhanced contact of air bubbles with the membrane surface, which induced continuous detachment of foulant from the membrane surface. The combination of aeration rate and tilting angle resulted in up to 83% permeability enhancement from 109 to 221.4 ± 10.8 (L/m²·h·bar). The system also offers 32% detergent recovery. Overall findings suggest that the system offers an attractive approach for both fouling management and detergent recovery and can potentially be applied under a simple setup in which filtration can be driven by gravity/hydrostatic pressure.

Biodiesel production has gained considerable importance over the last few decades due to the increase in fossil fuel prices as well as toxic emissions of oxygen and nitrogen. The production of biodiesel via catalytic transesterification produces crude glycerol as a co-product along with biodiesel, amounting to 10% of the total biodiesel produced. Glycerol has a low value in its impure form, and the purification of glycerol requires sophisticated technologies and is an expensive process. The conversion of crude glycerol into value-added chemicals such as solketal is the best way to improve the sustainability of biodiesel synthesis using the transesterification reaction. Therefore, the conversion of crude glycerol into the solketal was investigated in a batch reactor simulation model developed by the Aspen Plus V11.0. The non-random two liquid theory (NRTL) method was used as a thermodynamic property package to study the effect of four input ketalization parameters. The model was validated with the findings of previous experimental studies of solketal synthesis using sulfuric acid as a catalyst. The influence of the following operating parameters was investigated: reaction time of 10,000 to 60,000 s, reaction temperature of 303 to 323 K, acetone to glycerol molar ratio of 2:1 to 10:1, and catalyst concentration of 0.005 to 0.03 wt %. The optimum solketal yield of 81.36% was obtained at the optimized conditions of 313 K, 9:1, 0.03 wt %, and 40,000 s. The effect of each input parameter on the ketalization process and interaction between input and output parameters was investigated by using the response surface methodology (RSM) optimizer. The relationship between independent and response variables developed by RSM fit most of the simulation data, which showed the accuracy of the model. A second-order differential equation fit the simulation data well and showed an R² value of 0.99. According to the findings of RSM, the influence of catalyst amount, acetone to glycerol molar ratio, and reaction time were more significant on solketal yield. The effect of temperature on the performance of the reaction was not found to be significant because of the exothermic nature of the process. The findings of this study showed that biodiesel-derived glycerol can be effectively utilized to produce solketal, which can be used for a wider range of applications such as a fuel additive. However, further work is required to enhance the solketal yield by developing new heterogeneous catalysts so that the industrial implementation of its production can be made possible.