Critical review on the formations and exposure of polycyclic aromatic hydrocarbons (PAHs) in the conventional hydrocarbon-based fuels: Prevention and control strategies

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the atmosphere and primarily originate from the incomplete burning of fossil fuels and biofuels. Exposure to PAHs leads to harmful effects on human health and the environment. Diesel engines are a major source of PAH production in the transportation sector. Various approaches have been employed to reduce PAH emissions from diesel engines, including the use of biodiesel, green gaseous fuels, exhaust gas recirculation, exhaust after-treatment, and genetically modifying biodiesel with nanoparticles. This review focuses on PAH emissions from different generations of fuels and examines the remedial control actions taken to mitigate PAH formation. The study underscores the necessity for effective regulation of emissions from diesel engines, especially in developing countries where the reliance on fossil fuels is significant. Biodiesel has shown promise in reducing PAHs and carcinogenic pollutants, with higher biodiesel concentrations resulting in lower PAH formation. Replacing diesel with biodiesel and optimizing engine operating conditions are feasible methods to reduce PAH levels in the atmosphere. The use of nanoparticles in fuel blends and higher oxygen content in combustion chambers are also considered potential strategies for pollutant reduction. Additionally, the utilization of hydrogen and ammonia as secondary fuels has been explored as promising alternatives to fossil fuels. The study highlights the importance of further research on the presence of residual PAHs in the atmosphere and the implementation of strategies to curtail vehicular emissions.

Recovering biogas and nutrients via novel anaerobic co-digestion of pre-treated water hyacinth for the enhanced biogas production

The present investigation explores the feasibility of generating biogas from water hyacinth (WH) through a pretreatment process. The WH samples were subjected to a high concentration of H2SO4 pretreatment to enhance biogas production. The H2SO4 pretreatment aids in breaking down the lignocellulosic materials found in the WH. Additionally, it helps modify the cellulose, hemicellulose, and lignin, which assists in the anaerobic digestion process. The samples underwent pretreatment with 5% v/v H2SO4 for 60 min. Biogas production was conducted for both untreated and pretreated samples. Furthermore, sewage sludge and cow dung were used as inoculants to promote fermentation in the absence of oxygen. The results of this study demonstrate that the pretreatment of water hyacinth with 5% v/v H2SO4 for 60 min considerably enhances biogas production through the anaerobic co-digestion process. The maximum biogas production was recorded by T. Control-1, with a production rate of 155 mL on the 15th day compared to all other controls. All the pretreated samples showed the highest biogas production on the 15th day, which is comparatively five days earlier than the untreated samples. In terms of CH4 production, the maximum yield was observed between the 25th and 27th days. These findings suggest that water hyacinth is a viable source of biogas production, and the pretreatment method significantly improves biogas yield. This study presents a practical and innovative approach to biogas production from water hyacinth and highlights the potential for further research in this area.

High efficiency lipid production, biochar yield and chlorophyll a content of chlorella sp. microalgae exposed on sea water and TiO2 nanoparticles

This study explores the challenges facing microalgae biofuel production, specifically low lipid content and difficulties with algal cell harvesting. The purpose of the research is to investigate the effect of seawater content and nanoparticle concentration on freshwater microalgae growth and biofuel production. The principal results of the study show that increasing the proportion of seawater and nanoparticles enhances the lipid content and cell diameter of microalgae, while excessive concentrations of nanoparticles and low seawater content lead to reduced microalgae growth. Furthermore, an optimal cell diameter was identified at a nanoparticle concentration of 150 mg/L. The study also reveals that increasing seawater content can decrease zeta potential and increase chlorophyll a content due to the concentration of dissolved organic matter. Increasing the seawater content from 0% to 25% decreased zeta potential by 1% owing to the instability and aggregation of the cells. Chlorophyll a for the 0% seawater was 0.55 which is increased to 1.32 only due to the increase in the seawater content. This significant increase is due to the concentration of dissolved organic matter in seawater. Additionally, the presence of seawater positively affects microalgae metabolic activity and biochar yield. The findings of this study offer valuable insights into the potential for optimizing microalgae biofuel production. The use of seawater and nanoparticles has shown promise in enhancing microalgae growth and biofuel yield, and the results of this study underscore the scientific value of exploring the role of seawater and nanoparticles in microalgae biofuel production. Further research in this area has the potential to significantly contribute to the development of sustainable energy solutions.

Utilization of agricultural, industrial waste and nanosilica as replacement for cementitious material and natural aggregates - Mechanical, microstructural and durability characteristics assessment

This study examines the effect of rice husk ash (RHA) and nanosilica, and ground granular blast furnace slag (GGBS) on concrete mechanical and durability properties. The cement had been partially replaced with nanosilica and RHA having substitution percentages up to 6% and 10% respectively whereas the sand had been partially replaced by GGBS at 20% for all mixes. A water-to-cementitious materials ratio of 0.38 and a sand-to-cementitious materials ratio of 2.04 were used to cast eight different concrete mixes. The nanosilica used in the present research possessed some favorable effects such as rich fineness, higher surface area and greater reactivity which signified one of the best cement replacement materials. Both the durability and strength of concrete specimens possessing nanosilica, RHA and GGBS was evaluated using in-elastic neutron scattering, SEM image, piezoresistive test, split tensile strength, flexural strength and compressive strength test. Concrete specimens were also subjected to chloride penetration and water absorption to examine the impact of replacement materials on the concrete's durability attributes. Concrete performance was increased by the ternary blending of concrete because of the active participation of nanosilica in durability and strength at early ages, both RHA and GGBS played an important role in improving packing density. It was found that as the percentage of cement replaced with nanosilica increases, the durability of concrete also significantly increases. But the optimum strength parameter was found when 4% of cement was replaced by the nanosilica effectively. The proposed ternary mix may be eco-friendly by saving cement and enhancing strength and durability effectively.