• Energy Research

Thermochemical methods are regarded as promising approach for managing sludge, that can achieve resources and energy recovery, volume reduction followed by efficient elimination of microorganisms. This review highlights an extensive description of the implementation of thermochemical technologies involving pyrolysis, gasification and hydrothermal liquefaction for valorisation of sludge into bio-fuel thus reducing the issues related to surplus generation and accumulation of sludge in environment affecting human health followed by rapid depletion of energy resources. The paper addresses working mechanism of thermochemical processes, their implementation for sludge conversion to bio-fuel and common factors affecting the process efficiency. Various studies have proved possible potential of thermochemical techniques for conversion of sludge to bio-fuel obtaining a high yield of bio-fuel and syngas. However, few technical challenges are still there that requires further studies and understanding for a better commercialization on industrial-scale and subsequently the future perspectives have also been analysed. Data collected from existing studies revealed that hydrothermal liquefaction has the efficiency to be proved better than other thermochemical technologies for proper valorisation of sludge resulting in high bio-fuel yield.

AbstractThe demand for renewable fuels has risen as a result of increasing human population, urbanization, industrialization, and transport systems. Biodiesel production using metal oxide‐based heterogeneous catalysts is an efficient, sustainable, and environmentally friendly approach. Because of their recovery, reusability, and consistency, heterogeneous catalysts may be preferable to homogeneous catalysts. Since the last few decades, the metal oxides of alkali earth and transition metals and their composite materials have been used as nanocatalysts in the production of biodiesel fuel. Utilization of inorganic metal oxide nanoparticles (MONPs) and their composite materials in producing biodiesel has gained increased attention because of their advanced physical and chemical characteristics. In this review, the applicability of metal oxides and their nanocomposite‐based catalysts in biodiesel production, transesterification reactions with nanocatalytic systems, and the important parameters that affect these reactions are discussed.

Pyrene (polycyclic aromatic hydrocarbon), an anthropogenic organic pollutant prevalent in various ecological units, receives more attention for bioremediation and energy transformation using microalgae. In this study, we have used pyrene pollutant (50-500 ppm) to evaluate the half-maximal inhibitory concentrations (IC50) of Chlorella sorokiniana and the impact on metabolites as well as the induction of lipid biosynthesis to produce renewable biodiesel. Pyrene concentration at 230 ppm (IC50) caused half-maximum inhibition for the 96 h incubation. The harvest in the stationary stage (day 16) for C. sorokiniana revealed a biomass generation of 449 ± 7 mg L-1 and 444 ± 8 mg L-1 dcw in the control medium and pyrene IC50 medium, respectively. An insignificant decline in biomass generation (1.2%) was observed due to the stress effect of the pyrene IC50 medium on metabolic biosynthesis. Although contrary to biomass generation, IC50 of pyrene assisted to induce lipid biosynthesis in C. sorokiniana. The improvement in lipid biosynthesis was observed as ~24% higher in pyrene IC50 compared to the control medium. The chemical composition of the microalgae biomass, metabolites, and lipids was examined using FTIR spectra. The extracted lipid was transesterified to produce biodiesel via methanolic-H2SO4 catalysis. The renewable biodiesel obtained was evaluated using FTIR and 1H NMR spectra. The transformation efficiency of the lipid of C. sorokiniana in biodiesel was calculated as ~81%. This research offers the incentive in lipid biosynthesis in microalgae cells using pyrene for the production of renewable and sustainable ecological biofuels along with bioremediation of pyrene.

The ecological environment has been greatly affected by industrialization concerning various hazardous impacts on living beings. Climate change is one of the foremost issues that have been observed in recent decades as a concern of the upsurge in greenhouse gases (GHGs) in the global atmosphere. Industrialization has been marked as the central cause for triggering GHGs in the atmospheric environment. Moreover, carbon dioxide (CO2) is a major content of greenhouse gases that have increased risk at an alarming rate. The level of CO2 in the atmosphere must be addressed through efficient carbon sequestration technologies. Numerous technologies for carbon dioxide sequestration have been investigated with chemical and biological methods. Microalgae research emerged as an economical and beneficial approach for suppressing and balancing the amount of carbon dioxide in the environment. Microalgae have been used extensively for maintaining environmental CO2 levels and efficient generation of biomass, which can be used to generate a variety of biofuels and other valuable products. Many countries have started imperative steps towards the scaling up of microalgae. These crucial steps have led the rest of the world to consider the technology for a cleaner and safer environment by influencing them to start investing in carbon sequestration through microalgae cultivation. This review illustrates several approaches and products generated by photosynthetic microalgae in carbon dioxide sequestration. The critical analysis of the current algae research trend and advanced technologies has been also conferred for a sustainable environment.

In order to increase microalgal biomass productivity efficient cultivation and harvesting methods are needed against the available traditional methods. The present study focuses on the same by harvesting microalgae using agar gel. Agar medium containing bold's basal medium (BBM) undergoes a thermoreversible gel transition. As compared to the traditional protocols, this gel is used to cultivate microalgae without even affecting the total productivity. To develop the gel for microalgae cultivation, agar was boiled in BBM. Then the agar was cooled to 35°C and microalgae culture was added to it. After seeding the microalgae the temperature of the agar was further decreased by 10°C to induce gelation. Instead of isolated cells microalgae were grown in clusters within the agar gel. Microalgal clusters gravimetrically settle at the bottom within 2h. In this method agar can be reused.

The development of highly nutritious bakery products with optimum utilization of food waste is a major challenge for the food industry. The optimum utilization of food waste for the sustainable development goal of the country is important for the growth of the nation. The aim of the present work is to prepare value-added composite flour-mixed bread from waste fruit and vegetables. The composite flour was prepared in four formulations of peel and pomace with wheat flour (PPWF), as PPWF1, PPWF2, PPWF3, and PPWF4. Composite flour was blended with a mix of vegetable and fruit pomace powders and whole wheat flour. Indian gooseberry pomace powder, apple pomace powder, bottle gourd peel powder, and potato peel powder were used with whole wheat flour to make pomace and whole wheat flour compositions such as PPWF1, PPWF2, PPWF3, and PPWF4. Out of these four flours, PPWF3 contained a good amount of fiber 8.16%, crude protein 3.18%, total phenolic content 14.48%, moisture 9.5%, vitamin C 13.64 mg/100 g, and total phenolic compound 14.48 (mg/GAE/g), which are maximum and acceptable range values as compared to the other three composite flours and the control group flour. PPWF3 is used as a partial replacement ratio for wheat flour due to its high phenolic content, vitamin C content, and richness in fibers. This composite flour is used to make bread dough, and two samples, G1 and G2, are made, out of which G2 offers better nutritional, functional, and sensory evaluations in comparison with refined wheat bread, which is taken as a control group. Thus, such utilization of food waste in bread making can generate value from waste and improve the nutritional attributes of bread, which may improve an individual’s health.

The hydrothermal liquefaction of municipal sludge was investigated under isothermal conditions (255 °C, 45 min) with TiO2 as a catalyst. In this study, we used two separation methods (an organic solvent-assisted extraction method and the Soxhlet extraction method) for the production of bio-crude oil. The maximum yield of bio-crude oil was 20.7 wt. % reported with the Soxhlet extraction method. The aqueous phase was examined for TN, TP, COD, and TOC to determine the suitability of this phase for microalgae cultivation. Four strains of oleaginous microalgae were cultivated in the aqueous phase. The results show that the growth of microalgae in the aqueous phase was lower compared to the control medium; this may be due to the high COD value. Microalgae and yeast co-cultivation increases biomass and lipid productivity using nutrients in the aqueous phase.