Saurabh Jyoti Sarma

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) by fungal enzymes: A review

Polycyclic aromatic hydrocarbons (PAHs) are a large group of chemicals. They represent an important concern due to their widespread distribution in the environment, their resistance to biodegradation, their potential to bioaccumulate and their harmful effects. Several pilot treatments have been implemented to prevent economic consequences and deterioration of soil and water quality. As a promising option, fungal enzymes are regarded as a powerful choice for degradation of PAHs. Phanerochaete chrysosporium, Pleurotus ostreatus and Bjerkandera adusta are most commonly used for the degradation of such compounds due to their production of ligninolytic enzymes such as lignin peroxidase, manganese peroxidase and laccase. The rate of biodegradation depends on many culture conditions, such as temperature, oxygen, accessibility of nutrients and agitated or shallow culture. Moreover, the addition of biosurfactants can strongly modify the enzyme activity. The removal of PAHs is dependent on the ionization potential. The study of the kinetics is not completely comprehended, and it becomes more challenging when fungi are applied for bioremediation. Degradation studies in soil are much more complicated than liquid cultures because of the heterogeneity of soil, thus, many factors should be considered when studying soil bioremediation, such as desorption and bioavailability of PAHs. Different degradation pathways can be suggested. The peroxidases are heme-containing enzymes having common catalytic cycles. One molecule of hydrogen peroxide oxidizes the resting enzyme withdrawing two electrons. Subsequently, the peroxidase is reduced back in two steps of one electron oxidation. Laccases are copper-containing oxidases. They reduce molecular oxygen to water and oxidize phenolic compounds.

Toxicity of chlortetracycline and its metal complexes to model microorganisms in wastewater sludge.

Complexation of antibiotics with metals is a well-known phenomenon. Wastewater treatment plants contain metals and antibiotics, thus it is essential to know the effect of these complexes on toxicity towards microorganisms, typically present in secondary treatment processes. In this study, stability constants and toxicity of chlortetracycline (CTC) and metal (Ca, Mg, Cu and Cr) complexes were investigated. The calculated stability constants of CTC-metal complexes followed the order: Mg-CTC>Ca-CTC>Cu-CTC>Cr-CTC. Gram positive Bacillus thuringiensis (Bt) and Gram negative Enterobacter aerogenes (Ea) bacteria were used as model microorganisms to evaluate the toxicity of CTC and its metal complexes. CTC-metal complexes were more toxic than the CTC itself for Bt whereas for Ea, CTC and its metal complexes showed similar toxicity. In contrast, CTC spiked wastewater sludge (WWS) did not show any toxic effect compared to synthetic sewage. This study provides evidence that CTC and its metal complexes are toxic to bacteria when they are biologically available. As for WWS, CTC was adsorbed to solid part and was not biologically available to show measurable toxic effects.

Waste Biomass: A Prospective Renewable Resource for Development of Bio-Based Economy/Processes

Although industrial revolution is an important factor governing the development of a country’s economy, but at the same time, the industrial activities have been also accompanied by problem of waste biomass. This commensurate with the increase in industrialization, urbanization, and population growth is leading to production of enormous quantities of industrial waste biomass that may cause environmental and health hazards. However, the increased awareness and desire for a healthy environment among people leads to the need for better ways of waste minimization and pollution prevention and better use of resources in achieving the required industrial and environmental standards. The present book deals specifically with the valorization of waste biomass to small-volume high-value biochemicals only. The products which are produced in bulk quantities, such as biofuels, some organic acids, hydrolytic enzymes, biogas, and other traditional products from waste biomass, are not discussed. In this context, the current chapter discusses the different sources, types, and nature of waste biomass. The chapter also provides overview of the different management strategies applied for the value addition of different types of waste biomass. The chapter will provide insights into the role of waste biomass resources for developing bio-based economy/processes for industrial biotechnology and renewable energy in supporting sustainable development and economic competitiveness.

Genetic Engineering Strategies for Enhanced Biodiesel Production

The focus on biodiesel research has shown a tremendous growth over the last few years. Several microbial and plant sources are being explored for the sustainable biodiesel production to replace the petroleum diesel. Conventional methods of biodiesel production have several limitations related to yield and quality, which led to development of new engineering strategies to improve the biodiesel production in plants, and microorganisms. Substantial progress in utilizing algae, yeast, and Escherichia coli for the renewable production of biodiesel feedstock via genetic engineering of fatty acid metabolic pathways has been reported in the past few years. However, in most of the cases, the successful commercialization of such engineering strategies for sustainable biodiesel production is yet to be seen. This paper systematically presents the drawbacks in the conventional methods for biodiesel production and an exhaustive review on the present status of research in genetic engineering strategies for production of biodiesel in plants, and microorganisms. Further, we summarize the technical challenges need to be tackled to make genetic engineering technology economically sustainable. Finally, the need and prospects of genetic engineering technology for the sustainable biodiesel production and the recommendations for the future research are discussed.

Nanotechnology to Remove Contaminants

Emerging contaminants will be a major challenge for human health and environment since their concentrations are increasing. Contaminants occur in air, soil and aquatic media, then finally end up in drinking water. Contaminants cause many health issues to living organisms, by disruption of endocrine systems and feminization of male fish, for instance. Therefore, prevention of contaminant release, and cleaning of contaminated media are needed. Many processes, including physical separation, biological treatment and chemical transformation have been set up to remove contaminants. Here we review methods to remove contaminants using nanomaterials, such as nanoparticles, nanotubes, and nanostructured membranes. New processes based on nanostructured materials such as TiO2 nanowires or nanofiltration membrane can achieve up to 95 % removal of contaminants.

C3–C4 Platform Chemicals Bioproduction Using Biomass

Platform chemicals composed of 3–4 carbons are group of chemicals that can be used as important precursors for making a variety of chemicals and materials, including solvents, fuels, polymers, pharmaceuticals, perfumes, and foods. At present, most of the commercial platform chemicals composed of 3–4 carbons are produced from petroleum-based products. However, fossil-derived resources are nonrenewable and their amount is increasingly depleting. Additionally, application of these materials has number of environmental concerns. To overcome these problems, increasing interest has focused on the development of sustainable technologies for producing these platform chemicals from renewable resources. Researchers have made significant progress in biological production using metabolic of platform chemicals using engineering-modified microorganisms. However, the production efficiency still needs to be improved for it to become economically viable. Further work on engineering these strains and exploring their tolerances and the use of low-cost renewable substrate like biomass may increase the yields of green platform chemicals to an industrial scale. In this review we focused on the current status of the bio-based production of major C3–C4 platform chemicals, by direct microbial bioconversion of renewable materials.

Utilization of Agro-industrial Waste for the Production of Aroma Compounds and Fragrances

Agro-industrial wastes are unavoidable waste materials continuously generated in bulk quantity. Most of these materials can be used as nutrient source for industrial fermentation. However, commercial fermentation of low-value high-volume products generally suffer financial crisis. Alternatively, sustainable biotransformation of agro-industrial waste into fine biochemical, such as aroma compounds and fragrances, has been widely investigated. Significant variation of substrate quality imparts great variations in the production methodology of these processes. Further, a range of microorganisms are known to be used and different genetic engineering strategies have been applied for improved bioconversion. Moreover, novel strategies for detection, identification, and purification of the final products have been developed, and in some particular cases, successful commercialization has also been achieved. To have, however, further benefit from this potential strategy, a systematic study of the type and nature of the feedstock and their abundance should be evaluated. Similarly, presently used processes and their scale-up potential should be determined and different options for their economic competitiveness should be identified. The goal of this chapter, therefore, is to improve the basic understanding of the interesting strategy and to summarize the recent advancements in production of aroma compounds and fragrances.

Energy Recovery from Municipal and Industrial Wastes: How much Green?

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