Leather industries are key contributors in the economy of many developing countries, but unfortunately they are facing serious challenges from the public and governments due to the associated environmental pollution. There is a public outcry against the industry due to the discharge of potentially toxic wastewater having alkaline pH, dark brown colour, unpleasant odour, high biological and chemical oxygen demand, total dissolved solids and a mixture of organic and inorganic pollutants. Various environment protection agencies have prioritized several chemicals as hazardous and restricted their use in leather processing however; many of these chemicals are used and discharged in wastewater. Therefore, it is imperative to adequately treat/detoxify the tannery wastewater for environmental safety. This paper provides a detail review on the environmental pollution and toxicity profile of tannery wastewater and chemicals. Furthermore, the status and advances in the existing treatment approaches used for the treatment and/or detoxification of tannery wastewater at both laboratory and pilot/industrial scale have been reviewed. In addition, the emerging treatment approaches alone or in combination with biological treatment approaches have also been considered. Moreover, the limitations of existing and emerging treatment approaches have been summarized and potential areas for further investigations have been discussed. In addition, the clean technologies for waste minimization, control and management are also discussed. Finally, the international legislation scenario on discharge limits for tannery wastewater and chemicals has also been discussed country wise with discharge standards for pollution prevention due to tannery wastewater.

Environmental Pollution, Toxicity Profile and Treatment Approaches for Tannery Wastewater and Its Chemical Pollutants.

A technical review of bioenergy and resource recovery from municipal solid waste

Plastics are common in our daily lifestyle, notably in the packaging of goods to reducing volume, enhancing transportation efficiency, keeping food fresh and preventing spoilage, manufacturing healthcare products, preserving drugs and insulating electrical components. Nonetheless, massive amounts of non-biodegradable plastic wastes are generated and end up in the environment, notably as microplastics. The worldwide industrial production of plastics has increased by nearly 80% since 2002. Based on the degree of recyclability, plastics are classified into seven major groups: polyethylene terephthalate, high-density polyethylene, polyvinyl chloride, low-density polyethylene, polypropylene, polystyrene and miscellaneous plastics. Recycling technologies can reduce the accumulation of plastic wastes, yet they also pollute the environment, consume energy, labor and capital cost. Here we review waste-to-energy technologies such as pyrolysis, liquefaction and gasification for transforming plastics into clean fuels and chemicals. We focus on thermochemical conversion technologies for the valorization of waste plastics. This technology reduces the diversion of plastics to landfills and oceans, reduces carbon footprints, and has high conversion efficiency and cost-effectiveness. Depending on the conversion method, plastics can be selectively converted either to bio-oil, bio-crude oil, synthesis gas, hydrogen or aromatic char. We discuss the influence of process parameters such as temperature, heating rate, feedstock concentration, reaction time, reactor type and catalysts. Reaction mechanisms, efficiency, merits and demerits of biological and thermochemical plastic conversion processes are also discussed.

Thermochemical conversion of plastic waste to fuels: a review

Futuristic applications of hydrogen in energy, biorefining, aerospace, pharmaceuticals and metallurgy

Lignocellulosic feedstocks are gaining increased popularity for novel industrial applications because of their availability and bio-renewability. Using lignocellulosic materials, especially from agricultural and forestry sectors could help reduce the over-dependence on petrochemical resources while providing a sustainable waste management alternative. This review aims to describe the chemistry of different components of lignocellulosic biomass (cellulose, hemicellulose, lignin, extractives and ash). Besides, many novel industrial applications of lignocellulosic biomass have been comprehensively described, which includes biorefining for biofuel and biochemical production, biomedical, cosmeceuticals and pharmaceuticals, bioplastics, multifunctional carbon materials and other eco-friendly specialty products. The production and applications of lignocellulose-derived carbon materials such as activated carbon, carbon nanotubes, carbon nanohorns, etc. have been highlighted. The potential industrial utility of cellulose and lignin-based specialty materials such as cellulose fiber, bacterial cellulose, epoxides, polyolefins, phenolic resins, bioplastics are discussed in this review. The cutting-edge industrial utilization of lignocellulosic biomass described in this review suggests its major role in establishing a circular bioeconomy that consists of innovative design and advanced production methods to facilitate industrial recovery and reuse of waste materials beyond biofuel and biochemical production.

https://link.springer.com/content/pdf/10.1007/s12649-020-01123-0.pdf

Chemistry and Specialty Industrial Applications of Lignocellulosic Biomass

Biohydrogen Production Through Dark Fermentation

The host-microbe interaction established through natural evolution in plants sets the basis of plant growth and productivity benefits from a single microbe or a consortium. Select algal, fungal, bacterial (particularly LABs), actinomycetes and yeast groups are potential effective microbes (EMs) in agriculture. As environmental probiotics, EMs help in crop growth and wellbeing by fixing N2, solubilising K and P, unlocking soil trace elements, secreting exopolysaccharides, transforming organic matter into usable nutrients, enhancing soil water-holding capacity and improving the overall soil health. They also release bioactive compounds like vitamins, hormones and enzymes to stimulate plant growth, secrete biocontrol agents and enhance drought tolerance. As the soil profile and its intrinsic microbial ecology along geographical regions vary, a universal ‘one-size-fits-all’ effective microbial formulation cannot be envisaged. Although minerals cycling is majorly accomplished by specialised microbes, their activity is positively or adversely impacted by the interacting biotic community (microbe-microbe, microbe-plant or microbe-animal/human) and abiotic constituents. Crops benefit by positive associations with beneficial microbes as mutualism, symbiosis, commensalism, amensalism, photocooperation, etc., and by negative association against the harmful microbes like antagonism. The plant-growth-promoting role of microbes and the scope to formulate EM are the basis on these facts. EMs are applied for crop growth in the form of consortia which usually include phototrophs, lactic acid bacteria, actinomycetes, fermentative fungi, yeasts, etc. along with an effective carrier substrate (prebiotic) as formulations. The rDNA technology in plant growth promoting microbe (PGPM) with enhanced performance is also discussed. The review provides an insight into the dynamics of ecological interactions as the guiding principles of EM formulation with respect to plant growth promoting microbes, and the beneficial roles of effective microbial formulations in crop wellbeing and productivity enhancement.

Plant growth promoting microbes: Potential link to sustainable agriculture and environment

The aggregating usage of fossil fuels, rising demand for energy, fluctuating fuel prices, and increasing emissions of greenhouse gases are some of the concerning factors contributing to a shift in the interest from fossil fuels to biofuels. Biofuels are carbon-neutral sources of energy as the CO2 emissions resulting from their combustion is utilized by the plants during photosynthesis leading to no net increase in atmospheric CO2 levels. It is indispensable to focus on the new approaches to the research, development, and production of biofuels and their processing technologies to reshape a sustainable bioeconomy. Biofuels can be categorized into first, second, and third generation depending on the feedstock used for their production. The product range for first-generation biofuels is largely limited to ethanol produced from corn and distillers grains. In contrast, the second-generation biofuels are produced from non-food residues or lignocellulosic biomass such as agricultural biomass and forestry refuse, as well as energy crops. The third-generation biofuels are produced from algae, sewage sludge, and municipal solid wastes. This chapter comprehensively focuses on various first-, second-, and third-generation biofuels with emphasis on their biomass sources, fuel properties, and applications. The fuel products broadly discussed in this chapter are ethanol, butanol, bio-oil, biodiesel, algal oil, hydrogen, biomethane, and aviation fuel.

A Broad Introduction to First-, Second-, and Third-Generation Biofuels

Sustainable utilization of pineapple wastes for production of bioenergy, biochemicals and value-added products: A review.

In the current period, there is a high demand for the production of liquid fuel which is used for transport purposes all over the world. Therefore, the conversion of methane to methanol fuel is reported as an alternative option for natural gas. Some approaches such as the two-step syngas process, direct single step, and bacterial agent catalyzed reaction use steam reform of methane, methane oxidation processes (via methane selectivity), and methane gaseous form (via methane monooxygenase enzymes) respectively to produce methanol fuel from methane. Also, chemical routes have applied high temperature/pressure catalytic conversion of syngas to methanol. Most conventional approaches discussed are gas to liquid technologies that exploit and monetize nontraditional methanol sources. The utility of methanol as liquid fuel is discussed and now researchers have invented the greatest potential of methanol as a robust product that is produced or synthesized by using a commercial scale conversion process from methane. Normal conversion for methane to methanol via chemical routes is exploited by high temperature and pressure as an energy-intensive process. However, the biological modes of conversion of methane to methanol occur by using methanotrophic bacteria, exhibiting desired transformation capacity at ambient conditions via methane monooxygenase enzyme. Biotechnological modes of conversion have shown the potentiality for their application in an industrially relevant process in eco-friendly ways. Some approaches of biotechnological modes of conversion of methane to methanol by whole-cell, wild-type, and methanotroph cultures are discussed along with many chemical route approaches. In this paper, the authors emphasize the different chemical and biological approaches for methane to methanol conversion with their limitations and applications.

Prakash Kumar Sarangi

Papers

Biohydrogen Production Through Dark Fermentation

Plant growth promoting microbes: Potential link to sustainable agriculture and environment

A Broad Introduction to First-, Second-, and Third-Generation Biofuels

Sustainable utilization of pineapple wastes for production of bioenergy, biochemicals and value-added products: A review.

Conversion of methane to methanol: technologies and future challenges