Citrus is the largest grown fruit crop on the globe with an annual production of ~110–124 million tons. Approximately, 45–55% of the whole fruit post-processing is generally discarded as waste by the food processing industries. The waste is a huge problem to the environment in terms of land and water pollution along with displeasure from aesthetic viewpoint and spread of diseases owing to its huge content of fermentable sugars. The waste can be utilized as a raw material feedstock for producing a number of valuable chemicals and products, such as bioethanol, biogas, bio-oil, organic acids, enzymes, and so on. The production of these chemicals from waste biomass gives an inexpensive alternative to the harsh chemicals used during industrial synthesis processes as well as the possibility of controlling pollution from the waste discarded to the environment. The derived chemicals can be further utilized in the production of industrially important chemicals, as solvents and building blocks of newer chemicals. Furthermore, organic acids, pectin, enzymes, prebiotics, etc., derived from citrus wastes have an edge over their synthetic counterparts in practical applications in the food processing and pharmaceutical industries.

Industrial processes and anthropogenic activities generate huge amounts of wastes in the form of chemicals, such as heavy metals, dyes, fertilizers, pharmaceutically active chemicals, battery effluents and so on. When these chemicals are left untreated and discarded in the ground or surface waters, they not only cause pollution and harm the ecosystem but also cause toxic effects on the health of human beings, animals and food crops. There are several methods of removal of these toxic materials from the wastewaters, and adsorption by bio-sorbents has been demonstrated as one of the most inexpensive, efficient and convenient methods. Citrus is one of the largest grown fruit crops in the tropical and subtropical regions on the planet. After processing of the fruits at food processing industries, approximately half of the fruit mass is discarded as waste, which causes a number of pollution problems. Alternately, this biomass can be converted to bio-sorbents for the removal of harmful and toxic chemicals from the industrial effluents and wastewaters. The first part of this article contains a thorough review on the biotransformation of citrus waste for the production of biofuel and valuable compounds by fermentation involving microorganisms. The second and concluding part reviews the recent progress in biotransformation of citrus waste biomass (that may be remaining post-extraction of valuable compounds/biofuel generation) into efficient adsorbent substrate materials and their adsorption capacities. The article also includes the details of the synthesis process and mechanisms of adsorption processes.

Multifunctional ligand 5-cyano-6-(-4-pyridyl)-2-thiouracil (L) was prepared and allowed to react with trans [Co(en) 2 Cl 2 ] + Clresulting into [Co(en) 2 LCl] 2+ ⋅ ⋅2Clwhich upon further reaction with equimolar ratio of ligand [L] gave the complex [Co(en) 2 L 2 ] 3+ ⋅ ⋅3Cl-. These metal complexes were then separately reacted with thymine and adenine bases. Complexes thus prepared after characterization by their elemental analysis, FAB mass and spectral (IR, 1 HNMR, UV-visible) data were studied for their powder X-ray diffraction and optical microscopic characteristics.

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