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Biotechnological applications for metal recovery have played a greater role in recovery of valuable metals from low grade sulfide minerals from the beginning of the middle era till the end of the twentieth century. With depletion of ore/minerals and implementation of stricter environmental rules, microbiological applications for metal recovery have been shifted towards solid industrial wastes. Due to certain restrictions in conventional processes, use of microbes has garnered increased attention. The process is environmentally-friendly, economical and cost-effective. The major microorganisms in recovery of heavy metals are acidophiles that thrive at acidic pH ranging from 2.0-4.0. These microbes aid in dissolving metals by secreting inorganic and organic acids into aqueous media. Some of the well-known acidophilic bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans and Sulfolobus spp. are well-studied for bioleaching activity, whereas, fungal species like Penicillium spp. and Aspergillus niger have been thoroughly studied for the same process. This mini-review focuses on the acidophilic microbial diversity and application of those microorganisms toward solid industrial wastes.

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Kerosene is common adulterant utilized for mixing with diesel. Five fuel-adulterant mixtures in different proportions by volume were prepared and individually tested for density and kinematic viscosity. The mixtures were administered to six light cargo vehicles and the tail pipe exhaust emission was tested for opacity value. No appreciable density variation at different levels of adulteration was observed. Density was within the prescribed value even at higher adulteration. Considerable decrease in kinematic viscosity, a departure from prescribed viscosity, was noted at higher adulteration level. The percent opacity value decreased sharply even at small level of adulteration. The probable amount of kerosene present as an adulterant in diesel dispensed at filling stations in Kathmandu city ranged between 35% and 50%. The observations suggest density test is not a good indicator of diesel adulteration. Kinematic viscosity and opacity value are useful diesel adulteration test parameters. Existing diesel adulteration warrants initiation of strict compliance regulation.