Deepika Kumari

Microbially-induced Carbonate Precipitation for Immobilization of Toxic Metals.

Rapid urbanization and industrialization resulting from growing populations contribute to environmental pollution by toxic metals and radionuclides which pose a threat to the environment and to human health. To combat this threat, it is important to develop remediation technologies based on natural processes that are sustainable. In recent years, a biomineralization process involving ureolytic microorganisms that leads to calcium carbonate precipitation has been found to be effective in immobilizing toxic metal pollutants. The advantage of using ureolytic organisms for bioremediating metal pollution in soil is their ability to immobilize toxic metals efficiently by precipitation or coprecipitation, independent of metal valence state and toxicity and the redox potential. This review summarizes current understanding of the ability of ureolytic microorganisms for carbonate biomineralization and applications of this process for toxic metal bioremediation. Microbial metal carbonate precipitation may also be relevant to detoxification of contaminated process streams and effluents as well as the production of novel carbonate biominerals and biorecovery of metals and radionuclides that form insoluble carbonates.

Remediation of Cr(VI) from chromium slag by biocementation

Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM-EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.

Bioreduction of Hexavalent Chromium from Soil Column Leachate by Pseudomonas stutzeri

ABSTRACT Bioreduction of Cr(VI) to less toxic Cr(III) by chromate-reducing bacteria has offered an ecological and economical option for chromate detoxification. The present study reports isolation of chromate-resistant bacterial strain Cr8 from chromium slag, identified as Pseudomonas stutzeri, based on 16S rRNA gene sequencing and their potential use in Cr(VI) reduction. The reduced product associated with bacterial cell was characterized by scanning electron microscopy–energy-dispersive x-ray spectroscopy (SEM-EDS) and x-ray diffraction (XRD) analyses. At initial concentrations of 100 and 200 mg L−1 Cr(VI), P. stutzeri Cr8 reduced Cr(VI) completely within 24 h, whereas it reduced almost 1000 mg L−1 Cr(VI) at the end of 120 h. Further, soil column leaching experiments were performed and found that bacterial cells reduced Cr(VI) leachate at faster rate that almost disappeared at the end of 168 h. The leachate precipitates also revealed efficient chromate bioreduction. The remediation process utilizing P. stutzeri could be considered as a viable alternative to reduce Cr(VI) contamination, especially emanating from the overburden dumps of chromite ores and mine drainage.

Microbial Remediation of Heavy Metals and Arsenic-Contaminated Environments in the Arid Zone of Northwest China

The northwest arid zone accounts for nearly 25% of the total territory area of China. It has a wealth of oil, natural gas, and mineral resources. For example, Xinjiang, one of the provinces in Northwest China, possesses 2.19 trillion tons of coal, more than 40% of the total coal deposits in China. Apart from coal, metal mineral deposits, including chromium, gold, iron, vanadium, copper, nickel, tungsten, molybdenum, lead, and zinc, are also very ample in Xinjiang and are on the top list of mineral resources of China. Deposits of magnesite, fluorite, sulfur, kyanite, salt, kaolin, asbestos, vermiculite, gypsum, graphite, perlite, and zeolite are also abundant in Xinjiang (Pirajno et al. 2011). Over 3000 mines have been being exploited. Huge amounts of wastewaters and slags containing toxic metal elements have been produced during extraction and smelting. Soils, groundwaters, and surface waters in and around mines are seriously polluted by heavy metals and arsenic. In some sites near gold mines, mercury and arsenic concentrations in soils can be up to hundreds of ppm. Crops in some downstream areas are also polluted by heavy metals such as cadmium and mercury. In addition, large areas of soil in Xinjiang, Inner Mongolia, and Ningxia are polluted with high levels of arsenic due to geological reasons. For example, arsenic pollution of soil and groundwater was found from the Aibi Lake to the east of Manasi River, which covers 250 km in length (Sun 2004). Heavy metal and arsenic pollution poses a great risk to human being and ecosystem in Northwest China.

Microbiological Risk Assessment and Bioprocess Engineering

Abstract The Europe 2020 strategy (European Commission, 2010) calls a bioeconomy as a key element for smart and green growth in Europe. The development of a greener and more resource-efficient economy gives rise to new technologies and materials, which in turn may result in increased exposure to biological agents or combinations of different potentially harmful factors. For example, the expanding recycling industry employs an increasing number of workers which have to face various health problems (pulmonary, gastrointestinal and skin problems) as a result of exposure to biological agents such as airborne microorganisms. However, specific numbers for occupational diseases in this sector are still lacking. There are various workplaces and professional activities especially from the green industry for which exposure to microbiological agents occur unexpectedly and in an uncontrolled way. The issue of uncontrolled microbial exposure there is for example in waste treatment and for retrofitting activities, both growing sectors of employment in a greening society. As a result of the problem in the green industrial sector, there is a need to develop tools for risk assessment and prevention measures. In order to be able to develop suitable risk management strategies, a further development of detection and identification methods for biological agents is needed to cover the whole spectrum of microorganisms. the present paper focuses on the microbiological risk assessment in the context of the development of new and safe industrial products and processes of green industry (bioindustry and bioprocessing).