Hexavalent Chromium Removal Related to Scale-up Studies

FERNANDEZ P.M.; VIÑARTA S.C.; BERNAL A.R.; FIGUEROA L.I.C.

Strategies for Bioremediation of Organic and Inorganic Pollutants

Taylor & Francis Group

Lugar: London; Año: 2018; p. 263 - 274

Contamination of soil, air, and water with heavy metals and toxic chemicals is one of the major problems facing the world today. Environmental pollution by industrial effluents, especially those containing heavy metals, was previously reported (Klimaviciute et al.2010). Discharge of heavy metals became a worldwide severe socio-environmental problem due to the risks they can generate for ecosystems and human health. Many heavy metals (lead, arsenic, chromium, zinc, copper, cadmium, cobalt, antimony mercury, nickel, etc.) in their elemental forms or in various chemical combinations are considered toxic (Gavrilescu 2004, Wang and Chen 2006), but some of these are useful in low concentration. They are non-degradable toxic pollutants (Pavel et al. 2012, Modoi et al. 2014), thus persistent in nature that accumulate in the food chain, which, with time, reach detrimental levels in living systems, resulting in serious health diseases such as irritation and/or cancer in lungs and digestive tract, low growth rates in plants and death of animals (Cheung and Gu 2007, Orozco et al. 2008).Chromium is a geochemical element of anthropogenic origin and is widely distributed in rocks, minerals soils, and fresh water. Environmental risk due to Cr(VI) contamination is caused by different industrial applications and commercial processes, which eventually lead to environment pollution (soil, surface water or atmosphere), in both developing and developed countries. Effluents from electroplating, wood preservation, leather, mining industries, and others, are responsible for the release of chromium into the air, soil and water (Tekerlepoulouet al. 2013). Trivalent [Cr(III)] and hexavalent [Cr(VI)] forms are the dominant chromium oxidation states in the environment. Cr(VI) compounds (mainly CrO42− at neutral pH or alkaline conditions) are toxic to living organisms, causing allergies, irritations and respiratory diseases, being also mutagenic and carcinogenic due to their oxidizing nature (Costa 2003). This heavy metal has been designated a priority pollutant in many countries and by the United States Environmental Protection AgencyUSEPA (Ksheminska et al. 2003, Juvera-Espinosa et al. 2006). Its toxicity to biological systems is due to the fact that Cr(VI) complexes can easily cross cellular membranes and undergo immediate reduction, leading to a variety of oxidative intermediates harmful to organelles, proteins and nucleic acids (Morales-Barrera and Cristiani-Urbina 2006). Cr(VI) may also exert its toxicity as a redox active metal that can participate in Fenton reactions, being able to generate Reactive Oxygen Species (ROS) which causes cell oxidative stress (Jamnik and Raspor 2003). On the other hand, Cr(III) is more stable and it constitutes a trace element conventionally considered an essential micro-nutrient for living organisms related to cellular membrane stability, synthesis and stability of nucleic acids and proteins (Poljsak et al. 2010). From the toxicological point of view, Cr(VI) is soluble in water, being 100 times more toxic and 1,000 times more mutagenic than Cr(III) (Chojnacka 2010). However, at high concentrations, Cr(III) can complex with organic compounds interfering with metallo-enzyme systems (Krishna and Philip 2005, Poljsak et al. 2010), may also cause health problems, for example, lung cancer (Costa 2003), birth deficiency and the decrease of reproductive health (Marsh and McInerny 2001). Di Bona et al. (2011) recently reported that Cr(III) can no longer be considered as a dietary supplement because rats subjected to a diet with low content of trivalent chromium, suffered no adverse consequences when they were compared with rats subjected to a diet with a sufficient dose of Cr(III). Keeping in mind the toxic effects of chromium and tolerance limits for disposal of waste (0.5 to 270 mg l−1), the concerned industries must minimize the total chromium level in wastewaters. The removal of Cr(VI) from wastewater requires serious and immediate attention. The most widely used methods are the conventional physicochemical processes, for example, the electrochemical process, ion exchange, adsorption on activated carbon, excavation and solidification/stabilization, etc. (Witek-Krowiak 2013). These technologies are suitable to control contamination but they present cost-effectiveness limitations, generating unsafe by-products or inefficiency, high energy consumption or incomplete removal of the pollutant (Bahi et al. 2012). Numerous studies are conducted for the development of cheaper and more effective technologies, this being necessary to develop methods that are more economic, safe, and environmental friendly to remove Cr(VI) ions from industrial wastewaters. Biological methods solve these drawbacks since they are easy to operate, do not produce secondary pollution, and they are less expensive and highly efficient even at low heavy metal concentrations (Ahluwalia 2012, Chojnaka 2010). In this context, isolation and characterization of Cr-resistant microorganisms (e.g., bacteria, fungi, and yeasts) led to hypothesize that biological removal methods would be a sustainable alternative technology of lower impact on the environment. Different microorganisms have been isolated and identified as having the capacity to remove Cr(VI) contamination by different biological methods (biosorption, bioaccumulation, bioreduction). Since they use native biomass, they are considered an eco-friendly and economic option. The microbes that retain such properties have been isolated from a diverse range of environments, both those contaminated and uncontaminated with Cr(VI).Microbes may protect themselves from toxic substances in the environment by transforming toxic compounds through oxidation, reduction or methylation into more volatile, less toxic or readily precipitating forms (Ahmad et al. 2010). Also, they can be scaled up to pilot or large scales in various contacting systems bioreactors to ensure optimal operating conditions (hydrodynamic, mass transfer and growing conditions). The aim of this chapter is to present the state of the art related to Cr(VI) removal processes applied in different types of bioreactors, pilot scale studies and their potential to be applied at industrial scale to diminish the contents of Cr(VI) in their effluents till acceptable levels.