Evaluation of hexavalent chromium removal in a continuous biological filter with the use of central composite design (CCD)

Abstract

Hexavalent chromium is frequently found in industrial effluents as a result of the industrial applications of this compound and its anti-corrosive features. However, hexavalent chromium is extremely toxic, and its discharge in water is regulated, with a maximum limit of 0.1 mg/L in accordance with legislation established by CONAMA-Brazil (no. 397, April 3, 2008). To achieve lower discharge values, it is necessary to reduce from Cr(VI) to Cr(III), which is less toxic, and an economic alternative involves biological removal of this compound. Residence time distributions (RTDs) were measured to evaluate the behavior of actual biofilter operation conditions in a biofilter flow. The medium residence time distributions used were 8 and 24 h (recommended by the legislation). To optimize this process, a central composite design was used, considering the initial chromium concentration and pH as the independent variables and the removal of hexavalent chromium as the response. The boundary curves and surface response showed optimal behavior at 3.94 mg/L [Cr(0)] and a pH of 6.2. The removal process of hexavalent chromium is mathematically described by the Michaelis-Menten kinetic model. This model appropriately represents the variation of chromium concentration along the bioreactor.

Evaluation of the bioremoval of Cr(VI) and TOC in biofilters under continuous operation using response surface methodology

“…Preliminary tests with industrial support media (Dalcin et al 2011) were not very efficient. Then we started a search for a support media that: (i) has the ability to remove high loads of organic and of Cr(VI) per unit volume; (ii) has a structure that was widely open, to avoid clogging by biomass growth and to ensure an adequate supply of oxygen, without the use of forced aeration; (iii) provides structural strength enough to support its own weight and the weight of the biomass that grows attached to its surface; (iv) was light enough to allow significant reductions in the cost of construction; (v) was biologically inert; so it would not be attacked by micro-organisms or toxic to the process; (vi) was chemically stable and presented the lowest possible cost per unit of organic matter removed.…”

“…Dermou et al (2005) analyzed the concentration of carbon during the reduction of 33 mg l -1 of hexavalent chromium, and found that 265, 150, and 20 mg l -1 of carbon were obtained after 40, 30, and 340 min of operation, respectively, in the complete reduction of 33 mg l -1 of Cr(VI). Dalcin et al (2011) studied the Cr(VI) removal in a continuous biological filter using CCD methodology with successfully. The analysis of the CCD showed that the initial hexavalent chromium concentration was the most significant variable in the process and the pH value also contributed to the rate of hexavalent chromium removal but to a lesser extent than the initial concentration of Cr(VI).…”

“…Studies have shown that certain species of bacteria, mixed bacterial cultures, yeast, algae, and fungi are able to transform Cr(VI) to the trivalent form Cr(III), which is less toxic and mobile Desai et al 2008;Lee et al 2008;Molokwane et al 2008;Okeke et al 2008;Bankar et al 2009;Kong et al 2009;Quintelas et al 2009;Sanghi and Sankararamakrishnan 2009;Ahmad et al 2010;Elangovan et al 2010;Fernández et al 2010;Orozco et al 2010;Dalcin et al 2011;Ilias et al 2011;Orozco et al 2011).…”

Making Fe0-Based Filters a Universal Solution for Safe Drinking Water Provision

“…The fitness of the given models can be tested by ANOVA statistics (R 2 , adjusted R 2 , F-test and t-test) and residuals analysis. As Bezera et al [180] introduced RSM as a tool for optimization in analytical chemistry, this kind of design experiment has been widely used by different researchers in order to optimization of water and soil remediation [166,173,[181][182][183] or designing different types of water filters [184,185]. The experimental design and statistical analysis of the data were done by Design-expert10 statistical software.…”

Aplicação De Campo Magnético Em Cultura Mista

“…Em pesquisas desenvolvidas na Faculdade de Engenharia Química da Universidade Federal de Uberlândia, utilizando meios sintéticos simulando um efluente de curtume, foi utilizada aplicação de campo magnético em micro-organismos de culturas mistas para redução de Cr(VI) a Cr(III) (Dalcin et al, 2011, Leles et al, 2012, Moura, 2012.…”