Enhancement of anaerobic degradation of azo dye with riboflavin and nicotinamide adenine dinucleotide harvested by osmotic lysis of wasted fermentation yeasts

Abstract

The study presented here aims at identifying the source of redox mediators (riboflavin), electron carriers nicotinamide adenine dinucleotide (NAD) and carbon to perform decolorization of azo dye under anaerobic conditions after osmotic shock pretreatment of residual yeast from industrial fermentation. Pretreatment conditions were optimized by Doehlert experiment, varying NaCl concentration, temperature, yeast density and time. After the optimization, the riboflavin concentration in the residual yeast lysate (RYL) was 46% higher than the one present in commercial yeast extract. Moreover, similar NAD concentration was observed in both extracts. Subsequently, two decolorization experiments were performed, that is, a batch experiment (48 h) and a kinetic experiment (102 h). The results of the batch experiment showed that the use of the RYL produced by the optimized method increased decolorization rates and led to color removal efficiencies similar to those found when using the commercial extract (∼80%) and from 23% to 50% higher when compared to the control (without redox mediators). Kinetics analysis showed that methane production was also higher in the presence of yeast extract and RYL, and biogas was mostly generated after stabilization of color removal. In all kinetics experiments the azo dye degradation followed the pseudo-second-order model, which suggested that there was a concomitant adsorption/degradation of the dye on the biomass cell surface. Therefore, results showed the possibility of applying the pretreated residual yeast to improve color removal under anaerobic conditions, which is a sustainable process.

Anaerobic‐Aerobic Combined System for the Biological Treatment of Azo Dye Solution using Residual Yeast

“…Considering that yeast extract is source of riboflavin, some studies investigated the applicability of commercial yeast extract to improve color removal in anaerobic reactors (Baˆeta et al, 2012;Corrˆea et al, 2009). More recently, it has been shown that residual yeast (from fermentation processes) pretreated by osmotic lysis led to higher decolorization, when compared with commercial yeast extract, and exhibited color removal efficien-cies higher than those normally reported in the literature, that is, 86% compared with 81% (Victral et al, 2016). This highlights that yeast extract acts as source of redox mediator, as well as a nutrient source.…”

“…Residual Yeast. Residual yeast biomass belonging to Saccharomyces cerevisiae, and obtained from a small brewery, was pretreated through osmotic lysis as proposed by Victral et al (2016). To this aim, yeasts were taken directly from the fermentation vats, where the process was already over, and submitted to successive washing centrifugations, with ethanol for clarification.…”

“…Substances such as vitamin B2 (Riboflavin) and quinone are excellent redox mediators, because they are reversible organic molecules able to undergo oxidation and reduction (Santos, 2005). In this context, low cost redox mediators have been suggested, such as commercial yeast extract (e.g., riboflavin) or residual yeast from the brewing industry (Baˆeta et al, 2012;Corrˆea et al, 2009;Victral et al, 2016). In these studies, the yeast extract also provided macro and micronutrients.…”

Evaluation of a Combined System Based on an Upflow Anaerobic Sludge Blanket Reactor (UASB) and Shallow Polishing Pond (SPP) for Textile Effluent Treatment

“…Residual yeast biomass belonging to Saccharomyces cerevisiae species was obtained from a small brewery pretreated through osmotic lysis [11,12]. For this, yeasts were taken directly from fermentation vats and submitted to a clarification process, which consisted in a sequence of centrifugations and addition of ethanol solution 96% (10% M/M).…”

“…For instance, the application of immobilized redox mediators in microbial fuel cells was tested for electricity generation with simultaneous azo dye removal due to facilitated electrons transfer from bacteria to anodes and azo dyes [8]. In this context, the use of low cost redox mediators have been suggested, such as commercial yeast extract (source of riboflavin) [2,9,10] or residual yeast from the brewing industry [11,12]. Dyes are deficient in carbon and nitrogen sources, and the biodegradation of dyes without any supplement of these sources may be hampered.…”