The use of flocculating brewer's yeast for Cr(III) and Pb(II) removal from residual wastewaters

The use of inexpensive biosorbents to sequester heavy metals from aqueous solutions, is one of the most promising technologies being developed to remove these toxic contaminants from wastewaters. Considering this challenge, the viability of Cr(III) and Pb(II) removal from aqueous solutions using a flocculating brewer's yeast residual biomass from a Portuguese brewing industry was studied. The influence of physicochemical factors such as medium pH, biomass concentration and the presence of a co-ion was characterised. Metal uptake kinetics and equilibrium were also analysed, considering different incubation temperatures. For both metals, uptake increased with medium pH, being maximal at 5.0. Optimal biomass concentration for the biosorption process was determined to be 4.5 g dry weight/l. In chromium and lead mixture solutions, competition for yeast binding sites was observed between the two metals, this competition being pH dependent. Yeast biomass showed higher selectivity and uptake capacity to lead. Chromium uptake kinetic was characterised as having a rapid initial step, followed by a slower one. Langmuir model describes well chromium uptake equilibrium. Lead uptake kinetics suggested the presence of mechanisms other than biosorption, possibly including its precipitation.Instituto de Biotecnologia e Química Fina (IBQF) - Junta Nacional de Investigação Cientifica e Tecnologica (J.N.I.C.T), project PEAM/SEL/516/95

Trivalent chromium removal using flocculating yeasts : effect of pre-treatments on removal efficiency

Praxis XXI; Fundação para a Ciência e a Tecnologia (FCT)

Initial pseudo-steady state & asymptotic KPZ universality in semiconductor on polymer deposition

The Kardar-Parisi-Zhang (KPZ) class is a paradigmatic example of universality in nonequilibrium phenomena, but clear experimental evidences of asymptotic 2D-KPZ statistics are still very rare, and far less understanding stems from its short-time behavior. We tackle such issues by analyzing surface fluctuations of CdTe films deposited on polymeric substrates, based on a huge spatio-temporal surface sampling acquired through atomic force microscopy. A \textit{pseudo}-steady state (where average surface roughness and spatial correlations stay constant in time) is observed at initial times, persisting up to deposition of $\sim 10^{4}$ monolayers. This state results from a fine balance between roughening and smoothening, as supported by a phenomenological growth model. KPZ statistics arises at long times, thoroughly verified by universal exponents, spatial covariance and several distributions. Recent theoretical generalizations of the Family-Vicsek scaling and the emergence of log-normal distributions during interface growth are experimentally confirmed. These results confirm that high vacuum vapor deposition of CdTe constitutes a genuine 2D-KPZ system, and expand our knowledge about possible substrate-induced short-time behaviors.Comment: 13 pages, 8 figures, 2 table

Sorption of Cr(III) from aqueous solutions by spent brewery grain

Two types of spent brewery grains were tested for Cr(III) uptake from aqueous solutions: not treated spent grains (NTSG), obtained by abundant washing of spent grain obtained from a Portuguese brewing industry with distilled water, and treated spent grain (TSG), prepared by treating NTSG with NaOH 0.5 M for four hours followed by washing with distilled water. Both materials were mixed with chromium solutions (50 and 100 mg Cr(III)/L), varying medium pH from 3 to 5. Maximum metal uptake occurred at pH 5. Langmuir isotherm model well describes Cr(III) biosorption by NTSG and TSG. The maximum uptake capacity obtained was 17.84 mg Cr(III)/g NTSG and 13.87 mg Cr(III)/g TSG. Considering that Langmuir constant, b, reflecting the affinity between the sorbent and the sorbate is lower for NTSG (0.0749 L/mg) it is possible to conclude that the alkalis treatment does not improve spent grain uptake capacity for Cr(III).Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI/BD/15945/98

Cr(III) removal and recovery from Saccharomyces cerevisiae

Heavy metal recovery from biosorbents is of major importance in the assessment of competitiveness of biosorption processes. Several desorption agents (H2SO4, HNO3, HCl, CH3COOH and EDTA) were tested for the selection of the optimal elution conditions for Cr(III) recovery from Saccharomyces cerevisiae cells. Sorption time was optimised as it plays an important role in the sorption–desorption process, being shown that a 30 min sorption period is the best option to ensure metal removal from solution and good recovery from biosorbent. The optimal contact time with desorption agents was also studied, as long exposures to these ones may cause cell damage, affecting biosorbent metal uptake capacity in subsequent sorption cycles. Each eluant was analysed in terms of its desorption capacity and its effect on the biomass metal uptake capacity in multiple sorption–desorption cycles. Considering the effectiveness of chromium desorption from loaded biomass, it was possible to conclude that H2SO4 (pH≈1) was the most effective eluant tested, accomplishing the highest Cr(III) recovery from S. cerevisiae in three consecutive sorption/desorption cycles. Regarding the damage caused by acid treatment on S. cerevisiae cells, assessed by the reduction on metal uptake capacity after elution, it was possible to observe that sulphuric acid was the most harmful eluant causing long term negative effects in metal uptake. By the time the experiments were interrupted (nearly 26 h of continuous cycles) biomass uptake capacity was reduced to about 77% of the value reached before acid treatment.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BD/15945/98

Cr (III) recovery from Saccharomyces cerevisiae by elution : a preliminary study

To recover adsorbed metals from biosorbents, in order to recycle metal and reuse biomass in several adsorption/desorption cycles, elution conditions need to be optimized. The present work aimed to study the following elution parameters: eluant type and concentration (H2SO4, HNO3, HCl, CH3COOH and Na2CO3 0.1, 0.5 and 1.0 M, and EDTA 0.01, 0.05 and 0.1 M); biosorbent contact time with Cr (III) solution (15 min, 2 and 24 h), and S/L ratio (4 and 8 g/L). Experimental data show a decrease in Cr recovery efficiency with increasing sorption time, probably due to metal bioaccumulation. Concerning the S/L ratio, it was possible to observe, in most essays, that best recoveries were achieved using biosorbent concentration of 8 g/L. Comparing the eluants tested according to their metal recovery efficiencies, it can be concluded that Na2CO3 is not a good eluant (maximum recovery of 21 %). All the others showed equivalent behaviours, being necessary more assays to determine eluant treatment effect in Cr uptake capacity in subsequent sorption cycles.Fundação para a Ciência e a Tecnologia (FCT

Relationship between top executive compensation and corporate governance: evidence from large Italian listed companies

The modernization of corporate governance aims the alignment of the interests of managers with those of companies, promoting a new discipline of internal controls and risk analysis with an enforcement of shareholder rights of information. This research investigates the impact of corporate governance variables –ownership, board of directors and remuneration committee– on executive compensation. A balanced sample of 52 Italian listed companies has been adopted to test the hypotheses, covering 55.98% and 47.13% of market capitalization in 2011 and 2015 respectively and including 669 board members. Theoretical models evidence a certain stability of compensation schemes for Italian managers over time. Findings suggest that there is a statistically significant positive effect of familiar ownership on the amount of compensation. Along with nature of ownership, the number of directors in the remuneration committee appointed by minorities assume a determinant role. With statistical significance, it affects negatively the compensation level, but, contrarily to best practices, it affects negatively the adoption of forms of incentive compensation.info:eu-repo/semantics/acceptedVersio

Utilização de sub-produtos da indústria cervejeira na remoção de crómio trivalente de soluções aquosas

Tese de doutoramento em Engenharia Química e BiológicaO enquadramento legal que define as orientações relativas à protecção ambiental tem evoluído no sentido de restringir os valores paramétricos de descarga de águas residuais para limites mais apertados e fomentar uma gestão de resíduos e efluentes industriais assente na minimização da sua produção e na sua reutilização. Esta tendência é, a par da necessidade de reduzir os custos inerentes ao tratamento e deposição de resíduos e efluentes, um dos incentivos ao desenvolvimento tecnológico associado à biorremediação de águas residuais contaminadas com metais pesados recorrendo a biossorventes facilmente disponíveis e com baixo custo, nomeadamente resíduos agrícolas e sub-produtos de processos industriais de fermentação. A realização deste trabalho, que visou a avaliação do potencial de utilização de dois sub-produtos de uma indústria cervejeira Portuguesa, a levedura S. cerevisiae e as drêches, como biossorventes para o tratamento de soluções aquosas de Cr(III) e a contribuição para o desenvolvimento de uma tecnologia emergente que, comparada com os processos tradicionais (e.g. precipitação), tem um melhor desempenho ambiental, veio de encontro aos desígnios acima referidos. Os objectivos específicos do presente estudo incidiram sobre a caracterização da cinética, equilíbrio e mecanismo de interacção entre os biossorventes e o Cr(III), assim como a avaliação do respectivo desempenho em sistema aberto numa coluna de leito fluidizado. Os ensaios com as drêches envolveram a utilização da biomassa sem a aplicação de pré-tratamentos, e da biomassa submetida a um tratamento alcalino com NaOH, designados respectivamente por DST e DCT. Os estudos cinéticos, efectuado em sistemas fechados com soluções de Cr(III) de concentração inicial (Ci) entre os 10 e os 400 mg.L-1, revelaram que numa primeira fase, com uma duração de 2-7 h para as drêches e de 1-3 h para a S. cerevisiae dependendo de Ci, a acumulação de Cr(III) é mais rápida e segue um comportamento que é bem descrito pelo modelo de pseudo-segunda ordem, apontando para a quimiossorção como sendo a etapa limitante da sua velocidade. A partir desse período a acumulação de Cr(III) passa a ser mais lenta, verificando-se que a difusão intraparticular passa a contribuir significativamente para a velocidade global do processo. Os ensaios posteriores, realizados com a finalidade de esclarecer as interacções entre o Cr(III) e os biossorventes, nomeadamente pelo estudo da evolução do pH do meio, do efluxo de catiões e pela caracterização da superfície da biomassa por espectroscopia de infravermelhos, vieram corroborar estes resultados, apontando para a troca iónica como a reacção interveniente na fase inicial da sorção de metal. No caso da acumulação de Cr(III) pela S. cerevisiae foi ainda identificada, recorrendo respectivamente à observação de amostras por microscopia electrónica de transmissão (TEM) e de varrimento (SEM), a acumulação intracelular de Cr(III) e a sua deposição na superfície celular na forma de precipitados. A bioacumulação, observada a partir das 2 h de contacto com uma solução de Ci = 25 mg.L-1, revela que o metal se concentra em determinados locais do citoplasma onde também aparece P e outros metais (K, Ca e Zn), sendo provável que correspondam a grânulos de fosfato. A precipitação do Cr(III) foi notada para tempos de contacto longos (superiores a 74 h em sistema aberto). A natureza dos precipitados não foi averiguada, podendo corresponder a complexos do metal com compostos intracelulares azotados, libertados em consequência da permeabilização da membrana celular ou da lise das células, ou a hidróxidos metálicos formados pelo facto de o pH do meio tender para valores neutros ao longo dos ensaios, ou a ambos. A dessorção do Cr(III) acumulado pela S. cerevisiae demonstrou ser pouco eficiente com os vários eluentes testados (Na2CO3, EDTA, CH3COOH, HCl, H2SO4 e HNO3) e dependente do tempo de contacto da levedura com a solução de Cr(III). A irreversibilidade, que aumenta com o tempo de incubação, pode estar relacionada com a acumulação intracelular e a formação de precipitados. Em três ciclos de sorção-dessorção de 30 min, o eluente que conduziu aos melhores resultados de recuperação de Cr(III) foi H2SO4 que, à concentração de 0,1 M, apresentou uma eficiência de 52, 43 e 35 % respectivamente no primeiro, segundo e terceiro ciclo. No entanto quando se monitorizou a acumulação de Cr(III), que se sucede a um ciclo de dessorção, ao longo de 24 h, verificou-se o pior desempenho da biomassa nos 2º e 3º ciclos com este eluente. O modelo de Langmuir é o que melhor se ajusta aos resultados experimentais relativos às isotérmicas de sorção. A capacidade máxima de acumulação de metal (qmax) foi superior para as DST, seguindo-se as DCT e a S. cerevisiae, respectivamente com os valores de 16,68, 13,64 e 12,57 mg.g-1. No entanto, no sistema aberto, a previsão de desempenho obtida utilizando um modelo que resulta da aplicação da equação do modelo de Langmuir na equação de balanço mássico a um reactor contínuo perfeitamente agitado não descreve bem os resultados experimentais para nenhum dos biossorventes, nas condições operacionais testadas. Verificou-se ainda que a precipitação do Cr(III) induzida pela S. cerevisiae lhe permite superar a capacidade máxima de acumulação calculada pelo modelo de Langmuir, ultrapassando ainda o desempenho das drêches, com uma capacidade de acumulação superior num menor tempo de operação. Considerando a capacidade de acumulação de Cr(III) pela S. cerevisiae e pelas DST, os respectivos desempenhos em sistema aberto e atendendo ao facto de não terem sido submetidas a pré-tratamentos, conclui-se que ambas podem ser consideradas biossorventes promissores para o tratamento de águas contaminadas com Cr(III).In order to reduce the environmental impact associated to industrial activities, environmental regulations tend to become more restrictive concerning the contaminants concentration limits allowed in wastewater discharge. These circumstances, together with the wastewater and waste management guidelines, regarding integrated prevention and pollution control, encourages technological developments to achieve cleaner production methods and wastewater treatment technologies more eco-friendly and cost efficient. Heavy metal contaminated wastewater bioremediation, using highly available and low-cost materials such as agricultural by-products or biomass residual from industrial fermentation operations, is receiving increasing attention and can be considered a promissing alternative. The present work, seeking the evaluation of S. cerevisiae and spent grain residual from a Portuguese brewing industry as potential biosorbents for Cr(III) contaminated wastewaters and the development of an emerging technology more eco-friendly than the traditional ones (e.g. metal precipitation), can be considered to accomplish these purposes. The study main goals were the kinetics, equilibrium and interaction mechanism metal-biosorbent characterization and to assess their performance in a continuous column system, operating with a fluidized bed. The experimental essays with spent grain included the material without pretreatments (NTSG) and spent grain treated with NaOH, designated by treated spent grain (TSG). Kinetic studies were performed in batch systems with Cr(III) solutions at the initial concentration (Ci) ranging from 10 to 400 mg.L-1. Experimental data revealed that Cr(III) uptake follows a rapid initial step, well described by the pseudo-second order kinetic model up to 2-7 h and 1-3 h, respectively with spent grain and S. cerevisiae, indicating metal chemisorption to be the rate limiting step. Beyond this period Cr(III) uptake becomes considerably slower, with intraparticle diffusion assuming an important role in the process global kinetics. Additional investigation, involving changes in medium pH, cation efflux and biosorbent surface characterization with spectroscopic infrared analyses, contributed to elucidate Cr(III)-biosorbent interaction mechanism, and confirmed that chemisorption takes part of the metal uptake mechanism, with ion change being the most probable reaction occurring. Cr(III) uptake onto S. cerevisiae further involved intracellular accumulation and surface precipitation, identified respectively with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations. Bioaccumulation was recognized in cells with more than 2 h of contact with a 25 mg.L-1 Cr(III) solution. The presence of Cr(III) in electron dense areas was confirmed by EDS analyses, where P and other metals (K, Ca and Zn) were also identified, suggesting the occurrence of a cellular metal detoxifying mechanism involving phosphates. Metal precipitation was identified in samples colected after long sorption times (more than 74 h in the column system). Metal precipitates composition was not ascertained being possible that they consist of complexes with intracellular compounds rich in N, leaked in result of membrane permeabilization or cell lysis, or comprise metalic hidroxydes or both compounds. Cr(III) desorption from S. cerevisiae was not very effective with the eluents tested (Na2CO3, EDTA, CH3COOH, HCl, H2SO4 and HNO3) exhibiting a significant dependente with sorption time. The observed metal binding irreversibility increases with contact time, and can be related to intracellular accumulation and metal precipitation. In three consecutive soption-desorption cycles, each of them with a 30 min duration, the best eluant s was H2SO4 0,1 M with recovery efficiencies of 52, 43 and 35 % respectively in the first, second and third cycle. However, when Cr(III) uptake following a desorption cycle, was monitored for 24 h, data pointed out this eluant to be the one that gives rise to the lower performance in the succeeding sorption cycles. Langmuir model proved to be the equilibrium model that better fits to experimental data. Maximum uptake capacity (qmax) was determined to be higher for NTST, following TSG and S. cerevisiae, respectively with 16,68, 13,64 and 12,57 mg.g-1. Nevertheless, the modelling study of Cr(III) sorption in the column systems, using a mass balance model to a continuous stirred tank reactor which included the Langmuir equilibrium isotherm, did not give reasonable predictions for the biosorbents performances for the tested operational conditions. Furthermore it was observed that Cr(III) precipitation, induced by S. cerevisiae, enhanced its metal uptake to values higher than qmax preaviously calculated and even exceeding spent grain performance, with a higher uptake capacity for a shorter operation time. Considering S. cerevisiae and NTSG uptake capacities, their performances in the column systems and the fact that they were not submitted to pretreatments, in may be concluded that these industrial by-products can be both considered as promissing biosorbents to treat Cr(III) contaminated wastewaters

Field-theoretical renormalization group for a flat two-dimensional Fermi surface

We implement an explicit two-loop calculation of the coupling functions and the self-energy of interacting fermions with a two-dimensional flat Fermi surface in the framework of the field theoretical renormalization group (RG) approach. Throughout the calculation both the Fermi surface and the Fermi velocity are assumed to be fixed and unaffected by interactions. We show that in two dimensions, in a weak coupling regime, there is no significant change in the RG flow compared to the well-known one-loop results available in the literature. However, if we extrapolate the flow to a moderate coupling regime there are interesting new features associated with an anisotropic suppression of the quasiparticle weight Z along the Fermi surface, and the vanishing of the renormalized coupling functions for several choices of the external momenta.Comment: 16 pages and 22 figure

Mechanisms of Cr(III) biosorption onto residual brewer's yeast

The knowledge and understanding of metal-biomass interactions is crucial to develop and maximize biosorption processes potential to the concentration, removal and recovery of heavy metals from dilute solutions, as well as to define strategies to regenerate and reuse biosorbent in multiple cycles (Ahluwalia and Goyal, 2007; Volesky, 2001). It also turns possible biosorption optimization at a molecular level, including biomass genetic modification to induce changes in morphologic and physiologic characteristics in order to increase metal uptake (Srinath et al., 2002; Volesky, 2001). To reach that purpose, and considering that several mechanisms may contribute to the overall metal uptake depending on the metal and the biosorbent used, environmental factors, and the cell metabolic activity (Dhankhar and Hooda, 2011), it is necessary to study in detail the interactions established in each biosorption system. Heavy metal biosorption involves a combination of several passive accumulation processes, that may include: i) physical adsorption; ii) chemisorption, including ion exchange, coordination, complexation and chelation; iii) and inorganic precipitation (Ahluwalia and Goyal, 2007; Wang and Chen, 2006). According to Gadd (2004), metal-microorganism interactions may be seen as natural strategies to remove, recover or diminish metal toxicity in organic or inorganic forms. Different organisms exhibit different responses to the exposure to toxic ions, varying from transport through cellular membrane, biosorption onto cell walls, entrapment in extracellular structures, precipitation, complexation and redox reactions