Biological decolorization of xanthene dyes by anaerobic granular biomass

Biodegradation of a xanthene dyes was investigated for the first time using anaerobic granular sludge. On a first screening, biomass was able to decolorize, at different extents, six azo dye solutions: acid orange 7, direct black 19, direct blue 71, mordant yellow 10, reactive red 2 and reactive red 120 and two xanthene dyes—Erythrosine B and Eosin Y. Biomass concentration, type of electron donor, induction of biomass with dye and mediation with activated carbon (AC) were variables studied for Erythrosine B (Ery) as model dye. Maximum color removal efficiency was achieved with 4.71 g VSS L−1, while the process rates were independent of the biomass concentration above 1.89 g VSS L−1. No considerable effects were observed when different substrates were used as electron donors (VFA, glucose or lactose). Addition of Ery in the incubation period of biomass led to a fivefold increase of the decolorization rate. The rate of Ery decolorization almost duplicated in the presence of commercial AC (0.1 g L−1 AC0). Using different modified AC samples (from the treatment of AC0), a threefold higher rate was obtained with the most basic one, \textAC\textH2ACH2, as compared with non-mediated reaction. Higher rates were obtained at pH 6.0. Chemical reduction using Na2S confirmed the recalcitrant nature of this dye. The results attest that decolorization of Ery is essentially due to enzymatic and adsorption phenomena.This work was supported by the PTDC/AMB/69335/2006 project grants (Fundacao para a Ciencia e Technologia, FCT, Portugal), BRAIN project (ID 6681, European Social Found and Romanian Government and the grant of the Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project number PN-II-ID-PCE-2011-3-0559, Contract 265/2011

Laccase isozymes of Pleurotus sajor-caju culture on husk and bran of black sticky rice and their potential on indigo carmine decolourisation

Extracellular laccases of Pleurotus sajor-caju grown on solid state medium consisted of husk and bran of black sticky rice, were partially purified by DEAE–cellulose chromatography. These laccases could be separated into three groups: unboundLac and bound fractions (pool1Lac and pool2Lac). The optimum pH of these laccases was studied using ABTS as substrate. It was found that the pH optimum for unboundLac fell in the range of 3–5 and 3–4 for pool1Lac and pool2Lac. The indigo carmine decolourisation capacity was compared between unboundLac and pool2Lac. It was found that the optimal pH for indigo carmine decolourisation were 5 and 3 for unboundLac and pool2Lac, respectively. In the range of various dye concentrations tested, it was found that indigo carmine at 10 ìM with the enzyme activity of 0.01 U, gave the best dye decolourisation with 40.47% within 120 min for unboundLac and with 18.61% within 150 min for pool2Lac. High amount of enzyme used of these laccases might improve decolourisation ability