Abstract This work investigated the anaerobic degradation of the model azo dye Remazol Yellow Gold RNL in batch reactors using discharged residual yeast as the source of redox mediators (RM). Two yeast lysis methods (mechanical lysis and sonication) were tested and optimized to produce a riboflavin-rich yeast lysate. The reactors were operated at 25 ºC for 48 hours, evaluating the effect of external carbon source (glucose) and RM (from residual yeast lysate and commercial yeast extract) addition. The results showed that color removal efficiencies for the batch reactors fed with commercial yeast extract reached 90%, whereas those fed with discharged yeast lysate reached 80% (sonication) and 73% (mechanical lysis). These values were statistically higher when compared to reactors operating without RM (48 to 66%), demonstrating that yeast extract enhances azo dye degradation in anaerobic conditions and that the residual yeast is a cheap and alternative source of carbon and of the RM riboflavin.

Abstract This paper evaluated the treatment of textile wastewater in submerged anaerobic membrane bioreactors (SAMBR) operated on a bench scale. Particularly, the influence of operational conditions, such as the applied organic rate (OLR) and the dilution factor (for toxicity attenuation) of the textile wastewater, was evaluated on color and organic matter removal. In addition, the effect of powdered activated carbon (PAC) on SAMBR-1 and the addition of yeast extract (source of the redox mediator riboflavin) were also investigated. The results showed that reducing the textile wastewater dilution factor from 10× (phase 1) to 4× (phase 2) and 0× (no dilution) decreased the COD and color removal efficiencies in both SAMBRs, probably due to an increase in the toxic load. Nevertheless, PAC adsorbed toxic compounds found in the textile wastewater and helped biomass acclimatization, which led to higher COD and color removal efficiencies in SAMBR-1. The presence of yeast extract enhanced color removal efficiencies 3-fold in both SAMBRs when they were fed with undiluted textile wastewater.

AbstractThis paper investigates the simultaneous removal of arsenic [As(V) or As(III)] and manganese [Mn(II)] from natural waters of low and high turbidity by clarification (with polyaluminum chloride and aluminum sulfate as primary coagulants) associated or not with chlorine pre-oxidation. The results showed that the clarification process exhibited low Mn(II) removal, that varied from 6% to 18% and from 19% to 27% for natural waters of low and high turbidity, respectively. The use of chlorine as pre-oxidant increased Mn(II) removal up to 77% and was associated with the formation of birnessite. Regarding As(V) removal by clarification, particularly for high turbidity water, a concentration lower than that established by the National Drinking Water Quality Standards (10 μg.L-1) was achieved in almost all tests. Oxidation preceding the clarification led to AsIII removal efficiencies from 80% to 90% for both coagulants and types of water.

Abstract Reactor hydrodynamics is important for sulfidogenesis because sulfate reduction bacteria (SRB) do not granulate easily. In this work, the sulfate reduction performance of two continuous anaerobic bioreactors was investigated: (i) an upflow anaerobic sludge blanket (UASB) reactor and (ii) a fluidized bed reactor (FBR). Organic loading, sulfate reduction, and COD removal were the main parameters monitored during lactate and glycerol degradation. The UASB reactor with biomass recirculation showed a specific sulfate reduction rate of 0.089±0.014 g.gSSV-1.d-1 (89% reduction), whereas values twice as high were achieved in the FBR treating either lactate (0.200±0.017 g.gSSV-1.d-1) or glycerol (0.178±0.010 g.gSSV-1.d-1). Sulfate reduction with pure glycerol produced a smaller residual COD (1700 mg.L-1) than that produced with lactate (2500 mg.L-1) at the same COD.sulfate-1 mass ratio. It was estimated that 50% of glycerol degradation was due to sulfate reduction and 50% to fermentation, which was supported by the presence of butyrate in the FBR effluent. The UASB reactor was unable to produce effluents with sulfate concentrations below 250 mg.L-1 due to poor mixing conditions, whereas the FBR consistently ensured residual sulfate concentrations below such a value.

This paper presents data for the synthesis and characterization of layer double hydroxides (LDH) and their use for color and chemical oxygen demand (COD) removal from effluents generated by a textile industry. Adsorption studies with raw and biologically treated (activated sludge) textile effluent showed that the pseudo-second order model best fitted the experimental data, leading to adsorption coefficients of 39.1 and 102.9 mgCOD/gLDH for raw and treated effluents, respectively. The best conditions for color and COD removal were obtained at lower values of temperature and pH (25 °C and pH 7) and, in these conditions, an LDH dose of 10 g/L resulted in color removal efficiencies of 56% for samples of raw and 66% for samples of treated effluent. Recycling studies indicated that the reuse of thermally treated LDH led to a progressive loss in the removal efficiencies of COD and color. The reduction was more pronounced with samples of the raw textile effluent. LDH characterization performed before and after each adsorption and regeneration experiment showed that there was no intercalation of dye molecules in the interlayer region of the LDH, indicating that COD and color removal might be due to the adsorption of organic molecules onto the LDH surface.

This work presents results on the production and characterization (by both mass spectrometry and conventional chemical analyses) of Soluble Microbial Products (SMP) that accumulated in aerobic and anaerobic bench scale completely stirred tank reactors (CSTRs) fed with glucose or acetate under different hydraulic retention times (HRT) and temperatures. SMP accumulation varied from 2 to 68% of the influent COD in the aerobic reactor and from 9 to 27% in the anaerobic reactor and increased with the decrease in temperature and with the HRT reduction in the aerobic reactor. On the other hand, in the anaerobic reactor, the organic loading rate and the temperature had little impact on SMP production, implying that the SMP originated from different mechanisms in each system. For both reactors, a higher accumulation of SMPs was observed as the substrate was acetate when compared to glucose, and the chemical analysis showed that the majority of the SMP did not seem to be proteins or carbohydrates. Principal component analysis (PCA) of the mass spectra from positive and negative mode electron-spray ionization (LC-IT-TOF-MS) and results from matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) confirmed the chemical analyses and showed the absence of proteins in the effluents and the predominance of low molecular weight SMP. The PCA analysis also showed that the majority of the SMP from aerobic and anaerobic reactors did not seem to originate from soluble extracellular polymeric substances (EPS) or cell lysis products.