Nídia D. Lourenço

Colour in textile effluents – sources, measurement, discharge consents and simulation: a review

This paper aims to review the problem of colour in textile effluents, the different classes of dyes available and their contribution to the problem. Through new regulations, pressure is being placed on water companies all over the world to reduce the amount of colour in sewage effluent. Dyes exhibit low toxicity to mammals and aquatic organisms and therefore colour consents are normally applied for aesthetic and industrial reasons rather than for prevention of toxicity. The absorbance, ADMI values and concentrations of dyes in effluent are examined here with particular reference to reactive azo dyes used in cotton processing. Colour consents, the problem of colour in textile wastewaters and the importance for research in this area are also discussed. Dye concentrations of 0.01 g dm−3 up to 0.25 g dm−3 have been cited as being present in dyehouse effluent, depending on the dyes and processes used. ADMI values ranged from 50 to 3890 units for the dyeing of cotton. It was concluded that 1500 ADMI units was a reasonable value to aim for when simulating coloured effluents. Simulated textile effluents may be used for research purposes. These should resemble real wastes as closely as possible, but it is often difficult to replicate the ADMI values, absorbance and spectra of real effluents. The concentrations of dye used in simulated effluents examined in literature varied from 0.01 g dm−3 to 7 g dm−3. As absorbance and ADMI values change with the types of dye used, it is difficult to relate these values to dye concentrations. A concentration of 0.18 g dm−3 of a Red or Yellow dye or 0.43 g dm−3 of a blue dye would provide an ADMI of approximately 1500 units and fits within the range of dye concentrations presented in literature. A dye mixture simulating colour in a real textile effluent is suggested and some limitations of simulating actual wastewaters discussed. © 1999 Society of Chemical Industry

Effect of some operational parameters on textile dye biodegradation in a sequential batch reactor.

The combination of anaerobic and aerobic periods in the operation cycle of a Sequencing Batch Reactor (SBR) was chosen to study biological color removal from simulated textile effluents containing reactive, sulfonated, monoazo and diazo dyes, respectively, Remazol Brilliant Violet 5R and Remazol Black B. 90% color removal was obtained for the violet dye in a 24-h cycle with a Sludge Retention Time (SRT) of 15 days and an aerated reaction phase of 10 h. For the black dye only 75% color removal was achieved with the same operational conditions and no improvement was observed with the increase of the SRT to 20 days. For the violet dye a reduction of the color removal values from 90 to 75% was observed with the increase of the aerated reaction phase from 10 to 12 h. However, this increase did not promote the aerobic biodegradation of the produced aromatic amines. Abiotic tests were performed with sterilized SBR samples and no color removal was observed in cell-free supernatants. However color removal values of 30 and 12% were observed in the presence of sterilized cells and supernatants with violet and black dye, respectively and could be attributed to the presence of active reducing principles in the sterilized samples.

Bioreactor monitoring with spectroscopy and chemometrics: a review.

Biotechnological processes are crucial to the development of any economy striving to ensure a relevant position in future markets. The cultivation of microorganisms in bioreactors is one of the most important unit operations of biotechnological processes, and real-time monitoring of bioreactors is essential for effective bioprocess control. In this review, published material on the potential application of different spectroscopic techniques for bioreactor monitoring is critically discussed, with particular emphasis on optical fiber technology, reported for in situ bioprocess monitoring. Application examples are presented by spectroscopy type, specifically focusing on ultraviolet–visible, near-infrared, mid-infrared, Raman, and fluorescence spectroscopy. The spectra acquisition devices available and the major advantages and disadvantages of each spectroscopy are discussed. The type of information contained in the spectra and the available chemometric methods for extracting that information are also addressed, including wavelength selection, spectra pre-processing, principal component analysis, and partial least-squares. Sample handling techniques (flow and sequential injection analysis) that include transport to spectroscopic sensors for ex-situ on-line monitoring are not covered in this review.

Improved operational stability of peroxidases by coimmobilization with glucose oxidase

The operational stability of peroxidases was considerably enhanced by generating hydrogen peroxide in situ from glucose and oxygen. For example, the total turnover number of microperoxidase-11 in the oxidation of thioanisole was increased sevenfold compared with that obtained with continuous addition of H(2)O(2). Coimmobilization of peroxidases with glucose oxidase into polyurethane foams afforded heterogeneous biocatalysts in which the hydrogen peroxide is formed inside the polymeric matrix from glucose and oxygen. The total turnover number of chloroperoxidase in the oxidation of thioanisole and cis-2-heptene was increased to new maxima of 250. 10(3) and 10. 10(3), respectively, upon coimmobilization with glucose oxidase. Soybean peroxidase, which normally shows only classical peroxidase activity, was transformed into an oxygen-transfer catalyst when coimmobilized with glucose oxidase. The combination catalyst mediated the enantioselective oxidation of thioanisole [50% ee (S)] with 210 catalyst turnovers.

Carrageenan: A Food‐Grade and Biocompatible Support for Immobilisation Techniques

Immobilisation of both enzymes and whole-cell systems is of major importance in the improvement of the stability, activity and reusability of these biocatalysts. This review describes the use of the naturally occurring polysaccharide carrageenan as a support for the immobilisation of biocatalysts. Carrageenan is a food-grade and biocompatible support material extracted from red seaweeds. Before focusing on the use of carrageenan as an immobilisation support, an overview is given of the present uses of biocatalysts in industrial processes. The basic concepts of enzyme and whole-cell immobilisation are discussed, as well as the background of carrageenan as a biopolymer. Several examples of enzymes and whole-cell systems immobilised in carrageenan are discussed. A list of the most relevant patents in this field is presented as well as a list of enzymes and cell systems immobilised in carrageenan as described in the literature.

Effect of an azo dye on the performance of an aerobic granular sludge sequencing batch reactor treating a simulated textile wastewater.

This study analyzed the effect of an azo dye (Acid Red 14) on the performance of an aerobic granular sludge (AGS) sequencing batch reactor (SBR) system operated with 6-h anaerobic-aerobic cycles for the treatment of a synthetic textile wastewater. In this sense, two SBRs inoculated with AGS from a domestic wastewater treatment plant were run in parallel, being one supplied with the dye and the other used as a dye-free control. The AGS successfully adapted to the new hydrodynamic conditions forming smaller, denser granules in both reactors, with optimal sludge volume index values of 19 and 17 mL g(-1) after 5-min and 30-min settling, respectively. As a result, high biomass concentration levels and sludge age values were registered, up to 13 gTSS L(-1) and 40 days, respectively, when deliberate biomass wastage was limited to the sampling needs. Stable dye removal yields above 90% were attained during the anaerobic reaction phase, confirmed by the formation of one of the aromatic amines arising from azo bond reduction. The control of the sludge retention time (SRT) to 15 days triggered a 30% reduction in the biodecolorization yield. However, the increase of the SRT values back to levels above 25 days reverted this effect and also promoted the complete bioconversion of the identified aromatic amine during the aerobic reaction phase. The dye and its breakdown products did not negatively affect the treatment performance, as organic load removal yields higher than 80% were attained in both reactors, up to 77% occurring in the anaerobic phase. These high anaerobic organic removal levels were correlated to an increase of Defluviicoccus-related glycogen accumulating organisms in the biomass. Also, the capacity of the system to deal with shocks of high dye concentration and organic load was successfully demonstrated. Granule breakup after long-term operation only occurred in the dye-free control SBR, suggesting that the azo dye plays an important role in improving granule stability. Fluorescence in situ hybridization (FISH) analysis confirmed the compact structure of the dye-fed granules, microbial activity being apparently maintained in the granule core, as opposed to the dye-free control. These findings support the potential application of the AGS technology for textile wastewater treatment.

Analysis of secondary metabolite fate during anaerobic‐aerobic azo dye biodegradation in a sequential batch reactor

Abstract A great number of the reported examples of azo dye biodegradation comprise two main steps, the reductive cleavage of the azo bond under anaerobic conditions and the subsequent aerobic mineralization of the produced aromatic amines. Based on this possible metabolism a Sequencing Batch Reactor was chosen to study biological color removal from simulated cotton textile effluents containing a reactive azo dye. In previous studies high color removal levels of the azo dye Remazol Brilliant Violet 5R were achieved (up to 90% with an initial dye concentration of 100 mg l−1 ) during the anaerobic phase of Sequencing Batch Reactor operation. However, HPLC analyses revealed that the aromatic amines formed in the anaerobic phase were not mineralized during the subsequent aerobic phase. In an attempt to promote the aerobic biodegradation of these aromatic amines three different approaches were tested, the increase of the relative duration of the aerobic phase, the increase of the hydraulic retention time through the decrease of the daily fill flow and finally the increase of the dye/carbon source concentration ratio through the decrease of the fed volumetric organic load. The two aromatic amines directly resulting from azo bond reduction were detected by HPLC analysis. However, a third metabolite with significant peak area was also detected with a time profile suggesting an equilibrium with one of the aromatic amines. In spite of the conversions occurring between metabolites during the cycles of the tested approaches, no effective biodegradation of these metabolites was observed during the experimental period of over 810 days.

In situ UV-Vis spectroscopy to estimate COD and TSS in wastewater drainage systems

Ultraviolet-visible (UV-Vis) spectroscopy is a promising tool for fast and simple evaluation of wastewater quality, as it delivers spectra that may be correlated to various aggregate wastewater quality parameters, such as Total Suspended Solids (TSS) and Chemical Oxygen Demand (COD). Its application in drainage systems has scarcely been reported and is a step forward in water quality monitoring. Partial Least Squares (PLS) calibration models were developed for TSS and COD prediction, based on UV-Vis spectra. Spectra were acquired in two sites, in-line and off-line. Three approaches for model development were studied. Model evaluation statistics and guidelines were assessed, which allowed grading of the models from unsatisfactory to very good. Most of the developed models were rated very good according to those guidelines. The overall results strongly indicate UV-Vis spectra to be reliable for TSS and COD estimation in sewer systems, despite the rapid variations in hydraulic conditions and water quality.

Use of Spectra in the Visible and Near-Mid-Ultraviolet Range with Principal Component Analysis and Partial Least Squares Processing for Monitoring of Suspended Solids in Municipal Wastewater Treatment Plants

The present work assesses the possibility of using spectrophotometry in the near-mid-ultraviolet and visible wavelength ranges (282–790 nm) for the direct monitoring of treatment performance in municipal wastewater treatment plants (WWTPs). Principal component analysis (PCA) was used to analyze spectral data from samples collected along three WWTP process lines with different primary and secondary treatment units. The clustering observed in PCA score plots was mainly attributed to the suspended solids fraction present in the wastewater and highlighted differences in solids quality between plants and along the treatment lines. Thus, satisfactory partial least squares (PLS) calibration models to estimate total suspended solids (TSS) values from the acquired spectra could only be established per plant. The PLS models were established using 1–2 factors, with root mean error of cross-validation and coefficient of determination values in the 50–86 mg TSS L−1 and 82–95% ranges, respectively.

DEVELOPMENT OF PLS CALIBRATION MODELS FROM UV‐VIS SPECTRA FOR TOC ESTIMATION AT THE OUTLET OF A FUEL PARK WASTEWATER TREATMENT PLANT

Abstract In the present work ultraviolet (UV)‐visible spectra of water samples collected at the outlet of a fuel park wastewater treatment plant, including biological treatment, were acquired and used for the development of partial least squares (PLS) calibration models for the fast and simple estimation of total organic carbon (TOC). Three different PLS models were developed and compared on the basis of a common spectral range. The first model was obtained using spectra of raw samples, the second using spectra of diluted samples, to assess signal saturation in the UV region, and the third using spectra of both diluted and raw samples, in order to expand the narrow interval of TOC concentration values present in the original dataset. The root mean squared error of cross‐validation values for the developed PLS models were 2.3, 1.0 and 4.4 mg C l−1, respectively, and the validation results where highly satisfactory (root mean squared error of prediction values of 1.8, 0.8 and 4.5 mg C l−1, respectively).