H.M. Pinheiro

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

Microbial conversion of steroid compounds: recent developments

Steroid compounds can be ranked among the most widely marketed products from the pharmaceutical industry. Highly specific reactions are required to produce functionalized compounds with therapeutic use and commercial value. The complexity of steroid molecules renders the use of biocatalysts particularly interesting, due to the high regio- and stereo-selectivity of the reactions to be performed. These characteristics, together with the mild conditions required for bioconversions, led to the development of high yield biological production processes, which are more environmentally friendly than their chemical synthesis counterparts, a feature that is presently a major concern of industrialists. Although some of these bioconversions are well-established, efforts are ongoing in order to increase the efficiency of the existing processes as well as to identify new potentially useful bioconversions. In this work an overview of recent developments on the use of microorganisms for steroid production is presented.

Whole-cell biocatalysis in organic media

Abstract The use of water-immiscible organic solvents in whole-cell biocatalysis has been exploited for biotransformations involving sparingly water-soluble or toxic compounds. These systems can overcome the problem of low productivity levels in conventional media due to poor substrate solubility, integrate bioconversion and product recovery in a single reactor, and shift chemical equilibria enhancing yields and selectivities; nevertheless, the selection of a solvent combining adequate physicochemical properties with biocompatibility is a difficult task. The cell membrane seems to be the primary target of solvent action and the modification of its characteristics the more relevant cellular adaptation mechanism to organic solvent-caused stress. Correlations between the cellular toxicity or the extractive capacities of different solvents and some of their physical properties have been proposed in order to minimize preliminary, solvent-selection experimental work but also to help in the understanding of the molecular mechanisms of toxicity and extraction. The use of whole cells in organic-media biocatalysis provides a way to regenerate cofactors and carry out bioconversions or fermentations requiring multi-step metabolic pathways; some processes already are commercially exploited. Immobilization can further protect cells from solvent toxicity, and has thus been effectively used in organic solvent-based systems. Several examples of extractive fermentations and other whole-cell bioconversions in organic media are presented.

Anaerobic treatment of textile effluents: A review

The treatment of textile waste water is commonly carried out using biological (mainly aerobic) and physico-chemical systems. However, anaerobic bioreactors can be used to at least partially treat these effluents and provide a number of significant advantages. The most attractive feature for the treatment of textile effluents is the decolourisation of many dyes under the reducing conditions present in an anaerobic reactor. Laboratory-scale results on this particular topic are here reviewed. A second major advantage of anaerobic processing is its ability to treat wastestreams with high organic loads such as the effluents from the desizing and scouring operations currently employed in the textile manufacturing industry. Reports on successful, full-scale and pilot-scale plants are also reviewed and some limitations are discussed.

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.

Batch tests for assessing decolourisation of azo dyes by methanogenic and mixed cultures.

Most of the published studies on azo dye colour removal involve anaerobic mixed cultures and there is some interest in the knowledge of how dye reduction occurs, if by facultative, strictly anaerobic or both bacterial trophic groups present in classic anaerobic digestors. This paper describes the behaviour of methanogenic and mixed bacteria cultures on the colour removal in batch systems, of a commercial azo dye, C.I. Acid Orange 7, used in paper and textile industries. The aim of this study is to demonstrate, by analysing dye decolourisation, that it occurs with mixed cultures as well as with strictly anaerobic (methanogenic) cultures. Tests were performed with a range of dye concentrations between 60 and 300 mg x l(-1). The influence of dye concentration on the carbon source removal and decolourisation processes was studied. The effect of carbon source concentration on colour removal was also analysed for both cultures. The degradation rates in mixed and methanogenic cultures were compared. The consumption of carbon source was monitored by COD analysis and dye degradation by ultraviolet-visible spectrophotometry and thin layer chromatography.

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.

pH effects on the removal of Cu2+, Cd2+ and Pb2+ from aqueous solution by waste brewery biomass

Abstract An industrial strain of Saccharomyces cerevisiae collected from the waste of a brewing industry was used to remove lead, cadmium and copper from aqueous solutions (1 mm).Metal removal efficiency by using either biomass suspension directly diluted into the metal solutions or biomass previously incubated and washed in distilled water was compared. In all experiments with unwashed biomass a shift in the medium pH from 4.5 to a final value in the 7.0–8.0 range occurred. This pH increase was responsible for a metal precipitation effect associated to the metal biosorption. A very different pH profile was observed when washed biomass was used leading to different removal profiles for Cd2+ and Pb2+ and a similar one for Cu2+. In the absence of biomass, medium components and/or the excreted intracellular products proved to interfere in the metal removal and to be responsible for 80% Pb2+ precipitation, in the pH 4.5–5.0 range.To initial metal solution pH, leading to the lowest residual ion concentrations, after 96 h of contact with unwashed biomass and in the absence of pH adjustment, was 4.5–5.0. Continuous or stepwise adjustment of medium pH to this range during the process was unfavourable for metal removal, being the continuous adjustment the worst procedure. In this case, Cd2+ was not biosorbed and Cu2+ removal decreased from 76 to 33%. However, Pb2+ was always extensively removed (89%) and only slightly affected by pH control.The global results suggest different removal mechanisms for each cation. Cu2+ was removed by both metal sorption and precipitation, due to the pH shift that occurred during the process, while Cd2+ removal showed to be completely dependent of this pH shift. Pb2+ was totally and quickly removed, by precipitation, in the presence of the biomass suspension and at pH 4.5.Moreover, the biosorbent changes occurring during the process played an important role in the metal removal when non-viable microbial biomass is used.

Sterol side-chain cleavage with immobilized Mycobacterium cells in water-immiscible organic solvents

The possibility of using whole Mycobacterium sp. cells for the selective degradation of the side-chain of sitosterol in an organic bioconversion medium was investigated. Sterol solubility limits were estimated and free-cell biocompatibility tests were carried out, using a range of water-immiscible solvents. Among these, phthalates exhibited good biocompatibility and sterol-solubilizing capacities. Several organic and inorganic matrices were tested for the immobilization of Mycobacterium sp. cells by surface adhesion. Celite led to the best results, being thus selected for beta-sitosterol side-chain degradation tests in phthalates and in aqueous medium. Cells entrapped in kappa-carrageenan and in polyurethane foams were also used in these tests. The highest degradation activities were obtained with cells immobilized in Celite, with bis(2-ethylhexyl)phthalate as the conversion medium, resulting in molar conversion yields up to 70%, with respect to beta-sitosterol (5 g l-1). Further activity and stability tests revealed that this bioconversion system is markedly temperature dependent.