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Textile wastewater (TWW) represents a major source of pollution worldwide, carrying high organic loads, recalcitrant azo dyes and engineered nanoparticles (ENP), namely silver nanoparticles (AgNP). The development of cost-efficient, environmentally-friendly TWW treatment solutions is critical. Despite the successful biodecolorization of azo dyes under anaerobic conditions, clear evidence for subsequent aerobic biodegradation of the often toxic breakdown sulfonated aromatic amines is scarce. Moreover, the debatable AgNP toxicity mechanisms, and apparent AgNP retention in activated sludge have raised concerns regarding eventual negative impacts on wastewater treatment efficiency. The aerobic granular sludge (AGS) technology, which has recently been scaled-up and implemented for the treatment of domestic wastewater and some industrial wastewaters, seems highly promising for TWW treatment, due to the high biomass retention capacity, anaerobic/anoxic/aerobic microenvironments within granules and enhanced tolerance towards high organic loads and toxic compounds. A review of the existing literature on AGS application to TWW treatment is presented, with a focus on the removal of azo dyes and their metabolites and ENP. The applicability of AGS to dye-containing synthetic and real TWW has been tested in different SBR systems. Their hydrodynamic regimens and operational conditions have been optimized, namely regarding granulation, long-term stability, azo dye decolorization and biodegradation of aromatic amines. Although promising results have been published regarding AGS resistance towards ENP (particularly AgNP), their long-term effects on the physical stability, biochemical properties and microbial community of AGS deserve more investigation. Overall, this review provides relevant support for the application of AGS SBRs in TWW treatment as a potential sustainable alternative to avoid the pollution of natural water bodies with synthetic dyes and ENP.

This study focused on the biodegradation of an azo dye (Acid Red 14, AR14) in two anaerobic–aerobic sequencing batch reactors (SBRs) treating synthetic textile wastewater, operated with aerobic granular sludge under different hydrodynamic regimens. The aim was to investigate the fate of the anaerobic AR14 breakdown products (aromatic amines) during the SBRs’ aerobic reaction phase. Specifically, liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) was used for structural characterization of AR14 biodegradation metabolites, their molecular formulas being confirmed by accurate mass measurements. Nineteen molecules potentially related to AR14 were detected in the SBRs, and their relative abundances were followed along the aerobic stage of treatment cycles. The two SBRs shared most of the identified compounds but with differences in their metabolite profiles. Biodecolorization through AR14 anaerobic azo bond reduction was confirmed by the identification of the aro...

This study investigated the occurrence of storage mechanisms in biofilm from constructed wetlands (CWs) through respirometric studies and calculated the corresponding heterotrophic growth yields. Respirometric tests were performed in biofilm extracted from horizontal sub-surface flow CWs batch loaded with three different COD mass loads: 7.0., 15.6 and 35.2 g COD/(m2∙day). The bed removal efficiency remained above 96% for all mass loads and COD mass removal rates increased from 6.8 g COD/(m2∙day) for the lowest load to 34.5 g COD/(m2∙day) for the highest load. The percentage of tests with storage evidence decreased from 85% to 10% with increasing mass loads and the responses of the microbial community to the acetate pulse showed an adaptation to the feast-famine conditions, through storage mechanisms, for lower loads, and a metabolic shift to the use of COD for growth for higher loads. Heterotrophic biomass yield values varied from 0.54–0.56 g COD/g COD for low mass loads to 0.69–0.71 for higher mass loads, indicating that greater substrate availably triggers growth and reduces the occurrence of storage. Storage yield values supported this trend varying between 0.89 and 0.94 with increasing mass loads. Given the significant storage evidence obtained in the present study, it is suggested that a modified modelling architecture, which includes storage mechanisms, should be considered in future simulations of CW systems.

The increased demand for protein sources combined with a decrease in the available land and water resources have led to a growing interest in macroalgae as alternative protein sources. This review focuses on strategies for macroalgae protein extraction, enrichment and characterization. To date, the protein extraction methods applied to algae include enzymatic hydrolysis, physical processes and chemical extraction. Novel methods, such as pulsed electric field, microwave-assisted, pressurized liquid and supercritical fluid extractions, and the application of smart solvents are discussed. An overview of the use of membranes and other processes to generate high-value protein concentrates from algae extracts is also presented, as well as some examples of the methods used for their characterization. The potential bioactivities from macroalgae-derived proteins and peptides, including novel glycoproteins and lectins, are briefly reviewed.

The ability of microalgae to grow in nutrient-rich environments and to accumulate nutrients from wastewaters (WW) makes them attractive for the sustainable and low-cost treatment of WW. The valuable biomass produced can be further used for the generation of bioenergy, animal feed, fertilizers, and biopolymers, among others. In this study, Scenedesmus obliquus was able to remove nutrients from different wastewaters (poultry, swine and cattle breeding, brewery and dairy industries, and urban) with removal ranges of 95-100% for nitrogen, 63-99% for phosphorus and 48-70% for chemical oxygen demand. The biomass productivity using wastewaters was higher (except for poultry) than in synthetic medium (Bristol), the highest value being obtained in brewery wastewater (1025 mg/(L.day) of freeze-dried biomass). The produced biomass contained 31-53% of proteins, 12-36% of sugars and 8-23% of lipids, regardless of the type of wastewater. The potential of the produced Scenedesmus obliquus biomass for the generation of BioH(2) through batch dark fermentation processes with Enterobacter aerogenes was evaluated. The obtained yields ranged, in mL H-2/g Volatile Solids (VS), from 50.1 for biomass from anaerobically digested cattle WW to 390 for swine WW, whereas the yield with biomass cultivated in Bristol medium was 57.6 mL H-2/gvs. info:eu-repo/semantics/publishedVersion

Aerobic granular sludge technology has been extensively studied over the past 20 years and is regarded as the upcoming new standard for biological treatment of domestic and industrial wastewaters. Aerobic granules (AG) are dense, compact, self-immobilized microbial aggregates that allow better sludge-water separation and thereby higher biomass concentrations in the bioreactor than conventional activated sludge aggregates. This brings potential practical advantages in terms of investment cost, energy consumption and footprint. Yet, despite the relevant advances regarding the process of AG formation, instability of AG during long-term operation is still seen as a major barrier for a broad practical application of this technology. This paper presents an up-to-date review of the literature focusing on AG stability, aiming to contribute to the identification of key factors for promoting long-term stability of AG and to a better understanding of the underlying mechanisms. Operational conditions leading to AG disintegration are described, including high organic loads, particulate substrates in the influent, toxic feed components, aerobic feeding and too short famine periods. These operational and influent wastewater composition conditions were shown to influence the micro-environment of AG, consequently affecting their stability. Granule stability is generally favored by the presence of a dense core, with microbial growth throughout the AG depth being a crucial intrinsic factor determining its structural integrity. Accordingly, possible practical solutions to improve granule long-term stability are described, namely through the promotion of minimal substrate concentration gradients and control of microbial growth rates within AG, including anaerobic, plug-flow feeding and specific sludge removal strategies.

Microalgae can be used for wastewater bioremediation with simultaneous CO 2 biofixation producing valuable biomass. Wastewater from a brewery was treated using the Scenedesmus obliquus microalga in bubble-column photobioreactors (PBRs). The PBRs were fed with ambient air and the effect of a 10% (v/v) brewery CO 2 supplement was studied. The PBRs were inoculated and a range of mean hydraulic residence time (HRT) values were tested (2.1–10.4 days). The maximum ash-free dry weight (AFDW) biomass productivity was obtained for a HRT of 3.5 days (0.29 d −1 dilution rate; 0.2 g L −1 d −1 (in terms of AFDW). The highest pollutant removal efficiencies were 92.9 and 88.5% for ammonia and total nitrogen, respectively, 40.8% for phosphorus, and 61.9% for COD. Except a dilution rate of 0.48 d −1 trial, the treated wastewater always met the Portuguese legislation quality standard for discharge into natural water bodies. Aiming to simultaneously maximize biomass volumetric productivity, CO 2 biofixation rate and wastewater treatment efficiency, while minimizing residence time, 0.29 d −1 represents the optimal dilution rate value. The potential of the produced Scenedesmus obliquus biomass was evaluated for the generation of biohydrogen through dark fermentation with Enterobacter aerogenes , and of bio-oil, bio-char and bio-gas through a pyrolysis process. The yields obtained were 67.1 mL H 2 g −1 (in terms of volatile solids - VS) for bioH 2 and 64, 30 and 6% for bio-oil, bio-char and bio-gas, respectively (dry mass content (%) calculated over freeze dryer biomass basis).

The use of engineered nanoparticles in the textile industry has been rapidly increasing but their fate during biological wastewater treatment is largely unknown. The goal of the current study was to characterize the interaction of silver nanoparticles (AgNPs), used in the textile industry, with a biological wastewater treatment system based on aerobic granular sludge (AGS). The exposure tests were performed using a laboratory-scale sequencing batch reactor (SBR) system with AGS. The behavior and fate of textile AgNPs in the AGS system was studied with nuclear microscopy techniques. Elemental maps of AGS samples collected from the SBR showed that AgNPs typically clustered in agglomerates of small dimensions (

Treatment of the highly polluting and variable textile industry wastewater using aerobic granular sludge (AGS) sequencing batch reactors (SBRs) has been recently suggested. Aiming to develop this technology application, two feeding strategies were compared regarding the capacity of anaerobic–aerobic SBRs to deal with disturbances in the composition of the simulated textile wastewater feed. Both a statically fed, anaerobic–aerobic SBR and an anaerobic plug-flow fed, anaerobic–aerobic SBR could cope with shocks of high azo dye concentration and organic load, the overall chemical oxygen demand and color removal yields being rapidly restored to 80%. Yet, subsequent azo dye metabolite bioconversion was not observed, along the 315-day run. Moreover, switching from a starch-based substrate to acetate in the feed composition deteriorated AGS stability. Overall, the plug-flow fed SBR recovered more rapidly from the imposed disturbances. Further research is needed towards guaranteeing long-term AGS stability during the treatment of textile wastewater.

Phenolic aldehydes resulting from lignocellulosic hydrolysis have often been considered harmful to the anaerobic cultures. Depending on the type of lignin, syringaldehyde present in hardwood and grass lignin can be produced as a by-product of its breakdown in varying extents. The influence of two mixed co-substrates, glucose and sodium acetate, on syringaldehyde degradation by anaerobic thermophilic cultures (50±2 °C) was assessed in the present work. Based on the monitoring of pH, chemical oxygen demand (COD) levels and UV–visible spectra in samples collected from batch bioreactors, it can be concluded that syringaldehyde is more prone to undergo anaerobic degradation in the presence of co-substrates. Both a reduction of the acclimatization period and an improvement in the COD removal (92.0%) were observed. As the only carbon source, syringaldehyde seems to be hardly degraded rendering a low efficiency of COD removal (53.2%). Some insights on the main alterations of syringaldehyde by anaerobic thermophilic cultures are also given.

Making cheese manufacturing environmentally sustainable is a major concern in the integrated management of this industrial sector. This concern is mainly due to the environmental impact of the discharge of its wastewaters, carrying heavy loads of salinity, nutrients, organic matter, solids and oils and fats. These discharges must meet increasingly stringent quality requirements. Some physicochemical (e.g. coagulation-flocculation, precipitation, oxidation) and biological (e.g. aerobic and anaerobic bioreactors and wetlands) treatments have been studied to address this problem. However, these treatments involve costs that some producers cannot sustain, face difficulties with biological reactor operational stability and often fail to consistently produce effluents compatible with discharge standards. In this context, aiming at the design of a simple and economical treatment method, several precipitation processes were tested using a fixed dosage of CaCO3 (75 g/L), combined with different dosages of FeCl3, FeSO4 or Ca(OH)2. The goal of the treatment was to produce a supernatant that would be evaluated as to its suitability for discharge into natural water courses or municipal treatment systems, or for reuse applications. The generated sludge would be evaluated for possible agricultural valorization. Through the measurement of the relevant supernatant quality parameters and using statistical analysis, it was possible to choose the best dosages for each of the tested coagulants (1.0, 1.0 and 0.6 g/L for FeCl3, FeSO4 and Ca(OH)2, respectively). Among these, the most efficient treatment was obtained with CaCO3 75 g/L + FeSO4 1.0 g/L. For this best-case scenario, the treatment led to removal yield values of 55.1% for chemical oxygen demand (COD), 92.0% for total phosphorus, 95.7% for turbidity, 59.1% for total phenols, 94.3% for nitrates, 71.0% for nitrites, 51.0% for total solids (TS) and 97.2% for oils and fats. The treatment did not produce an effluent supernatant with adequate quality for direct discharge into water courses, serving however as an efficient pretreatment for agricultural reuse. All the sludges generated in these treatments showed good potential for agricultural valorization due to their high nutrient content, along with pH and conductivity values within the acceptable ranges for soil application. Thus, this work contributes for a better integration of the cheese manufacturing industry in the overall aims of water and nutrient resources recovery in rural, agricultural areas.

The biodegradation of dyes remains one of the biggest challenges of textile wastewater. Azo dyes are one of the most commonly employed dye classes, and biological treatment processes tend to generate recalcitrant aromatic amines, which are more toxic than the parent dye molecule. This study aimed to isolate bacterial strains with the capacity to degrade both the azo dye and the resulting aromatic amines towards the development of a simple and reliable treatment approach for dye-laden wastewaters. A mixed bacterial enrichment was first developed in an anaerobic-aerobic lab-scale sequencing batch reactor (SBR) fed with a synthetic textile wastewater containing the model textile azo dye Acid Red 14 (AR14). Eighteen bacterial strains were isolated from the SBR, including members of the Acinetobacter, Pseudomonas and Oerskovia genera, Oerskovia paurometabola presenting the highest decolorization capacity (91% after 24 h in static anaerobic culture). Growth assays supported that this is a facultative bacterium, and decolorization batch tests with 20–100 mg AR14 L−1 in a synthetic textile wastewater supplemented with yeast extract indicated that O. paurometabola has a high color removal capacity for a significant range of AR14 concentrations. In addition, a model typically used to describe biodegradation of xenobiotic compounds was adjusted to the results, to predict AR14 biodegradation time profiles at different initial concentrations. HPLC analysis confirmed that decolorization occurred through azo bond reduction under anaerobic conditions, the azo dye being completely reduced after 24 h of anaerobic incubation for the range of concentrations tested. Interestingly, partial (up to 63%) removal of one of the resulting aromatic amines (4-amino-naphthalene-1-sulfonic acid) was observed when subsequently subjected to aerobic conditions. Overall, this work showed the azo dye biodegradation potential of specific bacterial strains isolated from mixed culture bioreactors, reporting for the first time the decolorization capacity of an Oerskovia sp. with further biodegradation of a recalcitrant sulfonated aromatic amine metabolite.

Online monitoring programs based on spectroscopy have a high application potential for the detection of hazardous wastewater discharges in sewer systems. Wastewater hydraulics poses a challenge for in situ spectroscopy, especially when the system includes storm water connections leading to rapid changes in water depth, velocity, and in the water quality matrix. Thus, there is a need to optimize and fix the location of in situ instruments, limiting their availability for calibration. In this context, the development of calibration models on bench spectrophotometers to estimate wastewater quality parameters from spectra acquired with in situ instruments could be very useful. However, spectra contain information not only from the samples, but also from the spectrophotometer generally invalidating this approach. The use of calibration transfer methods is a promising solution to this problem. In this study, calibration models were developed using interval partial least squares (iPLS), for the estimation of total suspended solids (TSS) and chemical oxygen demand (COD) in sewage from Ultraviolet-visible spectra acquired in a bench scanning spectrophotometer. The feasibility of calibration transfer to a submersible, diode array equipment, to be subsequently operated in situ, was assessed using three procedures: slope and bias correction (SBC); single wavelength standardization (SWS) on mean spectra; and local centering (LC). The results showed that SBC was the most adequate for the available data, adding insignificant error to the base model estimates. Single wavelength standardization was a close second best, potentially more robust, and independent of the base iPLS model. Local centering was shown to be inadequate for the samples and instruments used.

Textile wastewaters are rated among the most polluting in all industrial sectors, including high organic loads and dyes that are generally resistant to aerobic biotreatment. Alternative, staged anaerobic/aerobic regimes have been tested, with clear success in the biodecolorization of the widely used azo dyes. The novel aerobic granular sludge (AGS) technology has excellent potential in this context, due to the anoxic/anaerobic zones within granules and their increased tolerance to toxicity. In this study the performance of anaerobic/aerobic, flocculent and AGS sequencing batch reactors (SBR) was compared in the treatment of a simulated textile wastewater. Similar color removal yields (75–80%) of an azo dye were attained in both systems but with higher anaerobic and overall COD removal yields in the AGS SBR, thus demonstrating the latter's good potential. Comparison of the toxicity of samples collected from both SBR using yeast-based assays highlighted the better performance of the AGS SBR as compared with the flocculent SBR, with respect to detoxification potential.

Aerobic granular sludge was successfully developed on a simulated textile effluent with an added azo dye, on a non-tubular sequential batch reactor (SBR), with better granulation results than in a dye-free control SBR fed with the same base medium. The overall performance of the treatment was very good, with high color and chemical oxygen demand (COD) removal yields (up to 85% and 80%, respectively). Operation under two sequencing batch cycle strategies, i.e., with a single anaerobic/aerobic reaction phase or under intermittent aeration, showed that the latter generally improved the treatment performance. Under intermittent aeration, biomass accumulation was induced, with faster settling aggregates, leading to a higher COD removal yield. Although a lower decolorization rate was observed in the first 30 min of anaerobic reaction, as compared to the single phase strategy, the overall color removal remained high. This work demonstrates the applicability of the new aerobic granular sludge technology for the treatment of textile effluents.

Anaerobic batch biodegradation of spent brewery grains (SBG) was investigated in the presence of co-substrates and a monoazo dye (Acid Orange 7 – AO7) under mesophilic and thermophilic regimes. The highest values for the yield coefficient of biogas (STP) on substrate (Ybs) were obtained under mesophilic conditions (0.381–0.516 Lbiogas/g CODremoved and 0.147 to 0.475 Lbiogas/g CODremoved for mesophilic and thermophilic regimes, respectively). A stimulation of the degradation of SBG associated with microbial growth was observed in the presence of co-substrates (glucose and acetate). Supplemented co-substrates also lowered the residual COD leading to an increase in the COD removal efficiency, particularly under thermophilic regime (from 41% to 70%). Although biogas yield (Ybs) indicates a decrease in the presence of the dye, suggesting that it has inhibitory effects, the overall COD removal was not significantly altered. An increase of colour removal was observed when the temperature of the operation was increased (87 ± 2% and 93 ± 1% for mesophilic and thermophilic reactors, respectively), which could be explained by both faster adsorption and biotic reductive cleavage of azo dye bond mechanisms. These results indicate that raw SBG is more prone to biodegradation under an anaerobic mesophilic regime; hence its bio-energetic valorisation is possible.

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.

Advances in measurement and automation have recently enabled the deployment of monitoring systems with high frequency data acquisition in Wastewater Treatment Plants (WWTP). In this context, this work aims to design soft sensors to predict hard-to-measure wastewater quality variables required for mechanistic modeling of biological treatment in a real municipal WWTP. Input data collected at the WWTP using a flowmeter, online spectrophotometric and electrochemical probes, sampling campaigns and off-line analyses, are here used for the development of soft sensors through multivariate methods, i.e., Principal Component Analysis (PCA) and Partial Least Squares (PLS) regression. Exploratory data analysis is performed to detect outliers, patterns and correlations. Soft sensor PLS models are optimized using leave-one-out cross validation and the root mean squared error (RMSE) for the prediction of an independent dataset is computed. Normalized RMSE values for organic nitrogen prediction result in 19.5 % and 18.1 % for sensors using analytical and spectral data, respectively. The possibility of using a single wavelength spectrophotometric probe is here evaluated aiming to reduce the online monitoring investment costs.

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.

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.

Biodecolourisation of an azo dye by anaerobic cultures using a liposomal textile levelling agent as primary substrate was assessed. Liposomes seem to facilitate the uptake of the dye (Acid Orange 7) by anaerobic biomass, leading to a fast decolourisation (colour removal of 96% was achieved in the first sample port of the reactor profiles). On the other hand, the presence of dye (60–300 mg l −1 ) caused a decrease in the chemical oxygen demand (COD) degradation rate (4.1–2.5 g COD removed l −1 d −1 for 60 and 300 mg l −1 of dye, respectively), suggesting inhibitory effects. Aerobic degradation of aromatic amines was investigated in aerobic respirometric assays with different types of inocula. Sulfanilic acid and aniline were mineralised by inocula with a significant microbiological diversity, even with domestic effluent. These results were confirmed by a significant reduction of COD, total organic carbon (TOC) and a high oxygen consumption (biochemical oxygen demand/theoretical oxygen demand), 92±4%. Kinetic analysis showed that a sigmoid function describes quite well the experimental data, even better than the exponential model. Orthanilic and metanilic acids and 1-amino-2-naphtol were persistent under the tested conditions.

A fixed-bed reactor (FBR) and an airlift reactor (AR) were compared as to their effectiveness for the bioremoval of cadmium from dilute aqueous solutions (1 mM in Cd(II)), using, as biosorbent, a strain of Saccharomyces cerevisiae collected from the waste of a brewing industry and immobilised by entrapment in polyurethane foam. A liquid recirculation flow rate of 0.027 dm3.dm−3.min−1, in the FBR, and an injection of air at a flow rate of 0.1 v.v.m., in the AR, both to promote turbulent flow around the biosorbent, were required to maximize Cd(II) removal yields. A pH increase associated with a release of intracellular compounds to the aqueous solution were apparently involved in this effect. The Cd(II) bioremoval capacity attained values of 7.06 mmol Cd.gbiomass−1 and 1.29 mmol Cd.dm−3reactor, in the AR and 1.90 mmol Cd.gbiomass−1 and 6.08 mmol Cd.dm−3reactor in the recirculated FBR.

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.

The decolorization kinetics of Remazol Brilliant Violet 5R (RBV-5R) and Remazol Black B (RB-B) (mono- and diazo reactive dyes, respectively) was investigated in the first 9 h (anaerobic phase) of a 24-h cycle anaerobic/aerobic sequencing batch reactor (SBR). Two distinct, successive decolorization periods were observed for both dyes, apparently due to different decolorization mechanisms. The apparent first-order rate constants were much lower for the second periods. First-order kinetics were apparently followed for both periods of RBV-5R but not for the first decolorization period of RB-B, possibly due to the occurrence of mass transfer limitations.

The use of organic solvent-based media for microbial 9α-hydroxylation of androstenedione (AD) by resting Rhodococcus sp. cells was evaluated. Product yields higher than 90% were observed in a two-phase phthalate-buffer transformation medium (3:1, v/v) containing 1.0 g L−1 AD. The results suggest that in these conditions the reaction of Δ1-dehydrogenation is considerably inhibited. The successful hydroxylation reaction with a product yield exceeding 60% was found to take place also in a phthalate medium under simultaneous forced aeration and maintenance of a minimum water content of about 3% (v/v).

In this work, the anaerobic period of an anaerobic–aerobic sequencing batch reactor was found to allow the reductive decolourisation of azo dyes. 1-l reactors were operated in 24-h cycles comprising anaerobic and aerobic reaction phases, fed with a simulated textile effluent including a reactive type (Remazol Brilliant Violet 5R) or an acid type (Acid Orange 7) azo dye. The aim was to assess the role of different redox phenomena in the anaerobic decolourisation process. Selective inhibition of sulphate reducing bacteria was carried out in the sulphate-containing, reactive dye fed reactor, resulting in nearly complete, though reversible and inhibition of decolourisation. The acid dye fed reactor's supplementation with sulphate, though resulting in sulphate reduction, did not improve decolourisation. Other redox mediators, namely quinones, were more effective in promoting electron transfer to the azo bond. Bio-augmentation of the acid dye fed reactor with a pure sulphate reducer strain known to decolourise azo dyes, Desulfovibrio alaskensis, was also carried out. Decolourisation was improved, but apparently as a result of the carbon source change required to support D. alaskensis growth. A chemically mediated reduction of the azo bond coupled to biological sulphate reduction, thus seemed to account for the high decolourisation yields of both dyes.

This work examined the performance of a sequencing batch reactor treating dyeing effluents from a factory that processes mainly wool and wool/polyester blends. Different operational conditions were evaluated, namely the influence of the anaerobic and the subsequent aerobic phase on the organic load removal, as well as the effect of the length of the aeration period (from 8 to 12 h) on process efficiency. A comparison between a fill stage in fast and slow modes was carried out. Results indicate that the cycle 2 conditions (fast fill and 12 h aeration time) improved the overall efficiency (85 ± 6% soluble COD and 95 ± 4% BOD5 removal yields) with a predominant COD uptake occurring in the aerobic stage. Slow, linear COD removal was observed in the anaerobic phase, in contrast with an exponential COD decrease in the oxic phase. For SS a level under 100 mg/l was general achieved in the exit of the reactor. With respect to dye degradation, a noticeable decrease of the absorbance measured in the UV–visible range was observed. This could be explained by the reduction of the azo bonds of some of the present dyes in the anaerobic step, in which ORP values lower than −400 mV were attained. Some oxidation of anthraquinone sulphonate dyes and of the aromatic amines resulting from azo bond cleavage could also have been taken place, as well as bioelimination mechanisms such as dye sorption.

Mixed anaerobic bacterial consortia have been show to reduce azo dyes and batch decolourisation tests have also demonstrated that predominantly methanogenic cultures also perform azo bond cleavage. The anaerobic treatment of wool dyeing effluents, which contain acetic acid, could thus be improved with a better knowledge of methanogenic dye degradation. Therefore, the decolourisation of two azo textile dyes, a monoazo dye (Acid Orange 7, AO7) and a diazo dye (Direct Red 254, DR254), was investigated in a methanogenic laboratory-scale Upflow Anaerobic Sludge Blanket (UASB), fed with acetate as primary carbon source. As dye concentration was increased a decrease in total COD removal was observed, but the acetate load removal (90%) remained almost constant. A colour removal level higher than 88% was achieved for both dyes at a HRT of 24h. The identification by HPLC analysis of sulfanilic acid, a dye reduction metabolite, in the treated effluent, confirmed that the decolourisation process was due mainly to azo bond reduction. Although, HPLC chromatograms showed that 1-amino-2-naphthol, the other AO7 cleavage metabolite, was removed, aeration batch assays demonstrated that this could be due to auto-oxidation and not biological mineralization. At a HRT of 8h, a more extensive reductive biotransformation was observed for DR254 (82%) than for AO7 (56%). In order to explain this behaviour, the influence of the dye aggregation process and chemical structure of the dye molecules are discussed in the present work.

The use of chrysotile, a plentiful and low-cost inorganic material, as an effective immobilisation matrix for mycobacterial cells was evaluated. The side-chain cleavage of β-sitosterol to 4-androstane-3,17-dione (AD), in an organic–aqueous two-liquid phase system, was chosen as model system. Bis(2-ethylhexyl) phthalate (BEHP), a biocompatible organic solvent, was used as organic phase. The biotransformation was carried out with either growing or previously grown cells. Mycobacterial cells were shown to adsorb onto chrysotile in both aqueous buffered system and in organic–aqueous two-liquid phase systems. Cells tend to aggregate among the chrysotile fibres during and after growth. The formed chrysotile/cells complex retained catalytic activity under bioconversion conditions for 1 week, at least. No mass transfer hindrances were observed when the immobilised form of the biocatalyst was used, as compared to the free form. However, among the several approaches to produce the most efficient immobilised biocatalyst, the use of previously grown cells in contact with chrysotile led to the highest product yields as well as highest bioconversion rates. The feasibility of this approach was further evidenced since it allowed the implementation of a continuous mode of operation. A constant product yield of 50% was observed for a 1-week period with this experimental set-up. This work clearly highlights the ability of chrysotile to provide an efficient immobilisation matrix for whole cells to be used as biocatalysts in organic–aqueous two-liquid phase bioconversion systems.

A systematic evaluation of the effect of key operational parameters on the selective cleavage of sitosterol to 4-androstene-3,17-dione (AD) with Mycobacterium sp. NRRL B-3805 in a dioctyl phthalate: aqueous buffer two-liquid phase system was performed. Of the parameters assessed, buffer composition, biomedium pH, temperature, and biomass and substrate concentration were those that mostly affected overall bioconversion rate. The optimum pH was 7.5 with Tris buffer. The highest bioconversion rate was observed at 35 °C, although at 40 °C bioconversion activity was virtually lost. Michaelis–Menten type kinetics adequately described the bioconversion system. Increasing biomass concentration from 10 to 70 gwet cell weight l−1 favored AD final yield, although the specific AD yield slightly decreased.

The selective side-chain cleavage of β-sitosterol by free cells of Mycobacterium sp. NRRL B-3805 is a well-established multi-enzymatic process for the production of the pharmaceutical steroid precursors androstenedione (AD) and androstadienedione (ADD). In this study, bis(2-ethylhexyl) phthalate (BEHP) was used as a reaction medium for carrying out the process with freely suspended cells. The work aimed to show that microbial sitosterol side-chain cleavage is possible in this essentially mono-phasic organic medium, provided that some important parameters are adequately controlled. The effects of the biocatalyst/substrate mass ratio, system aeration rate and minimum buffer addition to the organic medium on the product yield and the reaction rate were thus evaluated.

The present status of origins, known hazards, release restrictions and environmental fate of aromatic amines is reviewed. The specific case of aromatic amines arising from the reduction of the azo bond of azo colorants is addressed, with emphasis on the recalcitrance of azo dyes, their demonstrated vulnerability to azo bond reduction through different mechanisms and the lack of data on the biodegradability of the resulting amines. The evolution and present array of analysis methods for aromatic amines in water samples is reviewed, highlighting the increased sophistication and sensitivity attained, and referring a few efforts towards fast analysis methodologies. The case for the application of direct ultraviolet spectral analysis with advanced deconvolution techniques for the monitoring of aromatic amines in textile effluent treatment is presented.

Batch and continuous cultures conditions were studied in order to increase γ -linolenic acid production by Mucor fragilis CCMI 142, in response to the presence of ethanol. Continuous cultures were used to add ethanol pulses to steady state pellet cultures. It was demonstrated that pellet size, which allowed homogeneous fungal cultures, can be obtained by means of pH adjustment, thus enabling steady state continuous growth at 2.90±0.05. The 5 and 2% (v/v) ethanol pulses induced hyphal morphological changes with arthrospore formation. A 1% (v/v) pulse of ethanol did not immediately affect growth, but induced morphological changes, which led to autolysis at the pellet core. A 0.5% (v/v) pulse of ethanol did not affect neither the morphology nor the physiology of the microorganism to any significant extent. The 0.5 and 1% (v/v) ethanol pulses resulted in an increase in the proportion of γ -linolenic acid production up to 11%. Data from batch cultures showed a higher enhancement of ethanol, attaining 30% of γ -linolenic acid. The increase of γ -linolenic acid content observed in batch and continuous conditions appears to be a response associated with stress induced by the ethanol which seems to be of value as an industrial medium component.

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 biologicalcolor 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.

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.

The biodegradation of surfactants is a frequent and complex problem in domestic and industrial wastewater treatment processes. In addition to the resulting metabolites being sometimes refractory, the complete biodegradation of many of the most employed non-ionic surfactants requires long hydraulic retention times and the presence of specialised bacterial consortia. Preliminary acclimatisation tests highlighted the importance of the sludge acclimatisation state to a specific surfactant substrate for biotreatment efficiency. This paper reports on studies aimed at quantifying activated sludge acclimatisation and memory retention levels when subjected to changes in the type of surfactant included in the feed. Several transitions were tested, namely from an alkylphenol ethoxylate to a linear alkyl ethoxylate and the reverse, and between alkyl ethoxylates with different hydrophobic and hydrophilic molecular chain lengths. The kinetic results showed that sludge activation and memory loss were more dynamic for primary biodegradation It was found that the sludge was harder to adapt to alkylphenol ethoxylate than to alkyl ethoxylate. The former also apparently introduced an inhibitory effect, resulting in very slow degradation kinetics when imposed to alkyl ethoxylate acclimatised sludge. When replacing an alkyl ethoxylate with another surfactant of the same family, a longer ethoxylate chain reduced the degradation rates. This effect was further enhanced by simultaneously increasing the hydrophobic chain length of the substrate. The acclimatisation kinetic after the replacement of an alkyl ethoxylate by a longer counterpart was slower than the reverse case, and memory was also more easily lost.

The multi-step bioconversion of β-sitosterol by Mycobacterium sp. NRRL B-3805 for the formation of androstenedione (AD) as major product, a key intermediate in the production of therapeutic steroids, is a well established industrial application of a biocatalytic process. In the present work, this sterol side-chain cleavage was selected as model system for a study of whole-cell biocatalyst operational stability in prolonged bioconversions in two-phase aqueous-organic media. The aim was to evaluate the effect of phase composition in the process yields by using four high log Poctanol phthalates as organic phases and phosphate buffer and nutritional media as aqueous phases. The effect of a non-ionic surfactant added to the aqueous phase was also studied. Results show no relation between bioconversion yields and solvent log Poctanol values, suggesting that, in the used range, solvent molecular structures and the resulting specific interactions with the cell envelope are determining for the biocatalyst behaviour. Different responses were obtained from the use of different aqueous media, the complex nutritional media leading to the highest conversion yields, while the lowest were observed with the mineral nutritional media. The effect of surfactant addition in the bioconversion yields was apparently not significant. In the systems with bis-(2-ethylhexyl) and bis-(3,5,5-trimethylhexyl) phthalates as the organic phases, the fed-batch operational mode allowed the maintenance of stable biocatalytic activity levels up to at least 6 days of operation, with high androstenedione yields.

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.

The process performance of coagulation to remove reactive dyes from dyehouse effluent is affected by multiple factors, which can be best examined in factorially-designed experiments. A preliminary jar-test procedure was used to select coagulants and the optimal pH and coagulant dosage ranges. An inorganic salt (ferrous sulphate) and an organic polymer (DEC 50) were selected for further studies. Factorially-designed jar-test experiments were performed with different compositions of a synthetic cotton processing wastewater to determine which factors most affected colour removal and highlight interactions between them. Some additives, such as an oxidative desizing agent and a peroxide stabiliser, favoured colour removal within specific concentration ranges. The presence of sizing agents and surfactants reduced process efficiency. Increasing concentration of ferrous sulphate could counteract this, but would result in higher sludge disposal costs.

The composition of a textile industry wastewater is highly variable, as the industrial process has to follow fashion and season trends. Surfactants represent one of the largest COD fractions in a typical textile wastewater. Therefore, it was the aim of this paper to model the acclimatisation behaviour of an activated sludge system when subjected to composition variations in the surfactant containing feed. The model was based on data obtained in SBR experiments in which a linear alkyl ethoxylate as sole carbon source in the feed was replaced by another with a longer ethoxylate chain. A previously developed model (Fractionated Degradation Model) was applied to each of the 21 SBR cycles carried out in this study. The resulting best-fit parameters were investigated and sub-models were further developed, to create an acclimatisation model, able to predict the sludge acclimatisation level. Using the information given by this model, it was possible to propose an optimal operation scheme to pre-acclimatise the sludge before a surfactant replacement is made in the textile process. A cost analysis was carried out to compare different scenarios, with and without the application of this operation scheme. It was concluded that the proposed pre-acclimatisation process may be cost effective as compared to other scenarios if a cheap surfactant-containing product was employed.

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 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.

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.