Dyes-environmental impact and remediation

Dyes are an important class of synthetic organic compounds used in many industries, especially textiles. Consequently, they have become common industrial environmental pollutants during their synthesis and later during fibre dyeing. Textile industries are facing a challenge in the field of quality and productivity due to the globalization of the world market. As the highly competitive atmosphere and the ecological parameters become more stringent, the prime concern of the textile processors is to be aware of the quality of their products and also the environmental friendliness of the manufacturing processes. This in turn makes it essential for innovations and changes in these processes, and investigations of appropriate and environmentally friendly treatment technologies or their residues. The large-scale production and extensive application of synthetic dyes can cause considerable environmental pollution, making it a serious public concern. Legislation on the limits of colour discharge has become increasingly rigid. There is a considerable urgent need to develop treatment methods that are effective in eliminating dyes from their waste. Physicochemical and biological methods have been studied and applied, although each has its advantages and disadvantages, with the choice being based on the wastewater characteristics, available technology and economic factors. Some industrial-scale wastewater treatment systems are now available; however, these are neither fully effective for complete colour removal nor do they address water recycling. This chapter outlines the background of dye chemistry, the application areas and the impact of dyeing effluents in the environment. The processes/techniques being implemented and developed for wastewaters remediation are revisited

Strategies for the bioremediation of azo dyes containing wastewaters

Publicado em "Book of abstracts of the 2nd Meeting of the Institute for Biotechnololgy and Bioengineering"Azo dyes are an important class of wastewater pollutants resulted especially from textile industry. Biological treatment based on the anaerobic azo bound reductive cleavage, followed by a second step for the transformation of the resulted aromatic amines, seems promising. In our studies, the surface chemistry of a commercial activated carbon (AC) was selectively modified by chemical oxidation and thermal treatments and tested as a natural redox mediator on chemical and biological anaerobic azo dye reduction [1]. Batch experiments with 0.1 g L−1AC demonstrated an increase of the first-order rates, up to 9-fold, as compared with assays without AC. Thermal treated samples gave better results due to their positively charged surface, favouring electrostatic attraction between the carbon and the anionic dyes tested. The low amount of AC used and the positive results demonstrated, constitutes a significant breakthrough in the field of redox mediated processes which will certainly open new perspectives for wastewater treatment processes. In order to investigate the fate of aromatic amines, two UASB reactors were operated under denitrifying conditions: R1 contained nitrate and R2 a nitrate and nitrite mixture as terminal electron acceptors [2]. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the influent of R2, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an intense yellow solution. Based on the HPLC-MS analysis, the structures of possible products were proposed. Denitrification activity tests suggest some detoxification

Anaerobic biodegradation of aniline under different electron accepting conditions

Aromatic amines are important industrial chemicals. Due to their high toxicity and persistency in both water and soils, they are of environmental concern. Aniline is not biodegradable in normal anaerobic condition. A novel approach of anaerobic biodegradation coupled with selective redox mediators, is proposed. Different redox mediators, namely manganese dioxide, Ferric citrate, ferrous chloride and magnetic iron oxide nanoparticle were tested. Fe3O4 nanoparticles, with size of 10 nm, were shown as the best, leading to 98 % of aniline removal efficiency within 24 h of operation at 37 °C. Biodegradation of aniline followed a pseudo first order kinetic model. Products of reaction were identified by GC/MS, revealing that the biodegradation occurred via catechol pathway. Methanogenic activity tests suggest that an IC50 of aniline is ~10 mM and that Fe3O4 nanoparticles are not toxic on un-adapted biomass

Carbon nanotubes as novel redox mediators for dyed wastewaters biodegradation

Due to their large-scale production and extensive application, dyes have turned serious pollutants as when improperly handled and disposed, they may create serious public health and environmental problems. One of the problems that textile industry is facing is related with the incomplete exhaustion of dyes onto textile fibre from an aqueous dyeing process and the need to implement innovative and sustainable effluent treatment methods to remove colour. Biological treatment systems were shown to be promising technologies. The main limiting factor of the reductive transformations by anaerobic sludge is the electron transfer, a slow process. This limitation can be overcome by making use of redox mediators, compounds that accelerate the electron transfer from a primary electron donor to a terminal electron acceptor, to speed up the process. Activated carbon (AC) has been shown as a feasible redox mediator. Samples of microporous thermal treated AC (ACH2) and mesoporous carbons: Xerogels (XA, XB) and Carbon nanotubes (CNT) were tested on azo dye and textile wastewater biodegradation. ~80 % Mordant Yellow 10 (MY10) and 70 % of Reactive Red 120 (RR120) colour removal was obtained with all the carbon materials. Acid Orange 10 (AO10) is not biodegraded in the absence of Carbon Materials, but with XB a 98 % of colour removal at 4.48 ± 0.74 d-1 of reduction rate was achieved. For MY10 and RR120, rates increased in the order: control < ACH2 < XA < XB < CNT. HPLC analysis confirmed the reduction of dyes with the corresponding aromatic amines formation. Biological treatments of real wastewater lead to 65 % of colour removal with rate improvement in the presence of CNT

Decolorization of aqueous effluents using agro waste

In this study, the potential of agrowaste for a food dye sequestration from aqueous effluents was investigated. Initially, four local agrowaste waste namely pumpkin seed hull, bean null, oat straw and nut shells, were tested in natural condition. Bean hull (BH) revealed the best uptake capacity for Food Red 14 (FR14). The agro waste was characterised before and after dye sorption process using SEM and FTIR techniques. Those analyses were conducted in order to identify the principal connections contributing to the sorption process. The point of zero charge of BH surface, pHpzc was assessed at 4.6, which indicated a mostly acidic surface, favorable for dye adsorption at pH<6, when the sorbent is positively charged. The dye removal efficiency of the adsorbent has been established in relation to some factors, such as: pH, amount of adsorbent, dye initial concentration, contact time and temperature. In order to make the sorption process predictable, four empirical isotherms and four kinetics models were applied to the experimental data so as to enact the nature of the sorption process. Attempts have also been made for sorbent viability by testing different solvents for FR14 desorption. FTIR spectra reveal the main bands in FR14 sorption process: that at 1450 cm-1 corresponding to C=C bond from the aromatic ring appears greatly diminished for FR14-BH after the sorption process and suggests a horizontal orientation of the molecules. The movement of the band at 3442 cm-1, corresponding to -OH groups, to lower wave number suggests lower involvement of these groups in the sorption process. The others band movement from BH spectra after the sorption process is due to physical interactions (hydrogen bond, van der Waals force) that occur between functional groups of sorbent and dye. The present study shows that the agro-waste bean hull is very effective as biosorbent for Food Red 14 removal from aqueous solutions, from a large range of dye concentration in aqueous solutions (5-400 mg L-1) in batch system. Since the agricultural wastes used in this study are friendly, abundantly and locally available, the sorbents are economically viable for aqueous effluents decolorization

UV/Tio2 photocatalytic reactor for real textile wastewaters treatment

Textile dye wastewaters are characterized by strong colour, salts and other additives, high pH, temperature, chemical oxygen demand (COD) and biodegradable materials. Being aesthetically and environmentally unacceptable, these wastewaters need to be treated before their discharge. Anaerobic bioprocesses have been proposed as being environmentally friendly and relatively cheap; however, when applied to real effluent with a complex composition, they can fail. In this study, a photoreactor combining UV light and TiO2, immobilized in cellulosic fabric, was applied for the treatment of two industrial textile wastewaters. High colour and COD removal, and detoxification, were achieved for both wastewaters, at controlled pH of 5.5. Effluents showed very poor biodegradability due to their complex composition; thus, the proposed process is an efficient alternative

Effect of ferromagnetic nanoparticle on dyes biodegradation

In this study the biodecolourisation of two dyes, a xanthene dye, Erythrosine B (Ery B) and an azo dye, Reactive Red 51 (RR120), was investigated colourdecolourisationunder batch anaerobic conditions by using non - acclimated anaerobic granular sludge. The effect of ferromagnetic nanoparticle (FN) (as adsorbent or mediator) on dyes removal was experienced

Anaerobic biotransformation of nitroanilines enhanced by the presence of low amounts of carbon materials

Three microporous activated carbons -original (AC0), chemical oxidized with HNO3 (ACHNO3) and thermal treated (ACH2)-, and three mesoporous carbons - xerogels (CXA and CXB) and nanotubes (CNT)-, were tested on the biological reduction of o-, m- and p-nitroaniline (NoA) at a concentration above the half maximal inhibitory concentration (IC50) for a methanogenic consortium degrading a mixture of volatile fatty acids (VFA) containing acetate, propionate and butyrate. NoAs were only partially reduced in the absence of carbon materials (CM). Rates were dependent on the nitro group position, increasing in the order metha>para>ortho. CM lead to NoAs almost total reduction and at higher rates. With AC0 and ACH2, rates increased 3-fold, 4-fold and 8 fold for o-, m- and p-NoA, respectively

Improvement of the upflow anaerobic sludge blanket reactor performance for azo dye reduction by the presence of low amounts of activated carbon

Activated carbon (AC) was investigated as redox mediator of the azo dye Acid Orange 10 (AO10) anaerobic biodegradation in a laboratory scale Upflow Anaerobic Sludge Blanket (UASB). During reactor operation, the effect of AC concentration and the hydraulic retention time (HRT) were investigated and better results were obtained with 0.15 g of AC per g of Volatile Suspended Solids (VSS) and 10 h, respectively. In the mediated reactor, with an HRT of 10 h, high colour and COD removal was obtained, ~70% and ~85%, respectively. In the control, thought similar COD removal, AO10 decolourisation was only 20%, evidencing the ability of AC to accelerate the reduction reactions in continuous reactors

Fate of aniline and sulfanilic acid in UASB bioreactors under denitrifying conditions

Two upflow anaerobic sludge blanket (UASB) reactors were operated to investigate the fate of aromatic amines under denitrifying conditions. The feed consisted of synthetic wastewater containing aniline and/or sulfanilic acid and a mixture of volatile fatty acids (VFA) as the primary electron donors. Reactor 1 (R1) contained a stoichiometric concentration of nitrate and Reactor 2 (R2) a stoichiometric nitrate and nitrite mixture as terminal electron acceptors. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the influent of R2, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an intense yellow coloured solution. HPLC analysis of the influent solution, revealed the emergence of three product peaks: the major one at retention time (Rt) 14.3 min and two minor at Rt 17.2 and 21.5 min. In the effluent, the intensity of the peaks at Rt 14.3 and 17.2 min was very low and of that at Rt 21.5 min increased (~3-fold). Based on the mass spectrometry analysis, we propose the structures of some possible products, mainly azo compounds. Denitrification activity tests suggest that biomass needed to adapt to the new coloured compounds, but after a 3 days lag phase, activity is recovered and the final (N2 + N2O) is even higher than that of the control.Fundação para a Ciência e a Tecnologia (FCT