Anaerobic-aerobic treatment of high-strength and recalcitrant textile dyeing effluents.

Eco-friendly treatment of complex textile and dyeing wastewaters poses a pressing environmental concern. An approach adopting different treatment paths and integrated anaerobic-aerobic processes for high-strength and recalcitrant textile dyeing wastewater was examined. The study demonstrated that over 97% of suspended solids (SS) and more than 70% of chemical oxygen demand (COD) were removed by polyaluminum chloride pre-coagulation of suede fabric dyeing stream. Up to 58% of COD and 83% of SS were removed through hydrolysis pretreatment of other low-strength streams. Notable COD removal of up to 99% from a feed of 20,862 mg COD/L was achieved by integrated anaerobic-aerobic treatment of high strength stream. Besides achieving high COD removal of 97%, the anaerobic granular sludge process demonstrated multi-faceted attributes, including high feed loading, smaller footprint, little sludge production, and good stability. The integrated anaerobic-aerobic treatment offers a robust and viable option for highly contaminated and recalcitrant textile dyeing wastewater.

The microbial synergy and response mechanisms of hydrolysis-acidification combined microbial electrolysis cell system with stainless-steel cathode for textile-dyeing wastewater treatment.

Microbial electrolysis cell (MEC) has been existing problems such as poor applicability to real wastewater and lack of cost-effective electrode materials in the practical application of refractory wastewater. A hydrolysis-acidification combined MEC system (HAR-MECs) with four inexpensive stainless-steel and conventional carbon cloth cathodes for the treatment of real textile-dyeing wastewater, which was fully evaluated the technical feasibility in terms of parameter optimization, spectral analysis, succession and cooperative/competition effect of microbial. Results showed that the optimum performance was achieved with a 12 h hydraulic retention time (HRT) and an applied voltage of 0.7 V in the HAR-MEC system with a 100 µm aperture stainless-steel mesh cathode (SSM-100 µm), and the associated optimum BOD5/COD improvement efficiency (74.75 ± 4.32 %) and current density (5.94 ± 0.03 A·m-2) were increased by 30.36 % and 22.36 % compared to a conventional carbon cloth cathode. The optimal system had effective removal of refractory organics and produced small molecules by electrical stimulation. The HAR segment could greatly alleviate the imbalance between electron donors and electron acceptors in the real refractory wastewater and reduce the treatment difficulty of the MEC segment, while the MEC system improved wastewater biodegradability, amplified the positive and specific interactions between degraders, fermenters and electroactive bacteria due to the substrate complexity. The SSM-100 µm-based system constructed by phylogenetic molecular ecological network (pMEN) exhibited moderate complexity and significantly strong positive correlation between electroactive bacteria and fermenters. It is highly feasible to use HAR-MEC with inexpensive stainless-steel cathode for textile-dyeing wastewater treatment.

Direct dye wastewater photocatalysis using immobilized titanium dioxide on fixed substrate.

Photocatalysis is a promising technology that can be applied to the dyeing of wastewater. During the process of photocatalysis, titanium dioxide (TiO2) is often used as a catalyst due to its low cost and broad availability. However, the use of TiO2 powders can result in certain difficulties associated with separating TiO2 from the treated wastewater. Therefore, immobilization of TiO2 on two different substrates, including glass and iron beads, was studied in this body of research work. The composite materials were prepared by spraying liquid dispersion onto the substrates, and the materials were then calcined at different temperatures (600-750 °C). At 700 °C calcination temperature, SEM and EDS analyses revealed that the particles of TiO2 were evenly distributed on the substrates. Importantly, the deposited TiO2 particles are mixed-phase anatase and rutile structures, both of which are considered beneficial to the photocatalysis process. Ultimately, a degree of direct dye photodegradation efficiency of 64.0 % at 4 h was achieved from the composite materials that were calcined at 700 °C. The degradation efficiency of the reused catalyst was not significantly changed in the second cycle revealing their capability in reusable. The stability of immobilized TiO2 onto the fixed substrates was still high after the second use.

Comprehensive insights into core microbial assemblages in activated sludge exposed to textile-dyeing wastewater stress.

Microorganisms in activated sludge are widely recognized for their roles in wastewater treatment. However, previous studies were mainly concerned with the diversity and driving factors of microbial communities within domestic wastewater treatment, and those of domestic wastewater treatment systems mixed with industrial wastewater are poorly understood. In this research, three different full-scale aerobic activated sludge (AS) wastewater treatment systems fed with municipal, textile-dyeing, and mixed wastewater, respectively, were monitored over the operation course of three months. 16S rRNA amplicon sequencing analysis revealed that the microbial communities in textile-dyeing wastewater activated sludge (AS) exhibited significantly lower richness and diversity (p < 0.01, Adonis) compared to those fed with municipal wastewater. In contrast, textile-dyeing derived AS selectively enriched microbial taxa with aromatic degradation and denitrification potentials. Further, FARPROTAX and metabolomics indicated the inhibition of 72.5% metabolic functions (p < 0.01) in AS from the system fed with textile-dyeing wastewater, including the pathways of pentose phosphate metabolism, purine metabolism, and glycerophospholipid metabolism. Overall, this study corroborates textile-dyeing wastewater is a novel microbial niche and could suppress sludge performance by inhibiting microbial activity and metabolism, raising concerns on AS-based systems for industrial wastewater treatment.

Environmentally benign hybrid nanocomposite beads for azo dye remediation via synchronized dual degradation mechanisms.

Practically, 12% of used dyes are excluded as waste in the mobile aqueous environment. Methyl orange (MO), an industrial azo dye, is known to be carcinogenic. Accordingly, this work was engaged to fabrication of a high-efficiency visible light photocatalysts based on Ag-Alginate/Chitosan-coated MgO nanocomposite beads. MgO and Ag were prepared via precipitation and γ-radiation reduction technique as a green physical one, respectively. The degradation mechanisms depended on catalytic reduction by means of sodium borohydride/Ag and photooxidative degradation. XRD proved the periclase crystalline form of MgO of size 20 nm and the formation of face-centered cubic silver crystals of size 15 nm. The degradation yield varied directly with time, MgO, and dye concentration until certain limit. Five and twenty minutes were enough to get clear solution of MO (30 and 15 ppm, respectively) while 60 min was required to achieve the same target for 60 ppm MO solution. The catalysts showed high efficiency for MO of high concentration. The incorporation of Ag into catalytic beads could support both mechanisms as it could elevate the degradation efficiency up to 50% and save the time to a great extent. Thus, this carrier fruitfully converted wastewater into an effluent that can be repaid to the water cycle with minimal strike on the ecosystem.

Persistent organic and inorganic pollutants in the effluents from the textile dyeing industries: Ecotoxicology appraisal via a battery of biotests.

Today, the textile industry is considered as a leading economic sector in Tunisia. However, this sector demands a huge volume of water and a wide spectrum of chemicals, which is converted into potentially toxic wastewater leading to environmental perturbation and human health toxicity. Assessment of the environmental risks associated with textile wastewater becomes a necessity. In this study, textile dyeing wastewater samples were collected before and after the physico-chemical treatment carried out by textile companies located in Monastir-city-Tunisia and subjected to chemical analyzes in order to determine their physicochemical characteristics and the content of metals and textile dyes. The ecotoxicological assessment was performed using four organisms, namely Selenastrum capricornutum, Vibrio fischeri, Daphnia magna and Lepidium sativum, to represent different trophic levels. Based on chemical data, some physicochemical parameters (e.g. TSS, COD and TSS levels) and metals (e.g. Cr, Hg and Sb) in the textile dyeing effluents were revealed not in compliance with the Tunisian standard. Moreover, high quantities of three disperse dyes have been detected even in the textile dyeing wastewater samples before and after treatments. The ecotoxicological data confirmed that the textile dyeing influents displayed toxic effects to all the test organisms, with Selenastrum capricornutum being the most sensitive organism. While, the above toxic effects were decreased slightly when evaluating the treated effluents. Metals and textile disperse dyes could be associated with the observed toxic effects of the textile influents and effluents. In fact, the treatment process applied by the evaluated companies was only partially efficient at removing metals, disperse dyes and effluent ecotoxicity, suggesting potential risks to aquatic biota. These findings emphasize the importance of applying integrated chemical and biological approaches for continuous evaluation of the toxicity of the treated effluents to predict hazards on the environment.

Chlorobenzene levels, component distribution, and ambient severity in wastewater from five textile dyeing wastewater treatment plants.

Chlorobenzenes (CBs) present in synthetic dyes are discharged into natural waters during the treatment of textile dyeing wastewater, which may have adverse effects on human and environment. In this study, the existence and removal of 12 CBs in different units of five treatment plants were examined. The ecological risk of CBs in textile dyeing wastewater was assessed by ambient severity (AS) and risk quotients (RQs). The results showed that trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene were ubiquitous in textile dyeing wastewater, and their distribution was similar. In one of the plants, the content of hexachlorobenzene was found to be as high as 9.277 µg/L in the raw water, which was an oil-water mixture. In other plants, there was no significant difference in the content and composition of CBs among influent and effluent suggesting that the conventional wastewater treatment plants cannot improve the existence of them. Monochlorobenzene and dichlorobenzene were not detected, which may have been related to strong volatility, biochemical properties, and weak instrument sensitivity. In the treatment process and effluent, trichlorobenzene is the main pollutant and accounted for 39.51% of all CB. CB removal was found only in the anaerobic system, while the aerobic system did not have the corresponding removal effect on CB and total organic carbon. According to ecological risk assessment, CBs in effluent has not been found the significant potential harm to human health (AS < 1), but posed moderate ecological risk to aquatic ecosystem (RQs > 0.1).

Activated sludge bacterial communities of typical wastewater treatment plants: distinct genera identification and metabolic potential differential analysis.

To investigate the differences in activated sludge microbial communities of different wastewater treatment plants (WWTPs) and understand their metabolic potentials, we sampled sludge from every biological treatment unit of 5 full-scale waste water treatment systems in 3 typical Chinese municipal WWTPs. The microbial communities and overall metabolic patterns were not only affected by influent characteristics but also varied between different biological treatment units. Distinct genera in different wastewater treatment systems were identified. The important microorganisms in domestic sewage treatment systems were unclassified SHA-20, Caldilinea, Dechloromonas, and unclassified genera from Rhodospirilaceae and Caldilineaceae. The important microorganisms in dyeing wastewater treatment systems were Nitrospira, Sphingobacteriales, Thiobacillus, Sinobacteraceae and Comamonadaceae. Compared with the obvious differences in microbial community composition, the metabolic potential showed no significant differences.

Toxicity evaluation of textile dyeing effluent and its possible relationship with chemical oxygen demand.

Textile dyeing wastewater was the focus of much research because of its adverse effect on aquatic biota. In the present research, textile dyeing influent and effluent samples were collected from four textile dyeing wastewater treatment plants (TDPs) in Guangdong province, China, and their conventional indicators and toxicity were examined to reveal relationships. The relationship between toxicity and chemical oxygen demand (COD) was clearly established at individual TDPs. Results indicated the highest removal efficiencies of 94.4%, 90.6%, 91.9%, 94.6%, 92.8% and 97.5% for TOC, mixed-liquor volatile suspended solids (MLVSS), COD, ammonia nitrogen (NH3-N), total phosphorus (TP) and colour, respectively. The primary clarifier used in TDP3 and TDP4 was beneficial for removing macromolecular organic substances, and membrane filtration and sedimentation basin employed at TDP1 and TDP2, respectively, helped to remove toxic substances. Toxicity to V. fischeri or D. subspicatus was found to be related to certain conventional indicators such as TOC, COD, TP, colour, and MLVSS, and was positively correlated with COD in different textile dyeing effluents (R2 > 0.84). It was recommended that the relationship between toxicity and COD in wastewater should be established individually at each plant. Therefore, this study could be useful in providing suggestions for guiding effluent management when no toxicity experiments were conducted.

Elimination and ecotoxicity evaluation of phthalic acid esters from textile-dyeing wastewater.

Phthalic acid esters (PAEs), presented in fabrics, surfactants and detergents, were discharged into the ecosystem during textile-dyeing wastewater treatment and might have adverse effects on water ecosystems. In this study, comprehensive investigations of the content and component distributions of 12 PAEs across different units of four textile-dyeing wastewater plants were carried out in Guangdong Province, China. Ecotoxicity assessments were also conducted based on risk quotients (RQs). On average, 93.54% TOC and 80.14% CODCr were removed following treatment at the four plants. The average concentration of Σ12PAEs in effluent was 11.78 µg/L. PAEs with highest concentrations were dimethylphthalate (6.58 µg/L), bis(2-ethylhexyl)phthalate (2.23 µg/L), and dibutylphthalate (1.98 µg/L). The concentrations of the main toxic PAEs were 2.23 µg/L (bis(2-ethylhexyl)phthalate), 0.19 µg/L (diisononylphthalate) and 0.67 µg/L (dinoctylphthalate); corresponding RQs were 1.4, 0.55, and 0.54 for green algae, respectively. The RQs of Σ12PAEs in effluent of the four plants were >0.1, indicating that Σ12PAEs posed medium or higher ecological risk to fish, Daphnia and green algae. Physicochemical-biochemical system was found to be more effective than biochemical-physicochemical system for TOC and CODCr removal, because pre-physicochemical treatment helped to remove macromolecular organic substances, and reduced the competition with other pollutants during biochemical treatment. However, biochemical-physicochemical system was more effective than physicochemical-biochemical system for elimination of PAEs and for detoxification, since the biochemical treatment might produce the toxic PAEs that could helpfully be settled by post-physicochemical treatment. Moreover, ecotoxicity evaluation was recommended for current textile-dyeing wastewater treatment plants.

Long-term natural remediation process in textile dye-polluted river sediment driven by bacterial community changes.

The textile and dyeing industries are major sources of environmental water pollution all over the world. The textile wastewater effluents discharged into rivers often appear dark red-purple in color due to azo dyes, which can be transformed into carcinogenic aromatic amines. The chemicals used in dyeing are not readily degraded in nature and thus precipitate in river sediment. However, little is known about how dyeing chemicals affect river sediment and river water or how long they persist because they are difficult to monitor. To assess undetectable dyes and byproducts in river sediments, we evaluated the potential of river sediment bacteria to degrade dyes and aromatic amines. We describe the natural remediation of river sediment long-contaminated by textile dyeing effluent. After cessation of wastewater discharge, the dye-degradation potential decreased, and the aromatic amine-degradation potential increased initially and then declined over time. The changes in degradation potential were consistent with changes in the sediment bacterial community. The transition occurred on the order of years. Our data strongly suggest that dyes remained in the river sediment and that aromatic amines were produced even in transparent- and no longer colored-river water, but these chemicals were degraded by the changing sediment bacteria. Time-course monitoring of the degradation activities of key bacteria thus enables assessment of the fate of dye pollutants in river sediments.

Treatment and toxicity reduction of textile dyeing wastewater using the electrocoagulation-electroflotation process.

A pilot-scale study was conducted using the electrocoagulation-electroflotation (EC-EF) process to treat textile dyeing raw wastewater to evaluate treatment performance. The effects of some key factors, such as current density, hydraulic retention time (HRT), and removal of conductivity, total suspended solids (TSS), chemical oxygen demand (COD), and color were investigated. The operating variables were current density of 0-300 A m(-2), HRT of 0-30 min, and a coagulant (anionic polyacrylamide (A-PAM)) dosage of 0-30 mg L(-1). Daphnia magna was used to test acute toxicity in raw and treated wastewater. Under the operating conditions without added coagulant, maxima of 51%, 88%, 84%, and 99% of conductivity, TSS, COD, and color were removed, respectively, with a HRT of 30 min. The coagulant enhanced removal of all wastewater parameters. Removal maxima of 59%, 92%, 94%, and 98% for conductivity, TSS, COD, and color were observed, respectively, with an optimal dosage of 30 mg L(-1) and a shortened HRT of 20 min. The 48 h-LC50 D. magna test showed that the raw wastewater was highly toxic. However, the EC-EF process decreased toxicity of the treated samples significantly, and >70% toxicity reduction was achieved by the EC-EF process with the addition of 15-30 mg L(-1) coagulant, HRT of 20 min, and current density of 150-300 A m(-2). The pilot scale test (0.3 m(3 )h(-1)) shows that the EC-EF process with added coagulant effectively treated textile dyeing wastewater.

Textile dye degradation using nano zero valent iron: A review.

Water soluble unfixed dyes and inorganic salts are the major pollutants in textile dyeing industry wastewater. Existing treatment methods fail to degrade textile dyes and have limitations too. The inadequate treatment of textile dyeing wastewater is a major concern when effluent is directly discharged into the nearby environment. Long term disposal threatens the environment, which needs reclamation. This article reviews the current knowledge of nano zero valent iron (nZVI) technique in the degradation of textile dyes. The application of nZVI on textile dye degradation is receiving great attention in the recent years because nZVI particles are highly reactive towards the pollutant, less toxic, and economical. The nZVI particles aggregate quickly with respect to time and the addition of supports such as resin, nickel, zinc, bentonite, biopolymer, kaolin, rectorite, nickel-montmorillonite, bamboo, cellulose, biochar, graphene, and clinoptilolite enhanced the stability of iron nanoparticles. Inclusion of supports may in turn introduce additional toxic pollutants, hence green supports are recommended. The majority of investigations concluded dye color removal as textile dye compound removal, which is not factual. Very few studies monitored the removal of total organic carbon and observed the products formed. The results revealed that partial mineralization of the textile dye compound was achieved. Instead of stand alone technique, nZVI can be integrated with other suitable technique to achieve complete degradation of textile dye and also to treat multiple pollutants in the real textile dyeing wastewater. It is highly recommended to perform more bench-scale and pilot-scale studies to apply this technique to the textile effluent contaminated sites.

Coupling of acrylic dyeing wastewater treatment by heterogeneous Fenton oxidation in a continuous stirred tank reactor with biological degradation in a sequential batch reactor.

This work deals with the treatment of a recalcitrant effluent, from the dyeing stage of acrylic fibres, by combination of the heterogeneous Fenton's process in a continuous stirred tank reactor (CSTR) with biological degradation in a sequential batch reactor (SBR). Three different catalysts (a commercial Fe/ZSM-5 zeolite and two distinct Fe-containing activated carbons - ACs - prepared by wet impregnation of iron acetate and iron nitrate) were employed on the Fenton's process, and afterwards a parametric study was carried out to determine the effect of the main operating conditions, namely the hydrogen peroxide feed concentration, temperature and contact time. Under the best operating conditions found, using the activated carbon impregnated with iron nitrate, 62.7% of discolouration and 39.9% of total organic carbon (TOC) reduction were achieved, at steady-state. Furthermore, a considerable increase in the effluent's biodegradability was attained (BOD5:COD ratio increased from <0.001 to 0.27 and SOUR - specific oxygen uptake rate - from <0.2 to 11.1 mg O2/(gVSS·h)), alongside a major decrease in its toxicity (from 92.1 to 94.0% of Vibrio fischeri inhibition down to 6.9-9.9%). This allowed the application of the subsequent biological degradation stage. The combination of the two processes provided a treated effluent that clearly complies with the legislated discharge limits. It was also found that the iron leaching from the three catalysts tested was very small in all runs, a crucial factor for the stability and long-term use of such materials.

Fate of volatile aromatic hydrocarbons in the wastewater from six textile dyeing wastewater treatment plants.

The occurrence and removal of benzene, toluene, ethylbenzene, xylenes, styrene and isopropylbenzene (BTEXSI) from 6 textile dyeing wastewater treatment plants (TDWTPs) were investigated in this study. The practical capacities of the 6 representative plants, which used the activated sludge process, ranged from 1200 to 26000 m(3) d(-1). The results indicated that BTEXSI were ubiquitous in the raw textile dyeing wastewater, except for isopropylbenzene, and that toluene and xylenes were predominant in raw wastewaters (RWs). TDWTP-E was selected to study the residual BTEXSI at different stages. The total BTEXSI reduction on the aerobic process of TDWTP-E accounted for 82.2% of the entire process. The total BTEXSI concentrations from the final effluents (FEs) were observed to be below 1 µg L(-1), except for TDWTP-F (2.12 µg L(-1)). Volatilization and biodegradation rather than sludge sorption contributed significantly to BTEXSI removal in the treatment system. BTEXSI were not found to be the main contaminants in textile dyeing wastewater.

Enhancement of a solar photo-Fenton reaction with ferric-organic ligands for the treatment of acrylic-textile dyeing wastewater.

Literature describes a kinetic mineralization profile for most of acrylic-textile dyeing wastewaters using a photo-Fenton reaction characterized by a slow degradation process and high reactants consumption. This work tries to elucidate that the slow decay on DOC concentration is associated with the formation of stable complexes between Fe(3+) and textile auxiliary products, limiting the photoreduction of Fe(3+). This work also evaluates the enhancement of a solar photo-Fenton reaction through the use of different ferric-organic ligands applied to the treatment of a simulated acrylic-textile dyeing wastewater, as a pre-oxidation step to enhance its biodegradability. The photo-Fenton reaction was negatively affected by two dyeing auxiliary products: i) Sera(®) Tard A-AS, a surfactant mainly composed of alkyl dimethyl benzyl ammonium chloride and ii) Sera(®) Sperse M-IW, a dispersing agent composed of polyglycol solvents. The catalytic activity of the organic ligands toward the ferrous-catalysed system followed this order: Fe(III)-Oxalate > Fe(III)-Citrate > Fe(III)-EDDS, and all were better than the traditional photo-Fenton reaction. Different design parameters such as iron concentration, pH, temperature, flow conditions, UV irradiance and H2O2 addition strategy and dose were evaluated. The ferrioxalate induced photo-Fenton process presented the best results, achieving 87% mineralization after 9.3 kJUV L(-1) and allowing to work until near neutral pH values. As expected, the biodegradability of the textile wastewater was significantly enhanced during the photo-Fenton treatment, achieving a value of 73%, consuming 32.4 mM of H2O2 and 5.7 kJUV L(-1).