Efficiency assessment of Cu and Al electrodes in the removal of anthraquinone based disperse dye aqueous solution in electrocoagulation–an analytical approach

ABSTRACT Anthraquinone dyes are tough to degrade compared to azo dyes, due to the resonance in the anthracene structure that leads to more difficulty in the removal and challenges the possibility of an effective decolouration/degradation process. The purpose of this study was to examine the effect of copper and aluminium electrodes in electrocoagulation process for the elimination of an anthraquinone based aqueous solution of Red BFL dye. The efficiency of the electrodes in the dye removal was studied using X-Ray Photoelectron Spectroscopy of the collected sludge, in terms of the respective M(OH)n formation which contributes in coagulation of the dispersed dye molecules and the results indicated that Al formed four types of hydroxides and Cu only one type. The maximum removal of the dye solution obtained with Al was 99.17% at the optimum conditions: pH 8, contact time 15 min, current density 40 A m−2, and 91.88% with Cu: pH 9, contact time 25 min and current density 60 A m−2. Phytotoxicity and ecotoxicity studies with Vigna radiata and Artemia salina was done to investigate the toxicity of intermediate products in the treated Red BFL dye solution, results showed that the Al used Red BFL dye solution was less toxic in comparison to copper. Abbreviation: EC: Electrocoagulation; AQ: Anthraquinone; CD: Current density; CT: Contact time; ECE%: Efficiency in Colour Elimination percentage; HPLC: High-performance liquid chromatography; XPS: X-ray photoelectron spectroscopy; V. radiata: Vigna radiata; A. salina: Artemia salina


Introduction
Over the recent years, the scarcity of drinking water has been arising as a pressing issue for the humanity.Moreover, researchers have been reporting an increasing number of water systems to be contaminated by chemical compounds arising from human activities.Industries, especially textile industries generating high liquid effluents due to large quantities of water used [1].In reality, the textile industry is deemed to be the world's number one industrial water polluter.Water is used at each point in textile chemical wet processing to dissolve chemicals for use in one stage, then to wash and rinse out the same chemicals so they are ready for the next step.Wet processing produces the largest amount of wastewater of all the phases involved in textile processing, and these wet processing practices contribute to 70% of the textile industry's pollutants [2].Among the other units, the dyeing units from the textile industry are the most water pollution prevailing and the emphasis is laid on the tremendous use of drinking water in different operations of its production chain, such as washing, bleaching, dyeing, among others, and this process releases highly contaminated water.It is estimated that about 10-15% of the dyes used in this process are lost and enter industrial effluents during the dyeing process in baths [3], approximately 1 million tons of these compounds contaminate the environment [4], which is a great concern [5].The production of dyes worldwide is nearly 800,000 tons per year.More than 10 5 dyes are being used in textiles and worldwide production of dyes exceeds approximately 7 to 10 5 tons [6].The demand for textile chemicals is projected to jump 6.3% annually touching US 1.9 USD billion the forecast for 2012 has been made and about 100 tons/year of dyes are released into wastewater [7].
As part of the manufacturing sector, India's textile industry has been a significant contributor to the country's economy.It contributes 14% to industrial output, 3% to gross domestic product, and 8% to overall excise tax collection, 17% to the export earnings of the country and, most significantly, it provides over 35 million people in India with direct employment [8,9].Textile mills discharge approximately 1.2 × 10 3 million litres per day (MLD) of coloured wastewater into natural waterbodies without adequate treatment [10].Export demands associated with cheap labour determine the existence of small-scale textile factories in several regions of the world, such as India, that sneakily release toxic dyes into waterbodies [11].After China, India is the second largest exporter of seven dyes and intermediates among developing countries [12].
Tirupur, a rapidly expanding textile hub in Tamil Nadu, South India, has nearly 400 dyeing units and contributes around INR.11000 crores [Rs.110 billion] in foreign exchange earnings to our country per year, in addition to a sustainable contribution to the domestic market.Almost 80% of India's cotton knitwear exports are from Tirupur today.There are nearly 6,250 units working in various textile industry operations, such as 4900 weaving and stitching units, 736 dyeing and bleaching units, 300 printing units, 100 embroidery units, and 200 compacting, raising, and calendar catering units in total [13].These units discharge almost 90 MLD of waste on land or into the Noyyal River, resulting in ground and surface water and soil pollution in and around Tirupur and downstream Orathupalayam dam [Dimension: 2290 m (L) × 248 m (W)], area of 423 hectares was constructed during 1991, and it irrigates 9875 acres of agricultural land in the Karur and 500 acres of land in the Erode region on the Noyyal river side.One of the big concerns recently identified has been human infertility [14].In Tirupur, there are 600,000 people and about 800,000 along the river downstream, who are harmed by this pollution [15].For the district of Tirupur in Tamil Nadu, the Water Quality Index published in 2013 shows that water is unsafe for drinking purposes and shows that groundwater is deteriorating in many places and indicates that contaminant sources such as textile waste and fertiliser pollution need to be managed to protect this vital resource [16].

The environmental impact of textile dyes
During the dyeing phase of textile substrates, a large amount of synthetic colours is released into the environment due to a deficiency of affinity of the dyes with the fabrics [17].Effluents from textile industries are brightly coloured and characterised by high salinity and toxicity, especially in terms of water pollution and waste gases produced from effluent water, due to the widely used alkaline dyes [18,19].In lake and river sediments acquiring the treated wastewater, the colourants may be partially degraded or modified [20].Colourants and their degradation products are also carcinogenic, mutagenic, and teratogenic [21].In fact, about 40% of colourants in the world contain organically bound chlorine [22].Due to the complexity of their structure and synthetic path, most dyes are difficult to degrade [23].The heterogeneous, poorly biodegradable, and harmful compositions of raw textile effluents make the treatment processes difficult [24,25].
Contamination of surface waters due to dye effluent results in light penetration, photosynthesis activity and oxygen deficiency which can lead to ecosystem disruption [26,27].As a result, dye components in the food chain are highly resistant to biodegradation [28].The biodegradable products of dyes containing structural elements that are rare in nature and have negative aesthetic effects [29,30] and contribute toxicity to water and soil [31,32].Some colourants, such as aromatic amines, are known to be carcinogenic, mutagenic.Carcinogenicity is caused by acyloxy amines forming nitremium and carbonium ions, which bind to DNA and RNA, causing mutations and tumour growth.An aromatic compound benzidine forms reactive intermediates that can induce carcinogenesis through the mechanism of metabolic transformation [33].Employees exposed to benzidine have encountered dermal and immunological effects, as well as harmful effects in humans and animals.Depending on the concentration and duration of exposure of dyes, the severity of the effects on the organism.Since the dye effluents contain high levels of heavy metals and organic matter, the seed germination and plant growth is badly affected in certain crops, such as maize (Zea mays) [34] kidney bean (Phaseolous aureus) and Bengal gram (Cicer arietinum) [35], soybean crop (Glycine) [36].The amount of seedlings, plumule length, radicle length, pigment content and plant biomass, all decrease in crops grown with dye effluent, according to the findings.Dyes induce hepatocarinomoas and animal nuclear abnormalities, and mammalian aberration of Chromosomes [37].Many catastrophic and permanent effects have occurred, and the textile industry is to blame for a horrendously negative environmental impact [38].
Reactive and disperse dyes account for approximately 55% of the overall dyeing market in the textile industry, while direct and vat dyes each account for approximately 10%.Disperse dyes are a type of non-ionic dye that has low water solubility and is mainly present during the dyeing process in water in a highly dispersed state via the dispersing agent's action [39].The chemical composition of most disperse colours belongs to the monoazo group, which accounts for about 80% of all disperse dyes.And then, anthraquinone (AQ) accounts for about 15%, and other structural types around 5% [40][41][42][43].Owing to highly stable structure, AQ dyes are well known for their excellent fastness, stability, and colour intensity [44].
It is difficult to find current or factual information for the annual production of AQ dyes, in the US, over a period of approximately 15 years (1986-2002), the annual production of AQ increased by a whopping 5,000% (from 500 to 25,000 tons).With the rise in dye production, it is rational to believe that AQ colouring production has increased as well; an estimated amount of approximately 100,000 tons of AQ dyes can be produced yearly.After azo dyes, AQ colours are the second most common colouring due to their low cost, ease of access, and dyeing quality.Colouring AQ has a complex and stable structure and is more toxic than azo colouring to microorganisms and human cells [45].

Challenges in treating the AQ dyes
In comparison to azo dyes, the carbonyl group in the AQ structure acts as an electron acceptor, requiring an electron donor to react and break the structure, and analysis shows, however, compared to azo dyes, AQ dyes are hard to degrade [46].Compared to azo dyes, the combined effects of resonance in the anthracene structure leads to more difficulty in the degradation of AQ colours [47,48] and questions the possibility of an effective degradation/decolouration process [49].Many of the industrially relevant AQ colours, using sulphonation or nitrate, are derived from anthraquinonesulfonic acids [50] and the study has shown that the sulphone groups present in the structure of the dye can minimise their disintegration [51].Various methods of decolorisation of AQ dyes used in the industry are physical, chemical and biological methods, among the physical methods are adsorption and filtration using peat, zeolites, activated carbon and silica-based adsorbents.Physical methods for dye removal have a number of drawbacks, including the need for a long contact period, which necessitates wide spaces, and the need for membrane or adsorbent regeneration.These are topics that have received little attention in the literature but are critical for industrial application.Various methods like Fenton oxidation [52], photocatalytic oxidation [53], ozone oxidation [54], ultrasonic catalytic oxidation [55], and catalytic microwave oxidation [56] have been employed for the degradation of AQ dyes.
Chemical methods like coagulation and flocculation even though increase the removal efficiencies, but huge amount of sludge formation and disposal of the same is the problem.Another chemical method employed is advanced oxidation process (AOP) successfully applied for Reactive Blue 19 type of AQ dyes with combination processes such as Fenton reaction coupled with adsorption on pyrite ash [57], or ozonation together with UV radiation can be a lot more effective as compared to ozonation [58].When it comes to AQ dye degradation, AOP is notable for its extremely short reaction times, typically a few minutes, high performance, and dye sedimentation, but because of its high cost, which makes scaling up difficult [59,60].
Acid Green 25 was photocatalytically degraded with immobilised TiO 2 nanoparticles and UV light photocatalysis, resulting in an optimised device that could work at small concentrations of the dye [61].Nanoparticles can be very successful in the degradation of an AQ dye model, on the basis of the combination of copper nanoparticles, a current study investigated the degradation of Reactive Blue 4 and found that the colour is initially adsorbed into the nanoparticles followed by oxidation based on the formation of OH radicals from particular mediators and the reaction of copper monovalent ions [62].
Biological strategies for AQ dye degradation in aerobic and anaerobic cultures have recently been investigated [63,64].The challenge is to establish bioremediation methods that are efficient, cost-effective, and environmentally sustainable while overcoming the limitations of conventional methods [65,66].Bacterial degradation on AQ dye has been carried out [67], but little research has been done on the relationship between the structure of these dyes and degradation efficiency.Because of fused ring structure of AQ dyes, which improves stability and in effect limits the degradation of AQ colours, so choosing an alternative approach from the current conventional methods can be difficult.There are also no data available on the intermediate product formed during the degradation of some of the AQ colours that may be toxic, mutagenic or carcinogenic, making it difficult to choose the right type of treatment process.During our review of the literature, we discovered a major issue: the lack of consistency in the methodology used in various techniques of research.Another concern that arose from the research was the widespread use of unrealistic or idealistic solutions.
In this context, electrocoagulation method seems promising in comparison with physical and chemical approaches, because the process is easy in its application, requiring no additional chemicals as in chemical coagulation.EC appears to be a promising one [68], for the textile dyeing wastewater in the tertiary treatment step, aimed for the elimination of dissolved solids and colloidal particles.The efficiency of the EC process depends on metal ions from anode, hydroxyl ions formed from cathode, the resultant hydroxides of metal ions, size of the particles and the properties of the colloidal particles.To remove reactive Blue 19 [69], base Yellow 28 dye effluent [70,71], Red disperse, Blue reactive, and mixed dyes [72] the EC approach was successfully used [73].The impact of the operative parameters such as pH, electrolyte, CD, and CT were evaluated and the results were related for the efficacy of electrodes in two EC processes done, one with Al electrodes and other with Cu electrodes for the removal of Red BFL dye solution.Since it was not possible to research the exact dye derivatives, the total number of organic components in the dye solution was analysed using HPLC and mass spectroscopy before and after the EC procedure.XPS analysis was done to investigate the mechanism of the EC process in the sludge acquired during this study.Phytotoxicity with V. radiata seed was carried out to see whether the treated water could be used, and the results were compared to control (tap water) in terms of percentage of germination, radicle and plumule length.Using A. salina, the ecotoxic assessment of Al-and Cu-treated Red BFL dye aqueous solution was checked on the motility and morbidity of the nauplii.Optical microscopy was used to infer morphological variation in A. salina.

EC method
A 200 mg/L concentration of Red BFL dye from a dyeing industry in Thirupur was used in this investigation.Two sets of EC with Al-Al (Al electrodes) and Cu-Cu (Cu electrodes) were performed to optimise operational parameters such as pH, contact time (CT), current density (CD) and the introduction of NaCl as electrolyte (salt is commonly used with disperse dyes to achieve the binding between the fabric and dye), conducted at 25°C and comparison of performance of both electrodes.The impact of pH on the efficiency of colour elimination (ECE) percentage was investigated by holding the Red BFL solution at pH 5 to 10, by adding 0.5 M of NaOH or HCl to the experimental solution.With NaCl at various doses, such as 1 to 5 gm/L, and the impact of various CT at 5, 10, 15, 20 and 25 min was studied on ECE percentage.The effect of CD on dye colour removal efficiency was investigated at 20, 40, 60, 80 and 100 A m −2 .The electrodes were cleaned using distilled water before being placed in acid (HCl) solution for 15 min and then washed with purified water for each procedure.The space of 28.6 cm 2 of electrodes are then positioned in a 250 ml test solution, taken in a 500-ml beaker and coupled to a DC power source, maintaining the distance between the anode and the cathode of 10 mm and stirring the test solution with a magnetic stirrer.The dye absorbance was determined before and after the process with the Jasco V-670 spectrophotometer, and the dye concentration was assessed with the absorbance at 542 nm.
The ECE % to every variable was calculated as where A i and A f were the absorbance of dye solution before EC and at time t, respectively.

HPLC and mass analysis
HPLC and mass analysis were performed to assess the total number of compounds found in the dye solution before and after EC.

X-Ray Photoelectron Spectroscopy (XPS)
The sludge was isolated (for Al at pH 8, NaCl 1 g L −1 , CT 15 min, CD 40 A m −2 and for Cu at pH9, NaCl 1 g L −1 , CT 25 min, CD 60 A m −2 ), dried and examined by X-ray photoelectron spectroscopy (XPS) to investigate the anodisation of the Al, Cu and compare the efficacy of the electrodes used.The XPS spectra was acquired with Scienta Omicron Nanotechnology by Oxford Instrument, source -Al monochromatic, energy -1486.6 eV.

Phytotoxicity study
Dye components even at very less concentrations in water can affect the entire photosynthesis process and eventually suppress plant growth, and dye solution degradation releases a variety of intermediate products that must be non-toxic to the environment.In order to determine the probability of the treated water for reuse, a phytotoxicity analysis on the growth of V. radiata seeds was carried out.A phytotoxicity test was conducted using 200 mg/L Red BFL dye solution, the treated dye solution with Al and Cu, and tap water as the control.Twenty sterilised seeds with 0.1% (w/v) mercuric chloride and then splashed three times with distilled water to eliminate any traces of mercury were taken in a 250-ml capacity beaker with autoclaved soil of 150 g and exposed to sunlight.The analysis of seed germination and plant development was done with equivalent volume of treated and untreated Red BFL aqueous solution.After 10 days germination, percentage, plumule and radicle length were measured, and the outcomes were matched with the control.

Eco toxicity analysis
A basic zoological organism (marine invertebrate) around 1 mm in size is the brine shrimp (Artemia salina), also known as sea monkey.A. salina eggs' freeze-dried cysts can last for years and can be hatched into larvae without the use of special equipment.Since they are easy to hatch from dry cysts and are available all year, the brine shrimp A.salina nauplii are the most convenient research species for toxicity studies [74,75].This test has many benefits, such as swiftness, effortlessness, reliability, cost-effectiveness and high reproducibility [76].The quality of the treated Red BFL solution was assessed by means of a versatile and suitable aquatic model, A. salina [77].Newly hatched 24 h active A. salina nauplii was used on Red BFL-treated water at 1.5% NaCl without modification.The illumines were tested on treated dye water as N = 6 nauplii mortality, and no motion was observed for more than 10 seconds.Tap water as an experimental control and Red BFL solution as a negative control were used in this study.Viability of nauplii was noticed with 8, 12 h intervals for 24 h.Microscopy was conducted on mounting on a glass sheet using magnification at 40×.

Impact of initial pH on ECE%
Experiments with initial pH ranging from 5 to 10 were implemented under other optimised parameters and the findings are shown in Figure 1 .The magnitude of the electrical charge exerted by metal ions can be controlled by pH, which is a well-known decisive element in any aqueous solution-based adsorption process [78].It has an impact on the adsorbent's surface charge, as well as the ionisation degree and formation of the ions from the metal.For Aluminium and copper electrodes, at pH 8, the ECE% was found to be 99.17,91.88%, respectively.At pH >8, with aluminium electrodes, the colour removal of Red BFL solution in its efficiency started reducing (86.76%), and at pH 10, further, it dropped to 35.51%, indicating that at pH >8, with aluminium hydroxides (could be polyhydroxides) that are not able to form flocs to adsorb the dye molecules, from this study, the optimum initial pH for maximum colour removal of the dye with aluminium is found to be pH of 8 and above.At this particular pH, increasing the same was found to be ineffective in the colour removal of the dye under experiment.Both the hydroxides of aluminium and copper have a low solubility, and at intermediate pH levels, an amorphous precipitate is formed.This is extremely important in terms of the coagulant action of these materials.As thepH value increases, the soluble anionic form of metal hydroxides becomes foremost; the soluble species could be Al(OH) 4 − and polyhydroxides respectively at low and high pH [79].ECE percentage with copper electrodes was 91.88 at initial pH 8, and on increasing the pH above 8, the colour removal increased from 91.88 to 98.46 (pH 9), and at pH 10, it was 97.11.The optimum pH for Al and Cu for the high removal of colour of the Red BFL dye solution was found to be 8 and 9, respectively [80].

Impact of electrolyte on ECE%
Experiments were conducted with different NaCl concentrations ranging from 1 to 5 g L −1 under other optimised conditions, and the results are given in Figure 1 At 1 g L −1 of NaCl, the ECE% with aluminium was 98.96, with copper 99.74%.The efficiency remained almost constant (98%) with aluminium electrodes, even after raising the electrolyte concentration, likely because the anions from the salt would split the passivation layer and increase the anodic dissolution rate of metal, both by combining chloride ions into the oxide film or in the metal dissolution.As a result, the risk of effective contact among the organic pollutants and hydroxide free radicals has diminished [81,82].
With copper electrodes, at 2 g L −1 , the CRE% was 93.6%, reduced from 99.74%.This may be due to the salt deposition on the surface of the electrode, but as it increased to 3 g L −1 , ECE % increased, and on further increasing the concentration of the electrolyte, it remained constant.The increase in ECE% from the electrolyte concentration of 3-4 g L −1 (93.6-97.9%)may be due to the breakdown of the initial passive layer of the deposited salt, and as the concentration of chloride ions increased, it had interference in the electrode surface hindering the generation of copper ions for the floc formation; therefore, further addition of electrolyte caused in the reduction of ECE%.A further increase in NaCl concentration in both electrodes induced negative degradation by obstructing contact between the electrodes and the dye solution as a result of the salt deposition on the metal.The optimum concentration of the electrolyte for both electrodes was found to be 1 g L −1 for maximum removal of the dye.

Impact of contact time on ECE%
Experiments were carried out under other optimised conditions with different contact times ranging from 5 to 25 min, and the results are shown in Figure 1(c).[Al: pH 8, NaCl 1 g L −1 , CD 40 A m −2 with Cu: pH 9, NaCl 1 g L −1 , CD 60 A m −2 ].The formation of metal hydroxides and their concentration is time dependent, so contact time is another important parameter to be optimised for the removal efficiency.In both the cases, the ECE% was increasing as the contact time increased.The highest ECE% was obtained at 15 min with Al (99.08%),Cu at 25 min 99.89%.With copper the efficiency in colour removal occurred at elevated contact time, which will increase the cost of the process.For improved removal efficiencies, the optimum CT for Al and Cu electrodes was 15 and 25 min, respectively.S1 provides the EC experimental setup, the dye solution settling after EC, and the filtrate.

Impact of current density on ECE%
Experiments were performed with different current densities from 20 to 100 A m −2 under other optimised conditions, and the results are shown in Figure 1(d) (Al: pH 8, NaCl 1 g L −1 , 15 min, Cu: pH 9, NaCl 1 g L −1 , 25 min).The amount of current density influences the growth of flocs since it adjusts the rate and size of bubble production and influences the coagulant production rate.The applied current density has a direct effect on process efficiency and costs [83].As the current density increases, so does the amount of oxidised ion released by the electrodes.The increase in current density is advantageous to the aluminium and copper electrodes, according to the findings.Furthermore, as the cell current increased, the density of the bubbles increased and their size decreased, resulting in a reduction in contaminants [84].The optimum current density for maximum ECE was 40 A m −2 (98.79%) with aluminium and 60 A m −2 (98.84%) with copper electrodes.
From the findings on the impact of the operational parameters, EC with Al-treated dye solution was better in ECE than Cu.The results of the XPS analysis in the sludge collected were used to validate these findings and Al shows four types of hydroxides (Figure 2(a-c)), and Cu shows one hydroxide (Figure 2(d-f)), so as more floc formation with Al, the efficiency was superior in the treatment of Red BFL dye solution with Al.

XPS analysis of sludge
Al and Cu XPS survey spectra and core line spectra with high resolution [(Al, O1s, Al2p) and (Cu, O1s, Cu2p 3 )] are given in Figure 2(a-f).During the anodisation of Al, it is reported that the capacity of Al to form dimeric, trimeric, and polynuclear hydrolysis products such as Al 2 (OH)  [85][86][87].This analysis helps us to understand on the electrochemistry of metal hydroxide formations and gives us clear picture on what type of metal hydroxides are formed and in turn help in coagulation of the dye molecules and as well as evaluating the potential of the electrodes in terms of efficient removal of the dye pollutants.From the XPS data of the sludge obtained with Al electrodes, from Figure 2(b,c), it can be understood that O1s binding energy value of oxygen atom bonding with hydrogen in the form of hydroxide in gibbsite 531.8 eV (Al(OH) 3 ), bayerite 531.9 eV (Al(OH) 3 ), boehmite 532.1 eV (AlOOH), pseudo boehmite 532.2 eV (AlOOH) and from the high-resolution core spectra of Al2p, the binding energy value of Al as gibbsite 74.4 eV (γ-Al(OH) 3 ), bayerite 75.0 eV (Al(OH) 3 ), boehmite 73.9 eV (AlO(OH)) and pseudoboehmite, 74.3 eV (AlO(OH)) [88].From XPS study in the sludge separated using Al, it was observed that there are four types of hydroxides of Al formed, such as gibbsite (Al(OH) 3 ), bayerite (Al(OH) 3 ), boehmite (AlO(OH)) and pseudoboehmite (AlO(OH)).Pseudoboehmite and boehmite have the same chemical composition AlO(OH).However, the water content in pseudoboehmite is higher than in boehmite due to which it has larger unit cell [89].The possible EC mechanism using Al in the removal of Red BFL dye solution are deduced as given.
Aluminium oxidation takes place on the anode's surface.
Reduction of water takes place at the surface of cathode, From the XPS analysis obtained for copper electrodes, the binding energy value of O1s (Figure 2(e)) 531.8 eV indicated that the oxygen binding with hydrogen in hydroxide form (Figure 2(f)) for Cu2p 3 at 934.06 eV for copper in its +2 oxidation state so the metal hydroxide as flocs formed in EC process with copper was Cu(OH) 2 and its formation was supported by the spectrum of O1s [90,91].Based on this study, the proposed electrochemical mechanism with copper electrode in the removal of Red dye BFL solution is Overall reaction is

HPLC, Mass Analysis
HPLC chromatograms of untreated dye solution and with Cu and Al electrodes in the EC method are shown in Figure 3(a-c) and HPLC Data for Red BFL solution and Al, Cu-treated dye solution is given in Table 1.The HPLC chromatogram of untreated dye solution shows the seven different compounds with various polarities at 233 nm wavelength in the reverse-phase elution (Figure 3(a)).Interestingly, the HPLC chromatogram of dye solution treated with Cu electrodes displays (Figure 3(b)) the disappearance of high polar compounds peaks with the elution of four compounds at RT 5.828, 6.173, 6.761, 7.767 min, which correspond to the less polar organic compounds present in the original dye solution.It was also confirmed that the high polar compounds were removed due to the treatment of Cu electrodes, by the degradation of original dye present in the solution.It is note-worthy to report that the colour alteration was caused by the EC process due to the changes in the composition of dye compounds and its chemical structures.The compound elutes at RT of 6.173 min was considered as the main compound existing in the dye solution of around 50%.The compound elutes at 5.828 with the peak area of 3.97% appeared due to the Cu electrodes treatment and it was considered to be high polar due to the keto-enol transformation in its chemical structure.The structure of the dye, possible fragmentation is given S2-S5.
HPLC injections were also performed after the treatment of dye solution with Al electrodes, and the chromatogram is shown in Figure 3(c).The HPLC chromatogram shows the elution of four less polar compounds at RT 5.79, 6.055, 6.608, 7.464 min, which were not  affected by the electrocoagulation process.It was also observed that the organic compounds eluted at RT 6.055, 6.608, and 7.464 min were the same compounds eluted before and after the treatments.The new peak elution at RT 5.735 min with the peak area of 3.84% was significantly appeared after the treatment with Al electrodes.After the treatment, the resulting solution was observed as colourless and the respective chromatogram shows the less polar in nature, which corresponds to the keto-enol conversion in its chemical structure due to the electrocoagulation.The disappearance of peaks was responsible for colour imparting dye molecules which were eliminated during the treatment with aluminium electrode in EC process.
The successful abstraction by Al electrodes of dye contaminants from Red BFL aqueous solution was due to the formation of (Al(OH) 3 ), boehmite (AlO(OH)), pseudoboehmite (AlO(OH)), and bayerite (Al(OH) 3 ) due to the OH − radicals oxidising the organic compounds, which assisted the coagulation of dye as well as the degraded products (Figure 3(b,c)), and comparable results were stated [92][93][94][95].
The separated compounds were analysed by mass spectroscopy in both positive and negative mode of ionisations for the raw and treated Red BFL dye solutions with Cu and Al electrodes, and their corresponding mass spectra are shown in Figure 4(a-f).The elution behaviour of the dye in HPLC with respect to the polarity, the decolouration of the chemical compounds was mainly due to the coloured phenolate ions in its chemical structure and also contain glycone and a glycone fragments as it was water-soluble, which was also in good agreement with their respective mass spectra.In the mass spectrum of the untreated dye solution shows the peaks at m/z 848.6 and 882.6 in negative potential correspond to the molecular ion peak of (M • +2Na + ) and (M + 2 K + ) for the fragmented ions (C 38 H 46 N 2 O 15 SNa 2 ) + (S3) and (C 38 H 46 N 2 O 15 SK 2 ) + ,respectively.The molecular ion peak at 804.6 with 100% intensity was due to the formation of the fragment ion (C 38 H 48 N 2 O 15 S) + .The fragmentation patterns in negative and positive potential were attributed to the AQ moiety containing glycone units, which shows dark colour corresponds to the phenolate form of the dye.During the electrochemical process, the phenolate ions of the dye form reversibly, into phenol form which shows the molecular ion peaks at m/z 804.6 in both the process and the phenol form of dye was not showing the colour.The corresponding chemical structures are given in the supporting information (S3).The mass peak at 768.8 corresponds to the formation of fragmented ions (C 38 H 44 N 2 O 13 S) + due to the loss of two water molecules from the glycone part.It was noteworthy to report the removal of glycone unit under mass condition was also observed due to the appearance of peak at m/z 325 (S4) in positive mode for the fragment ion (C 12 H 22 O 10 ) + .The higher intensity peak at m/z 130.2 for (C 10 H 8 + 2H + ) fragment ion was attributed due to the residual hydrocarbon skeleton derived from the AQ part.
The ESI mass spectrum of treated dye with Al electrodes (Figure 4(c,d)) shows the molecular ion peak at 804.6 with 100% intensity due to the formation of the fragment ion (C 38 H 48 N 2 O 15 S) + during EC process.No evidence of the formation of corresponding Na + and K + ions after the treatment of dye solution with the Al electrodes.It is in good agreement with the fragmented ions formed after the treatment of Cu electrodes (Figure 4(e,f)).Under mass condition, the fragmentation patterns were identical for both Al and Cu electrodes which confirms the process discoloration occurs due to the same mechanism under the same condition.The treated dye solution with Al and Cu electrodes show the cleavage of glycone part from the AQ moiety by appearing the peak at m/z 325 in positive potential due to the fragmented ions (C 12 H 21 O 10 ) + .
The peak at m/z 306 in positive potential corresponds to the removal hydronium ion from the glycone unit.The higher intensity peak at m/z 129.2 was attributed due to the residual hydrocarbon skeleton (C 10 H 8 + H + ) ions derived from the AQ part in the positive potential.

Phytotoxicity study
Dye degradation produces a variety of intermediate products, all of which must be nontoxic by nature.To assess the toxicity of the raw dye solution being studied, phytotoxicity examinations were performed using V. radiata.The average values of total root growth (germination), length of plumule and radicle of V. radiata grown in the treated and raw dye solutions were related to the control, and the results are formulated (Table 2).The germination rate of the seeds grown in Red BFL solution was 55.8%, and the plants had an average length of plumule and radicle as 18.2 and 5.98 cm, respectively.With control, seed germination was 100%, and the average plumule and radicle length were 25.4 and 9.23 cm, respectively.Rate of germination in treated dye solution with Cu electrodes was 98.3%, with average plumule and radicle length of 24.95 and 8.83 cm, respectively.The rate of germination of the dye solution treated with Al electrodes was 99.87%, and the plumule and radicle length were 25.02 and 9.02 cm, respectively, very close to the results of the plants grown in the control (see Table 2).From this study, it was noticed that the dye solution treated with both the electrodes did not considerably impede germination, plant growth in its plumule and radicle length and related outcomes were recorded [96].S5 portrays V. radiata growth in (a) control (b) Red BFL solution (200 mg/L), with (c) Cu electrodes, and (d) Al electrodes.

Ecotoxicity study on A. salina
The reusability and lethal effect of the process of discoloration and degradation of toxic components found in industrial wastewater are considered highly effective rather than its physiochemical compliance [97]. A. salina was used to determine the ecotoxicity of the treated Red BFL solution.The findings of this study clearly showed that Red BFL-treated samples have a better effect than untreated Red BFL samples.However, the lower survival percentage of A. salina in the Cu electrode-used samples relative to the Al electrode-used samples indicates that the Al electrodes treatment was a better approach for reducing Red BFL (Figure 5).The morphological changes observed in A. salina during microscopic analysis confirm A. salina mortality in Cu electrode-treated samples.Cu electrode-used samples showed the most intracellular part deformation, while Al electrode-used samples showed the least (Figure 6).In previous studies, we observed dye aggregation and morphological changes in the same way [98].

Conclusion
This work investigated the efficacy of the EC process in extracting and reusing the simulated aqueous solution of Red BFL dye with two sets of electrodes.Maximum colour removal of dye solution for Al (99.17%) occurred at pH 8 with CD 40 A m −2 , CT 15 min, whereas for Cu (91.88%) at pH 9, CD 60 A m −2 , CT 25 min.In contrast to the Cu electrode used dye solution, the HPLC and mass analysis indicated that the Al electrode used Red BFL dye solution had a lower number of intermediate/breakdown products.When the Red BFL dye solution was studied with Al electrodes in a phytotoxicity analysis on V. radiata, the germination, plumle and radicle length of V. radiate were comparable to the plants grown in control, than the dye solution used with Cu electrodes.According to the ecotoxicity analysis on A. salina, the deformation of intracellular components was found in Cu-used samples, but not in Al-used samples.XPS analysis of the sludge obtained, confirmed the improved performance of Al electrodes in the generation of four different types of hydroxides of aluminium as coagulants, in comparison to the effect of copper electrodes in the treatment of Red BFL dye aqueous solution with one type of coagulant.For its simple operation, the same method can be checked for real-time wastewater.

Figure 3 .
Figure 3. HPLC chromatogram of (a) Red BFL dye solution, (b) treated Red BFL dye with Cu and (c) treated Red BFL dye with Al electrodes.

Figure 5 .
Figure 5. Survival rate of A. salina on Al and Cu electrodes treated with Red BFL solution.

Figure 6 .
Figure 6.Microscopic examination of A. salina after 24 h of incubation with treated and untreated dye solution.(a) Sequestration of Red BFL in the intercellular zone in nauplii treated with Red BFL.(encircled), (b) The absence of Red dye on Al electrodes treated indicates the effectiveness of the treatment procedure and (c) The intracellular area of Cu electrodes treatment displays a slight alteration, with contraction of the intestinal region shown by arrows.
Waters 1525 Binary HPLC pump00G-4608-EO Kinetex 5 U C8 100A was used to take HPLC chromatogram and positive ionisation mode analysis was conducted using the ESI ionisation technique.The test solutions were filtered with 2µ filter thicknesses after being diluted five times using HPLC grade water.The HPLC-MS method was used with various ratio of H 2 O and CH 3 OH as the mobile phase process.For 22 min, concentrations ranging from low B percentage (H 2 O:CH 3 OH 95:5 v/v) to high B percentage (5:95 v/v, H 2 O: CH 3 OH) were used.With methanol as the filtrate solvent, the study on column C18 (symmetry 4.6 9 250 mm) was done on the HPLC (Waters configuration No. 1525) with CH 3 OH -H 2 O (50:50) as the mobile phase and the UV detector operated at 233 nm.The dye and the treated dye solution are analysed spectroscopically with an Agilent 6125B SQ LC/MSD, LC Stack for Open LAB ChemSta 1260 Quat Pump 600 bar, Column Oven, Auto Samplers with UV-Detector, ESI and APCI mode mass spectroscopy.

Table 1 .
HPLC data for Red BFL solution and Al, Cu-treated dye solution.

Table 2 .
Parameters of V. radiata in (a) control and (b) Red BFL solution (200 mg/L), treated with (c) Cu (d) Al electrodes.