TOC and colour are the two major metrics of industrial wastewater quality that signifies the data sheet about the nature, type and loading of pollutants. In order to find the best conditions for reducing TOC and colour from industrial wastewater, a set of process factors, including the effect of pH, time, current density, adsorbent dose and comparison between ECP and ECP–PAC have been studied in this work.
Morphological analysis
Initially, scanning electron microscopic (SEM) analyses were used to investigate the PAC’s structural characteristics and surface morphology at different magnifications as shown in Fig. 2. The porosity exists in the SEM images of PAC provides insight into the material’s absorbent nature. Further, the porosity could be altered by the influence of activating agents such as CaCl2, which led to an increase in the PAC’s surface area, pore volume and subsequently decrease its polycrytallinity (Salcedo et al. 2021). Here, the activated carbon derived from coconut shells has a sheet-like morphology with a swell-like arrangement of nanosheets. Moreover, the larger pore size of activated carbon has proven advantages for charge storage applications such as batteries, supercapacitors, biosensors, electronic parts, and photocatalytic degradation (Yi et al.2003; Zhai et al. 2022; Joshi et al. 2021).
XRD and Raman spectroscopic analysis
The XRD pattern of PAC was used to determine its structural characteristics and compositions produced by the CVD method followed by chemical activation using CaCl2. Figure 3(a) shows the XRD pattern which depicts the crystalline structure of the prepared activated carbon layers under optimal preparation conditions at 450 ℃. The presence of carbonaceous crystalline structure was confirmed by the two distinct patterns in the intermediate’s XRD profiles, which are located at 26º and 43º due to (0 0 2) and (1 0 0) planes corresponding to standard graphite and graphite layer diffractions, respectively (Wang et al. 2017). After activation with CaCl2, the PAC had more irregular amorphous carbon structures, as evidenced by the relatively weak and broadened peak at 26º as shown in PAC material (Kabir Ahmad et al. 2022). It is understood that the carbon activated by CaCl2 remains as amorphous in nature.
Further, an effective analytical method for analyzing carbon is Raman spectroscopy. Carbonaceous materials exist in the PAC tend to show two bands where Raman spectroscopy can be performed. The first, referred to as “First order bands”, are found in the range of 1100 and 1800 cm− 1. The graphitic (G) band appears at 1600 cm− 1, and the disordered (D) band at 1350 cm− 1. Figure 3(b) shows the two primary bands that define the spectra of carbonaceous materials in this order (Le Van and Luong Thi Thu 2019). The G band denotes the presence of C = C stretching vibrations while the D band denotes lattice defects, edge surface defects, uncombed alignment, and low-symmetry graphitic structure in activated carbon material (PAC). The G band represents the stretching modes of the sp2 hybridized carbon atoms in the rings and chains while those of the carbon atoms in the planar terminations of the graphite structure are typically represented by the D band (Oginni et al. 2019). where the degree of surface modification can be calculated using the Eq. (9).
R = \(\frac{{I}_{D}}{{I}_{g}}\) (9)
where R, ID, and IG represent the level of surface modification and the intensity of D and G bands, respectively. The value of R or ID/IG was measured as 0.8437, which in part, referred to a higher graphitization index.
BET surface and pore size analysis
Figure 4(a) depicted the porosity measurement and adsorption properties of activated PAC using CaCl2 by nitrogen adsorption-desorption at 77 K. The presence of a distinct hysteresis loop and a sharp increase in N2 uptake at relatively higher-pressure ranges on a type IV isotherm for activated carbon indicated the mesoporous nature (Nasrullah et al. 2018). Thus, the isotherm is a typical type IV with microspores and the hysteresis loop is primarily caused by the mesoporous structure. Table 1 indicated the total pore volume, average pore diameter, and Brunauer Emmett Teller surface area (SBET) of activated carbon. The surface area for the PAC was calculated to be 38.49 m2g− 1. Also, the surface area and pore size diameter were calculated using the Eq. (10) (Barzinjy and Azeez 2020):
$$\frac{1}{Q\left(\left(\frac{Po}{P}\right)-1\right)}= \frac{1}{{Q}_{m}C}+\frac{C-1}{{Q}_{m}C} \left(\frac{P}{{P}_{o}}\right)$$
10
where (P/Po) denotes the relative pressure, Q, Qm, and C denote the weight of the gas absorbed, the adsorbate in the form of a monolayer, and the BET constant, respectively. PAC has pore size distributions that span a wide range and includes narrow mesopores as well as wider micropores. Since micropores have a significant impact on the adsorption of small molecules, such porosity is suitable for adsorption (Ferreira et al. 2022). Figure 4(b) depicts BJH analysis where the pore size distribution was studied concerning the differential volume. The average pore size of the prepared activated carbon was found as 8.321 nm. Besides, the corresponding average pore volume has been calculated as 0.9965 cm3 g− 1 and the magnified view of the BJH differential volume and distribution of pore size for PAC was shown in Fig. 4(b).
Table 1
The pore volume, average pore diameter, and SBET of activated carbon.
| Sample | Activating agent | Surface area (m2/g− 1) | Pore volume (cm3/g) | Pore size (nm) |
| Powdered activated carbon (PAC) form coconut shells | Prior to activation - Carbon | 3.740 | 0.1678 | 9.7569 |
| After activated with CaCl2 - Carbon | 38.49 | 0.9965 | 8.321 |
UV-Vis absorption studies of textile effluent degradation
For colour analysis, UV-visible spectrophotometer was used to study the absorbance parameters of textile effluents before and after the ECP or ECP–PAC carried out using a pilot scale batch-reactor. Eq. (11) was used to determine the colour removal efficiencies (%).
Colour removal = \(\frac{{A}_{o}-{A}_{t}}{{A}_{o}} \text{X} 100 \%\) (11)
UV-Vis spectrophotometry was used to determine the concentration of organic/inorganic matter in the effluent and provide data on the concentration of pollutants in the effluent, prior and after ECP studies. In order to test the efficiency of the pilot-scale ECP batch-reactor with Fe-Cu electrodes, 20-ppm solution of the respective VIBGYOR-coloured organic dyes was introduced for the ECP or ECP–PAC (Fig. S3), and the degraded effluents were collected at the interval of 15 min to study the UV-Vis spectral properties. After 15 min, the degradation efficiencies such as 60–70% was observed at the ECP carried out in the batch-reactor to remove VIBGYOR coloured samples. At the same time, degradation efficiency has further increased to above 90% by the combination of ECP–PAC (5g/L of PAC and 15 min) in the batch-reactor was shown in (Fig. S3).
Besides, Fig. 5 clearly demonstrates the enhanced UV-Vis absorbance spectral properties of raw wastewater spectrum, which is due to the existence of significant amounts of colour and dissolved matter. On the other hand, the UV-Vis absorbance properties have altered/decreased by the effective participation ECP or ECP–PAC treatment carried out in the batch reactor. Thus, the effective ECP led to a significant reduction in TOC and colour content as compared to the raw effluent. In the pilot-scale batch-reactor, the ECP was carried out for 15 min with uniform conditions for different sets of electrodes such as pH of 7.5, current density of 50 mA/cm2, and electrode distance of 5 cm. Among the different sets of electrodes used in the batch-reactor for ECP, the Fe-Cu electrode provided the maximum degradation in a short period as shown in Fig. 5(a). The degradation efficiencies of textile effluent in the batch reactor by ECP using Fe-Cu electrode at various time intervals was interpreted. After 15 min as shown in Fig. 5(b), ECP reaches a degradation level of ~ 60% using the Fe-Cu electrode. At the same time, in the batch reactor carried out by the introduction of PAC in the ECP, where Fe-Cu electrode coupled with the introduction of PAC to the effluent reached the degradation level of > 95% as shown in Fig. 5(c). As a result, the combination of ECP with PAC adsorption process delivers superior performance than standalone ECP in the batch-reactor Fig. 5(d). The other reaction conditions for textile effluent samples were maintained uniformly such as current density, I = 50 mA/cm2, time = 15 min, and inner electrode distance = 5 cm for either ECP or for ECP–PAC coupled batch-reactor.
FT-IR spectral studies and TGA analysis of PAC material
The functional groups that are present on the surface of the prepared bio-sorbents such as PAC were examined using FT-IR analysis. Figure 6(a) shows the FT-IR spectra of before and after activated CaCl2-activation of PAC in the 500–4000 cm− 1 range. The broad absorption band measured at 3356 cm− 1 and 2978 cm− 1 indicate the presence of alcoholic O-H and N-H stretching vibrations (Zacaroni et al. 2015). The peaks of PAC at 2965 cm− 1 are related to C-H stretching vibrations indicate the presence of saturated hydrocarbon. Evidently, the stronger band at 1700 cm− 1 corresponds to the stretching vibrations of C = O bonds with respect to carbonyl, ester or carboxyl bonds exist in activated carbon prepared from coconut shells (Sahira et al. 2013). The strong band of N-O stretching, which is a significant indicator exists at 1538 and 1540 cm− 1. The peak between at 1100 and 1048 cm− 1, indicates the presence of alcoholic O-H and an aromatic ring corresponds to the stretching of C-O groups representing the presence of primary alcohol. The strong bond of C-Cl stretching which is a major indicative positioned strong peak at 580 cm− 1 that represents the halo compounds (Mondai et al. 2007).
Thermogravimetric analysis is used to examine the thermal characteristics of PAC, and the results are depicted in Fig. 6(b) which is studied between 26 and 980 ℃. The removal of sample moisture has caused a weight loss of ~ 6% between 26 and 89 ℃. The calcium content exist in the activated carbon is eliminated and weight loss occurs between 100 and 400 ℃ (Bulca et al. 2021). Subsequently, the temperature between 480 and 826 ℃ is stable for PAC material whereas the weight loss related to the complete decomposition of PAC was observed between 826 and 980 ℃.
Comparison of TOC in the batch-reactor between ECP and ECP–PAC for effluent degradation
The choice of electrode material used in the pilot scale batch-reactor for ECP has a larger impact on the material’s adsorptive properties and ability to remove contaminants. In the batch reactor for ECP, electrodes like Fe, Cu, or Al were studied by the variations in the physicochemical properties by varying the arrangement of the respective anode and cathode. Usually, every metal electrode has distinct adsorptive qualities that can impact the effectiveness of the process (Shahedi et al. 2020). Using the current density of 50 mA/cm2, with the electrode distance of 5 cm, reaction time of 30 min, and a neutral pH of 7.5, the effectiveness of the TOC removal concerning different electrodes were examined. Accordingly, effluent treatment in the batch-reactor by ECP was carried out using a different set of electrodes such as Fe-Fe, Al-Al, Cu-Cu, Fe-Cu, Cu-Fe, Al-Fe, Fe-Al, Al-Cu, and Cu-Al performed in triplicate and the results showed convincingly with good repeatability in the error bar range of 1–3%. Among the different combinations of electrodes, the Fe-Cu electrode arrangement shows the maximum TOC removal (81%) as shown in Fig. 7. Here, the Cu electrode possesses higher conductivity and provides better coagulant in wastewater to improve contaminant removal (Huang et al. 2020). On the other hand, Fe and Cu electrode is readily available and less expensive than other electrode materials to improve contaminant removal. As a result, for ECP, Fe-Cu electrodes are effective and chosen due to their high electrical conductivity, high melting point, and heat conductivity. Besides, this electrode pair combination allows electricity to pass through easily and quickly dissipates heat (Cong et al. 2021). Therefore, the production of OH− ions at the cathode played a crucial part in removing the contaminants from wastewater (Graça et al. 2019). Hence, the removal of TOC from textile effluent wastewater has been accomplished by the use of Fe-Cu electrode arrangements. The operating parameters of the ECP with Fe-Cu electrodes were monitored for efficient and effective treatment. Thereby, TOC removal was effective by using the Fe-Cu electrode in ECP and the results are shown in Table 2.
Compared to chemical coagulation, this method remains as very simple, safe to dispose as landfills, and less toxic in nature. Initially, prior to effluent treatment, the effluent concentration was measured using TOC as 324.1 mg L− 1. As a result of ECP using Fe–Cu electrode in the batch-reactor, the concentration of the TOC in the effluent has drastically reduced to 27.84 mg L− 1. Similarly, TC concentration has reduced from 1410 mg L− 1 to 98.63 mg L− 1 and IC concentration has reduced from 1090 mg L− 1 to 66.95 mg L− 1 in 30 min interval of ECP using Fe-Cu electrode in the batch-reactor was shown in Table 2. Moreover, the addition of stipulated PAC adsorption to the effluent along with the ECP (ECP–PAC) in the batch-reactor shows a highly reduced concentration of TOC in 30 min, reaching above 96%. Initially, PAC was quantitatively optimized in the ECP (ECP–PAC) for the enhanced effluent degradation efficiency. As a result, the textile effluent degradation takes place effectively by the combination of ECP–PAC where the concentration of the TOC, TC and IC in the effluent has sharply further decreased to 17.55 mg L− 1, 50.04 mg L− 1, 32.49 mg L− 1, respectively was shown in Table 3. Thereby, in the pilot scale batch-reactor, the combination of ECP using Fe-Cu electrode with PAC-based adsorption has enabled the maximum degradation of textile effluent such as TOC removal of 96%, whereas in the absence of PAC-based adsorption process, ECP remains as 81.50%. Thus, the combination of ECP using a Fe-Cu electrode with PAC-based adsorption in the pilot-scale batch-reactor has resulted in a higher degradation rate of textile effluents. In addition, Table 3 shows the effluent degradation carried out at different time interval between 5 and 30 min in the batch-reactor carried out ECP or ECP–PAC. Among the different time interval, in either ECP or ECP–PAC, 30 min effluent degradation gives best performance. Further, in comparison to ECP at 30 min, the ECP–PAC convincingly shows maximum effluent degradation in terms of TOC, TC and IC. No further significant improvement in the reduction of TOC values was observed with increasing time. Hence, 30 min is considered as the optimal time for the degradation and reduction of TOC of contaminants in wastewater.
Table 2
Textile effluent degradation process carried out using different combinations of electrodes in the ECP concerning TOC, TC, IC, and corresponding degradation percentages.
| S.No | Different combinations of electrodes | TOC (mg L− 1) | IC (mg L− 1) | TC ( mg L− 1) | Percentage (%) |
| | Anode | Cathode | | | | |
| 1. 2. 3. 4. 5. 6. 7. 8. | Al Al Al Cu Cu Fe Fe Cu | Al Fe Cu Cu Fe Al Fe Al | 161.1 114.8 110.6 108.6 98.97 85.08 82.44 69.32 | 240.9 231.4 224.3 574.5 525.4 337.3 400.1 472.7 | 401.9 346.1 334.9 683.1 624.4 422.8 482.6 542.1 | 51 64 65 66 69 73 75 79 |
| 9. | Fe | Cu | 59.94 | 107.5 | 167.4 | 81.50 |
| 10. | Raw | Effluent | 324.1 | 1090 | 1410 | |
Table 3
Textile effluent degradation process carried out by the combination of ECP using Fe-Cu electrodes with PAC-based adsorption process (ECP–PAC) concerning TOC, TC, IC, and corresponding degradation percentages.
| S.No | Conditions | Experimental Values |
| | ECP pH = 7.5, I = 50 mA | ECP-PAC pH = 7.5, I = 50 mA, PAC = 5 g/L | ECP TOC IC TC % (mg L− 1) | ECP-PAC TOC IC TC % (mg L− 1) |
| 1. 2. 3. 4. 5. | t = 5 min t = 10 min t = 15 min t = 20 min t = 25 min | 148.1 113.1 100.2 87.8 74.1 | 166.6 157.5 130.6 121.9 92.8 | 315.2 270.8 230.8 209.7 166.9 | 54 65 69 73 77 | 42.48 26.91 25.54 20.80 18.86 | 90.01 81.63 42.56 27.80 32.57 | 132.5 108.5 63.3 53.3 51.4 | 86 90 92 93 94 |
| 6. | t = 30 min | 59.94 | 107.5 | 167.4 | 81 | 13.55 | 31.49 | 48.05 | 96 |
Effect of current density and pH on the ECP and ECP-PAC process
In the present study, an increase in the current density has speed up the electrolysis by increasing the production of hydroxide ions, which are responsible for the ECP. The variation in the current density has an effect on the efficiency of the ECP. Thereby, the reaction rate increases as the current density increases, resulting in faster effluent degradation (Chanikya et al. 2021). The effect of current density was studied by varying the current density from 10 to 50 mA/cm2 using pre-determined electrode operating variables, including inter-electrode distance, reaction time, PAC-based adsorption process, and the removal of TOC and colour was noticed from the wastewater. According to Faraday’s law, the increasing current density led to increase the dissolution rate of electrode material, which increases the sacrificial anode metal ion concentration and enhances floc formation (Muhammad Niza et al. 2020). Furthermore, the increased current density promotes a large number of small hydrogen bubbles, which removes the effluents effectively via flotation. When the current density increases from 10 to 50 mA/cm2, Fe-Cu electrodes used in ECP have the potential to increase the TOC removal in the textile effluent from 35 to 81% in a pilot-scale batch-reactor Fig. 8a whereas, by the combination of ECP with PAC based adsorption process resulted in further enhancement in the TOC removal from 49 to 96%. A high current density in the ECP system causes an increase in anodic oxidation, which increases the production of Fe(OH)3. It causes the formation of hydroxy cationic complexes, which accelerates coagulation and responsible for the removal of a significant amount of TOC from the wastewater (Kumar and Sharma 2020). No significant reduction in TOC variation was observed beyond the current density 50 mA/cm2 and the plot shows a very small proportion variation in TOC, which is not significant for further increasing the current density. Thereby, the optimum current density for ECP or ECP–PAC in the batch-reactor was fixed as 50 mA/cm2.
One of the important parameters for determining process efficiency is pH. Further, the removal of TOC is significantly influenced by other operating parameters such as pH. The effect of pH on ECP was investigated by varying the pH from 4 to 9 and Fig. 8b depicts the observed TOC with respect to pH. The TOC removal percentage was decreased for Fe-Cu electrodes in the ECP by varying the pH from mild acidic to mild alkaline conditions (Olvera-Vargas et al. 2019). In an alkaline pH, the excess formation of insoluble \({Fe\left(OH\right)}_{4}^{2-}\) precipitates caused a decrease in TOC removal. Increasing the pH from 4 to 7 has improved TOC removal from 57 to 81%. On the other hand, the combination of ECP with PAC-based adsorption (ECP–PAC) has improved the TOC removal rate from 64 to 94% for pH 4 to 7, which is due to the existence of amorphous PAC materials. Further increase in pH from 7 to 9 causes a decrease in effluent degradation. Upon, further increase in pH to 10, only 63% of TOC was removed at the Fe-Cu electrode. From the results, it is understood that the neutral pH is desperately required for effluent treatment in the batch-reactor to carry out an effective ECP–PAC. Besides, this process has a distinctive and significant feature that increases its viability for treating effluent. Fixing the current density and pH in the batch-reactor for ECP or ECP–PAC, time required for effluent degradation has to be monitored.
Effect of time and kinetic study on the ECP and ECP-PAC process
The solution was translucent at the start of the study, but it darkened over time. After a while, it begins to turn reddish brown, and by the end of the study, almost the complete colour and TOC content has been lost. This colour change could be caused by Fe ion releases from the electrode on anode side, which improves the coagulation process and results in a greater reduction in TOC and colour. After 5 min, a notable decrease in TOC and colour was observed with > 5% by the ECP or > 10% by the ECP–PAC process. The time from 0 to 10 min was gradually increased. At the same time, the TOC for ECP and ECP–PAC methods were decreased to 81.5% and 96%, respectively. After 30 min, the change in TOC reduction with the plot becomes constant due to long-term electrolysis process (Olvera-Vargas et al. 2019). Following that, no further significant improvement in the TOC studies with increasing time was determined. After 30 min, a meagre variation in TOC value was observed. Thus, the ECP or ECP–PAC in the batch-reactor was carried out for 30 min where the TOC has decreased to 81 or 96%, respectively as shown in Fig. 9a. Thereby, 30 min is fixed as the optimal time for the degradation and reduction of TOC in textile effluents.
The kinetics of the ECP–PAC in the batch-reactor was investigated to determine the rate of reaction. Industrial effluent is a mixture of various chemical compounds that exhibits a variety of reactivity’s. UV-Vis spectroscopy is an effective strategy used to interpret the order of the reaction. As a result, it is clear that the reaction is stationary and follows pseudo-first order kinetics by fitting the data of ln(C/C0) versus time. Accordingly, the reaction kinetics was fitted by the pseudo-first-order reaction for the effluent degradation in the batch-reactor coupled with ECP or ECP–PAC, respectively as shown in (Fig. S4), which has been determined critically using Eq. (12) (Deng et al. 2019).
$$\text{ln}\left(\frac{C}{{C}_{0}}\right)={K}_{app }. t$$
12
Where (Kapp) is the apparent kinetic rate constant that is studied from the plot of ln(C/C0) versus electrolysis time ‘t’, C0 is the initial concentration of original effluent and C is the concentration of the effluent at time ‘t’ as shown in Fig. 9b and 9c. The kinetic study has confirmed that the catalytic oxidation of effluent follows pseudo-first order kinetics and the rate constant was calculated and tabulated in (Table S2) for ECP and ECP–PAC, respectively.
Germination study of mung beans sprouts and determination of chlorophyll content using effluent treated water
The germination of mung bean and growth of the sprouts, formation study using raw textile effluent and ECP–PAC treated water were monitored for 7 days as shown in Fig. 10a. A petri dish was filled with 100 mung bean seeds of comparable size, and the surface of the mung beans was covered with filter paper. Average germination rate of mung bean watered with control water, raw effluent or ECP–PAC treated water for 7 days was shown in Fig. 10b. On the 3rd day, the raw effluent sprinkled seeds are deteriorated whereas treated water sprinkled seeds performs excellently in terms of next-level growth. Further, the growth of the mung bean sprouts has been observed up to 7 days at room temperature in darkness (Xu et al. 2020). When compared to the textile industry effluent, the ECP–PAC treated water has increased the seed germination. As shown in Fig. 10c, after sowing, seed germinate statistics for textile effluent was 60% whereas ECP-PAC treated water and control water show 83 and 96% in 7 days, respectively. Thus, the ECP–PAC treated water not only increased the rate of germination but also tend to improve the plant growth, which is useful for further studies on chlorophyll content. As a result, the treated water has a high potential for environmental safety.
Both underground water (control water) and ECP–PAC treated water showed the significant growth (P < 0.05) whereas the raw effluent showed the least. In the case of control water, the growth of root is 7.5 cm and the shoot is 25.7 cm long whereas in the case of ECP–PAC treated water, the root is 6.1 cm and the shoot is 22.5 cm long; On the other hand, in the case of raw effluent, the growth of root is 2 cm and the shoot is 3.5 cm long as shown in the (Fig. S5). Thus, a major decrease in seed germination, seedling growth, and biomass of mung beans attribute to the presence of high concentrations of COD, TOC, TDS, and other pollutants in raw effluent (Haq and Kalamdhad 2021). On the other hand, the length of the root, shoot, and plant is lengthy in ECP–PAC treated water indicating a drastic decrease in the colour, TOC, and other high concentration of pollutants.
The chlorophyll a, chlorophyll b, and total chlorophyll (a + b) contents were estimated for the mung bean leaves grown using control, industrial effluent or ECP–PAC treated water. From the results, it was understood that the chlorophyll a, b, and total chlorophyll (a + b) were significantly (P < 0.05) higher in the ECP–PAC treated water than in the effluent water. Moreover, there is no significant difference between control and ECP–PAC treated seedling in the case of chlorophyll b. However, chlorophyll a is (P < 0.05) slightly lower in the ECP–PAC treated water than that of control water seedlings. The total chlorophyll content of effluent water seedlings were significantly decreased when compared to the ECP–PAC water or control water Fig. 10d. Accordingly, effluent water severely affects the photosynthetic pigments in the seedlings as well as in the plant growth (Kasote et al. 2021). Thus, the ECP–PAC treated water shows significantly (P < 0.05) increased and far better than the effluent water in the plant growth and in the chlorophyll studies.
Stability and reuse of Fe-Cu electrode in the ECP involved in the batch-reactor
Repeated experiments were conducted to study the stability and reuse of electrodes with the ideal conditions (such as pH = 7.5, current density = 50 mA/cm2, time = 30 min, electrode distance = 5 cm). It was carried out to understand the stability and re-usability of Fe-Cu electrode in the ECP. The removal percentage of TOC is nearly the same after 3 runs, at ⁓ 80% as can be seen in the (Fig. S6). Fe-Cu electrodes are reused by washing with 0.1 M H2SO4 followed by cleaning with double-distilled water, polished with emery paper, and sonicated for 10 min. H2SO4 is commonly used to remove any oxide layers and attached surface impurities from the electrode surface. As a result, the treatment efficiency is nearly identical for the Fe-Cu electrode to that of fresh electrode material after 3 runs are shown in (Fig. S6).
Comparison study with the various processes
The EC process has been compared to other processes in terms of the removal efficiency of various pollutants such as COD, TOC, TDS, colour and so on. Using a combination of photocatalytic (TiO2/UV) and biological treatments, the colour and TOC removal rates were 97% and 63%, respectively (da Silva et al. 2019). The US/H2O2/EC process treated and mineralized the real textile wastewater sample, removing COD by 86.7% and TOC by 58.7% (Darvishi Cheshmeh Soltani et al. 2020). Combining electrocoagulation, electro-Fenton, and photocatalytic oxidation process for the treatment of pharmaceutical wastewater, the sequential treatment processes yielding results of 64.0% of TOC and 70.2% of COD (Başaran Dindaş et al. 2020). Similarly, the treatment of indigo-polluted industrial textile wastewater by a sequential electrocoagulation activated carbon adsorption process removes the colour, COD, and TOC to 96%, 72%, and 61%, respectively (Gilpavas E and Correa-sanchez 2020). After a comparison with several processes, the current study is found to be very economic and comparable to other process in terms of high removal efficiencies and suitable operating conditions with low current density applied in a short time period.
Treatment of textile effluents with ECP–PAC
The treated effluents data of the ECP–PAC process are shown in Table 4. The standalone ECP has removed up to 81% of the contaminants. On the other hand, the combined treatment of electrocoagulation followed by the adsorption (ECP–PAC) removes around 96% of the contaminants in the effluents. It is clear that during the combined adsorption treatment, each pollutant’s concentration in the treated water goes below its specific acceptable limit. Table 5 shows the performance of the proposed procedure is compared to other previously recorded textile effluent treatment systems studied TOC removal based on ECP. The performance analysis of the hybrid process using pilot-scale unit is very essential. Thus, the lab scale hybrid system combined with the activated carbon based adsorption unit was proven effective for the treatment of textile effluent. As a result, the developed methodology will help in producing the technical requirements for a large-scale device needed to put this technology to use in an industrial environment. Besides, the future plan is to construct a large-scale chamber where the ECP combined with different sets of porous activated carbon derived from sustainable materials for the development of other industrial effluent studies such as municipal sewage water treatment and so on.
Table 4
Comparative performances of initial and final textile industry effluent treated by ECP or ECP–PAC.
| Parameter (mg/L) | Initial concentration (mg/L) | Conc. after ECP (mg/L) | Conc. after ECP–PAC (mg/L) | % of removal after ECP | % of removal after combined process (ECP–PAC) |
| TC | 1410 | 167.4 | 48.05 | 88% | 96% |
| IC | 1090 | 107.9 | 31.49 | 90% | 97% |
| TOC | 324.1 | 59.94 | 13.55 | 81% | 96% |
Table 5
Comparative performances of industrial wastewater effluent treatment using existing techniques with the present study.
| S. No. | Wastewater | Applied Treatment Technique | Efficient electrode (Anode-Cathode) | Current density (mA/cm2) | Operating time (min) | Rate of removal % of TOC | Reference |
| 1. | Almond Industry | EC | Al- Fe | 4.5 | 15 | 79 | (Valero et al. 2011) |
| 2. | Dye House wastewater | EC EC | Al-Al Fe- Fe | 650 650 | 80 80 | 72 76 | (Kobya et al. 2016) |
| 3. | Textile wastewater | EC | Fe - Fe | 30 | 20 | 59 | (Darvishi Cheshmeh Soltani et al. 2020). |
| 4. | Jean manufacturing plant wastewater | EC/AC | Fe- Fe | 14 | 11 | 51 | (Gilpavas E and Correa-sanchez 2020). |
| 5. | Municipal wastewater treatment plant | EC | Al-Al | 1.875 | 60 | 94 | (Hawari et al. 2020) |
| 6. | Paint manufac-turing plant | EC | Fe – Fe Al-Al | 350 350 | 15 15 | 88 89 | (Akyol 2012) |
| 7. | CAN manufac-turing plant | EC | Al-Al | 20 | 40 | 37 | (Kobya and Demirbas 2015) |
| 8. | Real textile industrial effluent | ECP ECP–PAC | Fe-Cu Fe-Cu | 50 50 | 30 30 | 81 96 | This work |