Removal of Remazol Black B dye using recirculation batch electrocoagulation

Textile industry wastewater mainly contains high concentration of organic matter including the active dye of Remazol Black B. This wastewater effluent needs to be properly treated before discharge into water bodies. Electrocoagulation is one of physico-chemical methods that can be used as an alternative of wastewater treatment in the textile industries because it has a good efficiency in removing colour. A wide range of pH measured in the textile industry wastewater (i.e., 3.9-14) may affect the effectiveness of electrocoagulation process. Other factors that affect electrocoagulation process were current intensity and wastewater flow. This study aims to determine the optimum of electrocoagulation process in the recirculation batch method using recirculation batch reactor. The applied current tested were 10 A, 15 A and 20 A, with flow rate of 2 L/min, 3 L/min, and 4 L/min. A synthetic textile wastewater was prepared with a Remazol Black B dye colour concentration of 10 ppm, 3 g/L of NaCl, and pH of 11. The parameters tested periodically in this study were pH, TDS and removal of colour and COD. Result of this study showed that by increasing the electric current strength and decreasing the flowrate, efficiency of pollutants removal was increased. Highest removal percentage of COD and colour were 100% and 88,78%% with current strength of 20 A, and flow rate of 2 L/min, the final pH was 11,4, whereas total dissolved solid fluctuated (i.e., 1785 mg/L– 1902 mg/L).


Introduction
Characteristic of textile industry wastewater mainly contain of organic and inorganic chemicals such as surfactant, dyes, suspended solids, and the final ingredients in the textile production process.Dyes such as Remazol Black B are the main pollutant that must be removed because they can change the function and colour of water [1].There are some methods to remove dye contaminant from textile industry wastewater, such as physically method, chemically method, and biologically method to achieve the quality standards that have been set [2].Electrocoagulation can be used as an alternative technology to process textile wastewater.Electrocoagulation is a process of agglomerating pollutants using electrode material and electricity as a coagulant [3].The electrode consist of anode and cathode, anode as a sacrificed electrode because it can release a metal ions and corroded.Metal ions reacted with hydroxyl ion from cathode to form a coagulant.In cathode, it also releases hydrogen gas, coagulant that trapped the pollutant can rise to the surface [4].Use electrocoagulation as a treatment considered more efficient compared to other conventional processing [5].The advantages using electrocoagulation as treatment are 1250 (2023) 012012 IOP Publishing doi:10.1088/1755-1315/1250/1/012012 2 electrocoagulation didn't require additional chemical as coagulants, could remove various pollutant such as colour, and produce less sludge.Electrocoagulation has several factors that can effect the treatment process, such as pH value, current strength, electrolyte in wastewater, and flow rate [1,6].Based on the previous experiment, electrocoagulation process has a good ability to remove colour pollutant especially in textile industry.Batch system can be used for experimental because the system more dynamic system and it have ability to learn various wastewater parameters [1].In this experimental, there is modification using recirculation batch to analysis the effects of current strength and flow rate in system.

Dye Solution as Synthetic Textile Wastewater
Materials needed are Remazol Black B textile dye, NaCl solution, and NaOH solution 1 N. Initial concentration colour of 1000 mg/L was prepared by mixing 1 g of Remazol Black B with 1000 ml of distilled water using 1000 ml volumetric flask.NaCl solution was prepared by mixing 45 g of NaCl with distilled water using 1000 ml volumetric flask.Next, 150 ml of 1000 mg/L initial concentration colour and 1000 ml NaCl solution diluted with distilled water up to 15000 ml using a feed tank.50 ml NaOH solution was added to reach a pH value of 11.The amount of synthetic wastewater for this experimental were 15 L.

Electrocoagulation Configuration
Reactor capacity used in this study was ±5 L with diameter of pipe was 14 cm and height of 69,9 cm.Reactor details can be seen in Figure 1 The type of electrode used in this study were iron (Fe) for cathode and aluminium (Al) for anode.Anode configuration was solid cylinder with diameter of 4,8 cm and height of 50 cm, anode has connector with diameter of 1 cm, and height of 8 cm.Cathode configuration was spiral with diameter of 1 cm and height of 50 cm, cathode has connector with diameter of 0,8 cm and height of 9 cm.Inside the spiral cathode, contains of multyrod or cathode rods, the amount of cathode rods are 8 pieces with

Effect of electrocoagulation process with pH
In this study, initial pH was controlled in 11 using NaOH solution.Changes in the pH value on the research results always increasing. Figure 5 shows a graph of changes in pH values in synthetic textile wastewater based on variations in flow rate and current strength.The pH value increases in the range of 11 -11.47 in all variations of flow rate and current strength.
Meanwhile, the highest pH value is 11.47 at a flow rate of 3 L/min and a current of 15 A. There is no drastic change in the pH value for each variation.The increase in the pH value comes from the reduction reaction which occurs at the cathode where in the reduction reaction, hydrogen gas and OH - ions are formed because of the breakdown of water compounds and causes the pH value to rise during the electrocoagulation process [5,6] The pH value affects the formation of coagulants since pH plays a role in determining the dominant species produced.When the pH value is above 10, the dominant species produced is monomeric anion species; such as, Al(OH) 4 − so that the formation of Al(OH)3 can decrease [8].The formation of Al(OH) 4 − affects the adsorption capacity to be lower.The low adsorption capacity makes the pollutant unable to bind perfectly.Therefore, the pH value is recommended at optimum conditions to maintain the efficiency and effectiveness of the electrocoagulation process.The excess of OH -makes the wastewater in the electrocoagulation process saturated [6,8].The following is the reaction for the formation of Al(OH) - 4 which occurs as a result of alkaline conditions in synthetic wastewater [9]:

Effect off electrocoagulation process with TDS
TDS measurements are conducted to monitor the NaCl content in synthetic textile wastewater.NaCl is easily soluble in water.Changes in TDS values in synthetic wastewater based on variations in flow rate and current strength can be seen in Figure 6.The addition of NaCl to synthetic wastewater aims to increase electrical conductivity in the electrocoagulation process.NaCl in solution form has the ability to transfer electrons, make electrical conductivity maintained during the electrocoagulation process.Therefore, it is expected that the TDS value in synthetic wastewater has a value which is not too far away every minute [10].Furthermore, the addition of NaCl can help in removing pollutant levels.Research which had conducted by Dalvand et al [11] showed that with a voltage value of 20 A, a colour concentration of 50 mg/L and NaCl as an electrolyte solution with concentrations of 0.25 mM, 0.5 mM, and 1 mM, they are able to remove colour pollutants 99.45%, 99.95% and 100% respectively in waste with optimum pH.It is due to an increase in the production of hypochlorite ions at the anode as a result of NaCl in the solution, which can increase the reduction of dye through oxidation of dye molecules.
There is a decrease in the TDS value between the initial TDS value and the final TDS value.However, it is not too significant.It is due to the low voltage supplied to the system [12].The resulting low voltage comes from a strong current source which is varied in this study.

Removal of colour in electrocoagulation process
Colour characteristic of synthetic wastewater caused by Remazol Black B dyes with concentration of 100 mg/L.Meanwhile in textile industry, the appearance of colour occurs due washing process of fabric during refinement process.Excess dyes on fabric will fade, making the treated water in process has the same colour as fabric being produced.Changes in colour removal efficiency in synthetic wastewater based on variations in flow rate and current strength can be seen in Figure 7 Figure 7 shows that the highest percentage of removal at a concentration of 10 mg/L is at a flow rate of 2 L/min with a current of 20 A of 88.78%.The percentage graph in Figure 7 with the same current strength shows that the smaller the flow rate, the higher the resulting colour removal.Hendaoui et al [6] stated that an increase in wastewater flow rate has the potential to reduce the efficiency of pollutant removal.It is due to the relatively short electrolysis time so that pollutants have not been removed optimally.The results show that with variations in flow rate from 1 -3 L/min, the removal value decreased from 91.62% to 75.13% at neutral pH.In addition, the results of research which had conducted by Garajehdaghi and Seyyedi [13] show that with variations in flow rate from 1.7 to 2.4 L/min, the colour removal value decreases from the original 98.73% to 68.53% at neutral pH.Variation of electric current strength is a consideration to support pollutant removal by increasing the electric current strength, the rate of release of aluminium metal ions at the anode will increase.Furthermore, the increase in metal ions at the anode causes an increase in the amount of metal hydroxide floc.Floc as a pollutant binder will help the process of removing pollutants.Figure 7 shows that the higher the electric current, the higher the colour removal obtained.It is relevant to the results of research which had conducted by Lestari and Agung [14] showed that at a current strength of 2.5 A it has an efficiency of 88.51%, while at a current of 0.5 A it has an efficiency of 35%.Therefore, it means that the higher the current strength, the higher the colour removal obtained.However, if sufficient floc conditions are available in the wastewater, the increase in electric current will not be optimal since it is already saturated so that it cannot increase the percentage of colour removal [1,4].Furthermore, Aromatic compounds in Remazol Black B dye have an important role as colour formers.Its components consist of 2 main groups that are chromophore and auxochrome.A chromophore as a colour giver; for example, is an azo group (R-N=N-R).Meanwhile, auxochromes contain groups which are capable of forming covalent bonds during the dyeing process; for example, amine groups (-NH2) and hydroxyl groups (-OH).In addition, the bond in the auxochrome group can be broken as a result of an electrochemical process so that it can bind to the coagulant and a decrease in the dye occurs.Meanwhile, the colour can disappear quickly since the chromophore groups in the dye structure are fragmented [9,15].

Removal of COD in electrocoagulation process
Remazol is a synthetic material made by humans as a dye for textile products.The concentration of organic matter in remazol dyes comes from the organic matter components contained in the dyes.In the textile industry, organic matter is caused by the presence of several other materials which support the manufacture of textile products and processes; such as, fixing colours on fabrics and washing textile fabrics.Changes in removal efficiency of COD in synthetic wastewater based on variations in flow rate and current strength can be seen in Figure 8.In Figure 8, the highest percentage of COD removal for a colour concentration of 10 mg/L is found in all variations of flow rate and current strength with a percentage of 100%.Furthermore, the percentage of removal has a significant difference when compared to the research which had conducted by Fajardo et al [9], with current densities of 4 mA/cm 2 and 16 mA/cm 2 , COD removal after the electrocoagulation process is conducted for 120 minutes in order to process dye synthetic remazol waste reached 40%.
It is because at a colour concentration of 10 mg/L, the initial concentration of COD also has a very low value with an average of 17.99 mg/L.Therefore, when the electrocoagulation process is in progress it produces a very small COD value and it is not readable on spectrophotometry.Moreover, another possibility is that when measuring parameters, the COD which is measured is dissolved COD, resulting in a very small COD value when compared to the total COD.The graph in Figure 7 shows the increase in the percentage of removal every minute.At a flow rate of 2 -4 L/min with the same current strength, it shows that the lower the flow rate at a certain minute, the higher the percentage of removal.It also occurred in the study which had conducted by Hendaoui et al [8] with flow rate variations of 1 -3 L/min, the COD removal value decreases from 82.16% to 62.07% at neutral pH.Furthermore, at the same flow rate and lower current strength, Figure 7 (b) and (c) still shows a percentage of removal at certain minutes.It is relevant to the results of research which had conducted by Lestari and Agung [14] which showed a current strength of 2.5 A has an efficiency of 83.33%.Meanwhile, at a current of 0.5 A it has an efficiency of 48.66%.Therefore, it shows that the higher the current, the higher the COD removal obtained.

Conclusion
Result of this study showed the optimum of current strength and flowrate for electrocoagulation process in the recirculation batch reactor were 20 A and 2 L/min.The removal percentage of colour and COD were 88.78% and 100%.The pH was likely in the range of 11-11.4,whereas total dissolved solid fluctuated but not too far (i.e., 1785 -1902 mg/L).By increasing electric current strength and decreasing the flowrate, it has potential to increase efficiency of pollutants removal.

Figure 2 .
Figure 2. Aluminium anode Figure 3. Iron cathode 2.3.Experimental Procedure This study aims to analysis effect of flow rate with current strength and determine the optimum condition of electrocoagulation process in the recirculation batch for synthetic textile wastewater treatment.Various flow rate in this study were 2 L/min, 3 L/min, dan 4 L/min, meanwhile for current strength were 10 A, 15 A, dan 20 A. Based on Figure 4, synthetic textile wastewater flowed using submersible pump into reactor from feed tank for 20 minutes.Synthetic textile wastewater sample were taken within minutes: 2, 5, 8, 10, 15 dan 20.