Reuse of dye effluents into the fresh batch dyeing with the variation of chemical and dye percentages

Objectives: To study the reuse of dye effluents in order to minimize the dyeing cost.Methodology: In this study, the exhausted dye effluents were reused into 7 new dyeing baths along with 7 different percentages of dyes and chemicals to evaluate the color fastness properties as well as shade difference. Firstly, the exhausted dye effluents were collected from the dye bath of the standard sample after dyeing was completed. Then respectively added extra 80%, 70%, 60%, 50%, 40%, 20% and 0% of the dyes and chemicals in the 7 different new baths where dye effluents of standard sample dyeing existed. After dyeing, all the 7 samples were collected and tested with ISO methods for the assessment of color fastness toWash and color fastness to Rubbing.Moreover, all the samples were analyzed against the standard one with the help of a Spectrophotometer. Findings: From the overall testing reports, it had found that color fastness to wash and rubbing were satisfactory for all samples. But the CMC decision revealed that the sample which was treated alongwith the presence of an extra 80% dyes and chemicals in dye effluents showed minimum shade difference from the standard sample. So, it can be said that about 20% of dyes and chemicals can be saved by reusing dye effluents which can largely influence not only the environmental issues but also the cost-effectiveness of dyeing industries.


Introduction
In the traditional way of dyeing in textile industries, there were few approaches to environmental safety measures. Effluents from industries were discharged in the water sources. These obnoxious steps lead us to a disastrous consequence in today's earth. In this crisis, we need to focus on 3R principles i.e. Reduce, Reuse and Recycle through which sustainable movements in the manufacturing sectors will be accomplished.
Reuse of dye effluents in further dyeing process can make a tremendous turn in the dyeing industries, having a concern in mind about environmental risks along with minimization of dyeing cost. In this era of climatic climax, sustainable approaches for the development of textile processing are necessary for our future environment. Raising concern about sustainability through the recycling methods of effluents in textile manufacturing processes has become a buzzword in this climacteric situation of the world. Besides, the level of underground water is decreasing day by day due to use of this source at a large scale in the textile industry. Amidst all of the textile manufacturing industries, dyeing mills are the most water-consuming sector (1) . As this is the area of huge water consumption, it already made itself a reason for the water pollution by emitting all the pollutants, chemicals, dyeing liquor, etc. in the environment (2) . Along with high pH, temperature, BOD, COD, TDS, and TSS, exhausted textile effluents are usually colored. In the fabric coloration process because of using various dyes and pigments, dye molecules are permeated to the discharged effluents (3) . For marine lives, this discharged wastewater will be liable for creating an austere mess. Due to having a complex molecular structure in the dye molecules & a synthetic source, they become more stable and harder to be biodegraded in the environment (4,5) .
At first sight, the fascination of any fabric is color. Even though having an excellent composition, it is figured to be a failure as a commercial product if that is colored in an unsuitable way (6) . From ancient times people extracted dyes from natural substances and dyed with that (7) . But due to poor wash & colorfastness properties, those processes did not become popular (8) . In 1856, W. H. Perkins discovered synthetic dyes that have scattered a variety of dyes which are colorfast in nature and appear in not only a wide range of color but also brighter shades (9) . And by this sequence, many types of synthetic dyes had been invented and developed while some dyes are difficult to biodegrade; particularly the hydrolyzed reactive and certain acidic dyes are not readily absorbed by active sludge. Within all textile fibers, cotton fibers are nearly 48% that gets used for clothing all over the world and with reactive dyes, 20% of those are dyed (10) .
More than 85% of redundant matter can be removed by a certain combination of various effluent treatment methods (11) . As textile industries use a large amount of water, eventually they generate high wastewater and generate risky effluents for human health. Because of the diversification of products, the textile industry has a range of subsidiary industries with operations and processes (12) . For dyeing 1kg of cotton fabric, around 110 liters of water is required and consequently a textile mill in which the capacity could be only 8 tons/day and a consumption of about 1.6 million liters of water per day (13) . It is also roughly calculated that to process one meter of cloth, 12-65 liters of water are needed. To develop a cotton T-shirt, it requires 257 gallons of water (14) . Because of heavily charged with unconsumed dyes, this exhausts the effluent from textile industries, it becomes alarming for human life as well as very dangerous for aquatic life (15) . It is perceived that from different textile mills massive quantity of wastewater is discharged on a daily basis (16) .
In the recent days, for industrial air and water pollution, public concern is approaching notable restrictions on all industrial activities which are polluting our environment (17) . As soon as possible, it is needed to diminish the growth of consumption from fossil fuels, water, and energy and reduce the use of these natural resources. Wastewater and output to the environment from production should be lessened in volume which also decreases the negative impact on the environment (18) .
In this project, reuse of dye effluents has been done and an effective result has been obtained. By the result of this study, a statement can be developed that without using ETP or WTP, we can partially recycle the wastewater from the dyeing bath and it can save around 20% of the dyeing cost in the dyeing industry.

Fabric
Single jersey 100% cotton knitted fabric, the fabric weight per unit area was 150 g/m 2 and collected from Ambia Knitting and Dyeing Ltd., Chittagong, Bangladesh.

Sample preparation
The scoured and bleached fabric was collected from the mill. From that fabric 14 pieces of sample had been cut off for our experiment where the weight of each sample was 10gm. 1% stock solution of dyes and chemicals had been prepared. Dyes, chemicals, and fabric samples were weighted by using the digital electrical weight balance. Then the actual part of the experiment was started. By considering 2 Slots, 14 samples had been taken for this experiment. Firstly 7 samples (Batch-1 to Batch-7) were dyed with an ideal reactive dyeing recipe mentioned in Table 2.
After dyeing, dye effluents were collected from every batch and all samples were firstly washed with water then treated with acetic acid followed by soaping as mentioned in Table 2. Finally, the samples were squeezed and then dried in the oven dryer machine at 120 • C for 5 minutes.

Dyeing and after treatment process of Batch-A to Batch-G
Batch-A, Batch-B, Batch-C, Batch-D, Batch-E, Batch-F, and Batch-G had been prepared by using those dye effluents of Slot-1 and added extra 0% (Batch-A), 20% (Batch-B), 40% (Batch-C), 50% (Batch-D), 60% (Batch-E), 70% (Batch-F) and 80% (Batch-G) dyes and chemicals into all the batches of Slot-2. Here dyeing and after treatment parameters (Time, Temperature and ratio M: L) were carefully maintained as per standard sample treatment.         From Table 11, it is shown that the change in color due to wash is the same for all samples. But for color staining, there was a slightly better result for Batch A and Batch B in case of cotton fibre. These have happened because the low concentration dyes and chemicals were used for those batches, one consumes 0% extra dyes and another is 20%. Lower the dye uptake %, lower the possibility of color staining. Table 12 shows that the dry rubbing fastness of all samples is the same. But in case of wet rubbing, there was a slightly better result for Batch A and Batch B rather than other batches because they are a lighter shade among them and have a tendency to give better rubbing fastness.    Table 13, it is shown that Batch A exhibits higher color difference and this color difference gradually reduced for Batch B to Batch G. This has happened due to the addition of extra dyes and chemicals. But, only Batch G showed the color difference in the tolerable range as DE is less than 1. From the overall experimented assessments and results, it is visible that Batch G shows an impressive https://www.indjst.org/ result. It shows an excellent grey scale rating of color fastness to wash and rubbing. Moreover, the color difference value of Batch G (DE=0.83) is in the acceptable range.

Assessment of color fastness to rubbing
So, under the above circumstances, a final statement can be declared that not only effluents can be reused but also with using the effluents, same shade of certain color can be achieved by saving a maximum 20% of dyes and chemicals which also saves dyeing costs and can be less hazardous for our environment as well as the water source.

Conclusion
In this study, dye effluents had been successfully reused and 20% of dyes and chemicals were saved with a better-quality product. This experiment can be a great turn in the field of textile wet processing as well as the individuals who have a deep concern about water and chemical consumption. Looking forward to a green world, we have to be more conscious about our surroundings and not to avoid any of the elements that can be reused.