Treatment Of Textile Industry Effluent Using Multilayer Thin Films

Treatment Of Textile Industry Effluent Using Multilayer Thin Films

M. Geetha Devi1*, Khadija Ali Said Al Omairi2, S. Feroz3, Syed Murtuza Ali4

1,2,3,4 Department of Mechanical and Industrial Engineering, Caledonian College of Engineering, Sultanate of Oman

Abstract

In this work, investigation of possible use of multilayer nano thin films in the treatment of textile industry effluent and to optimize the processing conditions required to remove the pollutants has been reported. Multilayer thin films were fabricated by alternate adsorption of Chitosan and titanium dioxide on glass substrate. Various experiments have been carried out to study the effect of the treatment conditions such as pH, contact time, number of bilayers and initial dye concentration. The results indicated that optimum conditions obtained are at a pH of 2, a contact time of 90 minutes with an initial dye concentration of 60 ppm for 6 bilayers. The experimental investigation showed that layer-by-layer nano films could effectively reduce contaminants such as Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Total Solids (TS) and Turbidity.

Keywords: Adsorption, chemical oxygen demand, layer-by-layer, polyelectrolytes, textile mill effluent, thin films.

1. Introduction

   Rapid industrialization throughout the developing countries has created generation of toxic pollutants discharged in to the aqueous streams, that are harmful to the human and environment. The major concern is the presence of different types of contaminants that are not adequately removed by conventional water treatment technologies.

   The existing ecosystem need protection and new water resources must be developed in order to meet the worlds growing demand for clean water. This will require efficient and economic water treatment technology. Photo catalysis using semiconductor materials like TiO2, ZnO, Fe2O3, CdS, and ZnS finds wider application in waste water treatment as advanced oxidation technology. Among these catalysts, TiO2 is superior due to its availability, stability, low cost, and favorable band gap energy. Although the use of suspended TiO2 powder is efficient because of the large surface area of catalyst available for reaction, but the main drawback is that the catalyst cannot be recovered and reused efficiently and the process is economically not viable.

   One of the largest pollution causing industry in the world is the textile industry. Textile industries consume large quantities of water and discharges highly polluted effluent water to the environment. A typical textile

   industry effluent is characterized by high value of suspended solids, dissolved organic matters, chemical oxygen demand, biological oxygen demand, colour and turbidity. The discharge of untreated polluted water can cause depletion of dissolved oxygen in the water sources and could pose a risk to public health. High alkalinity and trace amounts of chromium can adversely affects the aquatic environment. Due to environmental constraints, it is necessary to adopt a sustainable approach to recover valuable resources such as water and chemicals. Conventional treatment methods are not very effective in the removal of pollutants such as colour, dissolved solids, suspended solids etc.

   Advanced treatment methods are effective due to the pollution removal efficiency and also to provide a scope for recovery of valuable chemicals.The conventional treatment methods include biological treatment, chemical oxidation, coagulation and flocculation methods, membrane technologies, adsorption etc [1- 7]. Biological methods are cheap and simple with high COD removal efficiency but the disadvantages of this process is complete removal of colour is not possible.

   Various experiments have been conducted on treatment of textile wastewater to minimize total suspended solids (TSS), chemical oxygen demand (COD), total dissolved solids (TDS) and turbidity [8- 19]. Coagulation and flocculation methods are effective on dye removal, but the main drawbacks of these methods are high cost, and generation of large amounts of mud [20-26]. The main objectives of the waste water treatment methods include reuse of treated water, save environment and to protect the public from health risks.

   In order to minimize environmental pollution and to protect our environment we have explored the possibility of using multilayer nano thin films in the treatment of textile industry effluent using Chitosan and TiO2 by layer- by- layer method.

   Chitosan is a natural biodegradable polymer made from shrimp or crab shell after deacetylation and purification. Chitosan is inexpensive, nontoxic and stable. Our earlier studies very well shows the application of chitosan in the treatment of waste water from vegetable oil mill [27], dairy [28] industry effluent and heavy metal [29] industries.

   The advantages of multilayer thin films by layer- by- layer method are control of film thickness by nanometre precision, possibility to use a wide variety of substrates differing in size, shape and geometry.

   The research was carried out in Muscat, Sultanate of Oman and the effluent was collected from a leading textile mill in Oman.

2. Experimental section

   High molecular weight Chitosan (MW = 650 kDa), and TiO2 (21 nm Degussa AG, Germany) are purchased from Sigma Aldrich, India. 0.1 N NaOH and 0.1 N HCl are used for pH adjustment. Millipore water (18.2M resistivity) was used in all experiments. To ensure the accuracy, reliability and reproducibility of the collected data, all the batch experiments were carried out in triplicate and the mean values of three data sets were presented.

   Investigations were carried out with the effluent before and after treatment. The waste water sample was collected from the outlet of an equalization tank in a textile industry in the sultanate of Oman. The effluent samples are allowed to settle before characterization. The samples are preserved at 40C in order to avoid bacterial action. The main parameters studied are COD, TS, TSS, and Turbidity. COD measurements were performed by calorimetric method using spectrophotometer (AQ 400, thermo Scientific Orion

   and Thermo Reactor Orion COD 125). Turbidity was measured by Turbidity meter (WTW Turb 550).

   The percentage removal efficiency was calculated by

   C0 C1

   Polyelectrolyte multilayers were fabricated by dipping the clean glass slides into polymer solution of opposite charge (Chitosan) for 20 minutes. After adsorption the excess polymer is removed by washing with water. Then next layer is coated with TiO2. This procedure is repeated till the desired number of layers is obtained. In all the dipping processes the adsorption time is kept constant. The coated slides are dried and kept ready for the effluent treatment. The whole sequence of the film deposition procedure was repeated till 8 bilayers are obtained. Each bilayers deposition was completed within 50 minutes.

   1. Effect of pH

      Effluent samples are prepared at different pH values ranging from 2 to 9 in order to determine the optimum removal efficiency. Coated slides are immersed into a beaker containing 500 ml of effluent sample and exposed to sunlight for a specified time and the samples are filtered and used for analysis.

   2. Effect of Contact time

      The effect of variation of contact time on reduction of parameters was studied by varying the contact time between 20 minutes to 140 minutes keeping all other parameters constant.

   3. Effect of number of bilayers

   The effect of variation of parameters with numbr of layers was studied by varying the number of

   % removal efficiency =

   C0

   × 100 (1)

   assembling layers from 1 bilayer to 8 bilayers.

   2.4. Effect of Initial Dye concentration

   Where, C0 and C1 are the initial and final concentrations in mg/l respectively.

   The effluent concentrations of COD, TSS, TS, and Turbidity are analysed according to standard methods [30].

   2.2. Fabrication of multilayer thin films

   Multilayer thin films are fabricated on glass slide by layer- by – layer method [31]. The fabrication of thin films using Layer by- Layer (L-b-L) method is used to deposit various materials on different types and shapes of substrates using adsorption technique. The catalyst used for the treatment was TiO2.

   The initial concentration of effluent was varied from 10 ppm to 90 ppm, while keeping other parameters constant (pH 2, contact time 90 minutes)

3. Results and discussion

   1. Effect of pH

      Effect of initial effluent pH was studied by varying the solution pH from 2 to 9. The coated slides are dipped into the effluent solution and exposed to sun light for 90 minutes.

      The maximum reduction in COD was noted at a pH of

      2 and the maximum TSS removal efficiency was achieved at the same pH. The optimum reduction

      occurred at pH 2 are due to the higher surface charge density of the surface and at this pH maximum ion transfer will take place, which will facilitate increase in efficiency. As the pH is above 2, the number of available sites decreased thus results in less adsorption and hence decreases in efficiency. The effect of percent reduction in parameters with different pH values are presented in Figure 1.

      90

      In order to study the effect of variation of number of layers on reduction of parameters, the number of assembling layers is varied from 1 to 8. The experimental results are indicated in Figure 3. The percentage reduction in COD increased with increase in number of layers up to 6 bilayers after which there is no significant reduction in COD. Reduction in turbidity and TSS also increased with increase in number of bilayers whereas the percentage reduction in TDS decreased with increase in number of bilayers.

      % Reduction in COD

      80

      80

      % Reduction in TDS

      % Reduction in parameters

      % Reduction in parameters

      % Reduction in TS

      % Reduction in Turbidity

      70

      60

      50

      40

      30

      20

      1 2 3 4 5 6 7 8 9 10

      pH

      Fig 1. Effect of pH

   2. Effect of Contact time

      The effect of variation of contact time on reduction of parameters was studied by varying the contact time between 20 minutes to 140 minutes at an optimum pH of 2. The percentage reduction in COD and TDS occurred at 90 minutes after that it shows a decreasing trend. The percentage reduction in TDS increased with increase in time, up to 90 minutes after which there is a decreasing trend. The percentage reduction in turbidity decreased with increase in contact time. Figure 2 shows the effect of variation of exposure time with parameter reductions.

      90

      % Reduction in parameters

      % Reduction in parameters

      80

      70

      60

      50

      40

      30 % Reduction in COD

      % Reduction in TDS

      20 % Reduction in TS

      % Reduction in Turbidity

      0 1 2 3 4 5 6 7 8 9

      Number of bilayers

      Fig 3. Effect of number of bilayers

   3. Effect of initial concentration

   The effect of variation of initial effluent concentration with parameter reduction was studied and the results are represented in Figure 4. It is seen that the percentage reduction in parameters increased with increase in initial dye concentration up to 60 ppm and above which there was no significant change in percentage reduction in parameters.

   80

   % reduction in parameters

   % reduction in parameters

   90 70

   % reduction in parameters

   % reduction in parameters

   80

   % Reduction in COD

   70 % Reduction in TDS

   % Reduction in TS

   % Reduction in Turbidity

   60

   50

   40

   30

   60

   50

   40

   30 % Reduction in COD

   % Reduction in TDS

   20 % Reduction in TS

   % Reduction in Turbidity

   0 10 20 30 40 50 60 70 80 90

   Initial dye concentration, ppm

   20 40 60 80 100 120 140

   Contact time, min

   Fig 2. Effect of contact time

   3.3. Effect of number of bilayers

   Fig 4. Effect of initial dye concentration

4. Conclusion

   Based on the above study it is seen that multilayer thin films fabricated by the L-b-L method finds good scope

   for the treatment of textile industry effluent in an efficient and environmental friendly manner. In this study titanium dioxide acts as a catalyst, which finds wider application due to its easy availability, stability, low cost, large surface area and a good band energy gap. There has been an increasing interest in the fabrication of thin films using Chitosan. Multilayer nano thin films are reported to be one of the most promising technologies for the treatment of textile effluents by saving considerable amount of money.

   Acknowledgements

   The authors express their sincere thanks to Industry Innovation Centre (IIC), for providing the research grant.

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