chapter i introduction 1.1. background...

Chapter I Introduction

PSG College of Arts and Science

1.1. Background information

The textile industry involves a wide range of raw materials, machineries and

processes to engineer the required shape and properties of the final products. Indigo dyes are

used by a wide number of industries, while textile mills predominantly use them. Today

denim is the basis of the Indian fashion industry in many cases. It is a challenging dye to use

because of its insoluble nature in water; to be dissolved; it must undergo a chemical change

under high alkaline condition. When a submerged fabric is removed from the dyebath, the

indigo quickly combines with oxygen in the air and reverts to its insoluble form producing

color on the fabric. This textile chain begins with the production of raw fiber continues with

pretreatment, dyeing, finishing, printing, coating, and other processes. Among these

processes, dyeing and finishing are major water consuming processes that generate highly

polluted effluents.

1.2. Problem statement

The textile industry is one of the oldest and largest sectors in India. At present it is

amongst the top foreign exchange earning industries for India. The textile units are scattered

all over India, out of 21,076 units, Tamil Nadu alone has 5285 units. The textile industry

involves processing or converting raw material into finished cloth employing various

operations. Dyeing, desizing and scouring are the major sources of water pollution in textile

effluent and it consume large quantities of water and produces polluting waste effluents.

Tirupur and Coimbatore are well known for its hosiery and knitwear industries and its

annual exports of these items are worth over US$ 550 million. According to records of the

Tamil Nadu State Pollution Control Board (TNPCB), there are 830 units engaged in textile

industry processes in Tirupur. Available studies clearly prove the accumulation effect of

pollution in this area. The available groundwater in this region is not suitable for domestic,

industrial or irrigation use.

Dyes in water bodies also affect photosynthetic organisms and consequently impact

negatively on the food chain. The reason for this global effect also lies in the weather

systems and the biogeochemical cycling of elements, which aid in rapid dispersal of the

pollutants.The dyeing step in the textile production has the largest risk on the environment

due to high concentrations of organic dyes, additives and salts used. Therefore, among the

processes applied in the textile industry, dyeing process wastewater should be dealt with

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seriously. The problem of disposal of textile wastes is likely to become serious in the days

ahead the possibility of affecting the groundwater. Most of the time, this process constitutes

the major part of the water consumption and generates wastewater distinguished by high

chemical oxygen demand (COD), high dissolved and suspended solids, and also high color

contents. Thus, dyeing wastewaters originating from rinsing operations are great candidates

for recovery and reuse. The stringent environmental regulations for discharge today and the

scarcity of the water resources are forcing the textile manufacturers to assess the potential

for reuse of water by innovative technologies (Reife, 1993).

Many of the conventional and even advanced treatment technologies suffer the

limitation of not being able to treat highly colored wastewaters from textile manufacturing

(Nigam et al., 1996). But one of the main drawbacks of these treatments is their high energy

costs and low efficiency in degrading the dye stuffs. Many industries generate large

quantities of sludge, the safe disposal of which is major problem. The sludge is generated

during clearing of storage tanks, cleaning and desalting of separator basins, distillation

column residues, exchanger tube bundle sludge and sludge generated from effluent

treatment plant. In some studies on membrane treatment of denim textile mill effluents for

reuse, the wastewater was directly filtered after a pretreatment to remove only coarse

particles to reduce membrane fouling and this problem has not yet been solved. An

alternative method of sludge management involves the use of microorganisms for in situ

degradation in the soil. The process called bioremediation is eco-friendly and more cost

effective compared to conventional methods.

A consortium of denim sludge degrading bacteria was developed in our laboratory to

expedite the rate of bioremediation in contaminated soil. Now the recent approaches in

microbiological as well as biotechnological are the most effective for the bioremediation

process of different textile wastewater. Bioremediation has been successfully applied for

cleanup of soil, surface water, groundwater, sediments and ecosystem restoration. It has

been unequivocally demonstrated that a number of xenobiotics can be cleaned up through

bioremediation. In biofilm, the microbial cells are enclosed in a self-produced polymeric

matrix adhering to a surface. It includes films of cells at a solid/ liquid interface and cells

that adhere to themselves in the form of floc, granule or pellicle. Biofilms can be composed

of either single or multiple species. It provides the benefit of a stable environment for the




enclosed microbes, which makes them such a prolific and widespread phenomenon in

nature.

The aim of present study involves the screening of potent adapted bacterial strains

from the denim industry wastewater. These strains were allowed to form a biofilm on an

inert substrate like the polyurethane foam (PUF) and retain the ability to efficiently degrade

H-chromophore of indigo dye in several optimum conditions and to check their efficiency in

industrial scale.

1.3. Objectives

The main objectives of the present studyfocuses on the biodecolorization and degradation of

indigo dye containing denim industrial effluent using immobilized adapted bacterial

consortium under different operational parameters.

The most specific objectives of the work as follows,

To evaluate the biofilm formation potential of screened adapted bacterial strains and also

to understand the attachment efficiency and dissimilatory role of microbial enzymes on

poly urethane matrix.

To optimize the cultural conditions for the maximum biodegradation ability on inert PU

foam immobilized adapted bacterial cells.

To experiment on indigo dye interaction with potent amino acid together with 3D

theoretical analysis of molecular docking.

To formulate the biodegradation efficiency of immobilized cells by adsorption

isothermal kinetics and Ghill shooting method of mathematical modeling.

To investigate on the efficiency of lab and large scale treatment trials on the toxic

pollutants from denim textile wastewater.




1.4. Thesis overview

This thesis includes five chapters. Chapter 1 (Introduction) presents a brief

description of Denim textile industry along with a very brief description of indigo dyeing

wastewater problem. This chapter also introduces the objectives of the study. In Chapter 2

(Literature Review), a brief description of textile manufacturing process and also the

importance of textile industry for Tirupur district, Tamil Nadu, India are given. Also

presented in this chapter is the integrated wastewater management concept. Chapter 3

(Experimental Methods) details the different methods can be used for screened adapted

bacterial strains were immobilized onto PU foam cubes and various treatment trials also

study the approach. Chapter 4 (Results and Discussion) evaluates the applicability of PUF

immobilized cells as efficient bioremediation than other treatment trials. Finally, Chapter 5

(Conclusions) summarizes the main conclusions of the present study and also the

recommendations.


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