Biodegradation of Textile Wastewater by an
Advanced Activated Sludge Process

By Dr. A. Mary Saral*, M. Sachidhanandam, P. Saravana Kumar
September 2006

The Authors are Research Scholars at the School of Science and Humanities, Chemistry Division of Vellore Institute of Technology in Tamil Nadu, India.

The Biodegradation of textile wastewater from Maruti textile industry of Vellore district has been carried out aerobically. An advance process, Submerged Aerated Fixed Film Reactor (SAFF) has been introduced in this present study. As far as the organic content of textile waste water is concerned, the aerobic biological activated sludge process at pH 6.0-9.0 is one of the most economic purification processes. It focuses on conventional activated sludge processes targeting removal of carbonaceous biochemical oxygen demand (BOD). The quality of raw and treated effluents from Maruti textile industry of Vellore district was assessed in respect to BOD (Biological Oxygen Demand) and COD (Chemical Oxygen Demand). Before the treatment, both parameters were found to be beyond the permissible limits. After the treatment it is found to be decrease in very much. There is remarkable decrease in BOD and COD. The pH does not make any significant in this study.

Keywords: Textile Effluent; Activated sludge process; SAFF;


Rapid industrialization and growth of population has led to the problems of environmental pollution, especially of the aquatic environment with a multitude of contaminants. Among all the pollutants (contaminants), colour appears to have a wide impact on various segments of the environment and has its origin due mostly, to the partially / untreated effluents generated from industries like dye manufacturing, textile, pulp and paper production, tanneries, chemical production, paints, varnishes and a host of others. Of these, textile dye effluents are the major contributors of the colour to the receiving water bodies. Discharge of untreated dye effluents not only impact colour to the receiving water but also interferes with its intended beneficial use.

Development of effective treatment technology for colour removal from dye wastes has been rather baffling. This is primarily due to their diverse and continuously changing character, complex chemical nature, persistent colour, inhibitory and non-biodegradable nature and toxicity.

Literature reveals conflicting findings concerning the capability of textile waste treatment processes such as physical, physicochemical, chemical and biological. Textile waster water treatment by physical processes is found to be negligible; various physicochemical processes, viz, chemical coagulation, chemical oxidation, adsorption and ion exchange etc., have been found to be high cost for treating textile dye wastes. Biological treatment methods are cheap and offer the best alternative with proper analysis and environmental control. Most reported treatment of dye waste has been achieved with activated sludge plants. When activated sludge is compared with biological filtters, the lower capital cost of the activated sludge plant and the the opportunities for extended treatment and control outweigh the higher operating costs and sensitivity to shock loads. There can also be technical advantages (Forster, 1977). Michaels and White (1978) showed that conventional biological treatment plants reduce BOD. Dyes can be adsorbed onto activated sludge solids; however (Hitz et al., 1978; Dohanyos et al., 1978). The mineralization or complete biodegradation of an organic molecule in water is always a consequence of microbial activity (Alexander, 1980).

The Maruti Textile Company considered in this study is basically a finishing plant where coloring works are processed for weaving. Dyes used in the plant are mainly reactive, Vat, Acid and Basic dyes. This study has been initiated of a major monitoring program with the following specific objectives:

  1. Characterization of wastewater from the textile finishing plant;
  2. Establishment of the treat ability parameters of textile effluents; and
  3. Assessment of alternative for the treatment of textile wastewater.

Materials and Methods

Laboratory experiment was performed at room temperature (25-30 Celsius) in experimental unit for activated sludge process. An advance process Submerged Aerated Fixed Film Reactor (SAFF) has been developed to overcome various operational difficulties arising during the operation of conventional activated sludge process. A schematic of the experimental system is illustrated in figure 1.

Figure 1
Figure 1

Submerged Aerated Fixed Film Reactor (SAFF) unit

A three compartment rectangular unit made of plexiglass used for continuous-flow studies. The unit is 135 cm long and 30 cm wide. The depth of the unit is 60 cm. The liquid depth in the unit reaches 50 cm though inlet and outlet pipes provided at the level. This SAFF reactor is mainly based on the principle of „ATTACHED GROWTH PROCESS” and comprises mainly of following components which includes:

  1. PLASTIC MEDIA – which provides surface area for the micro-organisms to grow
  2. DIFFUSED AERATION SYSTEM – Membrane type air diffusers are provided to ensure high oxygen transfer efficiency to fulfill from oxygen demand exerted by micro-organisms.
  3. BAFFLES – To facilitate smooth flow of effluent from one compartment to another.

Experimental procedure

The organic matter present in the waster water is degraded by a population of micro-organisms attached to the plastic media. Organic matter from the liquid is adsorbed onto the biological film (Slime) developed on the media. This biological film contains aerobic, anaerobic and facultative bacteria, fungi, algae and protozoan which are responsible for degradation of organic matter in the effluent. As waste water passes though SAFF reactor, nutrients and oxygen diffuse into the slime, where assimilation occurs and byproducts and CO2 diffuse out of the slime into the flowing liquid. As oxygen diffuses into the biological film, it is consumed by microbial respiration, so that defined depth of aerobic activity is developed. Slime below this depth is anaerobic.

As the slime layer increase in thickness, the adsorbed organic matter is metabolized before it can reach the micro-organisms near the bio-reactor media face. As a result of having no external organic source available, bacteria near the media face enters into an endogenous phase of growth (i.e. Micro-organisms starts consuming organic matter of their own cells and of other cells) and lose their ability to get attach to the media surface. The liquid then washes the slime off the media and new slime layer starts to grow.

Results and Discussion

Table 1   Characteristics of Raw Effluent
Month pH BOD COD
January 8.10 162.3 732.3
February 7.95 154.3 728.0
March 7.98 146.0 451.6
April 7.91 133.1 632.6
May 7.97 138.6 724.3
June 7.95 128.6 814.7
July 8.12 115.7 764.6
August 8.08 132.3 762.3
Table 2   Characteristics of Treated Effluent
Month pH BOD COD
January 7.71 15.2 78.5
February 7.82 13.7 92.4
March 7.68 11.4 110.1
April 7.84 14.8 88.5
May 7.80 9.4 79.4
June 7.63 12.7 92.7
July 7.92 13.6 82.4
August 7.81 11.8 68.3
Table 3   Characteristics of Permissible Limits (ISI:2490 1982)
S. No Parameters Permissible limits (mg/L)
1 pH 5.5 to 9.0
2 BOD 30
3 COD 250

As per the results given in the table 1, the average values of raw effluent parameters (BOD & COD) present in larger amount on comparing with permissible limits of ISI: 2490: 1982 standard (Table 3). It has been shown in the figure 2. In general, the higher the BOD, the water sample is most polluted. The more oxygen consumed by micro-organisms in degrading organic compounds and organic pollutants may contribute towards objectionable odor and taste of drinking water. As per results given in the table 2, the average values of treated effluent parameters (BOD & COD) present in smaller amount on comparing with permissible limits of ISI: 2490: 1982 standard (Table 3). It has been shown in the figures 3. BOD and COD could be reduced more than 85 %.

Figure 2
Characteristics of Raw Effluent BOD & COD
Figure 2

Figure 3
Characteristics of Treated Effluent BOD & COD
Figure 3


The characteristics of the textile wastewaters collected from the Maruti Textile plant are typical of industrial wastes. Daily variations n these characteristics were reasonable during the period of study. Activated sludge treatment was demonstrated to be a variable means of effective treatment of textile waste waters. The performance of the activated sludge system for treating textile wastewater could be improved by the application of lower organic loadings (0.1-0.2 Kg BOD5 / Kg MLSS / day).


We express our deep and profound sense of gratitude to Vellore Institute of Technology, for providing the necessary facilities throughout this work.


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