Effluent treatment plant

1. DEPARTMENT OF TEXTILE ENGINEERING
Course Title: Environmental Pollution & its Control (EPC).
Course Code: Tex-3037.
“Studies on Characterization of Textile Effluent in Bangladesh”
Submitted To:
Guha AK
Southeast University
Department of Textile
Submission Date: 15 Oct, 2012.
Prepared By:
Name: Suman Paul
ID: 2010000400010
Batch: 13th (I)

2. Textile Effluent in Bangladesh
Introduction
Bangladesh is heavily involved in textile production and export. A lot of textile mills were
established in the country mostly in and around Dhaka city in last two decades. A large number
of these mills generate and discharge waste waters. It was reported by the various organization
and monitoring authority that the pollution of the rivers and canals in and around Dhaka is well
above their acceptable level. Various agencies are trying to safeguard the clean environment.
Bangladesh Government has already issued various forms of warning and red alerts to the
concerned industries. A lot of textile wet processing industries have already installed effluent
treatment plants (ETP) and many of them are at various stages of installing ETP's.
Important Pollutants:
Various types of toxicities are found in the textile wastewaters. However in order to monitor
them Department of Environment (DOE) has identified the Biochemical Oxygen Demand
(BOD), Chemical Oxygen Demand(COD), Total Suspended Solids (TSS), Total Dissolved
Solids (TDS), pH, Oils and grease, color and temperature etc. are most harmful for environment.
The polluting parameters of other industries will vary to some extent. Pollutant concentration in
effluents for various textile industries varies significantly.
Sludge:
The settable solids separated from the liquid during sedimentation (clarification). The sludge is
very toxic in nature and needs to be deal with very carefully. Under no circumstances it should
be mix with the environment again.
Picture of sludge cake

3. Sludge tank:
In sludge tank there is a sand filtration system in which 2 feet of sand layer is kept
and above that sand sludge is deposited. At the ground of tank there is a pipe
arrangement with filtration which allows effluent without sludge passing to the collection tank.
This is again treated.
Picture: Sludge tank
Properties of effluent before processing:
1. Impart color to water bodies even if present in small quantity
2. Not harmful but undesirable for aesthetic reason
3. Reduces light penetration and photosynthesis
4. Carcinogenic or mutagenic
5. Azo dyes are more toxic as they affect microbes thereby affecting biological degradation
treatment.
6. Dyes increases BOD of effluent thereby affecting aquatic life.
7. Salts of chromium and aluminum & iron as mordents in dyes
8. Toxic to fish & microbial organisms
9. The discharge of heavy metals into aquatic ecosystems
10. Increase in alkalinity of water
11. The turbidity and color along with oil and scum create an unsightly appearance. The mineral
materials, mostly sodium salts increase salinity of the water.
Effluent’s Character
Wastewater discharged from a textile wet processing plant contains various types of impurities
depending on the type of dyes, chemicals, auxiliaries and process used. Some of these impurities
are considered toxic while some are not. Off course the toxicity or harmfulness also depends on
the amount present in a certain amount of wastewater. Various countries have different standards
for acceptable level of toxicity for various purposes. Different types of water application also
require different level of acceptable toxicity. For example water is used for drinking purposes,
irrigation in the fields, in various types of textile, chemical, food processing, leather processing
and pharmaceutical industries, and also to maintain the aquatic life in the canals and rivers. In all
these cases different level of purity in terms of toxicity and harmfulness is required. This is
mainly intended for wastewater generated in the various textile wet processing industries.
Therefore, the present discussion will mainly be concentrated on waste water generated in

4. various types’ textile-processing industries. Table 1shows the acceptable level of various
parameters of wastewater generated from textile wet processing industry. This is Bangladesh
Standard. The level of toxicity was considered for water intended to be discharged into river or
canals. The wastewater generated in a textile wet processing industry can be recycled back for
consumption in the plant or even can be used for drinking purposes but this is expensive enough.
So wastewater is generally discharged into the river or canals.
Table 2.1: Characteristics of wastewater to be discharged into the environment.(Stipulated by the
Dept. of Environment, Government of Bangladesh)
Parameter Limit
PH
6-9
BOD <50 PPM or mg/L
COD <200 PPM or mg/L
TSS <100 PPM or mg/L
TDS <2500 PPM or mg/L
DO 4.5-8 PPM or mg/L
OIL & GREASE <10 PPM or mg/L
COLOUR <CLEAN
Temperature <30° C
The typical characteristic of wastewater generated in a textile wet possessing plant is
given in table 2.2. Parameters have been referenced about a range rather than a particular
value of the parameters. This is because the characteristics of textile wastewater for
a factory are not always same which may be due to the variation of raw materials,
dyes, chemicals and process. For example a factory sometime process 100% cotton and
sometime process 50/50 cotton & polyester blend or even 100% polyester. The three different
cases will require two different dyes and chemicals of varying quantity. For white
goods no dyes are used at all, in that case too the effluent characteristics will be different from
that of dyeing effluent. For woven (sized) fabrics the effluent characteristics will be different
from that of knit fabrics. The values shown in table 2 are not actual tested values of a
particular industry rather they are average of various anticipated wet processing pollution
characteristics. The values are assumed on the basis of experience about the contaminants
present in a textile wet processing industry.
Table 2: Characteristics of wastewater of a typical textile wet processing industry.
As was mentioned textile wastewater may contain various types of contaminants but in most
cases the toxicity of the above eight parameters are considered important before
discharging them into the environment.

5. Different Characteristics of Effluent
Biochemical Oxygen demand (BOD):
The strength of the wastewater is often determined by measuring the amount of oxygen
consumed by microorganism like bacteria in biodegrading the organic matter. The
measurement is known as the Biochemical Oxygen Demand (BOD). Microorganisms such as
bacteria are responsible for decomposing organic waste. When organic matter such as
dead plants, leaves, grass clippings, cellulose components, manure, sewage, organic
waste like dyes, fats and oils, or even food waste is present in a water supply, the
bacteria will begin the process of breaking down this waste. When this happens, bacteria in
aerobic process, robbing other aquatic organisms of the oxygen they need to live, consume
much of the available dissolved oxygen. If there is a large quantity of organic waste in the
water supply, there will also be a lot of bacteria present working to decompose this waste. In this
case, the demand for oxygen will be high (due to all the bacteria) so the BOD level
will be high. As the waste is consumed or dispersed through the water, BOD levels
will begin to decline. Nitrogen and phosphates in a body of water can also contribute to high
BOD levels.
Chemical Oxygen Demand (COD):
This is a means of measuring the ability of wastewater to sustain aquatic life, essential for the
preservation of the environment. It also enables proper assessment of treatment plant
performance. Aquatic organisms and animals require dissolved oxygen to flourish. The Chemical
Oxygen Demand (COD) test gives an indication of the impact of discharge waters on
aquatic life by measuring the oxygen depleting nature of the discharge water. COD is
based on the fact that nearly all-organic compound scan be fully oxidized to carbon dioxide
with a strong oxidizing agent under acidic condition. COD is another common measure of water-
borne organic substances — the process of measuring COD causes the conversion of all
organic matter into carbon dioxide. For this reason, one limitation of COD is that it
cannot differentiate between biologically active and those which biologically inactive. One major
advantage of COD over BOD is that COD can be measured in just three hours whereas
BOD measurement takes at least five days. The value of COD is always higher than BOD;
this is because BOD accounts for only biodegradable organic compounds while COD accounts
for all organic compounds e.g. biodegradable as well as no biodegradable but chemically
oxidisable.
Total suspended Solids (TSS):
TSS is mainly organic in nature, is visible and can be removed from the wastewater by physical/
mechanical means e.g. screening and sedimentation. TSS is measured by filtering a certain
quantity of effluent and then drying the filtrate at certain temperature e.g. 1050
C
followed by weighing. TSS is expressed as parts per million or in milligram/liter.
The pore size of the filter paper is very important in estimating the TSS, the nominal pore size
1.58 micro metre.
Total Dissolved Solids (TDS):
TDS are the solids that are actually in solution, similar for example to mix sugar into hot coffee.
Dissolved solids generally pass through the system unaffected . TDS is the sum total of

6. all of the dissolved things in a given body of water. It is everything in the water that's not
actually water. It includes hardness, alkalinity, cyanuric acid, chlorides, bromides, sulfates,
silicates, and all manner of organic compounds. Every time we add anything to the water, we
are increasing its TDS. This includes not only sanitizing and pH adjusting chemicals, but also
conditioner, algaecides, and tile and surface cleaners. TDS also includes airborne pollutants and
bather waste as well as dissolved minerals in the fill water. TDS is referred to as the total amount
of mobile charged ions, including minerals, salts or metals dissolved in a given volume of
water, and are expressed in units of mg per unit volume of water (ppm).
Table 1. Textile wastewater analytical results of Chittagong, Narayongonj and other areas.
Areas Number
of
Sample
Sampling
Conditions
Color Odor Temp.(o
C) pH TDS
(mg/L)
Chittagong 9 Discharge
drain of
factory and
Dumping
point of
Kornofuli
river.
Blue, Pink,
Violet and
Gray.
Pungen
t and
Foul.
25-55 7.1-
11.1
411-1483
Narayango
nj
6 Discharge
drain of
factory and
Raw
wastewater.
Blue,
Black and
Pink.
Pungen
t and
Foul.
25-45 5-10.3 803-3260
Other areas:
Ashulia,
Dhamrai,
Gazipur,
Savar and
Narshindi.
30 Drain,
River,
Plane land
and Raw
waste
water.
Blue, Pink,
Gray,
Yellowish
and Green.
Pungen
t and
Foul.
Not
recorded
5-14 490-3226
Treatment Technologies
Effluent can be treated in a number of different ways depending on the level of treatment
required. These levels are known as preliminary, primary, secondary and tertiary (or
advanced).Three mechanisms for treatment can be divided into three broad categories: physical,
chemical and biological.
ETP manufacturers use these mechanisms and processes together either fully or partially in a
effluent treatment plant.

7. Conclusions:
Textile is a major source of income and of great importance for Bangladesh’s economy. At the
same time textile processing has major environmental impact. A large proportion of the
environmental issues are related to the use and discharge of water. Textile manufacturing
is among the major industrial water users. To produce one kg of textile fabrication about
200 liters of water is used. A lot of chemicals are added to the process for cleaning and
dyeing purposes. Obviously the wastewater effluent from this unit contains considerable
amounts of hazardous pollutants, and where heavy metals are very common. In Bangladesh
most of the effluent from the textile industry is discharged untreated into rivers. Today 20%
of available river water in Bangladesh is polluted by textile waste water. Water
treatment is a very important step to change these conditions and to achieve a sustainable
situation. Bangladesh’s government has an awareness of this and limits for water
effluent quality exist. Unfortunately, this regulation is not closely supervised and a lot of places
do not follow the regulation.
High pH and TDS values of textile wastewater found in Narayangong area and high pH values
obtained in Chittagong area. In our previous work we also found similar trend in other areas of
Bangladesh. This problem should consider seriously and prevention & control techniques of
pollution should be implemented in textile mills of Bangladesh.
Picture of raw effluent