TEXTILE EFFLUENT TREATMENT

CHAPTER THREE

Granch Berhe

EFFLUENTS DISCHARGED BY TEXTILE PROCESSING INDUSTRY

3.1

Total Textile Process at a Glance

Two types of waste are generated: process chemicals and fiber wastesThe nature of the waste generated depends on

Type of textile facilityProcesses and technologies Types of fibers and chemicals

05/01/23 4

05/01/23 5

Dispersible wastesHighly dispersed or mixed with other wastes: Waste water

Hard-To-Treat WastesResist treatmentContain non biodegradable or inorganic Cannot be removed by biological processes

High- Volume WastesHigh-volume wastes in textiles include wash water, alkaline wastes, warp sizes

Hazardous or Toxic WastesSubgroup of hard-to-treat wastes. Metals, chlorinated solvents, non degradable surfactants

6

General Waste Categorization

Acute ToxicitySingle or multiple exposures in a short space of time (usually less than 24

hours).Acute Toxicity of Textile Dyes

Skin Irritation VomitDiarrhea

Reactive dyes can cause respiratory or skin sensitisation problems in plant workers who manufacture the dyes and textile workers

Reactive Dyes + Human Serum Albumin [HSA]Dye-HSA conjugate, which acts as an antigen. The antigen produces specific immunoglobulin E (IgE) and, through the release of chemicals such as histamine, causes allergic reactions

7

Toxicity

Chronic Toxicity

Non Genotoxicity1.Water solubilityWater-soluble molecules are generally excreted rapidly by a living organism2.Water InsolubilityDue to the insolubility, toxicants gets large size particles [0.1 to 3 mm] in the body which are not transported across cell membranes.[e.g.] Pigments

Genotoxicity Mutagens Carcinogens Teratogens

Toxicants reach the DNA (which resides in the nucleus of the cell) in order for the chemical to interact with the DNA.

So the toxicants will be able to transport across the protective cell membranes

Active species of most carcinogens, known as the ultimate carcinogen, is an electrophile,

E.Nitrenium ion [R2N+] Carbonium ion [R3C+] Carcinogens attack a nucleophilic site in DNA, which may

be a carbon, nitrogen or oxygen atom, to form a covalent chemical bond E + [DNA] or E–[DNA] 9

The toxic effects of the azo dyes may result from the direct action of the agent itself or of the aryl amine derivatives generated during reductive biotransformation of the azo bond.

The azo dyes entering the body by ingestion can be metabolized to aromatic amines by the azoreductases of intestinal microorganisms.

If the dyes are nitro, they can be metabolized by the nitroredutases produced by the same microorganisms.

Mammalian liver enzymes and other organizations may also catalyze the reductive cleavage of the azo bond and the nitro reduction of the nitro group.

In both cases, if N-hydroxylamines are formed, these compounds are capable of causing DNA damage.

Moreover, the reduction of azo dyes by sodium hydrosulfite and the successive chlorination steps with hypochlorous acid, can form 2-benzotriazoles phenilbenzotriazol (PBTA) derivatives and highly mutagenic aromatic amines, often more mutagenic than the original dye.

Effects caused by other pollutants in textile wastewater, and the presence of very small amounts of dyes (<1 mg/L for some dyes) in the water, which are nevertheless highly visible, seriously affects the aesthetic quality and transparency of water bodies

11

Anthraquinone dyes of the solvent or disperse class containing one or more primary amino- or methyl amino-groups tend to be mutagenic or carcinogenic.

Cations bind to sulfhydryl (-SH) group (cysteine amino acid) in enzymes disrupting the vital metabolic reaction catalyzed by the enzyme.

The high alkalinity and traces of chromium (employed in dyes) adversely affect the aquatic life.

Imidazole is corrosive to skin and irritating to eyes in rabbits--may cause permanent eye injury, teratogenicity and developmental toxicity observed at doses maternally toxic in rats.

Chloroflorocarbon based chemicals like FR causes ozone layer depletion 12

Formaldehyde, a highly toxic, colourless gas, has been linked to skin irritation and allergic reactions. Even more worryingly, the chemical is classified as a human carcinogen

Sulphur dye cause even acid rain

Other worse Effects Brain function, decreased attention, retardationReproduction including miscarriage, until births

Most sensitive are children <7; immature blood-brain barrier; effects mental development etc……

Carcinogenic substances: 59 substances. Mutagenic substances: 9 substances . Substances toxic to reproduction: 39 substances. Allergenic substances:14 substances with respiratory sensitization 56

substances with skin sensitization properties. Substances with environmentally hazardous, long-term effects:

approximately 57 substances.

14

Carcinogenic aromatic amides

1. Organic chlorine carriers (dyed acceleration)2. Separation of chlorine bleach materials, except the sodium

chlorite from the bleached synthetic fibers3. The free chlorine after using sodium chlorite4. Arsenic, mercury and their mixtures5. Alkyl phenol as a bleaching agent6. Cr6 + compounds in the oxidizing of sulfur dyes and vat dyes7. EDTA, DTPA, and phosphate in the water treatment softeners8. Formadehyde based chemicals and gases9. Chloroflorocarbon based chemicals and gases10. Aryl and aromatic amide components11. Accumulation of chemicals dyes and textile auxiliaries

15

The following must not be in the wastewater

TREATMENT PROCEDURE PARAMETERS OF WET PROCESSING OPERATIONS

3.2

WASTE WATER FROM DIFFERENT PROCESS

COD

BOD

High pHWet process

Industrial effluents

SUSPENDED SOLIDS

GASES/CHLORINE,CO2,O2

Strong color

Heavy metals/ iron, magnesium, arsenic, copper

SALTS/chlorides,sulphate, nitrate

05/01/23 18

In most cases BOD/COD ratio of the composite textile wastewater is around 0.25 .This implies that the wastewater contains large amount of nonbiodegradable organic matter.

CLASSIFICATION OF WASTE WATER TREATMENT PROCESS

Remove organic color, suspended solids Helps in primary reduction of COD & BOD

PRIM

ARY

SCREENING

SEDIMENTATION

EQUALIZATION

NEUTRALIZATION

CHEMICAL COGULATION

MECHNICAL FLOCCULATION

The conventional treatment systems is a Physico-chemical treatment followed by biological treatment (Secondary) system

3.2.1

Purpose: to remove coarse suspended matters such as rags, pieces of fabric, fibers, yarns . bar screens and mechanically cleaned fine screens remove most of the fibers

05/01/23 22

SCREENING

SEDIMENTATION The fine suspended matter passed through the screens

can be removed efficiently and economically by sedimentation.

This process is particularly useful for treatment of wastes containing high percentage of settable solids

The sedimentation tanks are designed to enable smaller particles to settle under gravity.

The settled sludge is removed from the sedimentation tanks by mechanical scrapping into hoppers and pumping it out subsequently.

Sedimentation is sometimes combined with equalization operation.

05/01/23 23

EQUALIZATION

Effluent streams are collected into ‘sump pit’ (big tank).

The mixed effluents are stirred by rotating agitators or by blowing compressed air from below.

The pit has a conical bottom for enhancing the settling of solid particles.

05/01/23 24

The textile effluents are highly variable in terms of pH and extent of impurities Such individual process effluents from individual processes will severely affect

the secondary treatment processes of effluent treatment. It is therefore, necessary to mix the discharges from different processes.

NEUTRALISATION Normally, ph values of cotton

finishing effluents are on the alkaline side.

Hence, ph value of equalized effluent should be adjusted.

Use of dilute sulphuric acid and boiler flue gas rich in carbon dioxide are commonly used .

Since most of the secondary biological treatments are effective in the ph 5 to 9, neutralization step is an important process to facilitate these processes

USUALLY H₂SO₄ 1 gm/m³ TO BRING PH 8.5.05/01/23 25

CHEMICAL COAGULATION/MECHANICAL FLOCUALTION Finely divided suspended solids

and colloidal particles cannot be efficiently removed by simple sedimentation by gravity.

In such cases, mechanical flocculation or chemical coagulation is employed.

In mechanical flocculation, the textile waste water is passed through a tank under gentle stirring;

The finely divided suspended solids coalesce into larger particles and settle out.

Specialized equipment such as clariflocculator is also available, wherein flocculation chamber is a part of a sedimentation tank.

05/01/23 26

SECO

NDA

RYAERATED LAGOON

TRICKLING FILTRATION

ACTIVATED SLUDGE PROCESS

OXIDATION DITCH /POND

The main purpose of secondary treatment is to provide BOD removal beyond what is achievable by simple sedimentation.

Remove dissolved and residual organic matter aerobic mode (with air CO2 &CH4) or with anaerobic mode.Achieved by digestive action of bacteria under suitable conditions (PH 6-9,nuetrents,air/oxygen and temperatureReduce COD, BOD and toxicity. In such cases, the recent trend is to set up an activated adsorption system or and ozonation unit instead of biological treatment process.3.2.2

AERATED LAGOON

05/01/23 28

The effluents from primary treatment processes are collected in tanks and are aerated Air is blown in the form of stream of bubbles at the bottom with mechanical devices, for

about 2 to 6 days. During this time, a healthy flocculent sludge is formed which brings about oxidation of the

dissolved organic matter. BOD removal to the extent of 99% could be achieved with efficient operation.

TRICKLING FILTERS

05/01/23 29

Usually consists of circular or rectangular beds made of well-graded gravels media where micro-organisms deposited on i.e small stone, PVC, coal, synthetic resins of size 40 mm to 150 mm, over which wastewater is sprinkled uniformly on the entire bed with the help of a slowly rotating distributor (such as rotary sprinkler).

Thus, the waste water trickles through the media.

The filter is arranged in such a fashion that air can enter at the bottom; counter current to the effluent flow and a natural draft is produced.

Gelatinous film, comprising of bacteria and aerobic microorganisms known as “zooglea”, is formed on the surface of the filter medium, which thrive on the nutrients supplied by the wastewater.

ACTIVATED SLUDGE PROCESS

05/01/23 30

This is the most versatile biological oxidation method employed for the treatment of waste water

In this process, the waste water is aerated in a reaction tank in which some microbial floc is suspended.

The aerobic bacterial flora bring about biological degradation of the waste into carbon dioxide and water molecule,

While consuming some organic matter bacteria grow

The bacteria flora grows and remains suspended in the form of a floc, which is called “activated sludge”.

The effluent from the reaction tank is separated from the sludge by settling and discharged.

A part of the sludge is recycled to the same tank to provide an effective microbial population for a fresh treatment cycle.

The surplus sludge is digested in a sludge digester, along with the primary sludge obtained from primary sedimentation.

An efficient aeration for 5 to 24 hours is required for industrial wastes.

BOD removal to the extent of 90-95% can be achieved in this process.

Biological effluent treatment processes meets the standards of BOD,COD, and are suitable for discharge into river, lake or sea.

However, these treatments are not suitable for removal of inorganic impurities like salt which are present in the form of tds.

Biologically treated water is also not suitable for recycling.

05/01/23 31

OXIDATION DITCH /OXIDATION POND

05/01/23 32

Pond aeration or lake aeration Increase in the oxygen saturation of the water. Dissolved oxygen (DO) Fish and other aquatic animals and Aerobic bacteria Pond bottoms of organic soils demand larger amounts of oxygen.

TERT

IARY

OXIDATION TECHNIQUE

ELECTROLYTIC PRECIPITATION & FOAM

FRACTIONATION

MEMBRANE TECHNOLOGIES

ELECTROCHEMICAL PROCESSES

ION EXCHANGE

PHOTO CATALYTIC DEGRADATION ADSORPTION

THERMAL EVAPORATION

Remove dissolved solids (mineral salts) and residual color and odorAfter the treatment water can be safely discharged or reused for processing

In order to reduce TDS further purification of effluent is carried out using tertiary treatments

Membrane filtration techniques particularly RO has become popular due possibility of recycling treated water

3.2.3

ADSORPTION The most commonly used method of dye removal by

adsorption. The process also removes toxic chemicals such as pesticides, phenols,

cyanides and organic dyes. Adsorbent for treatment is activated carbon. It is manufactured from carbonaceous material such as wood, coal, petroleum

products etc. Others: activated clay, silica, fly ash, (inorganic) and bio-adsorbents-reactive

dyes• Effective for adsorbing cationic, mordant and acid

dyes, and to a slightly lesser extent, dispersed, direct, vat, pigment and reactive dyes

• Disadvantage: activated carbon is expensive; it has to be reactivated, which can result in 10-15% loss of sorbent.

Ion exchange process is normally used for the removal of inorganic salts and some specific organic anionic components such as phenol. All salts are composed of a positive ion of a base and a negative ion of an acid. Ion exchange materials are capable of exchanging soluble ions and cations with electrolyte solutions.

ION EXCHANGE

Removal of bacteria, salts, sugars, proteins, particles, dyes, and other constituents The separation of ions with reverse osmosis is aided by charged particles. Dissolved ions that carry a charge, such as salts, are more likely to be removed by the membrane than those that are not charged, such as organics.

MEMBRANE FILTRATION

1.REVERSE OSMOSISto pass pure water at fairly high rates and to reject salts at high pressures through the cellulose acetate or nylon membrane. Reverse osmosis can be used as end-of-pipe treatment and recycling system for effluent.

2.ULTRAFILTRATIONThe difference between reverse osmosis and ultrafiltration is primarily the retention properties of the membranes.Reverse osmosis membranes retain all solutes including salts. Ultrafiltration membranes retain only macro molecules and suspended solids.

• They are pressure driven membrane operations that use porous membranes for the removal of heavy metals. The main disadvantage of this process is the generation of sludge.

3.NANOFILTATION Nanofiltartion can be positioned between reverse osmosis and

ultrafiltration. This process is used where the high salt rejection of reverse

osmosis is not necessary. It is capable of removing hardness elements such as calcium or

magnesium together with bacteria, viruses, and colour. It operated on lower pressure than reverse osmosis and

treatment cost is lower than RO. Preferred when permeate with TDS but without colour, COD

and hardness is acceptable.

Nanofiltration membranes are similar to reverse osmosis membranes in several respects except the degree of removal of monovalent ions such as chlorides etc.

Filtration Spectrum Of Different Membranes

Passing water between two plates with opposite electrical charges. The metals attracted to negative charge Non-metals are attracted to positive charge. Both types of ions can be removedElectrodialysis is used on very hard water, more than 500 mg/L as calcium carbonate.

involves the evaporation of water. The evaporated water leaves behind all hardness compounds,

ELECTRODIALYSIS

DISTILLATION

ADAVNCED OXIDATION PROCESSES (AOP)Conventional oxidation treatment have found difficulty to oxidize dyestuffs and complex structure of organic compounds:

At low concentration or If they are especially refractory to the oxidants.

AOP processes are combination of : - Ozone (O3), - Hydrogen peroxide (H2O2) and - UV radiation, which showed the greatest promiseThese oxidants effectively decolorized dyes, however did not remove COD completely.

The goal of any AOPs design is to generate and use hydroxyl free radical (HO·) as strong oxidant to destroy compound that can not be oxidized by conventional oxidant.

OZONATION Ozone is a powerful oxidant agent for water and wastewater. Once dissolved in water, ozone reacts with a great number of

organic compounds in two different ways: By direct oxidation as molecular ozone or By indirect reaction through formation of secondary

oxidants like hydroxyl radical. The conventional fine bubble contactor is the most widely

ozone generator used because of the high ozone transfer efficiency (90%) and high performance.

Results presented by a few researchers revealed that ozone decolorize all dyes, except nonsoluble disperse and vat dyes which react slowly and take longer time.

Colour removal using ozonation from textile wastewater is depended on dye concentration.

According to Rein (2001), conventional ozonation of organic compounds does not completely oxidize organics to CO2 and H2O in many cases.

Remaining intermediate products in some solution after oxidation may be as toxic as or even more toxic than initial compound and UV radiation could complete the oxidation reaction by supplement the reaction with it.

O3/UV is the most effective method for decolorizing of dyes comparing with UV oxidation by UV or ozonation alone. (Hung-Yee and Ching-Rong (1995))

O3/UV treatment is recorded to be more effective compared to ozone alone, in terms of COD removal.

O3/UV

H2O2/UV

Oxidization of the textile wastewater with H2O2 alone has been found ineffective at both acid and alkali values (Olcay et al., 1996),

Under UV radiation, H2O2 are photolyzed to form two hydroxyl radicals (2OH•) that react with organic contaminants (Crittenden et al., 1999).

Nonefficient colour removal at alkaline pH Therefore the instantaneous concentration in HO* is lower than

expected. Furthermore, the H2O2/UV process is more sensitive to the

scavenging effect of carbonate at higher pH values.

O3/H2O2

The addition of both hydrogen peroxide and ozone to wastewater accelerates the decomposition of ozone and enhancing production of the hydroxyl radical.

At higher pH, even very small concentration of H2O2 will be dissociated into HO2¯ ions that can initiate the ozone decomposition more effectively than OH ¯ ion.

H2O2/O3 treatment of synthetic dye house highly depended on the pH of the effluent.

It is documented that it was 74% ozone absorption at pH 11.5 (and 10 mM H2O2) whereas at the same concentration of H2O2 and pH 2.5, ozone absorption was only 1

Complete decolourization of C.I. Reactive Blue 220 and C.I. Reactive Yellow 15 using H2O2 /O3 process is achieved in 90 min (Tanja et al., 2003).

O3/H2O2/UV

The addition of H2O2 to the O3/UV process accelerates the decomposition of ozone, which results in an increased rate of OH• generation.Among all AOPs, for dye house wastewater and acetate, polyester fiber dyeing process effluent; combination of H2O2/O3/UV appeared to be the most efficient in terms of decolouration.COD removal efficiency of raw textile wastewater increased from 18% to 27% by using sequential ozonation and H2O2/UV.In the case of bio-treated textile effluent, a preliminary ozonation step increased COD removal of the H2O2/UV-C treatment system from 15% to 62%.99% COD removal from acetate and polyester fiber dyeing process effluent in batch mode operation(O3/H2O2/UV in 90 min) was achieved.In raw textile effluent, TOC removal rate was accelerated from 14% (H2O2/UV-C) and 17% (O3) to 50%.

BENEFITS OF ADVANCE TREATMENT METHODS

Recover water and salt. Low TDS water when used in textile processing minimizes

consumption of sequestering agents. Corrosion and scale formation can be minimized Efficiency of boiler can be improved Reusing Brine in dyeing requires less additional salt. Reduce problems relating to disposal of high TDS effluentsIS THERE ANY DISADVANTAGE??

Unknown oxidation products & Expensive

MODEL WASTEWATER TREATMENT PLANT FOR TEXTILE

MILLS

3.3

WHAT IS ETP?

ETPINFLUENTTREATMENT

EFFLUENT

SLUDGE

ETP OR EFFLUENT TREATMENT PLANT IS USED TO TREAT THE INDUSTRIAL WASTE WATER.

INFLUENT: UNTREATED INDUSTRIAL WASTE WATER.

EFFLUENT: TREATED INDUSTRIAL WASTE WATER.

SLUDGE: SOLID PART SEPARATED FROM WASTE WATER BY ETP.

EFFLUENT TREATMENT PLANT OF DELTA KNIT COMPOSITE LTD

DELTA KNIT COMPOSITE LTD

3.3.1

SCREENING

DRUM SCREENER

SCREENING IS THE FILTRATION PROCESS FOR THE SEPARATION OF COARSE PARTICLES FROM INFLUENT.

STAINLESS STEEL NET IS USED FOR SCREENING.

HARD PLASTIC BRUSHES ARE USED TO CLEAN THE NET, WHICH ARE DRIVEN MECHANICALLY.

(DRUM SCREENER IS USED IN THIS ETP)

SCHEMTIC DIAGRAM OF DRUM SCREENER

EQUALIZATIONEQUALIZATION IS THE PROCESS TO MAKE THE WASTE WATER- -HOMOGENOUS & -COOL

EQUALIZATION TANK IS ALSO CALLED HOMOGENOUS TANK.

EQUALIZATION TANK

INFLUENT FROM SCREENING

SPRAY OF WATER COMING FROM DYEING UNIT

AIR FOR DIFFUSION

COOL & HOMOGENOUS INFLUENT TO PH

CORRECTION TANK

PH CORRECTION IN THIS TANK PH OF THE INFLUENT IS CORRECTED TO MEET THE STANDARD.

ACID OR ALKALI IS ADDED TO THE EFFLUENT BY DOZZING TO INCREASE OR DECREASE THE PH OF INFLUENT RESPECTIVELY.

MULTI-METER TYPE PH METER IS USED.

PH CORRECTION

ACID OR ALKALI

INFLUENT FROM EQUALIZATION

TANK

INFLUENT OF DESIRED PH TO DISPERSE UNIT

DISPERSE UNIT FUNCTION OF DISPERSE TANK IS TO MIX THE SLUDGE COMING FROM RECYCLE TANK WITH WASTE WATER.

IT HELPS FOR PROPER AERATION.

DISPERSE UNIT

( MIXING OF SLUDGE & WASTE)

SLUDGE FROM RECYCLE TANK

INFLUENT FROM PH CORRECTION

TANK

MIXED INFLUENT & SLUDGE TO AERATION

AERATION FUNCTION OF AERATION IS OXIDATION BY BLOWING AIR. AEROBIC BACTERIA IS USED TO STABILIZE AND REMOVE ORGANIC MATERIAL PRESENTS IN WASTE. ABOUT 200 KG AEROBIC BACTERIA IS GIVEN TO THE PLAN FOR 5 YEARS.

AERATION TANK

MIXTURE OF WASTE

WATER & SLUDGE

AEROBIC BACTERIA

AIR

DISCHARGE TO SEDIMENTATION

TANK

O2

ORGANIC MATTER + O2

BACTERIA

NUTRIENTCO2+ H2O + HEAT

Sedimentation packIN THIS TANK SLUDGE IS SETTLED DOWN PARTIALLY

SEDIMENTATION PACK PROVIDES THE ADVANTAGE OF FAST SLUDGE SEPARATION

Sedimentation tank IN THIS TANK SLUDGE IS SETTLED DOWN FINALLY.

EFFLUENT IS DISCHARGED FROM PLANT THROUGH A FISH POND.

SLUDGE IS PASSED TO THE THICKENING UNIT.

SCHEMTIC DIAGRAM OF Sedimentation tank

SEDIMENTATIONTANK

WASTE WATER FROM

SEDIMENTATION PACK

SLUDGE TO THICKENING UNIT

EFFLUENT

EFFLUENTDISCHARGE

FISH POND

FISH POND INDICATES THE HIGHER DEGREE OF TREATMENT IN THIS ETP

SLUDGE THICKENING UNITIN THIS UNIT SLUDGE IS DRIED AND DISCHARGED.

A PARTIAL AMOUNT OF SLUDGE IS RETURNED BACK TO THE AERATION TANK FROM THICKENING UNIT THROUGH RECYCLE TANK CALLED RETURN SLUDGE TANK AND DISPERSE TANK.

SLUDGFE THICKENING UNIT

SLUDGE FROM SEDIMENTATION UNIT SLUDGE DISCHARGE

SLUDGE TO RECYCLE TANK

RETURN SLUDGE TANKFUNCTION OF RETURN TANK OR RECYCLE TANK IS TO MIX WATER WITH SLUDGE

THIS MIXTURE IS THEN PASSED TO AERATION TANK THROUGH DISPERSE TANK. SLUDGE AGAIN OXIDIZED TO MINIMIZE THE POLLUTION FROM SLUDGE.

ALIVE BACTERIA OF SLUDGE IS AGAIN USED IN AERATION TO UTILIZE THIS BACTERIA.

SLUDGE RECYCLE TANK

SLUDGE FROM THICKENING UNIT

MIXING OF SLUDGE & WATER

SLUDGE TO AERATION TANK THROUGH DISPERSE UNIT

800 KLD ELECTRO-CHEMICALS TREATMENT PLANT FOR TEXTILEPROCESSING EFFLUENT

ENVIROS INDIA PRIVATE LIMITED

3.3.2