18

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

In this chapter, a brief review of literature on existing methods of

textile effluent treatment, namely wastewater treatment by Reverse Osmosis

(RO), RO separation of organic pollutions from wastewater, membrane

filtration, RO membrane preparation, structure and properties, RO membrane

modules and module configurations, RO membrane characterization

techniques are considered and discussed.

2.2 EXISTING METHODS OF TEXTILE EFFLUENT

TREATMENT

In an early study, Anderson et al (1972) reported some of the factors

influencing the separation of several different organics (including acetone,

urea, phenol, 2, 4 - dichlorophenol, nitrobenzene) by cellulose acetate

membranes. Rejections varied considerably for the different solutes, and

rejections of ionizable organics were greatly dependent on the degree of

dissociation. Nonionized and hydrophobic solutes were found to be

strongly sorbed by the membranes and exhibited poor rejection. Duvel and

Helfgott (1975) also found organic separations that varied with molecular size

and branching. They postulated that organic separation was also a function of

the solute's potential to form hydrogen bonds with the membrane.

19

Edwards and Schubert (1974) reviewed some of the early separation

results of herbicides and pesticides with RO membranes. They also conducted

studies with the herbicide 2, 4 - D and found that the separations were < 51%.

It was noted that solute adsorption could occur on the cellulose acetate

membranes. Fang and Chian (1976) conducted studies on the separation of

several polar organic compounds with various functional groups using

cellulose acetate and several other types of membranes. That study found that

the organic rejection varied considerably not only with solute but also with

membrane type. Chian et al (1975) reported high rejections (> 99%) for

several pesticides with cellulose acetate and a composite membrane.

However, a significant adsorption of the pesticides on the membranes was

noted. Light (1981) studied dilute solutions of polynuclear aromatic

hydrocarbons (PAHs), aromatic amines, and nitrosamines and found

rejections of these compounds to be over 99% for polyamide membranes.

Williams et al (1999) developed two models namely a modified

steady-state solution diffusion model and an unsteady-state diffusion

adsorption model which are able to predict flux and permeate concentrations

from a single RO experiment. Further, the development of these models

allows for the understanding of the mechanisms of organic membrane

interactions. For instance, it has been proposed that increased adsorption

inherently leads to an increase in flux drop. However, we have found, on one

hand, that due to specific interactions with membrane water transport groups,

chloro and nitrosubstituted phenols cause significant flux drops. On the other

hand, benzene had a high physical adsorption but caused negligible flux drop.

The results were further extended to nanofiltration experiments with an

aromatic pollutant containing two types of charge groups.

Various techniques for textile effluent treatment such as coagulation

/ flocculation Hasani et al (2009), activated carbon adsorption Kadirvelu et al

20

(2003), oxidation Malik and Saha (2003), ozonation Selcuk (2005),

electrochemical oxidation Radha et al (2009), membrane separation Chiu et al

(2009), biological degradation Gopinath et al (2009), etc have been applied

for the treatment of dye containing effluents. Yet most of these techniques are

reported to be expensive and not environment friendly. So a cheap and

effective treatment method needs to be put in place for the sake of the

environment.

Tang and Chen (2002) focused on the production of a large amount

of wastewater that is highly colored with high loading of inorganic salt.

Crossflow nanofiltration using thin film composite polysulfone membrane

was used to recover the electrolyte solution and reject the color. Using a

synthetic textile effluent of reactive dye and NaCl solution, the study dealt

with the mechanism controlling flux and rejection by varying four main

parameters, namely cross flow velocity, initial dye concentration, feed

pressure, and electrolyte concentration. The results showed that flux was

dominated by the osmotic pressure, created from the presence of NaCl, and

that dye concentration did not significantly affect the flux or rejection.

Working at low pressures of upto 500 kPa, relatively high fluxes were

obtained, with an average dye rejection of 98% and NaCl rejections of less

than 14%. Thus, a high quality of reusable water could be recovered.

Siireyya Merif et al (2005) evaluated the effectiveness of Fenton's

oxidation (FO) process and ozone (O3) oxidation, compared with a

coagulation-flocculation (CF) process to remove effluent toxicity as well as

color and COD from a textile industry wastewater. The operational

parameters for each process were determined on the basis of complete toxicity

removal. The FO process removed COD at a higher rate (59%) than O3 (33%)

while color removal was similar (89% and 91%, respectively). The CF

21

process removed both COD and color at rates similar to the FO process. A

color range of 150-250 platin-cobalt (Pt-Co) unit was assessed for toxicity.

Gomez et al (2007) discussed a case study in one of the textile units

on upgradation of a full scale effluent treatment plant comprising chemical,

biological, tertiary and advanced treatment processes. Based on the adequacy

assessment of chemical and biological processes, an improvement in the

performance of the unit processes was achieved through optimization of

coagulant dosage for chemical coagulation and build-up of active biomass in

the activated sludge system. In addition, the application of membrane

separation processes comprising ultrafiltration and reverse osmosis units are

also highlighted including disposal of reverse osmosis (RO) rejected through

evaporator leading to zero liquid effluent discharge.

Experiments on the decolorization and decomposition of reactive

and disperse dyes using electron beam technologies were carried out by Ting

and Jamaludin (2008). It was found that the dose of irradiation and initial

concentration of pollutants affected the removal of color and they were

dependent on each other. At an irradiation dose of 108 kGy, the color removal

was in the range of 87% – 96%.

Yi et al (2008) investigated the electrochemical degradation of

Alizarin Red S using an activated carbon fiber felt as an anode. The results

indicated that an increase in current density would increase dye

removal efficiency. It was found that the larger surface area of the

activated carbon fiber anode (1682 m2/g) could ensure more effective

electrochemical degradation of dye (83.9%).

Adebayo et al (2009) studied the textile industry effluent analysis

for biochemical oxygen demand (BOD), Total Solids (TS), Chemical Oxygen

Demand (COD), Suspended Solids (SS), Dissolved Solides (DS), Odour and

22

color intensity prior to biological treatment with mixed culture of Aspergillus

niger and Aspergillus wentil. The product of biological treatment was

analyzed after 5 days of treatment. The result revealed that the effluent was

initially of high BOD, COD, TS, DS, SS and color intensity. The method

used in this work significantly reduced COD to well below 250 ppm and

BOD < 30 ppm, TSS < 30 ppm which are the upper limits for disposal into

surface water. The result indicated remarkable overall COD reduction from

800 ppm to 200 ppm (75%); BOD from 750 ppm to 20 ppm (97.3%) and

bioremediation of TSS < 30 ppm (99.5%); DS (99.60%) and SS (99.30%).

Rekha et al (2009) reviewed a zero effluent process by using a

membrane type solute separation system for a wet process house. In that

study, reactive and disperse dyes were used for the dyeing process and the

textile wastewater. It contained size, thickeners, pigments and soaps passed

through ultrafiltration, nanofiltration and reverse osmosis membranes.

Experimental results showed that only a small fraction of about 15% of salt

and water resulted from membrane filtration.

Ramachandran et al (2009) reinforced the decolorization of textile

dye effluents through current technologies, such as aerobic and anaerobic

bacteria, fungi and physical-chemical methods. They found that

biotechnological applications not only removed color but also completely

degraded dyes. Promising results were obtained in enhancing dye removal

rate by the addition of mediating compound or by changing process

conditions to a higher temperature.

Bharat Patil et al (2010) analyzed the treatment of colored

wastewater from the dyeing and printing industries by the semiconducting

photocatalysis. The wastewaters wear a lot of color and have toxic odour,

COD and BOD. This treatment study proved that the semiconductor photo

23

catalysis process cold be an appropriate tool for the treatment of textile dyeing

and printing wastewater.

Ong et al (2010) observed the treatment performance of Acid

Orange 7 containing wastewater by using up-flow constructed wetland

(UFCW) at different Acid Orange 7 concentrations. Various concentrations

of AO7, from 50 to 100 mg/L, had an effect on the performance in

biodegradation of organic matter and nitrification in the non-aerated

wetland reactor as well as denitrification and decolorization in the aerated

wetland reactor. For the removal of organic matter, NH4-N and aromatic

amines, the aerated wetland reactor outperformed the non-aerated one. The

usage of constructed wetland (CW) for dye-rich textile wastewater

treatment was carried out under a series of dynamic experiments by Bulc

and Ojstrsek (2008). The CW model was packed with gravel, sand and

zeolite tuff. The results indicated that the CW model could reduce color by

upto 70%.

Sheth and Dave (2010) performed an enhanced biodegradation of

Reactive Violet 5R manufacturing wastewater using a down flow fixed

film bioreactor (DFFR). Charcoal was used as a support material in DFFR. In

less than eight hours of contact time, more than 88% COD reduction, 95%

degradation of Reactive Violet 5R and 99% of copper remediation were

observed under both batch and continuous operation of DFFR. The

biodegradation rate increased more than three-fold with an additional 0.25%

of peptone.

Kozakova et al (2010) attempted the usage of direct current (DC)

diaphragm discharge for the decolorization of Direct Red 79. A high removal

rate was observed after 40 minutes. This method can lead to a change in

solution properties such as pH of the solution and solution conductivity.

24

Sadri Moghaddam et al (2010) sought to make a comparison on

Acid Red 119 dye removal by using two different types of waterworks sludge,

ferric chloride sludge (FCS) and polyaluminium chloride sludge (PACS).

These water work sludges acted as coagulants to remove Acid Red 119 under

a series of batch experiments. The results indicated that FCS was more

effective than PACS for the Acid Red removal due to its higher maximum

adsorption capacity.

The feasibility of using wasted basic oxygen furnace (BOF) slag in

the removal of diazo dye C.I. Acid Black 24 revealed that BOF slag

efficiently removed Acid Black 24 by upto 99.7%, according to Chang et al

(2010). The color removal efficiency was dependent on slag dose and initial

dye concentration.

Shafaei et al (2010) analyzed capable of removing Mn2+

ions by

electro coagulation with aluminum under an optimum pH of 7.0. The authors

concluded that were the density and electrolysis time, along with initial

concentration served as factors capable of determining removal rates

successfully.

Meas et al (2010) determined that by using an electrocoagulation

with sacrificial electrodes, with COD (95%), color (99%) and turbidity (99%)

can be reduced when testing fluorescent penetrated liquid for non-destructive

testing of parts. In this context, the water was reused 4 times.

Balla et al (2010) studied the efficiency of an electrocoagulation /

electroflotation having a 90% removal rate of color with synthetic mixture,

compared to 78 – 90% removal of color in textile wastewater by providing a

mixture of Red S3B 195, Yellow SPD, Blue BRFS, Yellow terasil 4G, Red

terasil 343 and Blue terasil 3R02.

25

Katal and Pahlavanzadeh (2011) determined that by using aluminum

and iron electrodes for electrocoagulation, an optimum pH between 5 and 7,

current density of 70 mA/cm2 was capable of efficiently treating the

wastewater at a low cost. In addition, temperature relationship also poorly

affects the performance.

Electrochemical oxidation of organic pollutants present in the dye-bath

and wash water effluents from the textile industry was carrier out in batch,

batch recirculation and recycle reactor configurations under different

conditions of current density treatment duration effluent flow rate and

electrode specific surface. It is concluded that the complete removal of COD

could be achieved in batch reactor and in recirculation reactor if the

electrolysis time is long enough, but the specific energy will be very large

compared with continuous operation. The purpose behind this investigation is

to estimate the energy demand for the electrochemical mineralization that

enhances biodegradability and the results would be helpful for optimization of

electrochemical oxidation technology. (Ahmed Basha et al, 2012).

Organic pollutants in Reverse Osmosis concentrates from wastewater

reclamation are mainly comprised of low molecular weight biorefractory

compounds. Generally, advanced oxidation methods for oxidizing these

organic require relatively high level of energy consumption. Organic

pollutants were satisfactorily removed with less consumption of powdered

Activated Carbon. Effluent from this combined technology can be further

reclaimed by Reverse Osmosis process to improve the overall recovery rate to

between 91.0% and 93.8% with both economic and environmental benefits.

(Chunia Zhas et al, 2012)

The present study was stimulated by an authoritative review on there

have been significant efforts on investigating the decontamination of

26

wastewater containing synthetic dyes by electrochemical methods. Tested in

this method, including Boron Doped Diamond (BDD) anodes. The use of a

BDD thin film in electrochemical oxidation provides total mineralization with

high current efficiency of different organics in real wastewaters. Treating

electrochemically synthetic dyes wastewaters using BDD, there are few

reports on the use of electro oxidation processes to degrade real textile

effluents. This paper discuss the most important and recent results available

in the literature about the applications of BDD electrodes for removing azo

dyes in synthetic and real wastewaters. (Paralta –Hernandez et al., 2012)

2.3 WASTEWATER TREATMENT BY REVERSE OSMOSIS

The RO processes includes the treatment of wastewater containing

organic substance, wastewater from textile, electroplating and metal finishing,

pulp and paper, mining and petrochemical, food processing industries,

radioactive wastewater, municipal wastewater, and contaminated groundwater

Slater et al (1983), Cartwright (1985) and Ghabris et al (1989).

Since the development of the first practical cellulose acetate

membranes in the early 1960's and the subsequent development of thin-film,

composite membranes, the uses of reverse osmosis have expanded to include

not only the traditional desalination process but also a wide variety of

wastewater treatment applications. Several advantages of the RO process

make it particularly attractive for dilute aqueous wastewater treatment and

they include:

RO systems are simple to design and operate, have low

maintenance requirements, and are modular in nature, making

expansion of the systems easy

27

RO membrane processes can remove simultaneously both

inorganic and organic pollutants

RO systems allow recovery / recycle of waste process streams

with no effect on the material being recovered

RO membrane systems often require less energy and offer

lower capital investment and operating costs than many

conventional treatment systems and

RO processes can considerably reduce the volume of waste

streams so that these can be treated more efficiently and cost

effectively by other processes such as incineration in the

opinion of these experts in water treatment processes:

Cartwright (1985), Cartwright (1990), and Cartwright (1991).

In addition, the RO systems can replace or be used in

conjunction with other treatment processes such as oxidation,

adsorption, stripping, or biological treatment. In addition

many other processes can be adopted to produce high quality

product water that can be reused.

Treffry Goatley et al (1983) observed that a 30 m³ /day pilot plant

consisting of screening, alum coagulation, micro filtration and reverse

osmosis could be operated for 2 years on cotton/ nylon/ polyester dye house

effluents. The reverse osmosis modules used were brackish and seawater

UOPPA 300 type. The pilot – plant was operated at water recoveries of 85%

- 95% and temperatures of 30 - 45° C. The micro filtration unit was used to

remove suspended solids and colloidal dyestuffs from the effluent prior to the

spiral-warp membranes. The average permeate quality was 60 mg/l of TDS,

15 mg/l of sodium, 11 mg/l of TOC and 21 ADMI color units. Water, the end

product was reused.

28

In the recent years, the use of Reverse Osmosis (RO) technique in

wastewater treatment has been studied by different authors Abdul Sattar

Kahdim et al (2003). They found that the RO technique is a highly efficient

process, in terms of high recovery, and cost effectiveness in the opinion of

Shahid Naveed et al (2006) and Garcia-Figueruelo et al (2009). Not only that

the RO is easy to operate and also easy to maintain.

Ciardelli et al (2000) carried out an investigation by treating

wastewater in a pilot plant, reproducing on a smaller scale a separation system

based on ultrafiltration and reverse osmosis. Significant indications for the

exploitation of this approach on the fouling industrial scale were gained

during the work. The effluent from dyeing and finishing plants, after activated

sludge oxidation, was treated at 800 l/h by means of sand filtration, followed

by a separation in an ultrafiltration membrane module. The last separation

step, namely reverse osmosis at 8 bar pressure, produced a permeate (60% of

the inlet flow) relying on the analytical screening performed, was of much

better quality with respect to processed water presently in use.

Koo et al (2001) described that the process involved in RO is the

most efficient way to remove colloidal and dissolved silica, which can be

found in high concentrations in brackish water. The presence of silica and its

ability to foul membranes limit the use of silica bearing waters for

desalination and when used, it entails many economic penalties. The cleaning

of membrane using distilled water, cleaners MT5010 and MT 3100 did not

restore the membrane although cleaner MT3100 proved to be a better cleaner

compared to MT5010 when the fouling was due to colloidal deposition. So it

is desirable to investigate the effectiveness of different cleaners and the

economics of their usage.

Bodalo-Santoyo et al (2003) benefited from an analysis and

comparative study of four different polyamide membranes (RO) that were

29

tested for their ability to reduce the concentration of pollutants in a synthetic

effluent stream containing acrylnitrile and three inorganic species (sulphate,

ammonium and cyanide). The rejection percentage of sulphate ion was high

in all the membranes tested (96% to 99.4%) regardless of the working

pressure. Ammonium rejection values ranged between 72.3% and 83.9%,

while acrylnitrile rejection showed a low value (10.5% to 28.8%) compared

with the results obtained for the other pollutants. Cyanide rejection was

negative for all membranes tested except for HR95PP, which produced a

rejection percentage of 16.5%. The same membrane also produced higher

rejection percentages for cyanide and acrylnitrile than the other membranes.

Finally, this membrane was selected to study the influence of the feed stream

pH on the rejection of ammonium and cyanide ions.

Mousa Mohserf et al (2003) mulled over the treatment of brackish

water by RO and NF into potable water. Brackish water samples were

collected from Zarqa basin, Jordan, and characterised in terms of pH,

conductivity, total solids (TS), total suspended solids (TSS) and total organic

carbon (TOC). The brackish water samples were pre-treated through

microfiltration (MF) cartridges in order to get rid of the suspended matter.

The results revealed that both processes are efficient, as they highly reduce

the organic and inorganic contents present in the raw waters. The technical

and economical feasibilities of NF and RO processes for the production of

potable water from brackish water were compared. This study contributes to

the development of efficient technologies for the production of affordable

potable water in Mediterranean countries where the threat of water shortage is

a serious problem, especially in summer.

Abdul Sattar Kahdim et al (2003) gave a theoretical model to predict

the performance of reverse osmosis (RO) systems and compared the

theoretical results with experimental values obtained from the pilot plant. The

30

study was conducted using two types of membranes, viz. Saehane, type

RE8040BE of South Korean origin and TFC-KOCH system membranes

model 8822XR of American origin. The recovery of Saehane membranes is

larger than KOCH membranes due to the difference in the effective area for

both types of membranes whereas the salt passage of KOCH was always

lower than Saehane membranes for brackish water. It contained TDS that are

larger than S50 ppm and indicated that there was an agreement between

theoretical and experimental results.

Jian-Jun Qin et al (2005) arrived at the relationship between feed pH

and permeate pH in the reverse osmosis (RO) process which was investigated

in a pH range of 1.6 - 7.0 when the town water was used as feed. Three types

of flat-sheet RO membranes with varying isoelectric points in a pH range of

3.2 - 6.5 were tested in the laboratory. The experimental results showed that

for each RO membrane tested, there was a critical feed pH, below which RO

permeate pH was higher than feed pH, but above which RO permeate pH was

lower than feed pH. The critical feed pH for all membranes was 4.4 - 4.5,

which was independent of the isoelectric point of the RO membrane used.

Explanations on the constant critical feed pH are offered. It was found that

the existence of HCO3 in the feed and its transmission in the RO process

might have played a key role on the critical feed pH and the co-existing

divalent ions had an influence on reducing the rejections of monovalent ions.

Suksaroj et al (2005) stressed on the treatment of textile plant

effluent after making use of the conventional biological process. In fact, dead-

end filtration by microfiltration (MF), ultrafiltration (UF), Nanofiltration (NF)

and RO tests showed that a primary physico chemical treatment

(coagulation/flocculation) was necessary to limit membrane fouling. The

results made it clear that the percentage production rate increased with the

31

transmembrane pressure. NF, performing at 18.5 bar transmembrane pressure,

allowed a higher yield (22.6%) than RO (18.3%).

Tapan N Shah et al (2006) compared the performance of the rotating

RO device with a standard spiral wound RO module, using a commercially

available RO membrane under the conditions of very high recovery and

similar permeate flux. The results for 100% recovery of water from 0.01N

sodium chloride solution denoted that the spiral wound RO had poor rejection

(< 5%) compared to the rejection ratio for the rotating RO (> 75%) over a

period of 2 days.

Shahid Naveed et al (2006) focused on the membrane technologies

and found that different types of dyes and chemicals could be recovered from

the textile effluent. Using this technology a large proportion of wastewater

can be reused. Hence, the approach that employs primary treatment

methods, followed by coagulation and Reverse Osmosis through membranes,

is recommended.

ElDefrawy and Shaalan (2007) analyzed the utilisation of thousands

of tons of various chemicals for wet and dry processing. Effluents from wet

processing, for instance, are characterized by the presence of coloring,

hazardous and toxic pollutants. Numerous studies indicated the possibility of

using several opportunities for membrane based interventions for reuse /

recovery of water and chemicals. This work is concerned with a hybrid

treatment-recycling approach for decision making in the textile industry. The

results indicated that the use of membrane systems within the treatment-

recycling scheme reduces the wastewater treatment cost through the recovery

of chemicals and water. Further, the developed program proved to be a sound

software for decision making in the textile industry.

32

Garcia Figueruelo et al (2009) concentrated the wastewater

reclamation and reuses and found that NF of a secondary effluent from a

municipal wastewater treatment plant had been evaluated for increasing feed

concentration in order to reach a final conversion of approximately 75%.

Experiments were carried out with a laboratory plant containing a spiral

wound membrane with an active area of 2.2 m2.

A study on treatability of textile wastewaters in a bench – scale

experimental system, comprising an anaerobic biofilter, an anoxic reactor and

an aerobic membrane bioreactor (MBR). The MBR effluent was thereafter

treated by a Reverse Osmosis/Nanofiltration. The proposed system was

demonstrated to be effective in the treatment of the textile wastewater under

the operating conditions applied in the study. The MBR system achieved a

good (90 – 95%) removal, due to the presence of the anaerobic biofilter, also

effective color removal was obtained (70%). The addition of the RO/NF

membrane allowed the further improvement in COD (50 – 80%), color (70 –

90%) and salt removal (60 – 90% as conductivity). In particular the RO/NF

treatment allowed the also complete removal of the residual color and a

reduction of the conductivity such as to achieve water quality. (Selene Grilli

et al, 2011).

By employing fluids of the some composition (regarding foulants

and ionic strength) specific fouling resistances are unmeasured in the constant

flux filtration mode, indeed-end Ultrafiltration and cross flow Reverse

Osmosis tests, and compared with the respective resistances determined under

constant pressure. At the higher alginate proportions and for the greater

salinity (TDS 2000mg/L), the resistance from both Ultrafiltration and Reverse

Osmosis tests are correlated satisfactorily, versus pressure constant by a

single expression. These results significantly contribute towards developing

reliable tools for assessing water fouling potential and predicting Reverse

33

Osmosis membrane fouling evaluation in desalination plants. (Dimitrios et al,

2012)

Characterization of the concentrations and potential health risks of

chemical in recycled water is important if this source of water is to be safely

used to supplement drinking water sources. This research was conducted to

determine the concentration of volatile organic compound (VOCs) in

secondary Treated Effluent (STE) and post – Reverse Osmosis (RO)

treatment. The screening health risk assessment indicates that the individual

volatile organic compounds (VOC) measures in recycled water have a low

potential to affect humans from long – term consumption after Reverse

Osmosis treatment. Detection of Volatile Organic Compounds in secondary

Treatment Effluent can occur as a result of the widespread use of these

compounds. However, the impact on potable supplies through augmentation

with recycled water treated by Reverse Osmosis is likely to be negligible at

the concentration observed in Perth. (Clemencia Rodriguez et al, 2012)

2.4 REVERSE OSMOSIS MEMBRANE TECHNOLOGY

The concepts of "osmosis" and "reverse osmosis" have been known

for many years. In fact, studies on osmosis were carried out way back in

1748 by the French scientist, Nollet and many other researchers investigated

these phenomena over the next two centuries Mason (1991). However, the use

of reverse osmosis (RO) as a feasible separation process is a relatively nascent

technology. In fact, only in the late 1950’s, the work of Reid showed that

cellulose acetate RO membranes were capable of separating salt from water,

even though the water fluxes obtained were too small to be practical, Reid

and Breton, (1959), Ferguson (1980), Lonsdale (1982), Applegate (1984).

Since then, the development of new-generation membranes such as

the thin-film, composite membrane came into practice. They can tolerate wide

34

pH ranges, higher temperatures, and harsh chemical environments and have

highly improved water flux and solute separation characteristics, resulting in

many RO applications. In addition to the traditional seawater and brackish

water desalination processes, RO membranes have found many uses in

wastewater treatment, production of ultrapure water, water softening, and

food processing as well as in several other applications, Bhattacharyya et al

(1992).

The driving force for the development and use of RO membranes

stems from the advantages that these have over traditional separation

processes such as distillation, extraction, ion exchange, and adsorption.

Reverse osmosis is a pressure-driven process and hence no energy-intensive

phase changes or potentially expensive solvents or adsorbents are needed for

RO separations. Reverse osmosis is a process, inherently simple to design

and operate compared to many traditional separation processes. It also makes

it possible to implement simultaneous separation and concentration of both

inorganic and organic compounds.

Reverse osmosis membrane separations are, most importantly,

governed by the properties of the membrane used in the process. These properties

depend on the chemical nature of the membrane material (almost always a

polymer) as well as its physical structure. Properties for the ideal RO membrane

include that it is resistant to chemical and microbial attack, mechanically and

structurally stable over long operating periods, and that they have the desired

separation characteristics for each particular system. However, only a few

membranes satisfy all these criteria and so compromises must be made to select

the best RO membrane available for each application. Excellent discussions of

RO membrane materials, preparation methods, and structures exist in studies by

Cadotte et al (1981), Kesting (1985), Lonsdale (1987), Cabasso (1987), Koros

et al (1988), Baker (1990), Petersen and Cadotte (1990).

35

Some of the currently available RO membranes fall into two

categories: asymmetric membranes containing one polymer, and thin-film,

composite membranes consisting of two or more polymer layers.

Asymmetric RO membranes have a very thin, selective skin layer supported

on more porous sublayer of the same polymer. The dense skin layer

determines the fluxes and selectivities of these membranes while the porous

sublayer serves only as a mechanical support for the skin layer. It has a little

effect on the membrane separation properties. Since the skin layer is very

thin (from 0.1 to 1 µm), the membrane resistance to water transport (which is

proportional to the dense skin thickness) is much lower and, as a result, water

fluxes appear much higher than those through comparable symmetric

membranes in the investigations of Lonsdale (1987), Baker (1990).

Asymmetric membranes are most commonly formed by a

phase inversion (polymer precipitation) process. In such a process, a

polymer solution is precipitated into a polymer-rich solid phase that forms the

membrane and a polymer-poor liquid phase that forms the membrane pores or

void spaces. The rate of precipitation is a factor in determining pore

characteristics: a rapid precipitation tends to produce pores that are small and

asymmetric while a slow precipitation produces more symmetrical pores that

are relatively large, vide Kesting (1985), Cabasso (1987), Baker (1990).

The thin-film composite membranes consist of a thin polymer barrier

layer formed on one or more porous support layers (almost always a different

polymer from the surface layer). The surface layer determines the flux and

separation characteristics of the membrane; the porous backing serves only as a

support for the barrier layer and also has almost no effect on membrane transport

properties. The barrier layer is extremely thin, of the order of 0.1 µm or less,

thus allowing high water fluxes, in the studies of Cadotte et al (1981), Lonsdale

(1987), Baker (1990), Petersen and Cadotte (1990).

36

The most important thin-film, composite membranes are made by

interfacial polymerization, a process in which a highly porous membrane

(usually polysulfone) is coated with a polymer or monomer and then reacted

with a cross-linking agent. A dense, cross-linked polymer layer forms at the

solution interface and since the cross-linking reaction occurs mostly at the

solution interface, the resulting barrier layer is extremely thin. A less cross-

linked, more permeable layer forms under the surface layer and fills the

pores of the support membrane, vide Cabasso (1987), Baker (1990),

Petersen and Cadotte (1990). These thin, highly cross-linked polymer

membranes can have much higher selectivities and water fluxes compared to

the asymmetric type since the barrier layers of the composite membranes are

usually much thinner than those of the asymmetric membranes. One of the

most widely used thin-film, composite membrane consists of cross-linked

aromatic polyamide on a polysulfone support layer.

The exact nature of the structure of the thin skin of asymmetric or

thin-film, composite RO membranes are unclear and are still a point of

debate. In order to model RO membrane separations, some researchers have

viewed the skin as a homogeneous film of polymer containing no pores or

voids unless these are present as imperfections Lonsdale et al (1965),

Sherwood et al (1967), Pusch (1986), Soltanieh and Gill (1981) and Bitter

(1991). They assumed that solvent or solute transport occurred through the

interstitial spaces of the polymer chains. Other researchers believed that the

barrier layer is microporous. That is, extremely small pores or voids (usually

< 30 A radius) are formed during casting and transport occurs through these

pores Merten (1966), Jonnson and Boesen (1975), Soltanieh and Gill (1981),

Bhattacharyya et al (1986), Mehdizadeh and Dickson (1989). However,

others have considered a more complex view of the barrier layer in RO

membranes. Kesting (1990) postulated that the layer consists of polymer

nodules (clusters of polymer macromolecules) and nodule aggregates; he

37

indicated that transport can occur through chain segment displacements in the

polymer nodules (interstitial spaces) and through spaces between nodule

aggregates (defect pores). Likewise, Tam et al (1991) considered the fractal

(random) nature of pore distribution and geometry in the barrier layer. Their

analysis recognized the randomness that could occur during the formation of

the barrier layer pores.

Characterization of RO membranes is important since this allows an

insight into the relationship between membrane chemistry, structure, and

transport properties. The measurement of water flux and solute (usually NaCl)

rejection for the membrane is the most widely used characterization method.

These can be easily measured because they give a quick indication of the

suitability of a particular membrane for an application. However, fluxes

provide only limited information about the characteristics and structure of the

membrane and the role these play in water and solute transport. As a result,

other characterization techniques are to be employed in order to determine

parameters such as pore size, barrier layer thickness, and membrane elemental

composition.

Simon and Calmon (1986), Pusch (1986) discussed the

measurement of several RO membrane characteristics, including overall

membrane thickness, water content, membrane potential, ionic exchange

capacity, etc. In addition, Bhattacharyya et al (1986), Han (1989) Han and

Bhattacharyya (1991) described the use of vapor adsorption data of carbon-

dioxide and nitrogen gases in order to determine pore volumes and pore size

distributions for cellulose acetate and composite aromatic polyamide

membranes. Alternatively, several researchers have used experimental flux

data and solute-membrane interaction parameters in order to calculate pore

sizes and distributions, vide Jonnson and Boesen (1975), Mehdizadeh and

Dickson (1989). Glaves and Smith (1989) indicated that nuclear magnetic

38

resonance (NMR) may also be suitable for determining membrane pore

structures. Kesting (1985), Cabasso (1987). Petersen and Cadotte (1990)

and Kesting (1990) designed Scanning Electron Micrographs (SEM) for

asymmetric and composite membranes. Although they indicated that no

information on the barrier layer pore structure was discernible from the

micrographs, they pointed out that the asymmetric or composite nature of the

membranes was clearly visible and that it was possible to approximate

the barrier layer thickness from the micrographs. Bartels (1989) also

examined the membrane barrier layer for composite membranes with both

SEM and Transmission Electron Microscopy (TEM).

Considerable attention has been given to the application of

spectroscopic techniques to the characterization of RO membranes. Bartels

(1989) examined RO membranes using infrared (IR) spectroscopy; it found

that IR provided valuable information on the functional groups (such as

carboxylic acid or amide groups) present in the composite membrane studied.

Arthur (1989) made similar studies with several different composite RO

membranes. Avlonitis et al (1992) studied changes in aromatic polyamide

membranes caused by chlorine degradation by following changes in the

membranes IR spectra. Koo et al (1986), Bartels (1989) and Arthur (1989)

used X-ray photoelectron spectroscopy (XPS), to examine elemental

compositions of composite RO membranes near the surface. This technique

supplied verification of the polymer chemical structures, expected from the

interfacial polymerization reactions that formed the membranes. Bartels,

(1989) also used Rutherford backscattering spectroscopy (RBS) to determine

elemental composition. Interestingly the results were similar to those obtained

by XPS.

The membrane material largely determines the water and solute

fluxes in RO process and Bhattacharyya et al (1992) pointed out that the

39

packaging of the RO membrane is also extremely important to the feasibility

of the process. In their opinion, the requirements of a membrane module

include: (i) that it offers mechanical support to the fragile RO

membrane even at high operating pressures (upto 8 MPa); (ii) that the design

minimizes pressure drop across the module as well as fouling and

concentration polarization and (iii) that the module is relatively inexpensive

and easy to replace in the membrane process. The most common and

commercially available membrane modules include plate-and-frame, tubular,

spiral-wound, and hollow-fiber elements.

Plate-and-frame modules consist of stacks of flat sheet membrane

placed on supports. In this modules, each membrane and support are

separated by spacers which direct the feed across each membrane and channel

the permeate out of the module Allegrezza (1988), Baker (1990),

Bhattacharyya et al (1992). While this module is resistant to fouling, it has a

low membrane surface area per element (defined as packing density) and this

makes it expensive and can limit its use in areas with space restrictions.

Tubular membrane elements consist of membrane tubes (typically 1.3 cm in

diameter) supported within perforated stainless steel tubes. As the feed flows

through the tubes, the permeate passes through the membrane and support

Allegrezza (1988), Bhattacharyya et al (1992). While these elements are also

fouling-resistant and are easy to clean, the modules have a low packing

density and can be expensive to operate because of the necessity of high feed

flow rates. With the same drawbacks in plate-and-frame and tubular element,

these will continue to occur if modules are used.

The spiral-wound and hollow-fiber elements are the most widely

used. A spiral-wound element consists of flat sheets of membrane separated

by spacers that are rolled around a perforated collection tube. The feed is

channeled across these rolled membrane sheets, permeating through the

40

membrane. Then it is collected in the center tube, Allegrezza (1988),

Bhattacharyya et al (1992).

Calabro et al (1990) analyzed the membrane processes in the textile

industry and found that they could minimize pollution phenomena and also

decrease energy consumption; increase product quality and improve the

overall process efficiency. In this study, the energy consumption of simulated

textile processes have been analyzed and compared with systems where

membrane technologies have been introduced. The value of dye and salt

concentration which might be reached has been tested in a reverse osmosis

pilot plant. The hydrodynamic characteristics of the spiral wound modules

used and the evaluation of their efficiency in terms of rejection, fluxes and the

life time of the membranes are reported. Based on experimental results, the

electrical energy consumption in reverse osmosis and in an integrated reverse

osmosis - membrane distillation process has been calculated and compared to

the cycles with chemical recovery and without recovery.

Rosa Maria Ribeiro et al (2002) compared the membrane study of

asymmetric polymeric membranes synthesis, made for color and turbidity

removal of an industrial textile effluent. It was previously treated by a

biological treatment. This resulted in 8 membranes, which were synthesized

by a phase inversion process. The physical process of separation by

membranes (ultrafiltration) was studied to improve the color and turbidity

removal of the textile effluent. In addition to the color and turbidity

parameters, an analysis was made for the permeate flux through synthesized

membranes. The best results of these parameters were obtained with the

membranes: Ml (polysulfone 13% and salt 0%), M2 (polysulfone 13% and

salt 5%) and M3 (polysulfone 18% salt 5%). Working with these results, three

more membranes were synthesized for checking the performance of the

membranes and the results confirmed these performances.

41

Hsing-Yuan Yen et al (2002) studied the membrane separation and

its influence. Different operating parameters on the treatment of effluent by

polyamide membrane separation for reuse in the textile factory were used

systematically in the temperature range 15-45 °C and applied pressure ranging

between 50-200 psi. The results showed that the flux of water increased and

solute rejection also increased with an increase in applied pressure. The flux

of water increased and solute rejection decreased with an increase in

temperature. The flux of water decreased and solute rejection increased with

an increase in solute concentration in the feed. Moreover, the flux of water

was proportional to the applied pressure. The solute rejection was found to be

a nonlinear function of the applied pressure and temperature. In a comparison

of the values of rejection, the separation ability of polyamide membrane

decreases in the order of inorganic less than organics.

Reverse Osmosis membranes are becoming increasingly popular

for water purifications application that require high salt rejection such as

brackish and sea water desalination. Biofouling leads th the use of higher

operating pressure, more frequent chemical cleaning, and shorter membrane

life. This paper reviews the causes, consequences and control cost biofouling

in RO membranes used for sea water desalination. A section of consequence

of biofouling on membrane processes with particular emphasis on water

permeability and salt rejection. The most notable deleterious consequences of

membrane biofouling include increased hydraulic resistance, decreased

membrane permeability, enhanced concentration polarization, and decreased

salt rejection. The most notable deleterious consequences of membrane

biofouling include increased hydraulic resistance, decrease membrane

permeability, enhance concentration polarization, and decreased salt rejection.

The siginificant deterioration in the performance and efficiency of the RO

membranes and hence the whole plant translates to more expenditures

42

associated with more frequent cleaning and replacement of the membranes.

(Asif Matin et al, 2011)

A major breakthrough in the preparation of the thin film composite

(TFC) membrane via interfacial polymerization techniques has resulted in

tremendous achievements in producing a membrane with a right combination

of flux and salt rejection, and generating huge interest in industrial sections.

In this paper reviews the recent research progress of the TFC membrane

science and technology, particularly in the fields of water related separation

progresses. Continuous improvements in TFC membrane performances with

respect to permeability, selectivity and stability perhaps in the future will

wider the applications of membranes to new areas. (Lauo et al, 2012)

Polyvinylidene fluoride (PVDF) hollow fibre membrane with

interconnected bicontinuous structures were produced from Polyvinylidene

fluoride (PVDF)/Triethyl phosphate (TEP) solution using a single – step

phase inversion method. Hollow fibre with excellent mechanical strength and

very dense inner and outer skin layers were obtained using PVDF/TEP

solutions. Due to the hydrophobic nature of PVDF and formation of the

dense skin layers, the produced membranes were not suitable for water and

wastewater applications. In order to improve the water flux, two different

molecular weight Polyethylene glycol (PEG) employed to eliminate the dense

skin and as pore – forming agent additives. A wide range of Reverse Osmosis

hollow fibre membranes suitable for water and wastewater treatments and

similar to modified industrial PVDF Reverse Osmosis membrane were

produced by using PVDF/TEP/PEG dope solutions with the adjusted spinning

parameters. (Mogharesh Abed 2012).

The purification of wastewater from various industrial processes is

a worldwide problem of increasing importance due to the restricted amount of

43

water suitable for direct use, the high price of the purification and the

necessity of utilizing the waste product. Maintaining the drinking water

quality is essential to public health. Municipal agricultural and industrial

liquid or solid wastes differ very much in there chemical, biological and

biological characteristics. The diverse spectrum of waste requiring efficient

treatment has focused the attention of researches on membrane, iron-exchange

and biological technologies. Membrane and membrane separation techniques

with immobilized microorganism on enzyme have significant in treatment of

distillery water. (Pawar Avinash Shivajirao 2012).

2.5 MEMBRANE FILTRATION

Rekha et al (2009) recommended a zero effluent process by using a

membrane type solute separation system for a wet process house. In this

study, reactive and disperse dyes were used for the dyeing process and the

textile wastewater, which contains sizes, thickeners, pigments and

soaps. It was passed through ultrafiltration, nanofiltration and reverse osmosis

membranes. Experimental results reported that only a small fraction of

about 15 ± 3%, resulting from membrane filtration, was not reusable

and unsuitable for processing.

Altenbaher and Turk (2009) treated the wastewater generated by a

textile factory during dyeing of cotton with reactive dyes using membrane

filtration. Three membranes were used in this study, one membrane for

nanofiltration (NF) and the other two membranes for reverse osmosis

(RO). The value of pH, COD, conductivity and coloration in terms

of SAC were determined before and after filtration. The results revealed

that the treated wastewater could be reused in the dyeing process.

A novel aromatic polyamide asymmetric nanofiltration membrane

has been used for the treatment of dye aqueous solutions, Ren et al (2010).

44

The nanofiltration membrane was prepared using a phase inversion method.

The effects of various parameters such as pH and feed temperature were

evaluated and the results showed that the rejection of acid, direct and

reactive dyes were all above 95%. The copoly (phthalazinone biphenyl

ether sulfone) (PPBES) ultrafiltration (UF) membrane with a low molecular

weight cut-off possesses excellent thermal resistance which is suitable

for use in dye wastewater treatment at a high temperature Han et al (2010). It

showed 100% rejection for congo red, sulfur black B and gentian violet.

Arulchinnappan and Rajendran (2011) analyzed the model used for

estimation of reverse osmosis permeate parameters pertaining to the data

obtained from Tirupur textile dyeing industry. They examined the variables

that contribute to the deterioration of membrane. The result demonstrated the

capability and effectiveness of the proposed model to assign membrane. The

study system requires an accurate and efficient prediction model. The

proposed model utilizes different membership values adequately to fit fuzzy

regression models on for RO process data.

2.6 SCOPE FOR THE PRESENT STUDY

From the literature survey, it was found that there were lot of

researches has been done on the textile effluent treatment especially on

Reverse Osmosis. But till there is gray area towards the selection of suitable

membrane depends upon the nature of dyeing industry, chemicals used,

processes involved and type of wastewater generated etc., Hence there is a

scope for selection of unique RO membrane for different types of industries

based on the simulation studies and validation for the better performance of

RO.