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CHAPTER I INTRODUCTION 1.1 GENERAL

Reverse Osmosis (RO) was invented in 1959 by Prof Reid of the University of Florida, and was put into practical use by Sidney Loeb and Srinivasa Sourirajan. Reverse osmosis is a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low

solute concentration, through a membrane, to an area of high solute

1

concentration

when

no

external

pressure

is

applied.

Figure 1.1 Reverse Osmosis Process The membrane here is semi permeable, meaning it allows the passage of solvent but not of solute. The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane. Reverse Osmosis is the phenomenon of water flow through a semi permeable membrane that blocks the transport of salts or other solutes through it. It removes both dissolved organics and salts. Reverse osmosis is used to reject bacteria, salts, sugars, proteins, particles, dyes, and other constituents. Separation of ions with reverse osmosis is aided by charged particles. This means that dissolved ions that carry a charge, 2

such as salts, are more likely to be rejected by the membrane .The larger the charge and the particle, the more likely it will be rejected.

Figure 1.2 Reverse Osmosis Principle Reverse

Osmosis

is

for

de-salination

and

purification

of

brackish(other than sea water) and sea water for drinking and industrial use. This can also be used for a variety of specialized membrane applications for chemical recovery and waste water reclamation projects. The process achieves rejections of 99.9% of viruses, bacteria and

pyrogens. So

osmosis is widely used in waste water treatment.

3

now a days

this reverse

Figure 1.3 MOLECULE SIZE COMPARISON 1.2. CLEAN-IN-PLACE CIP (Clean-in-Place) is a method of cleaning the interior surfaces of pipes, vessels,

process

equipment,

and

associated

fittings,

without

disassembly . The closed systems were disassembled and cleaned manually. The advent

of CIP was a boon to industries that needed frequent internal

cleaning of their processes. Industries that rely heavily on CIP are those requiring high levels of hygiene, and include: dairy, beverage, brewing, processed foods, pharmaceutical, and cosmetics. The benefit to industries that use CIP is that the cleaning is faster, less labour intensive and more repeatable, and poses less of a chemical exposure risk to people. CIP started as a manual practice involving a balance tank, centrifugal pump, and connection to the system being cleaned. Since the 1950s, CIP has evolved to include fully automated systems 4

with programmable logic controllers, multiple balance tanks, sensors, valves, heat exchangers, data acquisition and specially designed spray nozzle systems. Simple, manually operated CIP systems can still be found in use today.

CHAPTER 2 LITERATURE REVIEW

5

1) Brackish water RO desalination plants installed by CSMCRI. Base on the indigenous TFC membranes, CSMCRI has designed, fabricated and installed several brackish water RO desalination plants having product water capacities in the range 1000-5000 LPH to cater to the needs of rural community in TN., Gujarat, W.B., and Rajasthan in the last few years. In this regard, Department of Science and Technology, New Delhi has provided the financial assistance while state Science & Technology Councils of different states have provided the logistic support like site selection and infrastructure. The success of RO desalination units has made considerable impact on decision making authorities who are now more amenable to the idea of RO desalination of providing water in problem villages. Before RO the water is sent to the cartridge filter where 10 and 5 micron pore size is used. CSMCRI has also fabricated a mobile desalination unit by mounting a small RO unit (500 LPH product water) on a mobile van.

2) Characterization of foulants by autopsy of RO desalination membranes

F. H. Butt, F. Rahman and U. Baduruthamal Research Institute, King Fahd University of Petroleum and Minerals, Box 1891, Dhahran 31261, Saudi Arabia Received 16 October 1996; accepted 21 July 1997.Available online 14 April 1998

A study was undertaken to identify various types of scales that were responsible for shortening the useful life span of the membrane permeators in a commercial reverse osmosis (RO) desalination plant. Compositions of the raw and treated feed water and of the reject brine were determined using the inductively coupled plasma (ICP) spectrometry and ion chromatography (IC). Various scaling index calculations showed that the feed and brine were non-scale forming with respect to CaCO3 (calcite), SrSO4, CaSO4.2H2O (gypsum), and silica 6

(SiO2). Two completely fouled membrane permeators, retired from stage 1 and stage 2 of a commercial plant, were subjected to membrane autopsy using scanning electron microscopy (SEM), X-ray diffractometry (XRD), optical microscopy (OM), and energy dispersive x-ray florescence (XRF). The deposits were predominantly amorphous in nature. The membrane autopsy showed that CaCO3, SrSO4, and CaSO4.2H2O (gypsum) scales did not constitute a serious problem in the plant. The advanced phosphonate+polyacrylate based scale inhibitor had itself formed Ca phosphonate sludge, but the amount was quite small. Though below saturation, silica is believed to have been precipitated due to the catalyzing effect of trivalent Al3+ and Fe3+ ions. Iron fouling was the major cause of reduced life span of the membranes and, to a lesser extent, calciumalumino-silicates

3) Fouling Development on Reverse Osmosis Membranes Fouling is a major obstacle that prevents efficient operation of reverse osmosis (RO) systems, causing deterioration of both the quantity and quality of treated water, and consequently resulting in higher treatment cost.

4) Chemical cleaning of reverse osmosis membranes

Fouling is the most important problem associated with the application of membranes. A strategy for membrane regeneration is chemical cleaning of the fouled

membranes. One

of

the

major

applications

of reverse osmosis

membranes is processing of water from different resources or for various applications. This includes desalination or ion removal for makeup water for boilers. In all cases fouling restricts membrane performance. In this work reverse osmosis membranes were fouled with water. Chemical cleaning of the RO membranes using acid, alkaline, surfactant and detergent solutions has been discussed. Cleaning efficiency depends on the type of the cleaning agent and 7

its concentration. It has been shown that the efficiency increases with increasing the concentration of the cleaning agent. Operating conditions such as crossflow velocity, turbulence in the vicinity of the membrane surface, temperature, pH and cleaning time also play a role in the cleaning process. Optimum

membrane

cleaning

requires

in

depth

understanding

of

the

interactions between the foulants and the membrane as well as the effect of the cleaning

procedure

on deposit removal and membrane

performance.

5) Membrane autopsy — a case study L. Y. Dudley and E. G. Darton Houseman Desalination Products, The Priory, Burnham, Slough SL1 7LS, UK Received 31 May 1995; accepted 30 June 1995. Available online 11 December 1998. This paper describes the authors' experiences of membrane autopsy procedures to identify the cause of poor membrane performance at a European power plant and the subsequent proposals made for improvement to the operating, pretreatment and cleaning programmes. The reverse osmosis (RO) system is a 2,500 m3/d unit producing water for cooling purposes. The 3-year-old plant experienced continual output loss, which required the membranes to be cleaned on a twice weekly basis, which increased to every 4 days in warm weather. The autopsy objective was to carry out a destructive analysis on a fouled membrane to identify the major causes of the fouling. These were identified as being biological in nature with the significant presence of iron, which together formed a biomass on the membrane surface.

CHAPTER 3 CONFIGUREURATIONS OF REVERSE OSMOSIS

8

3.1 GENERAL CONFIGUREURATIONS 3.1.1 FEED PRESSURE The feed pressure is the most important parameter, which helps the membrane to provide good efficiency. The pressure varies from 10kg/cm

2

to 28

kg/ cm 2. Usually 2–17 bar (30–250 psi) for fresh and brackish water, and 40–70 bar (600–1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome. 3.1.2 PERMEATE PRESSURE The permeate pressure is the output pressure of the membrane, it will be lower than the feed pressure. But the pressure difference

between feed pressure and permeate

pressure should be less than 4.

P = feed pressure – permeate pressure = less than 4

3.1.3.

FLOW RATE The waste water which should be treated through the membrane is let in to

the membrane input. That is known as flow rate. This flow depends upon the production of the industry. It may vary.

3.1.4. PERMEATE FLOW The out let flow from the membrane is called permeate flow. This will be lesser than the feed flow because of the filtration process done inside the membrane and some amount is rejected.

9

3. 1.5 DIRECTION OF FLOW OF WATER: The direction of water inside the membrane is in two types. They are 1) Cross - flow membrane filtration In cross flow filtration, the feed is passed across the filter membrane (tangentially to the filter membrane) at some pressure difference. Material which is smaller than the membrane pore size passes through the membrane as permeate or filtrate, and everything else is retained on the feed side of the membrane as retentive. In this the feed water direction and reject water flow will be in same direction. The permeate water direction will be perpendicular to that. Most probably spiral wound membrane has this filtration.

Figure 3.1 CROSS-FLOW MEMBRANE FILTRATION

2) Dead – end membrane filtration This is a filtration technique in which all the fluid passes through the membrane, and all particles larger than the pore size of the membrane are retained at its surface. This means that the trapped particles start to build up a "filter cake" on the surface of the membrane, which has an impact on the efficiency

of

the filtration process. 10

Figure 3.2 DEAD-END MEBRANE FILTRATION

3. 1.6 TYPES OF MEMBRANE BASED ON SOURCE OF WATER 1) Brackish water membrane 2) Sea water membrane The sea water membrane is used for treating the sea water only having high TDS vale(more than 3500 mg/lt). So the brackish membrane is used for treating the effluents of municipal and industrial waste water.

3. 1.7 MEMBRANE MATERIALS 1. CTA (cellulose triacetate or CA), 2. Polyamides (TFC – Thin Film Composite)

11

Figure 3.3 TFC- POLYAMIDE WITH CARBOXYLATE GROUPS

The membrane material refers to the substance from which the membrane itself is made. Normally, the membrane material is from and

a

synthetic

metallic

membranes polymeric

polymer,

“membranes,” manufactured

material,

since

for

although

other

may

available.

be

drinking

they

are

water

forms,

including

Currently,

production

significantly

manufactured

less

ceramic

almost

are

all

made

expensive

of

than

membranes constructed of other materials. The material properties of the membrane

may

significantly impact

the

design

and

operation

of

the

filtration system. For example, membranes constructed of polymers that react with oxidants commonly used in drinking water treatment should

not

be used with chlorinated feed water. Mechanical strength is another consideration,

since a membrane

with greater strength can withstand

larger transmembrane pressure (TMP) levels allowing for greater operational flexibility and the use of higher pressures with pressure-based direct integrity testing Similarly, a membrane with bi-directional strength may allow cleaning operations or integrity testing to be performed from either the feed or the filtrate side of the membrane. Material properties influence the exclusion characteristic of a membrane as well. A membrane with a particular surface charge may achieve enhanced removal of particulate or microbial contaminants of the opposite surface charge due to electrostatic 12

attraction.

In

addition,

a

membrane

can

be

characterized

as

being

hydrophilic (i.e., water attracting) or hydrophobic (i.e., water repelling). These terms describe the ease with which membranes can be wetted, as

well as

the propensity of the material to resist fouling to some degree. MF membranes may be constructed from a wide variety of materials, including cellulose acetate

(CA),

polyvinylidene

fluoride

(PVDF),

polyacrylonitrile

(PAN),

polypropylene (PP), polysulfone (PS), polyethersulfone (PES), or other polymers. Each of these materials has different properties with respect to surface charge, degree of hydrophobicity, pH

and oxidant tolerance, strength, and

flexibility. RO membranes are generally manufactured from cellulose acetate or polyamide materials (and their respective derivatives), and there are various advantages

and

disadvantages

associated

with

each.

While

cellulose

membranes are susceptible to biodegradation and must be operated

within

a relatively narrow pH range of about 4 to 8, they do have some resistance

to

continuous low-level oxidant exposure. In general, for example, chlorine

doses

of 0.5 mg/L or less may control biodegradation as well as biological

fouling

without damaging the membrane. Polyamide (PA) membranes, by contrast, can be used under a wide range of pH conditions and are not

subject to

biodegradation. Although PA membranes have very limited tolerance for the presence of strong oxidants, they are compatible with weaker

oxidants such

as chloramines. PA membranes require significantly less pressure to operate and have become the predominant material used for RO characteristic that influences the performance of all membranes

applications. A is the trans-

wall symmetry, a quality that describes the level of uniformity throughout the cross-section of the membrane. There are three types of construction that are commonly used in the production of membranes: symmetric, asymmetric (including both skinned and graded density variations), and composite. Crosssectional diagrams of membranes with different trans-wall symmetry are material, while composite membranes use different

(i.e., heterogeneous) materials.

Symmetric membranes may be either homogeneous or heterogeneous. In a symmetric membrane, the membrane

is uniform in density or pore structure

throughout the cross-section, while in

an asymmetric membrane there is a

change in the density of the membrane material across the cross sectional area. 13

Some asymmetric membranes have a graded construction, in which the porous structure gradually decreases

in density from the feed to the filtrate side of the

membrane. In other asymmetric membranes, there may be a distinct transition between the dense filtration in layer (i.e., the skin) and the support structure. The denser skinned layer is exposed to the feed water and acts as the primary filtration barrier, while the thicker and more porous under structure serves primarily as mechanical support. Some hollow fibres may be manufactured as single- or double- skinned membranes, with the double skin providing filtration at both the outer and inner walls of the fibres. Like the asymmetric skinned membranes, composite membranes also have a thin, dense layer that serves as the filtration barrier. However, in composite membranes the skin is a different material than the porous substructure onto which it is cast. This surface layer is designed to be thin so as to limit the resistance of the membrane to the flow of water, which passes more freely through the porous substructure. NF and RO membrane construction is typically either asymmetric or composite, while most MF, UF, and MCF membranes are either symmetric or asymmetric

3. 1.8 TYPES OF MEMBRANES MODULE: Membranes are never applied as one flat plate, because this large surface often results in high investing costs. That is why systems are built densely to enable a large membrane surface to be put in the smallest possible volume. 3. 1.8.1 TUBULAR MEMBRANES Tubular membranes are not self-supporting membranes. They are located on the inside of a tube, made of a special kind of material. This material is the supporting layer for the membrane. Because the location of tubular membranes is inside a tube, the flow in a tubular membrane is usually inside out. The main cause for this is that the attachment of the membrane to the supporting layer is very weak. Tubular membranes have a diameter of about 5 to 15 mm. Because of the size of the membrane surface, plugging of tubular membranes is not likely to 14

occur. A drawback of tubular membranes is that the packing density is low, which results in high prises per module

. Figure 3.4 Tubular membranes

3. 1.8.2 CAPILLARY MEMBRANES With capillary membranes the membrane serves as a selective barrier, which is sufficiently strong to resist filtration pressures. Because of this, the flow through capillary membranes can be both inside out and outside in. The diameter of capillary membranes is much smaller than that of tubular membranes, namely 0.5 to 5 mm. Because of the smaller diameter the chances plugging are much higher with a capillary membrane. A benefit is that the packing density is much greater.

15

Figure 3.5 Capillary membranes

3. 1.8.3 HOLLOW FIBRE MEMBRANES Hollow fibre membranes are membranes with a diameter of below 0.1 µm. consequentially, the chances of plugging of a hollow fibre membrane are very high. The membranes can only be used for the treatment of water with a low suspended solids content. The packing density of a hollow fibre membrane is very high. Hollow fibre membranes are nearly always used merely for nanofiltration and Reverse Osmosis (RO). These membranes are mostly used for gas separation and filtration. • • • •

Outside diameter: 0.5 – 2.0 mm Inside diameter: 0.3 – 1.0 mm Fiber wall thickness: 0.1 – 0.6 mm Fiber length: 1 – 2 meters

16

Figure 3.6 HOLLOW FIBRE MEMBRANE

3. 1.8.4 SPIRAL WOUND MEMBRANES The design of spiral wound elements contains two layers of membrane glued back to back onto a permeate collector fabric(permeate channel spacer). This membrane envelope is wrapped around a permeate empties from the permeate channel spacer. A plastic netting into the device and maintains the feed stream channel spacing. It also promotes mixing of the feed stream to minimize concentration polarization. Spiral membranes consist of two layers of membrane, placed onto a permeate collector fabric. This membrane envelope is wrapped around a centrally placed permeate drain (see picture below). This causes the packing density of the membranes to be higher. The feed channel is placed at moderate height, to 17

prevent plugging of the membrane unit.Spiral membranes are only used for nano filtration and Reverse Osmosis (RO) applications.

Figure 3.7 Spiral wound membrane module

3. 1.8.5 DISK MEMBRANE MODULE

18

Figure 3.8 DISK MEMBRANE MODULE

3. 1.8.6 PLATE MEMBRANE MODULE These type of membrane will be in flat.

Figure 3.9 PLATE MEMBRANE MODULE 3. 1.8.7 PILLOW-SHAPED MEMBRANES

Membranes that consist of flat plates are called pillow-shaped membranes. The name pillow-shaped membrane comes from the pillow-like shape that two membranes have when they are packed together in a membrane unit. Inside the ‘pillow’ is a supporting plate, which attends solidity. Within a module, multiple pillows are placed with a certain distance between them, which depends on the dissolved solids content of the wastewater. The water flows through the 19

membranes inside out. When treatment is done, the permeate is collected in the space between the membranes, where it is carried away through drains.

3. 1.9 MEMBRANE SYSTEMS The choice for a certain kind of membrane filtration system is determined by a great number of aspects, such as the benefits of membrane filtration , costs, risks of plugging of the membranes, packing density and cleaning opportunities. The arrangement of the RO membranes in the vessels are termed as membrane system arrangement. Generally system of RO is many types .They are 1) Single module system:

Single module system retreats its own reject water along with feed water.

Figure 3.10 SINGLE MODULE SYSTEM

20

2) Single array system: In this system the permeate and reject are collected separately and the reject is not again taken as feed and treated.

Figure 3.11. SINGLE ARRAY SYSTEM

2) Multi array system

This system is twice of single array system, which takes first system’s concentrate as feed for second system

21

Figure 3.12 MULTI ARRAY SYSTEM 4) Permeate staged system: This system is differed from others, here first membrane’s permeate is used as feed water to second membrane module and second membrane’s concentrate is mixed with first membrane’s feed water.

Figure 3.13 PERMEATE STAGED SYSTEM

3. 1.10 SYSTEM COMPONENTS: 1) High pressure pump. 22

2) Pressure vessel 3) Shut down switches 4) D.C.S. system(control room) 5) Control instruments. 6) Tanks 7)

Pressure gauges.

3. 1.11 SAMPLING METHODS The two most common approaches for sampling are the grab and composite methods. 1) Grab sampling involves the collection of one or more aliquots from the feed or filtrate stream, 2) composite sampling involves collection of the entire process stream for processing and subsequent analysis.

3. 1.12 FACTORS INFLUENCING R.O. PERFORMANCE 1) Flow rate 2) TDS value 3) Decrease in permeate flow and pressure 4) Scaling 5) Fouling (major problem caused) 6) Recovery of permeate Table 3.1 FACTORS INFLUENCING MEMBRANE PERFORMANCE

23

INCREASING

PERMEATE FLOW

SALT PASSAGE

Effective pressure

Increase

Decrease

Temperature

Increase

Increase

Recovery

Decrease

Increase

Feed salt

Decrease

Increase

FOULING Foreign materials which may be present in the feed water such as hydrates of metal oxides, calcium precipitates, organic and biological mater. This includes all kind of build–up of layers on the membrane surfaces. Inner surface of the feed line tubing and the feed end scroll of the membrane element if it is reddish brown, fouling by iron material may be considered.

Three kinds of fouling that reduces membrane performance A membrane treatment system can be fouled by virtually anything present in the water being fed to the unit. However, in common treatment systems such as reverse osmosis, the fouling materials may be generally categorized as inorganic, organic, or biological. Inorganic compounds that cause fouling of membrane modules include inorganic salts with low solubility. These may enter the treatment system in particle form, or they may precipitate inside the system as a result of concentration changes occurring in the feed water as permeate is recovered through the membrane. The highest concentration of dissolved solids happens to occur immediately adjacent to the surface of the membrane in the treatment module. If the feed water contains salts of low solubility, it is likely that these salts will precipitate on the surface of the membrane to form scale. Salts such as 24

calcium carbonate (CaCO3) and calcium sulfate (CaSO4) are common in most feed waters. Other salts such as barium sulfate (BaSO4), strontium sulfate (SrSO4), and calcium fluoride (CaF2) also may be in solution. In many feed water sources these salts are present at or near their solubility limits and will precipitate as the concentration of the feed water increases in the system. Although this precipitation can be controlled with proper pretreatment, fouling due to these salts does occur frequently because of operator error or unknown changes in feed water quality. Metal hydroxides are other inorganic compounds that cause fouling. The most common culprits are iron hydroxide, (Fe(OH3)) and aluminum hydroxide, (Al(OH3)). As in the case of inorganic salts, these hydroxides may enter the system as suspended particles or they may form inside the system. Unlike the inorganic salts however, metal hydroxides do not deposit a hard crystalline scale but rather a soft, gelatinous layer. Clay, silt and other silica-based materials can cause fouling if the particles are not removed in the pretreatment equipment located in the process train ahead of the membrane treatment system. In some feed water sources clay occurs as very finely divided (1 to 5 micron) particles. These small colloidal particles can be very difficult to remove with conventional equipment. Silica may also enter the membrane system in the dissolved or reactive form. This low molecular form of silica will polymerize as the feed water concentration increases at the surface of the membrane. The resulting solid silica deposit on the membrane can be extremely difficult, if not impossible, to remove. Organic compounds make up the second category of fouling materials. Surface water sources like rivers and lakes may contain naturally occurring organics, for example humic acids. Clarified water may contain residual polymers, and wastewater influents may contain any number of organic compounds. The mechanism behind organic fouling depends upon the size and chemical nature of the specific substance causing fouling. High molecular weight compounds may act more as particles and can plug the feed spacer in the membrane element.

25

This plugging may be worsened if inorganic particles, such as clays and metal hydroxides, also are present.

Figure 3.14 FOULED MEMBRANE Low molecular weight organics may foul the surface of the membrane through chemical interaction. As an example, chlorinated phenols will adhere to the surface of an RO membrane by means of hydrogen bonding. In this situation, a small concentration of the chlorinated phenol in the feed water can cause a large loss of flux in the treatment system. Biological organisms also are troublesome because of their tendency to foul membrane surfaces. Although they are technically organic, biological organisms demand special consideration. In terms of fouling, the concern is primarily with single cell organisms. These include bacteria, algae and fungi. Of these, bacteria cause the majority of problems in membrane water treatment systems for a variety of reasons. First, many types of bacteria can adapt to the environment inside the membrane modules. Unfortunately, a great number of these species are found in

26

typical feed waters, particularly water from a surface source, such as a river or lake. Second, since the bacteria are rejected by the membrane, they end up on its surface. While their presence there is bad enough, their food, consisting of organic matter, also is being concentrated at the membrane surface. When bacteria are placed in a liveable environment with sufficient food, they multiply rapidly. This means that even more bacteria end up on the membrane surface. Finally, bacteria have a number of defence mechanisms. Several have small hair like appendages, called fimbriae, which stick out from all sides of the cell. These allow the bacteria to attach themselves, and remain attached, to the surface of the membrane or to the feed spacers. In addition, bacteria secrete a mucous capsule, or slime, which coats the cell and protects them from any harsh elements entering their environment. TABLE 3.2. THICKNESS OF FOULANT VS EFFICIENCY LOSS Thickness

of

foulant

materials

on Percentage loss of efficiency

membrane surface 0.4 mm

4%

0.8mm

8%

3. 1.13 BENEFITS OF MEMBRANE FILTRATION • Osmosis offers a unique advantage that it is a process that can take place while temperatures are low. Therefore, this enables the treatment of heat-sensitive matter. That is why these applications are widely used for food production. • It is a process that does not require much energy and thus, energy costs are low. The process just requires energy to pump liquids through the membrane. This is far too low when compared to the total amount of energy required for a technique such as evaporation. 27

• The process can easily be expanded. • Process management of membrane filtration systems is simple. Membrane filtration systems can be managed in both dead-end flow as well as cross-flow. The purpose of the optimization of the membrane techniques is the achievement of the highest possible production for a long period of time, with acceptable pollution levels.

28

CHAPTER 4 CONFIGURATIONS OF MFL RO PLANT 4.1 GENERAL The project work was done at Madras Fertilizers Limited in Manali, Chennai. M.F.L. was incorporated on dec. 8, 1966 as a joint venture between GOI AND AMOCO India incorporated of U.S.A. (AMOCO) in accordance with the fertilizer formation agreement executed on 14.5.1966 with equity contribution of 51% and 49% respectively. About 1000 employees are at present working in the company. The company has a very good relationship with public and farmers. So the feed back given by the formers are updated at every moment The company produces the following products: 1. UREA 2. NPK-complex 3. NK-mixture 4. MOP-IMPORTED 5. DAP-IMPORTED

4.2 WATER NEEDS OF MFL Water is vital material for the production of fertilizers. Approximately 630 m3/hr of water is processed every day at R.O. Plant. The potable water is supplied by Chennai Metro Water Supply and Sewage Board(CMWSSB). The boiler and feed water for fertilizer production is taken from the treated sewage water from MFL’s treatment plants. 29

CMWSSB supplies water for fertilizer production. Due to increase in population and scarcity at summer seasons the supply of raw water was restricted. In order to eliminate raw water shortage and to reduce the cost of raw water the Tertiary treatment plant and R.O. plants were installed in the year 1993/94. The sewage water is taken from Kodungaiyur sewage treatment plant. Owned by CMWSSB and supplied to M.F.L. Tertiary treatment plant and R.O. plant. Which reduces the raw water cost/consumption. After 1995 the full need of water is being supplied by R.O. Plant. The primary treated sewage water is being bought for Rs. 9/m3 (approximately) and taken to tertiary treatment plant. After tertiary treatment of the sewage the cost is Rs. 56/m 3 (approximately).Then the T.T.P. water is supplied to R.O. plant. The R.O. plant production is then taken to the Demineralisation plant and stored and then to the boilers as feed water.

30

Figure 4.1 REVERSE OSMOSIS PLANT DIAGRAM

1.Pilot plant

2. R.F. sump

5. Chlorine retention tank pumps 9. Membrane stack

3. Roughing filters

4. Filtered water storage tank

6. Dual media filters 10. Blended storage tank

7. Cartridge filters 8. Hp 11.Settlement tank

12.Backwash tank13.Chlorine storage tank &Injection tank dosing tank 5.Digital control system room pond

31

14.Chemical

16.Tertiary treated water storage

4.3 DETAILS OF RO PLANT IN MFL 4.3.1 MULTI ARRAY SYSTEM.

In MFL multiple array system is being used. Three trains operates in parallel, each designed to produce 120 m3/hr of permeate. Each of the three trains will be a three staged system with the reject from each stage forming the feed of the following stage. The product water from the three stages are combined to form the train product(permeate) stream. 1) 3 trains 2) Each have 4 banks 3) Each banks are named as A, B,C,D. 4) A,B,C banks have 10 vessels each and D bank has 7 vessels. 5) Each vessel houses 6 membranes connected in series (8”

diameter and 1m long, RO membranes). Table 4.1

TRAIN AND ITS COMPONENTS

BANK

No. OF VESSELS

No. OF MEMBRANES

A1& A2

5+5=10

60

B1& B2

5+5=10

60

C1& C2

5+5=10

60

D

7

42

Total No. Of membranes

222

32

Figure 4.2 MULTIPLE ARRAY SYSTEM AND BANK ARRANGEMENT Each trains are designed to operate with a permeate recovery of 75% and at this recovery it is anticipated to give the efficiency of 95% at ambient temperature.

4.3.2. SPECIFICATIONS OF R.O. PLANT 33

Feed water supply

: 160 m3/hr/train.

Permeate water flow

: 120 m3/hr/train.

Reject water flow

: 40 m3/hr/train.

Feed water pressure : 16 kg/cm2 g. P

: less than 4.

R.O. membrane material type: T.F.C Spiral wounded brackish water membrane. Size of a membrane

: 8” dia. : 40” long.

Feed temperature

: not more than 40 o c

Percentage recovery : 75 % (Permeate) Percentage recovery = permeate flow x 100/ feed flow Dimensions of pressure

: 200 mm dia.

vessels

: 6 m long.

MOC of pressure vessels : GRP.

Thin film composite R.O. membrane give excellent performance for a wide variety of application including low pressure tap water use, single – pass sea water &

brackish water desalination, chemical processing and waste

treatment. This membrane exhibits excellent performance in terms of flux, salt rejection and microbial resistance. R.O. element can operate over a pH range of 2 to 11, are resistant to compaction and are suitable for temperature upto 45 o c. Salt rejection 99.5% and flux – 24 l/m2hr 4.3.3 PROBLEMS FACED BY R.O. PLANT 34

The main problem is caused by fouling and scaling. Because the sewage water contains more organic matter, microbes and dissolved organic solids. These will accumulate on the surface of the semi permeable membrane. The foreign materials which may be present in the feed water such as hydrates of metal oxides, calcium precipitates, organic and biological matters.The term includes the build up of all kinds of layers on the membrane surfaces, including scaling. Inner surface of the feed line tubing and the feed end scroll of the membrane element, if it is reddish brown fouling by iron content. Biological fouling (or) organic material is often shinny or gelatinous. Due to the increase in accumulation of these particles day by day the efficiency of the membrane will be slowly decreased. After efficiency will be very much low. The pressure difference (

some years the P

) will be

increased to 4 and above. It leads to failure of membrane by wear and tear of brine seal and membrane.

Figure 4.3. FOULED MEMBRANE PHOTO(unrolled) 4.3.4 . MAINTENANCE OF RO ELEMENT

35

The R.O. element are frequently washed by chemicals, so as to keep the membrane surfaces clean and face of deposits. Table: 4.2

RO WASH PROCEDURES Solution

Chemical

Quantity of

concentration for

Wash

concentration

permeate

circulation

sequence

Duration

HCl 33%

4000 lts

0.5%

ACD

30 min.

HCl 33%

4000 lts

0.5%

BCD

30 min.

HCl 33%

4000 lts

0.5%

A

4 hrs

HCl 33%

4000 lts

0.5%

B

4 hrs

HCl 33%

4000 lts

0.5%

C

4 hrs

HCl 33%

4000 lts

0.5%

D

4 hrs

HCHO 37%

1700 lts

1.0%(60 kgs)

ACD

8 hrs

HCHO 37%

1700 lts

1.0%(60 kgs)

BCD

8 hrs

All banks are flushed with permeate SLS(85 %)+ EDTA(98%) do

1700 lts

0.2%(3.5 kgs+

30 min ACD/BCD

each

A

2hrs

do

3.5kgs) do

do

do

do

B

2hrs

do

do

do

C

2hrs

do

do

do

D

2hrs

SLS + EDTA Soaking 12 hrs Solution

Chemical

Quantity of

concentration

permeate

NaOH (10-11 pH )

500 lts

A

30 min

NaOH (10-11 pH )

500 lts

B

30 min

concentration for circulation

36

Wash sequence

Duration

NaOH (10-11 pH )

500 lts

C

30 min

NaOH (10-11 pH )

500 lts

D

30 min

Total wash hours 80 hrs . The R.O. elements are washed when any one of the following conditions arrives: 1) Permeate flow reduction 2)

P change

3) Increase in Salt passage

Acid wash: 0.5% HCl is being used to wash the membrane for the acid wash. Alkaline wash: NaOH is used for alkaline wash. Acid wash is desirable for

removing organic and inorganic salts like

CaCO3, CaSO4 and BaSO4. Alkaline wash is desirable

for removing silica, biofilms and organic matters.

These leads to foul the membrane. These results with low efficiency, recovery change and increase in

P, decrease in salt passage.

CHAPTER 5 MATERIALS AND METHODS 5.1 SOURCE After identifying the solution the same membrane was performed to treat the tertiary treated waste water. 37

5.2 SAMPLE COLLECTION AND ANALYSIS The inlet water

and out let water of the membrane

were taken. These

samples were analysed at Laboratory in Madras Fertilizers Limited, Manali.

5.3 ANALYSIS OF THE VARIUOS PARAMETERS The following parameters of the samples were analysed.

5.3.1 COLOUR: After the collection of the sample the colour of the sample was noted.

5.3.2

pH Value:

The pH value was found by pH meter.

5.3.3 CHLORIDES: Procedure: 100 ml of sample was taken in two flasks, 1 ml of potassium chromate indicator is added in each flask. The liquid is literate with N 35.5 silver nitrate solution from burette drop with constant stirring unit

there is a

permanent change from yellow to brick red. The volume of titrant is recoded as ‘A’ml. The above procedure is repeated for distilled water to obtain ‘B’ ml. Quantity of chlorides present in the sample

= ((A-B)XNX35450)/Volume of sample mg/l.

N : Normality of AgNO 3

38

5.3.4 SULPHATES: Procedure: 20 ml of the sample was taken in a beaker. 10 ml of 2N HCl acid was added to it and heated till it was boiled. At the time of boiling 30 ml of barium chloride solution was added. The solution is filtered in the beaker through wattman after No. 42. The barium Chloride

react with

sulphate present in the sample in the presence of HCl and barium sulphate was allowed to settle. The filtered sulphate was taken in the weighed crucible and was placed in the muffle furnace till got charged. Then it was weighed (W2). The difference between the weight of empty crucible and weight W2 gives the amount of sulphate present in the sample . mg of residue X molecular weight of BaSO4 Amount of sulphate = Volume of samples

5.3.5

TOTAL DISSOLVED SOLIDS:

Total Dissolved Solids 20 ml of the sample was filtered through No. 42 wattman filter paper and it was cooled in a weighed crucible. It is heated in the water bath and evaporated to dryness in the oven for one hour, then the container was weighed and the increased weight was noted down. The increased weight is known as dissolved solids present in the 20 ml of sample. mg of residue present in the filter paper Total Dissolved solids =

X1000 in mg/l ml of sample taken

39

5.3.6 TOTAL HARDNESS: Procedure Standardisation of EDTA with standard Hardwater 20 ml of standard hard water was taken in a clean conical flask. 5 ml of ammonia buffer solution was added and a pinch of Erichrome Black–T indicator was added and it was titrated against EDTA solution which was taken in the burette. At the end point wine red colour changes to blue. The volume was noted (V1).

Estimation of hardness 20 ml of sample was taken in a clean conical flask. 5 ml of ammonia buffer solution and a pinch of Erichrome black – T were added and titrated against EDTA solution. The end point was just the change from wine red to blue colour. The volume was noted (V2).

1ml of standard hard water = 1 mg of CaCO3 20 ml of standard hard water = V1ml of EDTA 1 ml of EDTA = 20/V1 mg of CaCO3 20 ml of sample water = V2 ml of EDTA Therefore total hardness of sample = (20 X V2) / (V1X 20) X 1000 mg/l.

5.3.7 CALCIUM HARDNESS: Take 50 ml sample add 1N NaOH solution followed by pattern reading indicator then titrate vs EDTA solution. End point : pink to blue colour. 40

Calcium Hardness = Titrant volume X Normality of EDTA X equivalent weight volume of sample taken

5.3.8. LOSS

OF IGNITION (LOI):

Take 1 gram sample make it to dry at 105o c. After drying keep the crucible at 500 o c in muffle furnace for half an hour. Weight difference is the loss of ignition. LOI =

weight difference X 100 weight of the sample

5.3.9. TOTAL IRON : Take definite volume of sample add conc. HCl

followed by Hydroxyl

Ammonium Hydrochloride solution. Reduce the volume to 5 ml by drying over hot plate.

Then cool it add Ammonium Acetate buffer

orthophenonthroline indicator.

followed by 1,10-

Then take the absorption at 510 nm, run a

standard and blank along with the sample. Take the absorbance using spectrophotometer. Total Iron =

Sample OD X Std. Conc. X 1000 (Std. OD X Volume of sample taken)

5.3.10. PHOSPHATES: Take the definite volume of sample add Conc. HNO3 and H2 SO4 then keep it for fuming. After

fuming over, cool it then add phenolphthalein followed 41

by sodium hydroxide solution.

Then add

Ammonium Molybdenum solution

followed by stannous chloride solution. Take the absorbance at 690 nm, in spectrophotometer. Run a standard and blank along with the sample.

Phosphate =

Sample OD X Std. Conc. X 1000 ( Std. OD X Volume of sample taken)

5.3.11. SILICA: If the sample is turbid filter it through wattman 42 filter paper take the definite volume of filtered sample add 1:1 HCl and Ammonium Molybdate solution followed by oralic acid. Take

the

Absorbance at 410nm

using

Spectrophotometer. Run a blank and standard along with the sample.

Silica = Sample OD X Std. Conc. X 1000 (Std. OD X Volume of sample taken)

5.3.12. TURBIDITY: Calibrate

the Nephelo turbidity metre using standard solution. Now

shake the sample well and find out the turbidity using Nepheloturbidity metre.

5.3.13. OIL AND GREASE: Take a definite

volume of sample ( in a separate funnel) add small

volume of concentrate HCl followed by Petroleum Ether(W 1). Shake well. Discard the bottom layer. Collect the upper layer and dry it in a weighed beaker (W 2). Weight difference ( W1- W2) is the oil and grease. 42

CHAPTER 6 RESULTS AND DISCUSSION 6.1 MEMBRANE AUTOPSY 6.1.1. MEMBRANE SELECTION Old used membrane was selected in wet condition. Its last performance was noted. The efficiency of the old membrane was less than 70%.The same 43

membrane was opened. Then it was unsealed and the brine Then

it was unrolled

seal

removed.

carefully and one membrane sheet was selected

to cut.

Figure 6.1 MEMBRANE SELECTION It was marked 0.5 m x0.5 m area in one membrane sheet. In the same way the other membrane sheets were marked. They were cut as the mark. They were spreaded over then

the

membrane

was

scrapped

without

surface. The sample collection was grab sample. Membrane specifications: Pore size of the membrane : 0.01 µm. Feed rate

: 8 m3 / hr

Diameter of the membrane : 8 inches. 44

a white sheet and

damaging

the membrane

Length of the membrane

: 40 inches.

Type of membrane

: Brackish water membrane(spiral wound).

Feed pressure

: 16 kg /cm 2 g.

Percentage recovery

: 75% (permeate)

Membrane maintenance washes: The membrane is washed by the following chemicals, when ever there is a change in

p (feed pressure – permeate pressure), efficiency, flow rate,

recovery and time period. 1) 0.5% HCl wash 2) 1.0% HCHO wash 3) 0.2% (SLS+ EDTA) wash 4) NaOH (10-11 pH ) wash The efficiency of the membrane will be slowly decreased through out the operation period due to accumulation of particles over the membrane surface. After some period there will be no change in efficiency, between pre and post wash of these chemicals mentioned above. This may occur inbetween the life time of the membrane mentioned by the manufacturer or after the life time. This depends on the pre-treatment and solids presented in the feed water of reverse osmosis membrane. So it is considered as the membrane should be discarded and disposed or removed from the vessel and new membrane shall be installed.

45

.

Figure 6.2 PHOTO OF UNROLLED MEMBRANE

Figure 6.3 PHOTO OF FOULED MEMBRANE

46

The Figure. 6.3 shows the film of the deposited particles. The scrapped materials were collected from membrane surface in wet condition and they were analysed.

TABLE 6.1 Sl.

INGREDIENTS OF SAMPLE (SCRAPPED MATERIAL)

PARAMETERS

RESULTS(mg/l)

1

Total hardness as CaCO3

352

2

Calcium hardness as CaCO3

264

3

Loss Of Ignition(LOI)

99.26%

4

Total Iron

10.10

5

Phosphates

7.18

6

Sulphates

795

7

Silica

45.0

8

Chlorides

556

9

Total Dissolved Solids

5300

10

Turbidity(NTU)

30.0

11

Total Organic Compounds

440

No.

As per the results, the Loss Of Ignition is 99.26%. So the organic compound materials are high as foulant materials which were deposited throughout the period of membrane, which were not washed out by ordinary wash. 6.1.2 METHODOLOGY 47

The membrane wash was done by 0.5% of HCl. By overcoming this the deposition and accumulation on the membrane seen. Another used old membrane was selected which was same batch and same efficiency while disposed.

So now 0.6%, 0.75%, 1.0% HCl solutions were tried over the old

membrane. 0.6 & 0.75% of HCl gives no improvement in removing the depositions. 1.0% HCl (washed for 5 min) removes the deposition easily without any stress. The analysis of 1% HCl washed solution is given below. TABLE 6.2 HCL WASH SAMPLE Sl. No.

Parameters

Results(mg/l)

1

Total hardness as CaCO3

220

2

Calcium hardness as CaCO3

120

3

Loss Of Ignition

96%

4

Total Iron

9.77

5

Phosphates

1.77

6

Sulphates

285

7

Silica

40.0

8

Chlorides

920

9

Total Dissolved Solids

1440

10

Sodium EDTA

1983

11

Total Organic Compounds

360

12

SLS(Sodium Laurel Sulphate)

1525

13

Oil & grease

10.0

6.2 RESULTS: After

the

autopsy and washing by 1 % HCl

the same

membrane’s removal efficiency was checked. The 75% recovery of permeate water was set.

48

The collected samples were tested to find the amount of pollutants available in both feed and permeate water of reverse osmosis membrane. So the efficiency of the membrane could be easily found.

Table 6.3 MEMBRANE PERFORMANCE AT STARTING STAGE.

Sl.

Efficiency

Parameters

Feed mg/l

Permeate mg/l

1

Na

420

56

86

2

Ca

64

12.8

83.2

3

Cl

620.3

75.4

86.3

4

TDS

1348.5

210

84.4

5

pH

7.4

7.3

-

6

Total hardness

340

60.7

82.3

7

Sulphates

230

17.5

76.08

8

Total iron

13.4

2.7

79.8

No.

%

The overall efficiency was 82.58 %. Then the membrane was experimented for more than 100hrs and the performance and efficiency was found out. It is tabulated below.

Table 6.4 MEMBRANE PERFORMANCE AFTER 100hrs

49

Sl.

Permeate

Efficiency

mg/l

%

385

60.45

84.3

Ca

72.3

11.56

83

3

Cl

630.5

87.0

86.2

4

TDS

1403.5

227.36

83.8

5

pH

7.2

7.1

-

6

Total hardness

365.3

55.8

84.7

7

Sulphates

276

60.16

78.2

8

Total iron

12.7

2.6162

79.4

Parameters

Feed mg/l

1

Na

2

No.

Now the overall efficiency was 82.9%. So from the above results, the efficiency was maintained throughout the experimented time period. So 1 % HCl wash may be adopted followed by high pH and detergent washes.

CHAPTER 7 CONCLUSION

50

From the above project study it can be seen that the major foulants are iron and fouling. More over Loss Of Ignition (LOI)of pre and post cleaning is found to be more than 95% which clearly indicates the presents of fouling to a greater extent. Owing to the reason the source of feed water is treated sewage, hence

it is concluded that one of the methods of membrane maintenance

is to adopt membrane cleaning with 1% HCl using Cleaning In Place(CIP) followed by high pH and detergent washes.

BIBILIOGRAPHY

1.N.Manivasakam, “Industrial Effluents Origin, Characteristics, Effects, Analysis and Teatment”, 1987. 51

2.Evaluation of Membrane Processes and their Role in Wastewater Reclamation, Final Report of Contract for US Department of interior OWRT,David Argo and Martin Rigby, November 30,1981.

3. “Analysis of Water and Waste Water”,BIS Publication (1993),New Delhi

4. Wesley Eckenfelder Jr. W (2000), “Industrial Water Pollution Control” Tata McGraw Hill Publishing Co.Ltd, New Delhi.

5. Metcalf and Eddy (1979), “Waste Water Engineering Treatment and Disposal”. McGraw Hill publishing Co.Ltd, New Delhi.

6. Nemerow N.L (1978), “Industrial Water Pollution”, Wesely Publishing Company Inc., USA.

7. Control of Fouling of Reverse Osmosis Membranes When Operating on polluted Surface Water, J.E.beckman, E.Bevage, J.ECurver, I.Nusbaum, and S.S.Kremen, Office of Saline Water Report CA-10488, Gulf Environmental System, February 1971.

8. M.N.Rao and A.K.Dutta (1995), “Waste Water Treatment”. Oxford I.B.H Publishers.

9. Evaluation of Membrane Processes and their Role in Wastewater Reclamation, Final Report of Contract for US Department of interior 52

OWRT,David Argo and Martin Rigby, November 30,1981.

10. Syed R.Qasim, Waste Water Treatment Plants, Planning, Designing and operation”. 11. S.K.Garg (1986), Volume – I, “Environmental Engineering and Pollution Control”, Khanna Publisher, New Delhi.

12. Study and Experiments in Waste water Reclamation by Reverse osmosis, I. Nusbaum, J. H.Sleigh and S.S.Kremen, Water pollution Research Series 17040-05/70 (1970).

13. Design Study of Reverse Osmosis pilot Plant, D.T.Bray and H.F.Menzel, Office of Saline Water, Research and Development Progress Report No.176 (1966).

14. Reverse Osmosis-Producers for Replacing Elements, Mr. Jacy Choi, Journal of Environmental Science and Engineering, 2005.

15. M.Wilf, “New generation of Low Pressure High Salt Rejection membranes”, Proceedings of the 1996 Biennial Conference and Exposition, Monterey, California (August 1996).

53