Presantation on Reverse Osmosis

WATER The earth is so blessed with water resources that it is called the `WATER PLANET’. But a mere 2.5% of the earth`s water is fresh Water usable by human beings; the remaining 97.5% is Sea water.  Now a days due to increase in population & industries, demand of  Water has been increased rapidly. Pollution is also increases. Due to lack of water resource, Human Beings find new technology, called ` Reverse Osmosis’

Reverse Osmosis

Technical Presentation q q q q

Reverse Osmosis Terminology Principles of Reverse Osmosis Types of R O Membranes Membrane Configurations

Typical Applications of Reverse Osmosis

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Industrial process water Production of potable water Food processing Waste treatment

Principles of Reverse Osmosis

Osmosi s

Dilute Solution

semi-permeable membrane

Concentrated Solution

The spontaneous flow of water from a dilute solution to a concentrated solution, when the two solutions are separated by a semipermeable membrane.

Osmotic Pressure P Dilute Solution

Concentrated Solution

P=

The pressure that must be applied to a concentrated solution to prevent osmosis.

Reverse Osmosis

Dilute Solution

Concentrated Solution

P>

Reversing osmotic flow by applying a pressure in excess of the osmotic pressure

Three Cases of Osmosis P

π1

π2

π2

osmosis

equilibrium

reverse osmosis

π1 < π2

P = ∆π

P > ∆π

Factors Influencing Permeation Rates of Dissolved Materials

Greatest Influence: Electrical Charge Moderate Influence: Molecular Weight Slight Influence: Molecular Structure

FEED WATER LIMITING CONDITIONS Oxidizing Agents like chlorine - Nil  COD & BOD with in limit.  OIL & GREACE NIL  SDI LESS THAN 5.  pH range 3 to 11  Turbudity – less than 1 NTU 

Permeation Rates of Other Dissolved Species •

Dissolved Gases pass freely through the membrane.

•

Many Dissolved Organics are weak acids. Their  rate of permeation will depend not only on their  molecular weight and structure but on their degree of ionization. HX H+ + X-

Permeation Rates of Weak Acids

Weak acids are those acids that do not become completely ionized in water. Included in this group of acids are chromic, boric and many organic acids. H2CrO4

H+ + HCrO4-

HCrO4-

H+ + CrO4- -

H3BO3

H+ + H2BO3-

Reverse Osmosis Terminology PRODUCT

FEED

REJECT RECOVERY = PRODUCT FLOW / FEED FLOW SALT PASSAGE = PRODUCT TDS / FEED TDS SALT REJECTION REJECTION = 100 – SALT PASSAGE PASSAGE IN %

Reverse Osmosis Terminology

FEED PRESSURE

PRODUCT

REJECT PRESSURE

P = FEED PRESSURE – REJCT PRESSURE

REVERSE OSMOSIS System has divided into three parts. • PRE-TREATMENT • R.O. SYSTEM • POST TREATMENT

Reverse osmosis system Cleaning tank Pump (SS)

Pretreatment Cartridge filter Dosing system De-chlorination Filteration

Cartridge filter

RO hydra block Membrances Pressure tubes

Cleaning system

DM plant pH adjustment Degassification

Coagulation Clarification

HP pumps Control pannel

Post treanment

Schematic diagram of RO unit for waste water Activated carbon filter Coagulation, sedimentation, Chlorination

Product water

Sand filter

DESALATION SECTION Membrane modules

 Waste brine

Dechlori nation.

High pressure pump

Anti scale

Cartridge filter

Block Diagram of RO M  E   M  B  R A  N  E  

SALT WATER

HIGH PRESSURE PUMP

REJECT WATER (CONCENTRATE)

PRODUCT WATER (PERMEATE )

RO System components The basic expanded design of a single system includes the following: q Raw water feed pump to supply water to the pre treatment q Pre treatment system for Turbidity,TSS,Colloidal particles & Organic matter. q Cartridge filter to remove micron size particle to control the SDI( Silt density index) of feed water q Anti scalant dosing system. q High pressure pump&feed control valve to pressurize the feed water. q Membranes housed in Pressure tubes.

A reject control valve to control the recovery of the RO system. q

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A skid to mount to all mechanical equipment .

Flow indicators to measure permeate and reject flow rates. q

Pressure gauges for monitoring the differential pressures across the RO feed, reject and intermediate stages. q

Conductivity & pH meter for measuring the quality quali ty of the permeate water. q

And other necessary instruments for monitoring easy operation and critical parameters. q

A cleaning system consisting consisting of Tank,CF,Pump Tank,CF,Pump and necessary instruments. q

Recovery Rate Ratio of permeate flow to feed flow q Expressed as % q Recovery = (permeate flow/feed flow) * 100 q

Role of Pretreatment in RO q

To reduce particulates & improve i mprove SDI. Clarification / Filtration.  –  Polymer/coagulant addition.  –  Micro-filtration.  – 

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Minimize Scaling &fouling. Softening.  –  Acid & anti scalant addition.  –  Anti scalant addition.  – 

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Chlorine Removal. Carbon Filtration.  –  Bisulfite Addition.  – 

Role of Pretreatment in RO q

Minimize Silica Scaling. Antiscalant addition.  –  Softening & pH control.  –  Turbocirculator.  – 

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Controlling Organic. Dissolved Organic.  –  Colloidal Orgabic.  – 

Role of Pretreatment in RO q

Silt De Silt Dens nsit ity y In Inde dex x : It is th the e se seco cond nd parameter used to determine colloidal quantity of the RO Feed water. A test is run to determine the rate of the pluggage of a 0.45 micron filter at 30 psig for 15 minutes. This test consists of determining amount of time it takes to collect a 500 ml sample at the start of the 15 minutes test and comparing  this time to the amount of time it takes to collect a 500 ml sample at the end of the 15 minutes.

Cross section of Spiral Wound Membrane Permeate Tube

Membrane Backing “O” Ring

Mesh Spacer  Permeate Carrier  Membrane

Outer Cover 

Membrane Assembly

Reverse Osmosis Membranes Types q Cellulose

Acetate q Thin Film Composite q Polysulfones

Thin Film Composite Membrane Characteristics q

q q

q q

Lower Operating Pressure High Salt Rejection Available for Sea Water Stable to pH 11 Sensitive to Oxidants

Operating Parameters Feed

Pressure Concentration  pH Temperature

Permeate

Concentration Flow Pressure

Concentrate

Flow Pressure Concentration

INSTRUMENTATION

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Instruments used in RO System

•PH •Conductivity Meter •Rotameter •Pressure Gauges

* ORP * Level Switches * Pressure Switches * Electrical Control

Fouling There are Six main causes of membrane Fouling. •Scaling

by hardness salts. •Scaling by Silica. •Fouling by Metal Oxides. •Plugging by suspended solids. •Biological Fouling.

Scaling The deposition of sparingly soluble salts onto the membrane surface and/or the feed channel material.  –  Scaling occurs primarily in the downstream elements because of the higher concentrations existing in this portion of the RO system.  –  Common scalants include calcium sulfate, silica and calcium carbonate.