WATERThe 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 freshWater 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, HumanBeings find new technology, called ` Reverse Osmosis’

Reverse Osmosis

Technical Presentation

Reverse Osmosis Terminology

Principles of Reverse Osmosis

Types of R O Membranes Membrane Configurations

Typical Applicationsof

Reverse Osmosis

Industrial process water

Production of potable water

Food processing Waste treatment

Principles ofReverse Osmosis

Osmosis

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

Dilute Solution

semi-permeable membrane

Concentrated Solution

Osmotic Pressure

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

P =

P

Dilute Solution

Concentrated Solution

Reverse Osmosis

P >

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

P

Dilute Solution

Concentrated Solution

Three Cases of Osmosis

osmosis equilibrium reverse osmosis

P

P

P = P >

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 AcidsWeak 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

TerminologyPRODUCT FEED

REJECT

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

Reverse Osmosis

TerminologyPRODUCT

FEED PRESSURE

REJECT PRESSURE

P = FEED PRESSURE – REJCT PRESSURE

REVERSE OSMOSIS

System has divided into three parts.

1. PRE-TREATMENT2. R.O. SYSTEM3. POST TREATMENT

Reverse osmosis system

Pretreatment

RO hydra block

Cleaning system

Clarification

Coagulation

Filteration

De-chlorination

Dosing system

Cartridge filter

Membrances

Pressure tubes

HP pumps

Control pannel

Cleaning tank

Pump (SS)

Cartridge filter

DM plant

pH adjustment

DegassificationPost treanment

Coagulation, sedimentation, Chlorination

Sand filter

Activated carbon filter

Dechlorination.

Anti scale

High pressure pump

DESALATION SECTION Membrane modules

Product water

Waste brine

Cartridge filter

Schematic diagram of RO unit for waste water

Block Diagram of RO

(PERMEATE )

PRODUCT WATER

REJECT WATER

(CONCENTRATE)

MEMBRANE

HIGHPRESSURE

PUMP

SALTWATER

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

RO System components

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

A skid to mount to all mechanical equipment .

Flow indicators to measure permeate and reject flow rates.

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

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

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

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

Recovery Rate

Ratio of permeate flow to feed flow

Expressed as % Recovery = (permeate

flow/feed flow) * 100

Role of Pretreatment in RO To reduce particulates & improve SDI.

– Clarification / Filtration.– Polymer/coagulant addition.– Micro-filtration.

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

Chlorine Removal.– Carbon Filtration.– Bisulfite Addition.

Role of Pretreatment in RO Minimize Silica Scaling.

– Antiscalant addition.– Softening & pH control.– Turbocirculator.

Controlling Organic.– Dissolved Organic.– Colloidal Orgabic.

Role of Pretreatment in RO Silt Density Index : It is the second

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 ofSpiral Wound Membrane

Mesh Spacer

Permeate Carrier

Membrane

“O” Ring

Permeate Tube

Membrane Backing

Outer Cover

Membrane Assembly

Reverse Osmosis

Membranes - Types

Cellulose Acetate Thin Film Composite Polysulfones

Thin Film Composite Membrane Characteristics

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

Instruments used in RO System

•PH * ORP•Conductivity Meter * Level Switches•Rotameter * Pressure Switches•Pressure Gauges * 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.