RO Membrane Cleaning

8/12/2019 RO Membrane Cleaning

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instrumentation, however, it may be advisable to add a low level switch to the tank to preventthe pump from running dry. Additionally, a temperature controller and heater/cooler unit maybe added to maintain solution at the optimum temperature range.

Refer Fig.1

Cleaning ProceduresGenerally, low pH solutions are used to clean metallic scales while alkaline solutions areused to clean biological and organic fouling. Relatively high flow (governed by the size of theelement) with low pressure is recommended. (Do not, however, exceed maximum flow limitsfor the elements). Table 1 provides guidelines for pressures and flows per vessel for a rangeof element diameters. ( Refer Figure No. 1 Drawing).

To clean a system, follow these six basic steps:

1. Prepare the cleaning solution per the instructions found

2. Displace the solution in the vessels either by flushing with permeate water or by pumpingcleaning solution at a low pressure and low flow. To prevent dilution of the cleaningsolution, the process water can be dumped to drain until the cleaning solution has filledthe vessels.

3. Recycle the solution through the elements and back to the tank.

4. Soak the elements for 1 hour. (For heavy foul ing, overnight soaking may be required).

5. Recycle at the flow rates listed in Table 1 for an hour. The turbulence created in this highflow regime will help to displace the foulants from the membrane. Do not exceed 10 psipressure drop per element; if the pressure drop is too great, reduce the flow.

6. Flush the system with clean permeate water or pre-filtered raw water.

Instructions for Cleaning Solution Preparation

♦ Use of chlorine or other strong oxidants on polyamide membranes can cause irreversibledamage to the membrane.

♦ Warm water, i.e 32 0C - 37 0C gives significantly better cleaning than lower temperaturesolutions.

♦ If the pH of an acid solution increases during recirculation, add more acid to return the pHback to the target value. What is occurring is that acid is being consumed as it dissolvesinorganic scale.

♦ Do not use sulfuric acid for low pH solutions as this creates a risk of creating sulfate scale.♦ Permeate water is preferred for mixing solutions.♦ Use of filtered tap water for high pH solutions can result in carbonate fouling if the water is

hard.♦ Flush the membranes with permeate water following cleaning to remove the cleaning

solutions.♦ Under severe fouling conditions, it may be necessary to soak overnight. ♦ Check the residue before using the water for the process



Table:1

Flow Rate : 1500 lit/hrNo. of membranes : 5 no.Size of the membranes : 4” x 40”Tank Size : 100 litPressure : 1.5 – 2 kg/cm 2 Temp. (optimum) : 32 0C -35 0CTotal quantity of Solution : 75 lit

Cleaning Solutions for Removal of Organics

1.DissolveSodium Tripolyphosphate 1 kgSodium Dodecylbenzenesulfonate 200 gmRO permeate 75 lit .

Note: When mixed at these dilutions, the cleaning solution will be at pH 9.6 to 10.

2. Sodium Hydroxide Solution (pH = 12)DissolveSodium Hydroxide 150 gmRO permeate 75 lit

3.Citric Acid Solut ion (pH _ 2.5)DissolveCitric Acid : 1.5 kg.

RO permeate : 75 lit

Sanitis ation of the membrane :

Formaldehyde MethodDissolve 2.5 li t of Formaline solution of 30% strength in a 75 lit of RO permeate. Circulatethe solution for 2 hours. Keep the solution overnight for better results. Flush-out the solutionwith water by passing the water for about 30 mts. Check the water for residual formaldyhide( formaline ). Ensure that formaline is absent in th e water after the flushing .

Peracetic Acid Method:

Dissolve 1.5 kg. of Peracetic acid solution of 5% strength in a 200 lit of RO permeate.Circulate the solution for 2 hours.. Flush-out the solution with water by passing the water forabout 30 mts. Check the water for residual peracetic acid.

Precautions f or s afe handling During handling, wear personal protective equipment. Drain and clean pipes and facilities before any maintenance. Operate in a well ventilated area. Maintain eye wash and safety showers facilities.



Storage conditions

Store in a cool (<5 ºC), dark, clean and well ventilated area. Containers should only be half-filled with peracetic acid at storage temperatures below 0 ºC as

the containers may burst and leakage will occur. Keep away from incompatible and combustible materials

Test for Formaldehyde: Incompatible with oxidizing agents and alkalis. Reacts explosively with nitrogen dioxide atca. 180 C (356F). Reacts violently with perchloric acid, perchloric acid-aniline mixtures, andnitromethane.

Conditions to Avoid: Heat, flames, ignition sources and incompatibles.

Analy ti cal met hod t o tes t t he Per acet ic Ac id

1. Fill test tube to 10 ml line with sample water.2. Add 10 drops of Sulfuric Acid, Swirl to mix.3. Add 1 drop of Ferroin Indicator Swirl to mix.4. Add 1 drop of Potassium Iodide 20% Solution . Swirl to mix.Solution will turn a cloudy brown if peracetic acid is present.

Hydrogen Peroxide methodDissolve 1000 gm of Hydrogen peroxide solution of 30% strength in a 200 lit of ROpermeate. Circulate the solution for 2 hours. Flush-out the solution with water by passing thewater for about 30 mts. Check the water for residual hydrogen peroxide.



FigureNo. 1 :

For Further information contact :Komal Industries108 Creative Ind. Centre12 N M Joshi MargLower Parel (E)

Mumbai 400 011India

E mail: [email protected] Phone: 91 22 23091090Fax # 91 22 23062711

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RO Membrane Cleaning