FIELD OF THE INVENTION
The present invention relates to chemical cleaning process for trouble shooting of reverse osmosis membrane at high pH at slightly higher temperature or more particularly, this invention relates to a method involving cleaning of RO system with lesser variant of Cleaning Chemicals & effective in reduction of membrane pressure drop (DP).
BACKGROUND OF THE INVENTION
The RO chemical cleaning (CC) operation need to be performed based on either pressure drop across membranes or increased salt passage through the membrane as per the manufacturer’s recommendation. In which majority of the cleaning will be done due to higher differential pressure.
Fouling is of two kinds one is organic (biological) fouling & another is inorganic (metal scaling) fouling. Inorganic foulants will be removed by analyzing the type of salt layer formation, whereas removal of organic fouling is a difficult task by normal/regular method and also it involves various combination of chemicals like Ethylenediaminetetraacetic Acid (EDTA), Sodium lauryl sulphate (SLS), Sodium tri poly phosphate (STPP) and Biocide.
To overcome the disadvantages/problems, we have invented novel method of cleaning of RO membranes at elevated pH (10.0 – 11.5)
Chemical cleaning system for RO (Reverse Osmosis) is an auxiliary system provided for the off line cleaning of the RO membranes to remove the scaling/foulants in the membrane. The same system is also used for long-term preservation of the membranes.
The RO chemical cleaning system consists of the following equipment.

The above cleaning system is connected to the RO section with necessary piping / valves for recirculation, brine/product return to the tank and drain.
But the conventional method needs different combination of chemicals like Ethylenediaminetetraacetic Acid (EDTA), Sodium lauryl sulphate (SLS), Sodium tri poly phosphate (STPP) and Biocide.
But such difficult combination or additional arrangement makes this troubleshooting of reverse osmosis more is complicated, time consuming, expensive and often does not provide effective result as well.
But the present invention overcomes all the drawbacks and disadvantages.
OBJECTS OF THE PRESENT INVENTION
It is therefore the primary object of the present invention is to provide a method of chemical cleaning for RO membrane which does not need combination of different chemicals at different pH level.
Another object of the present invention is to provide a method of chemical cleaning for RO membrane, which does not require any additional arrangement.
Yet another object of the present invention is to provide a method of chemical cleaning for RO membrane, which substantially improve the feed flow.
Further object of the present invention is to provide a method of chemical cleaning for RO membrane, which can reduce the feed pressure.
Another object of the present invention is to provide a method of chemical cleaning for RO membrane, which can be operated at high pH.
SUMMARY OF THE INVENTION:
As per the above objective, it has been provided a method for carrying out the high pH chemical cleaning of the RO system by NaOH. Normally high pH (EDTA, SLS, STPP, Biocide), Low pH (citric acid) chemicals are used as per the recommendation of the membrane manufacturer. In this invention we have formulated a methodology to clean the RO system without usage of combination

of the above referred cleaning chemicals & without any other additional arrangement.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Figure 1 illustrates the typical scheme for chemical cleaning.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present subject matter relates to chemical cleaning process for reverse osmosis (RO) membrane at high pH.
The chemical cleaning process is carried out by NaOH. Normally both high pH chemicals such as EDTA, SLS, STPP, Biocide ( pls give us the full ) and low pH chemicals such as citric acid are used in case of membrane manufacturing. But the present invention provides a methodology to clean the RO system without usage of combination of such chemical or any other additional arrangement.
The method of chemical cleaning comprises the steps of :
i) preparing of chemical cleaning (CC) solution (1) in chemical cleaning tank
(7) at a preferred temperature;
ii) re-circulation by RO clean in place feed pump (8) and addition of NaOH until the pH value reaches to 10.5 to 11.5;
iii) transfer of the CC solution (NaOH solution with pH range 10.5 to 11.5) to RO system with a flow 8-9 m3/hr/per RO vessel and the feed pressure should not exceed 2.0 to 2.5 bar.

iv) repetition of re-circulation process through chemical cleaning product return (2) and system will be boxed up with the CC solution for 30 mins. and;
after completion of total cycle, total CC solution is drained out from the RO skid (4) and RO membrane is flushed with RO permeate (3) water for 10 mins. and balance flushing to be carried out with RO feed water (5) and drained through RO brine return (6) for 5 mins.
The temperature of the CC solution is maintained in between 33-34°C and the feed pressure should not exceed 2.0 to 2.5 bar.
Fig 1 clearly illustrates the process for chemical cleaning.
The re-circulation process is carried out for 15 minutes through chemical cleaning product return (2) and system will be boxed up with the solution for another 30 minutes. Again same chemical solution recirculation will be carried out for 15 min and allowed for soaking for another 30 min. The above process will be repeated for 4-5 cycles.
The skid can be taken into operation & before taken into the service feed water will be drained through RO brine return (6) for five minutes.
High pH RO cleaning with NaOH by maintaining the media temperature around 33 to 34 Degree C will yield good result. The pressure drop will drastically comedown after the repeated cleanings. The DP value will come to the normal condition & total bio-fouling will be removed by this method and the plant will be in good working condition.

WE CLAIM
1. A method of chemical cleaning for reverse osmosis (RO) membrane comprises
the steps of :
i) preparing of chemical cleaning (CC) solution in chemical cleaning tank (7)
at a preferred temperature;
ii) re-circulation by RO clean in place feed pump (8) and addition of NaOH until an optimum pH is reached;
iii) transfer of CC solution (NaOH solution with pH range 10.5 to 11.5) to RO System with a definite range flow and at a definite feed pressure;
iv) repetition of recirculation process and system will be boxed up with the CC solution for 30 mins. and
after completion of total cycle, total CC solution is drained out from the RO skid (4) and RO membrane is flushed with RO permeate (3) water for 10 mins. and balance flushing to be carried out with RO feed water (5) and drained through RO brine return (6) for 5 mins.
2. The method of chemical cleaning for reverse osmosis (RO) membrane as
claimed in claim 1, wherein the pH is maintained at 10.5 to 11.5 for recirculation
with addition of sodium hydroxide (NAOH).
3. The method of chemical cleaning for reverse osmosis membrane as claimed in claim 1, wherein the temperature of the chemical cleaning solution is between 33 to 34ᴼC.
4. The method of chemical cleaning for reverse osmosis membrane as claimed in claim 1, wherein the CC solution is fed to the RO system with a flow rate of 8-9 m3/hr per RO vessel and feed pressure is not exceed 2.0 to 2.5 bar.
5. The method of chemical cleaning for reverse osmosis membrane as claimed in claim 1, wherein the recirculation process is carried out for 15 minutes and the CC solution is kept for another 30 mins.

6 The method of chemical cleaning for reverse osmosis membrane as claimed in claim 1, wherein the overall process is repeated for 4 to 5 cycles.