Introduction:Water is the wellspring of life. It is a universal solvent; many types of salts dissolve in water. It is the most important liquid in the world for maintaining the plant and animal life. It fills lakes, streams, the vast oceans, and flows under the ground. Water is a remarkable chemical, an excellent solvent capable of dissolving, to varying degrees, almost anything with which it comes in contact. Water picks up suspended matter as it runs across the ground and absorbs gases from the atmosphere. Impurities in the water come from various sources.

There are different sources of water namely
• Sea Water
• Surface Water
• Ground Water
• Waste Water [Sewage / Industrial]

Common impurities in water:

Total Dissolved Solids [TDS]: TDS as name signifies is dissolved salts in water.
Hardness: Hardness is the part of TDS which forms hard scales, which composes of calcium Sulfate,
Barium Sulfate, Calcium Carbonate, Calcium Fluoride and others like
Silt.
Organic Impurities
Biological Impurities.
Metal Oxides etc.

1. Principle:

During the process of RO ,a permeate is produced with low/acceptable TDS, while the reject would have much higher TDS than inlet , as the TDS removed from permeate now becomes part of TDS in the reject. Elevated levels of TDS cause scaling and fouling of membrane, which is the heart of RO system. The fouled membrane results into poor permeate quality and poor recovery.

Because of these building deposit of impurities in concentrated water causes scaling and fouling on membrane surface results in increase rejection and loss of recovery.

2. What is scaling?

Scaling refers to precipitation and deposition of sparingly soluble salts such as Calcium Sulfate, Barium Sulfate, Calcium Carbonate, Silica, Calcium Fluoride and any other super saturated salt on the immediate surface of the membrane. Typically scaling starts on the tail elements of the last stage(on the rejection side), since they are treating water with the highest concentrations of ions. Once a crystal of scale forms within the membrane element, it acts as a nucleation site for additional scale to form and the rate of scale formation increases exponentially.

3. What is fouling?

Fouling refers to entrapment of particulates, such as silt, clay, suspended solids, biological slime, algae, silica, iron flocs and other matter on the surface, or even worst, within the membrane pores. Typically fouling occurs in the lead elements of the first stage initially and then it works itself through the following elements.

Membrane:

Normally the life of membrane is 2 to 4 years or more depending on plant design, operating conditions and quality of antiscalant and cleaning chemicals. It is assuming that the fluxdecline and salt passage increases to 5 to 10% per year. Membrane material is spiral wound, hollow fiber, flat sheet or tubular configuration but in RO system mostly spiral wound membrane is used.

Impact of Scaling and Fouling:

• Poor permeate water Quality.
• Degradation of membrane.
• Low pressure flow.
• Low recovery Rate.
• Low rejection Rate.
• Increasing Operational & Maintenance Cost.

Advantage Membrane Cleaner:

• Restores flux rates close to that of new membranes
• Prolongs membrane life
• Improves % recovery and % rejection rates
• Protects membranes from irreversible fouling

When to Clean

Foulant removal is controlled by cleaning and flushing or by changing the operating conditions.
As a general guide, foulant removal is required when any of the following conditions occur:
• Permeate flow has dropped to 10 to 15 % below rated flow at normal pressure.
• Temperature-corrected feedwater pressure has increased 10 to 15 % to maintain rated product water flow.
• Product water quality has decreased 10 to15 %; salt passage has increased 10 to15 %.
• The differential pressure across an RO stage has increased noticeably.

RO Membrane Foulant SymptomsIn Treatment Options:

S.No Foulant General Symptoms Treatment

*ΔP (Delta P) is a mathematical term used to illustrate a change (Δ) in pressure (P) between feed and concentrate.

General steps of Membrane Cleaning

For the first cleaning sequence, it is recommended that a membrane cleaner in the same pH range as that of the feed be used. This is essential if precipitation from the feed is expected due to pH variation. In other words,If the filtrated feed is alkaline, an alkaline cleaner should be used at first and vice versa.

For water purification plants, the first cleaning step should be done with an alkaline cleaner to remove the organic fouling and scaling first. Having removed the organic deposits on the membrane, acidic cleaning is more efficient in removing non-organic scaling, if necessary. If this step is not sufficient, a second cleaning with an acidic product is the most efficient way to remove non-organic scaling. In any case, acidic cleaning should be used from time to time as it eliminates water hardness residues.

RO Cleanup Skid:

Limit forpH range according to the manufacturer:

Deliver with heating.

Specifications