Reverse Osmosis Design - Basic Reverse Osmosis Terminology-Hezhong Environment (Beijing) Co., Ltd. was established in 2003

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Reverse Osmosis Design - Basic Reverse Osmosis Terminology

Published Time:

2022-10-14

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01 Reverse Osmosis Membrane Element Construction

The desalination layer is very thin (approximately 200 nanometers)
The desalination layer is coated on a polysulfone support layer (approximately 45 micrometers thick)
The polysulfone support layer is attached to a polyester non-woven fabric base layer (approximately 100 micrometers thick)

Pressurized feed water flows axially through the feed water/concentrate grid;
Pressure forces some of the feed water through the membrane, while most of the dissolved salts remain on the feed water side of the membrane; the water passing through the membrane is called permeate;
The permeate is collected by the freshwater screen;
The freshwater screen is located between two flat reverse osmosis membranes;
The permeate ultimately flows to the central permeate pipe;
An 8-inch membrane element consists of many membrane sheets.

02 Reverse Osmosis Membrane Assembly

Membrane assembly = membrane element + pressure vessel;

In a reverse osmosis system, many membrane elements are connected in series in a pressure vessel, generally one

A pressure vessel typically houses 6-7 reverse osmosis membrane elements;

The pressure vessel has feed water inlet, concentrate outlet, and central permeate outlet.

03 Recovery Rate and Concentration Ratio

Using high desalination membrane elements, the concentration factor gives us an intuitive impression: how many times the salt content in the concentrate has been concentrated.

04 Arrangement

The combination of pressure vessels containing membrane elements is commonly known as an arrangement. A stage refers to the number of pressure vessel filtrations the concentrate has undergone, and a level refers to the number of filtration separations the permeate has undergone.

1-stage system: Low recovery SWRO (<45%)

2-stage system: BWRO (<80%); High recovery SWRO (<60%); Two-stage high recovery system (<90%)

3-stage system: High recovery BWRO (<90%); Two-stage high recovery system (<95%)

05 Inter-stage Booster Pump

Inter-stage booster pumps are used to balance inter-stage flow and recovery rate.

06 Permeate Backpressure

Permeate backpressure is likely to occur when the water level in the permeate tank/degassing tower is higher than the RO system;

Permeate backpressure can also be used to balance the permeate flux and recovery rate of each stage. A common method is to adjust the permeate flow rate of the first and second stages, which can be achieved by installing a regulating valve on the permeate pipelines of the first and second stages.

07 Flux

The average system flux and the maximum membrane element flux are important factors affecting the good operation of the RO system. Different permeate fluxes are recommended for different raw waters and pretreatment methods.

08 Desalination Rate

Removal refers to the ability of specific dissolved ions and compounds to be retained on the feed water side of the membrane element.

Salt passage is defined as the ratio of the concentration of permeated dissolved ions or composite salts to the concentration of the same ions or compounds in the feed water.

08 Pressure Difference

Pressure difference = feed water pressure - concentrate pressure;
An increase in standardized pressure difference indicates that the membrane system is fouled;
Causes of increased pressure difference:

(1) Front: Membrane fouling (suspended solids, colloids, bacteria, silt, clay, iron corrosion and pretreatment coagulants, etc.);

(2) Rear: Scaling

(3) Any location: Biofouling