Reverse Osmosis Membrane Installation Methods and Steps (Part 1)

I. What is RO membrane?

RO membrane is also called reverse osmosis membrane. RO is the abbreviation for Reverse Osmosis. Reverse osmosis is a membrane separation technology developed in the 1960s. It is a process that relies on a reverse osmosis membrane to separate the solvent and solute in a solution under pressure. The pore size of the RO reverse osmosis membrane is as small as the nanometer level. Under a certain pressure, water molecules can pass through the RO membrane, while impurities such as inorganic salts, heavy metal ions, organic matter, colloids, bacteria, and viruses in the raw water cannot pass through the RO membrane, thus strictly separating the pure water that can pass through from the concentrated water that cannot pass through.

1. Working principle of RO membrane

Osmosis is a physical phenomenon.

When two kinds of water containing different salts are separated by a semi-permeable membrane, it is found that the water in the side with less salt will permeate through the membrane to the side with more salt, while the salt content does not permeate. Until the salt concentration on both sides is gradually merged into equilibrium, this process is called osmosis. However, this process takes a long time. But if pressure is applied to the side with high salt content, the result can also stop the above osmosis, and the pressure at this time is called osmotic pressure. If the pressure is increased further, the direction can be reversed, and the salt will remain.

The principle of reverse osmosis desalination is to apply a pressure greater than the natural osmotic pressure to the water containing salt (such as raw water), so that the osmosis proceeds in the opposite direction, forcing the water molecules in the raw water to the other side of the membrane to become clean water, thus achieving the purpose of removing impurities and salts from the water.

Reverse osmosis, also known as reverse osmosis, is a membrane separation operation that uses pressure difference as the driving force to separate the solvent from the solution. When pressure is applied to one side of the membrane, when the pressure exceeds its osmotic pressure, the solvent will undergo reverse osmosis in the opposite direction of natural osmosis. As a result, the permeated solvent, i.e., permeate, is obtained on the low-pressure side of the membrane; and the concentrated solution, i.e., concentrate, is obtained on the high-pressure side. If reverse osmosis is used to treat seawater, fresh water is obtained on the low-pressure side of the membrane, and brine is obtained on the high-pressure side.

2. Reverse osmosis calculation formula

During reverse osmosis, the permeation rate of the solvent is the liquid flow energy N is: N=Kh(Δp-Δπ)

Where Kh is the hydraulic permeability coefficient, which increases slightly with temperature;

Δp is the static pressure difference between the two sides of the membrane;

Δπ is the osmotic pressure difference between the two sides of the membrane.

Osmotic pressure of dilute solution π is: π=iCRT.

Where i is the number of ions generated by the ionization of solute molecules;

C is the molar concentration of the solute;

R is the molar gas constant;

T is the absolute temperature.

Reverse osmosis usually uses asymmetric membranes and composite membranes, and the equipment used is mainly hollow fiber or spiral wound membrane separation equipment. Reverse osmosis membranes can retain various inorganic ions, colloidal substances and macromolecular solutes in water, thus obtaining purified water. It can also be used for pre-concentration of macromolecular organic solutions. Because the reverse osmosis process is simple and energy-efficient, it has been widely used in seawater and brackish water desalination, boiler water softening and wastewater treatment, and combined with ion exchange to produce high-purity water. Its application range is expanding, and it has begun to be used in the concentration of dairy products and fruit juices, as well as the separation and concentration of biochemical and biological preparations.

II. Installation and operation procedures of reverse osmosis membrane

1. Confirmation of feed water quality

The pressure vessel should be flushed with water for at least 30 minutes to confirm that the feed water of the reverse osmosis membrane meets the requirements. For polyamide composite membranes, it is necessary to confirm that there is no residual free chlorine.

2. When taking out the membrane element from the plastic packaging bag, it should be operated in a well-ventilated environment, wearing protective glasses, protective gloves, and protective clothing. A respiratory protector should be worn in places with poor ventilation.

3. Before operation, the safety standards for the use of chemicals must be consulted.

III. Loading of reverse osmosis membrane elements

Before loading the membrane element into the pressure vessel, carefully read the pressure vessel user manual.

Prepare the necessary tools, materials and protective equipment, such as snap ring pliers, wrenches, screwdrivers, glycerin, rubber hammer, gloves, safety glasses, etc. Remove the end plates at both ends of the pressure vessel according to the user manual, clean and wipe the pressure vessel, and apply glycerin evenly to the inner wall of the pressure vessel with a towel or sponge to lubricate the inner wall and facilitate the loading of the membrane element.

1. Preparation before installation of reverse osmosis membrane components

(1) Remove garbage, oil and metal powder from the feed water pipe. Chemical cleaning or injection of cleaning agent can be carried out in the piping system as needed.

(2) Preparation of necessary parts

Take out the parts from the accessory box in the cardboard box. First confirm the number of auxiliary parts and necessary quantity of membrane elements.

(3) Install O-rings

Install the O-ring on the connecting fitting. During installation, a silicone-based lubricant, petroleum jelly, or other lubricant can be applied to the O-ring as needed.

(4) Inspection of the inside of the pressure vessel

Remove the end plates from both ends of the pressure vessel. Rinse the opened pressure vessel with clean water and remove any debris or foreign objects from inside the vessel.

(5) Installation of the pressure vessel end plate

According to the pressure vessel assembly guide, install the end plate on the concentrate water side of the pressure vessel.

2. Installation of reverse osmosis membrane elements

(1) Remove the membrane element from the cardboard box and remove the plastic packaging bag. Please note that the membrane element contains protective liquid, so be careful when operating.

(2) Install the brine seal on the membrane element. If installed in reverse, it will not function, so please pay attention.

(3) Loading membrane elements

Insert the end of the membrane element without the brine seal parallel from the water supply side (upstream) of the pressure vessel, and slowly push 2/3 of the element in. At this time, be careful not to touch the edge of the pressure vessel.

(4) Installation of connecting plug

After inserting the initial membrane element into the pressure vessel, insert the connecting joint between the elements into the central water pipe of the element. Before installing the joint, silicone-based lubricant can be applied to the O-ring of the joint.

(5) Loading the second membrane element

Install the brine seal on the membrane element, and insert the central water collecting pipe of the membrane element into the installed connecting plug. After confirming that the central water collecting pipe is fully inserted into the connecting plug, insert the second membrane element. If the element is pushed in too far and needs to be pulled out, it will detach from the connecting plug or cause the brine seal to twist, resulting in poor performance. Therefore, push it in slowly to avoid pushing it too far.

(6) Loading subsequent membrane elements

Repeat steps (4) and (5) until all elements are loaded into the pressure vessel. The number of elements loaded is determined by the length of the elements and the pressure vessel. Push the last element in until the connecting joint of the first element is tightly inserted into the end plate interface on the concentrate water side of the pressure vessel.

(7) Installation of connecting plug

After loading all the elements, install the connecting joint.

(8) Installation of the water supply side end plate

According to the pressure vessel assembly guide, install the end plate on the water supply side of the pressure vessel.

(9) Connect the pipes at the end plate.

3. Inspection after loading membrane elements

(1) Water flow confirmation:

Carefully check whether the pipe fittings are correctly connected and the screws are tightened before starting the water flow test. When flowing water, pay attention to gradually increasing the water pressure.

(2) Adjust to the predetermined water production and recovery rate:

While closely monitoring the flow meters of the feed water and concentrate water, adjust to the predetermined water production and recovery rate. If there is no pressure loss or other problems, maintain this operating state for one hour.

(3) Check the quality of membrane permeate water:

Sample the permeate water from each membrane module to check the water quality (conductivity). If there is any abnormality in the water quality of the membrane module, the O-rings, brine seals, etc. must be re-checked, and the defective parts must be replaced.

IV. Removal of reverse osmosis membrane elements

First, remove the external hard pipes at both ends of the pressure vessel and remove the end plate assemblies at both ends of the pressure vessel. Push the membrane element from the water supply side (upstream), let part of the membrane element protrude from the concentrate water side, and slowly pull out the exposed membrane element parallel from the concentrate water side. The connection between the membrane elements is only connected by a connecting plug (O-ring), which can be easily removed. Remove the membrane elements one by one according to the previous instructions. When removing the second to sixth elements, when pushing in the second element, there must be one pushing tube acting on the central pipe of the membrane. If a tube with the same diameter and length as the central pipe of the membrane element and a connecting plug are available, connect a pushing tube for each membrane element removed to complete the above operation.