Process description of R.O.
The reverse osmosis purification process consists of the following operations:
Pretreatment
Pretreatment is done to optimally use the membranes and to increase the membrane’s operating time, and during this operation it prepares water to pass through the membrane. These operations include:
A) Separation of suspended solid particles in the inlet water: suspended solids and colloids in the water cause membrane cramps. Eclipse of the membranes is determined by the eclipse index, and the eclipse of water passing through a membrane must be below the prescribed limit for the membrane.
For this purpose, the water passes through cartridges of 5 to 10 microns.
B) Removal of microorganisms: Microorganisms, like bacteria, can cause membranes to crash. Even in some cases, the enzymes secreted from microorganisms on membranes have had a destructive effect. For this purpose, it is necessary to disinfect the water before discharging over the membrane by ultraviolet radiation or chlorine. If chlorine is used to prevent membrane useful life, the extra chlorine should be removed. This action is carried out using the activated charcoal substrate and sulfites. Acetate cellulose membranes have severe damage to microorganisms.
C) It is essential to adjust the pH of the water in order to increase the membrane’s life and prevent the sedimentation of some of the salts. The useful life of membranes at an inappropriate pH due to hydrolysis is greatly reduced. The pH is inappropriate for polyamide membranes between 4-11, while for acetate cellulose membranes it is between 4.5 and 6.5. Therefore, the use of acetate cellulose membranes requires careful attention.
D) Temperature control: To protect the membrane, the water supply temperature must be controlled at 20 to 25 degrees Celsius at different times. The maximum allowed temperature is 35 ° for polyamide membranes and 30 ° C cellulose acetate membranes. High temperature at improper pH increases the velocity of hydrolysis of the membrane.
E) Control of Sedimentation: Oxidizing materials, such as iron oxides and hydroxides, manganese and silica, can create problems during de-melting processes, thereby reducing the membrane’s efficiency. The hexamethaphosphate compound can be used to control these sedimentation factors.
increase pressure
The feed water is compressed after a preliminary purification by a pump to allow for the potential to pass through the pump. The maximum permissible pressure for the polyamide membranes is 28 atmospheres and for acetone cellulose 60 atmospheres according to the equipment used. A control valve is used to adjust the pressure. For waters with T.D.S. The high pressure requirement requires a cellulose membrane to be selected.
Reverse Osmosis System Components
The membrane is the main refining but the reverse osmosis system has the following equipment:
Soluble preparation reservoirs and phosphate acid injectors
These products are used to prepare acid at appropriate concentrations and to inject them to feed water to adjust the pH of water and supply and inject phosphate into water due to preventing the precipitation of calcium and magnesium salts.
Filter cartridge and activated carbon
This equipment is used to increase the membrane’s life by introducing suspended water and removing chlorine residues from water disinfection.
High pressure pump
The pump is required to offset osmotic pressure, compensating for the pressure drop due to the presence of membranes and equipment on the track.
Frames (modules)
Membranes are extremely sensitive and damaging. Because of the high pressures of the reverse osmosis system, frames are used. The frames are solid metal or polymeric enclosures that hold the membrane in place. The frames place the surface of the membrane in a low volume. Modules carry the task of fluid guidance.
Improper design of the modulus reduces membrane performance. An appropriate design module should have the following features.
Provide the necessary mechanical strength.
Covering the upper surface of the membrane.
Good fluid control.
Ease of physical and chemical cleaning of the membrane.
Ease of repair and maintenance.
Membranes
Industrial osmotic membranes are made of different polymer materials and are varied in terms of geometric shape and materials used. The most important membranes are:
Tubular membrane
These membranes are mostly made of acetate polyethyl cellulose composites, in the form of tubes of 20 to 30 mm in diameter and 200 to 250 cm in length. About 20 of these membranes fit inside a steel frame.
Spiral-Wound membrane
This membrane is also made from a 100 micron thick acetate polythene composite. Two or three layers of these membranes, which are placed between the plastic tubes, rotate around a polymeric lattice or steel grid and place the set inside the frame.
Hollow fiber membrane
These membranes are plastic-shaped and made of polyamide. A bunch of these fibers, including thousands of strands, fall into a frame. Feeding water is passed through the membrane and the water is filtered into the longitudinal cavity of the fibers. A collection of leaked water is directed out of the frame.
Instrumentation and measuring instruments
Luminescent automatic pressure control, temperature, pH, electrical conductivity meter, pressure gauges and flowmeters are other devices used in a reverse osmosis system.
