Reverse Osmosis Chemicals

Introduction

Reverse osmosis (RO) is one of the most effective technologies for desalting water. The application of reverse osmosis technology in industrial and civil pure water manufacturing is more and more popular. Up to now, the technology has been widely used in power, electronics, medicine, municipal administration, coal chemical industry, seawater desalination, food, cosmetics and other aspects. However, after a period of time of running of reverse osmosis system, the reverse osmosis membrane will inevitably be polluted, resulting in the decrease of water yield or desalination rate, and even the membrane components scrapped in advance. In order to ensure the economic, safe and smooth operation of reverse osmosis system, it is very important to select the appropriate reverse osmosis chemicals to prevent or slow down chemical pollution of reverse osmosis system.

Fig. 1. The reverse osmosis system.

Classification

Reverse osmosis chemicals mainly include reverse osmosis scale inhibitor, reverse osmosis biocide, reverse osmosis flocculant and reverse osmosis cleaner.

• Reverse osmosis scale inhibitor: The scale deposition is one of the problems in reverse osmosis membrane pollution. Reverse osmosis scale inhibitor can effectively prevent or slow down the formation of inorganic scale on the surface of reverse osmosis membrane. Different from the conventional circulating water scale inhibitor, the reverse osmosis scale inhibitor mainly plays the role of scale inhibition, while the conventional circulating water scale inhibitor has the ability of corrosion inhibition in addition to the role of scale inhibition. At present, common reverse osmosis scale inhibitors are polyphosphate, organophosphate, organophosphate ester and polymers (such as polycarboxylic acid etc.).

Fig. 2. The mechanism of scale deposition on reverse osmosis membrane ^[1].

• Reverse osmosis biocide: Microbial growth is the most common and serious problem that can contaminate the reverse osmosis membrane, especially when the influent water source is surface water or bacteria-rich water. Reverse osmosis biocide can effectively inhibit the growth of microorganisms. Reverse osmosis biocides include oxidizing biocides (e.g., peracetic acid, hydrogen peroxide and chlorine) and non-oxidizing biocides (e.g., formaldehyde, glutaraldehyde and quaternary ammonium compounds, isothiazolinone, etc.). Generally, the use of non-oxidizing biocides in reverse osmosis systems for the production of potable water is not considered acceptable.
• Reverse osmosis flocculant: Reverse osmosis flocculant can remove colloids and suspended solids from water to prevent colloids and suspended solids blocking and polluting the reverse osmosis membrane. Generally, reverse osmosis flocculant is used in the pretreatment stage of reverse osmosis system and in raw water with high SDI pollution index and turbidity. Reverse osmosis flocculants are divided into organic reverse osmosis flocculants and inorganic reverse osmosis flocculants. Inorganic flocculants mainly include aluminum and iron salts and organic flocculants mainly include synthetic organic polymer flocculants and natural polymer flocculants.
• Reverse osmosis cleaner: Although the above reverse osmosis chemicals can effectively prevent the problem of membrane pollution, but with a long time of operation, the reverse osmosis system still inevitably occurs the problems of scaling, particles and colloid fouling and microbial pollution. Thus, it is necessary to carry out reverse osmosis membrane cleaning. Reverse osmosis cleaner can take the chemical reactions of exchange, chelate, demulsification and others with the pollutants in the membrane channel or on the membrane surface, so as to remove the pollutants. And because of fine effect of reverse osmosis cleaner, it has become the most used method in reverse osmosis membrane cleaning. Commonly used reverse osmosis cleaners are acid, alkali, complexing agent, surfactant and enzyme. In general, acid cleaners can be used to remove inorganic salt scale deposited on reverse osmosis membrane, and alkaline cleaners can be used to remove organic matter and colloidal pollutants. Enzyme cleaners are very effective in removing protein-containing contaminants because they can cut the peptide chains of proteins and rapidly dissolve short protein fragments.

Fig. 3. The reverse osmosis membrane without (left) and with polluted (right).

Alfa Chemistry can offer you with various reverse osmosis chemicals such as reverse osmosis scale inhibitors, reverse osmosis biocides, reverse osmosis flocculants and reverse osmosis cleaners. If you can't find the desired product in our product catalog, we also offer you with custom synthesis service. Please contact us, if you have any needs.

Reference

• Xie D., et al. Syntheses, applications and mechanism of reverse osmosis scale inhibitors[J]. Materials Guide A, 2016, 30(12): 29-37.