Description of the classification of pollutants that may be encountered during the operation of the pretreatment system

biological pollutants

Such pollutants are also present in surface water or wastewater. When dealing with such water sources, pollution is often reflected on the membrane elements at the front end of the reverse osmosis system. When such a phenomenon occurs, the pressure at the front end of the R/O system rises rapidly, and the desalination rate of the reverse osmosis system will also increase accordingly. However, with the continuous operation of the membrane system, biological fouling will gradually spread to the entire reverse osmosis system, thus forming a large area of ​​membrane fouling. When biological fouling occurs in the membrane system, the operating pressure of the system will increase significantly and the water production will decrease. Such pollutants are also commonly bacteria, biofilms, algae and fungi. Generally, when designing the reverse osmosis process system, we must pay attention to controlling the activity of the raw water. When the bacterial content of the raw water is more than 1000cfu/100mg, removal measures must be considered in the design.

Organic Pollutants

We have said that the composition of organic matter in raw water is complex, and its pollution and impact on reverse osmosis membrane elements are also very unpredictable. However, this indicator is the main pollutant that needs to be carefully considered for protection when designing a reverse osmosis system. The sources of organic pollutants are generally divided into two types: one is the natural humic organic matter formed by the decay of animals and plants; the other is the organic matter formed by industrial waste pollution. When organic matter fouls the reverse osmosis membrane, the organic matter is often adsorbed firmly on the membrane surface, making it difficult to clean. Generally speaking, it is difficult to predict the fouling consequences of organic matter on the membrane system: some organic matter in the water has almost no destructive effect on the reverse osmosis membrane; however, there are individual trace organic matter once adsorbed on the membrane surface, which can not only pollute the reverse osmosis membrane, but also It can even cause degradation and degradation of the membrane. Therefore, we must attach great importance to the organic matter present in the raw water. So in principle, when we design a reverse osmosis system, when the TOC content of the raw water reaches 3mg/l, the corresponding removal measures must be considered in the system. Generally speaking, in the reverse osmosis pretreatment system for the treatment of surface water and wastewater, most organic pollutants should be removed or decomposed during the pretreatment process such as flocculation, clarification and oxidation as much as possible. If the water inlet requirements cannot be met after the above treatments, it can be considered to be further removed by the setting of activated carbon adsorption filters, organic matter cleaners or ultrafiltration equipment to meet the water inlet requirements of the reverse osmosis system.

suspended solids

Such pollutants are commonly found in surface water and wastewater sources, and their particle diameters are often larger than 1 micron. Such impurities can be completely deposited when the water flow is not agitated, and it is easily filtered out by the fine sand filter and multi-media filter set in the reverse osmosis system; when the reverse osmosis pretreatment system is set with flocculants During the dosing process, such impurities can also be adsorbed by the flocculent formed by the flocculant, and then filtered out by the fine filter of the multi-media filter or the sand filter.

colloidal contaminants

This type of pollutant is also commonly found in surface water and wastewater sources, and its particle diameter is often less than 1 micron. Even when it is not agitated by the water flow, these impurities will not settle freely and will always remain in a suspended state. Such impurities may be monomeric compounds composed of organic or inorganic components, or may be complex compounds composed of multiple types of compounds. Such as silicic acid compounds, iron and aluminum oxides, sulfides, tannins, humic substances, etc.

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Further reading:

operation of the pretreatment system

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