Effect of various water quality on reverse osmosis system

Brackish water

In a certain sense, brackish water can be defined as a low TDS water source whose TDS value is greatly increased due to the invasion of seawater. In the RO category, brackish water can be defined as a reverse osmosis feedwater having a salt content TDE value at a medium to low level (up to 10,000-15,000 ppm) and which can be treated with a brackish water RO membrane having a maximum feed water pressure of 600 psi.

River water

Water that falls on the surface due to rain, flows into the river through the surface or through the ground. The water passing through the surface contains suspended matter, while the water passing through the ground contains more soluble inorganic salts flowing through the formation. When the rainwater flowing through the surface flows into the river, the concentration of suspended matter will increase sharply. Therefore, the characteristic of the river water is that the suspended matter in the river water changes greatly. Moreover, the seasonality of river water is obvious, such as changes in water temperature, reproduction of aquatic organisms, and sediment content from organisms and the content of colloidal substances derived from organic matter. In addition, the amount of humus and organic matter in rivers flowing through forest areas and mud-borne areas will also be high. Rivers are also polluted by municipal wastewater treatment water, factory discharges, or irrigation water containing pesticides. Therefore, we are required to conduct sufficient investigations on the water quality, to grasp the extent of the changes, and to make necessary considerations for the pretreatment equipment or operating conditions.

lake

When the river water is left in a lake or a reservoir for a long time, the suspended matter will be reduced due to sedimentation, but on the other hand, it is susceptible to microorganisms. Lakes or reservoirs are prone to eutrophication, resulting in over-reproduction of algae with a lighter weight, resulting in poor sedimentation and agglomeration of the lake, which may sometimes cause blockage of the filter pool. It also consumes carbon dioxide dissolved in water due to carbonation assimilation, causing the pH of the lake to increase.

When water stratification is formed inside the lake, the bottom layer of water will be beneficial to the growth of anaerobic bacteria due to the state of lack of oxygen, as well as the formation of hydrogen sulfide, including redissolution of iron and manganese. Therefore, when using lakes or reservoirs as raw water, it is necessary to thoroughly study the treatment methods, and if necessary, consider the water that does not deteriorate at the bottom of the lake when taking water.

groundwater

The flow rate of groundwater in the formation is extremely slow. Due to the natural filtration effect, there is almost no suspended matter, but the influence of the flowing formation is very obvious. For example, the concentration of calcium in the water flowing through the limestone zone is very high, and the concentration of silicon in the groundwater passing through the volcanic zone is also high. Usually, groundwater is reductive due to insufficient oxygen. It may contain iron or manganese in a reduced state. It may also contain hydrogen sulfide or helium or neon depending on the formation.

There is less suspended solids in the groundwater, and the water temperature change in the whole year is also relatively stable. As the raw water of the RO system, it is necessary to consider the hardness components, silicon, and metal ions that need to be removed in the pretreatment.

Municipal water

When the RO system uses tap water as the raw water, it is necessary to confirm the tap water treatment process, the pipeline condition, and pay attention to residual chlorine.

seawater

The standard seawater has a NaCl content of 3.5% or more, and more than 10 kinds of soluble components such as magnesium, calcium, potassium, sulfate, carbonate, bromine, boron and fluorine. Due to the influence of precipitation, tidal or water temperature in the estuary, there are certain differences in the concentration of salt in the seawater. The content of suspended solids and organic matter is affected by rivers and human activities, and there will be regional differences. Therefore, the water intake point and water intake mode of the desalination system are crucial, which directly affects the water quality and pretreatment method of the raw water.

Waste water

In recent years, the reverse osmosis process has been adopted in the deep treatment of more and more municipal sewage and industrial sewage. The sewage used for reverse osmosis treatment is generally industrial cold circulating sewage and tertiary treatment water that meets the standard of misuse of water. The COD is less than 50mg/L, and the oil content and turbidity must meet the RO water inflow requirements after further processing. Pay special attention to whether the raw water contains organic substances such as surfactants that cause serious pollution of the reverse osmosis membrane, and organic solvents that are incompatible with the membrane material. Due to the complexity and volatility of wastewater quality, the collection and investigation of water quality data is particularly important. Wastewater Treatment Reverse osmosis systems require extremely stringent pretreatments, using a very conservative low-throughput design with high-performance, low-pollution membrane components (such as LFC3-LD).