Key Knowledge and Application of Reverse Osmosis Recovery

The standard test recovery rate, actual recovery rate, and system recovery rate of membrane components are three key concepts in reverse osmosis technology. The standard test recovery rate is determined by membrane component manufacturers under standard conditions, such as the standard recovery rate of 15% for the brackish water membrane elements BW8040 and BW4040 of HID brand industrial membrane, and 8% for the seawater membrane elements SW8040 and SW4040. The actual recovery rate is determined during actual use, in order to extend the lifespan of membrane components and slow down pollution, manufacturers will make clear regulations. For example, the actual recovery rate of a single 8040 membrane elements should not over 18%. However, in the second stage reverse osmosis system water treatment, the actual recovery rate can slightly exceed 18%, but it is best to control it below 20%.

The system recovery rate refers to the total recovery rate of the entire reverse osmosis device during actual operation. It is influenced by various factors such as water quality, number and arrangement of membrane components. Due to the small number of membrane elements and short process, the recovery rate of small reverse osmosis devices is usually low; On the contrary, jumbo industrial reverse osmosis devices generally have a system recovery rate of 75% or more, and sometimes the recovery rate of the second stage reverse osmosis can even reach 90%.

While pursuing high system recovery rates, it is also important to avoid certain issues. Such as a decrease in desalination rate of product water, an increased risk of precipitation of slightly soluble salts, and a decrease in component water production due to high osmotic pressure of concentrated water. Therefore, in practical operation, it is necessary to reasonably control the system recovery rate to ensure the stable operation and optimal performance of the reverse osmosis device.

How to determine the system recovery rate?

For large-scale industrial reverse osmosis devices, due to the large number of membrane elements and long water flow path, the actual system recovery rate is usually about 75%. In some cases, such as when the incoming water quality is excellent, the recovery rate of the secondary reverse osmosis system can even reach up to 90%. When determining the system recovery rate, the following two points should be considered:

The length of membrane element series connection: The longer the series connection length, the higher the system recovery rate may be.

Concentrated water circulation and its flow rate: If there is no concentrated water circulation, the recovery rate of membrane components and systems needs to be determined according to specific regulations.

In addition, in practical operation, attention should be paid to avoiding problems such as a decrease in product water desalination rate, an increase in the risk of micro soluble salt precipitation, and a decrease in component water production caused by high osmotic pressure of concentrated water. Therefore, reasonable control of system recovery rate is crucial to ensure the stable operation and optimal performance of reverse osmosis devices.

The formula for calculating the recovery rate of a reverse osmosis system is:

Recovery rate=(purewater flow rate/feedwater flow rate) × 100%

Among them, the purewater flow rate refers to the purified water flow rate obtained after reverse osmosis treatment, while the feedwater flow rate is the original water flow rate entering the reverse osmosis system. This formula is used to quantitatively describe how much proportion of raw water can be effectively converted into purified water during the treatment process of a reverse osmosis system.