Double Pass Reverse Osmosis Systems

The two-stage reverse osmosis system refers to the situation where the permeated water flows into the second reverse osmosis unit to further purify the water to a higher degree of purity. Therefore, a two-stage or two-phase reverse osmosis system means that the concentrated liquid or waste liquid is input into the second reverse osmosis system separately to recover water. Thus, we design the reverse osmosis system to purify water by removing approximately 99% of the total dissolved solids from the incoming water. At the same time, a single-stage reverse osmosis system will simultaneously produce product water (permeated water) and waste liquid (concentrated liquid).

How does the two-pass reverse osmosis system work?

Firstly, the two-pass reverse osmosis system consists of two reverse osmosis systems (the first pass and the second pass). The flow capacity of the first pass is greater than that of the second pass. A middle water storage tank can be set between them. Therefore, the permeated liquid or concentrated water from the first pass reverse osmosis system can be stored and sent to the second pass reverse osmosis system for further filtration. At the same time, if water recovery is required in the application, the system needs to provide pre-treatment for both the first pass and the second pass reverse osmosis systems. Afterwards, since the concentrated water from the first pass is close to the saturation point, while another application may only require the pre-treatment of the first pass. If it is used as the permeated water for the second pass, it can be used as the incoming water for the second pass accordingly.

Why should I use a two-stage reverse osmosis system?

Sometimes, the total dissolved solids (TDS) level of the final permeate water needs to be extremely low. And a single-stage reverse osmosis system might not be able to achieve this level. Therefore, a combination of two saltwater reverse osmosis systems can be used, or a seawater reverse osmosis system can be used first, followed by a saltwater reverse osmosis system to achieve it. Some factories have begun to reuse water. Due to community requirements to minimize the use of urban water supply or to extract water from the original source, this can lead to the depletion of the groundwater resources in the area. Therefore, these factories use two-stage reverse osmosis systems to improve the water efficiency of their systems. The design of a single-stage reverse osmosis system can only recover about 80% of the influent water. Therefore, adopting the two-stage reverse osmosis membrane technology can increase the water recovery rate to over 90%.