Questions about the impact of feedwater temperature on membranes in ultrafiltration and reverse osmosis?

In most cases, membrane flux increases as the temperature of the feed increases, but due to the properties or capacity of the feed, not all feeds can result in an increase in flux at any temperature. The water flux of most membranes increases by 3.3% for every 1 degree Celsius rise; therefore, a 30-degree Celsius increase will double the water flux. However, since chemical and microbial phenomena can limit membrane flux in many ways, this rule is only valid for wastewater reuse in a very small number of industries such as pure water treatment or pulp and paper manufacturing. In most cases, it is more reasonable to calculate it as an increase of 1% in membrane flux for every additional 1 degree Celsius. Increasing the operating temperature may cause: 1. Precipitation of calcium salts, such as calcium hydrogen phosphate; 2. Precipitation of proteins, such as albumin; 3. Growth of microorganisms, leading to the formation of sludge. Therefore, for many dairy and pharmaceutical products, starting the system at low temperature and low flux results in a higher membrane flux after one day of operation compared to starting it at high temperature and high flux. For more details, please visit Environmental Protection - Communication. High-temperature operations are truly beneficial only when the material is viscous, such as when dealing with gels. It may not increase the flux, but it can at least prevent the system from getting clogged with material.

The factory currently has a rainwater recycling system; basically, the rainwater is processed through a simple ultrafiltration system before being sent directly into the tap water tank. Tests show that the hardness of this treated rainwater is much lower than that of tap water. Moreover, since I have multiple tanks and the new factory requires less water, the amount of rainwater collected is sufficient for my production needs. I’m not concerned about scaling issues caused by rising temperatures ； But it’s not ruled out that the total amount of bacteria in my water could be very high; however, I don’t have any means to determine this at the moment. I just want to know if water at 40°C has a destructive effect on the membrane itself. Additionally, it has been recently observed that the quality of the water produced by my secondary reverse osmosis system is worse than before; previously the conductivity was around 1, while now, due to the increased temperature, it is around 4–5. Is it possible that, as you said, it has become too permeable and the water quality has deteriorated?

This post was last edited by CoCo070563 on 2015-7-1 08:45. Operating limits: Membrane type – Polyamide composite membrane. Maximum operating temperature: 113 ℉ (45°C). Maximum operating pressure: 600 psig (41 bar). Maximum pressure drop: 15 psig (1.0 bar). pH range for continuous operation: a 2 – 11; pH range for short-term cleaning (30 minutes): b 1 – 13. Maximum water flow rate: 85 gpm (19 m3/hr). Maximum SDI15 of the feed water: 5. Allowable free chlorine content: c 10. Maximum allowable temperature for continuous operation: 95℉ (35°C). b Refer to the cleaning guidelines in Specification 609-23010. c Under certain conditions, the presence of free chlorine and other oxidizing agents can cause premature degradation and damage to the diaphragm. Since oxidative damage falls outside the warranty coverage of Dow membranes, Dow Chemical recommends that users remove residual free chlorine through pretreatment before it comes into contact with the membrane elements. For more relevant information, please refer to the technical bulletin: 609-22010. These are the operational limit conditions for Dow’s reverse osmosis desalination of brackish water, but it is generally required that operations be carried out at 25°C.

For reverse osmosis membranes, the conductivity of the water produced by the membrane system is highly sensitive to changes in water temperature; as the water temperature rises, the water flux increases almost linearly, mainly because the viscosity of water molecules passing through the membrane decreases and their diffusion capacity increases. Increasing the water temperature leads to a decrease in desalination efficiency or an increase in salt permeation rate, mainly because the diffusion rate of salts through the membrane accelerates as the temperature rises. If it operates at 40 degrees Celsius continuously, it will have a certain impact on both the lifespan and performance of the membrane.