What is the impact of water temperature on reverse osmosis systems?
Water temperature directly affects the water production, desalination rate, energy consumption and service life of membrane elements of reverse osmosis by changing the physicochemical properties (viscosity, diffusion rate) of water and the performance of membrane materials. The ideal water temperature control range is 15-25℃. Generally, a heat exchange device needs to be added before pretreatment to adjust the water temperature.
Impact on water production: An increase in water temperature reduces water viscosity and improves the diffusion rate of water molecules, thus increasing the water permeability of RO membranes. Generally, for every 1℃ increase in water temperature, the corresponding water production increases by about 2-3% (specific values vary with membrane models), and vice versa.
Impact on desalination rate: An increase in water temperature reduces water viscosity and the diffusion resistance of salts, leading to easier permeation of salts through RO membranes. The desalination rate fluctuates with water temperature. Generally, for every 1℃ increase in water temperature, the desalination rate decreases by 0.2-0.3%, and vice versa.
Impact on operating pressure of reverse osmosis system: An increase in water temperature reduces water viscosity, so the operating pressure required by the system for the same water production will decrease, and vice versa.
Long-term impact on RO membrane materials: Excessively high water temperature (long-term higher than 35℃) will cause hydrolysis reaction of RO membrane elements, loose membrane structure, and irreversible decrease in desalination rate. Too low water temperature (lower than 5℃) will make RO membranes brittle and prone to mechanical damage. Therefore, membrane manufacturers require the water temperature to be controlled at 5-45℃.
pH control requirements for reverse osmosis systems?
Under normal circumstances, the pH of feed water for the first-stage reverse osmosis system should be controlled within 6.5-7.5, and hydrochloric acid and sodium hydroxide should be used for adjustment if it is too high or too low.
For the second-stage reverse osmosis system without a decarbonization fan, sodium hydroxide is needed to adjust the pH. Generally, the pH of feed water for the second-stage RO is controlled within 7.8-8.5, which is adjusted according to on-site conditions, with the maximum pH not exceeding 9.5.
Under normal circumstances, the pH of feed water for concentrated water reverse osmosis should be controlled within 6.5-7.5. Normally, the pH of concentrated water feed water will not be lower than 7.5, so hydrochloric acid is needed to adjust the pH.
pH control requirements for reverse osmosis systems?
Under normal circumstances, the pH of feed water for the first-stage reverse osmosis system should be controlled within 6.5-7.5, and hydrochloric acid and sodium hydroxide should be used for adjustment if it is too high or too low.
For the second-stage reverse osmosis system without a decarbonization fan, sodium hydroxide is needed to adjust the pH. Generally, the pH of feed water for the second-stage RO is controlled within 7.8-8.5, which is adjusted according to on-site conditions, with the maximum pH not exceeding 9.5.
Under normal circumstances, the pH of feed water for concentrated water reverse osmosis should be controlled within 6.5-7.5. Normally, the pH of concentrated water feed water will not be lower than 7.5, so hydrochloric acid is needed to adjust the pH.
What matters need attention when considering membrane system cleaning schemes in general?
The impact of cleaning discharge waste liquid on the environment should be considered.
The pollutant removal in this cleaning process should be maximized as much as possible.
The damage to the membrane during cleaning should be minimized.
In actual cleaning operations, the cleaning cost should be controlled as much as possible on the premise of ensuring the cleaning effect.
What improper dosing will cause reverse osmosis failures?
1 Reverse osmosis failures caused by scale inhibitor and flocculant dosing systems
a. Mismatch between the performance of scale inhibitors/flocculants and water quality, and pollution by Fe³+ and Al³+;
b. Unreliable performance of metering pumps, excessive dilution of scale inhibitors, and serious pollution of chemical tanks;
c. Flow deviation caused by scale inhibitor dosing.
2 Reverse osmosis failures caused by other dosing systems
a. Membrane element fouling caused by inappropriate flocculants;
b. Oxidation of membrane elements caused by excessive addition of oxidants;
c. Severe fouling of membrane elements caused by excessive addition of reducing agents.
What are the factors affecting ORP determination?
pH
Dissolved oxygen content
Concentration of redox substances
Temperature
Electrode status and quality
Conductivity and ion concentration
Water sample flow rate
Electromagnetic interference.
