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Views: 0 Author: Site Editor Publish Time: 2026-11-12 Origin: Site
Clean water supply and wastewater recycling are increasingly critical constraints for modern industries. Traditional water purification routes such as ion exchange, distillation and evaporation consume large quantities of acid, alkali and steam, with high energy cost and heavy secondary pollution. Since the commercialization of thin‑film composite polyamide RO membranes, reverse osmosis has reshaped the whole water treatment industry.
In food and beverage, biopharmaceutical, semiconductor, power and chemical sectors, stable low‑conductivity process water is mandatory. For wastewater recovery projects, RO serves as the core polishing unit after MF/UF pretreatment, removing dissolved salts so that treated water can be reused on site. Meanwhile, concentrated brine generated by RO can be further processed by high‑pressure RO or evaporators for zero‑liquid discharge. Compared with other membrane grades, RO faces stricter requirements for feed quality; inadequate pretreatment is the primary cause of premature membrane failure in most industrial projects.
Osmosis describes the natural phenomenon in which pure water spontaneously passes through a semi‑permeable membrane toward the side with higher solute concentration. Reverse osmosis applies external pressure exceeding the natural osmotic pressure to reverse this mass transfer. Under driving pressure, water molecules penetrate the dense polyamide separating layer, forming low‑TDS permeate, while dissolved ions and most soluble organics are retained in the concentrate stream.
Commercial spiral‑wound RO elements adopt multi‑layer thin‑film composite structure: a non‑woven fabric substrate provides mechanical support, a porous polysulfone intermediate layer reduces flow resistance, and an ultra‑thin cross‑linked polyamide skin layer delivers selective separation. This structure balances high water permeability and salt rejection, which normally reaches 98–99.5% for sodium chloride under standard test conditions.
A complete industrial reverse osmosis system relies heavily on pretreatment to protect membrane elements. The typical sequence runs as follows: raw water → multimedia filter → activated carbon filter → cartridge security filter → dosing system for antiscalant, reducing agent and pH adjustment → high‑pressure pump → RO membrane skid.
For feed water with high colloid and organic loading, ultrafiltration is installed ahead of RO to control SDI and turbidity. The high‑pressure pump delivers feed to spiral‑wound membrane vessels. Permeate is collected for direct use or further polished by EDI or mixed bed resin to reach ultrapure water specification. Concentrated brine, also known as reject, is partially recycled or discharged for subsequent brine treatment. Online instruments continuously monitor conductivity, permeate flow, concentrate flow, feed pressure and differential pressure. Multi‑stage RO configuration is adopted when higher recovery or deeper desalination is required.
Recovery rate and salt rejection are the two most important performance indicators. Recovery refers to the proportion of feed converted into product permeate. Boosting recovery cuts raw water consumption, yet it elevates salt concentration in the concentrate and raises scaling risk. For brackish water RO, recovery usually ranges from 50% to 75%, while seawater RO generally operates below 50%.
Operating pressure depends on feed salinity. Brackish water systems commonly run at 10–25 bar; seawater RO requires 55–70 bar. Feed temperature affects both flux and rejection. Rising temperature increases water permeability but lowers salt rejection. In addition, pH must be kept within the membrane tolerance window to avoid hydrolysis of the polyamide active layer, especially in the presence of free chlorine. Even trace chlorine will cause irreversible damage to polyamide RO membranes, hence sodium metabisulfite dosing is essential to eliminate residual chlorine.
Four typical fouling types frequently occur in RO systems: colloidal fouling, organic fouling, biological fouling and inorganic scaling. Colloids such as iron hydroxide and clay deposit on the membrane surface when SDI is out of limit. Humic substances, oil and microbial extracellular polymers lead to organic adsorption. Biofouling forms sticky biofilms and gradually blocks flow channels. Inorganic scaling happens when calcium carbonate, calcium sulfate, barium sulfate or silica exceed solubility limit along the concentration polarization layer.
Once normalized permeate flux drops by 10–15% or differential pressure rises sharply, clean‑in‑place is triggered. The standard CIP sequence begins with low‑pressure flushing with permeate water. Alkaline cleaning solution is circulated first to remove organic contaminants and biofilm. Acid cleaning follows to dissolve mineral scales. If biofouling persists, biocide circulation can be applied under strictly controlled concentration. After cleaning, the loop is thoroughly rinsed and performance is tested before restarting production. Preventive measures including antiscalant dosing, regular flushing and reliable pretreatment are far more economical than remedial chemical cleaning.
Against ion exchange, RO eliminates frequent regeneration with acid and alkali, reduces chemical consumption and sludge generation, and runs continuously with stable effluent conductivity. Compared with thermal evaporation, RO has much lower energy consumption for moderate‑salinity streams, though evaporation gains advantages for highly concentrated brine.
Relative to ultrafiltration and microfiltration, RO can remove dissolved ions rather than merely particles, but it demands far higher feed quality and operating pressure, and the membrane cost per unit area is higher. Tubular or hollow fiber RO modules exist for special applications, while spiral‑wound elements dominate the mainstream market thanks to high packing density and mature supply chain.
Reverse osmosis covers a wide spectrum of industrial scenarios: seawater and brackish water desalination for municipal and island water supply; boiler makeup water for thermal power plants; ultrapure water for semiconductor, display and pharmaceutical production; desalination of permeate from prior membrane separation in plant extraction and fermentation lines; advanced treatment of electroplating, printing and dyeing wastewater for water reuse; and pre‑concentration before brine crystallization for zero‑liquid‑discharge projects.
Reverse osmosis has established itself as the core technology for desalination and high‑purity water preparation. By intercepting dissolved salts and trace soluble pollutants, it supports clean production and water resource recycling across numerous industries. Current research focuses on low‑pressure high‑rejection membranes, chlorine‑resistant modified polyamide materials and integrated RO‑brine concentration processes. With the continuous optimization of energy‑recovery devices and intelligent online fouling warning systems, reverse osmosis will further reduce operating costs and expand its role in water conservation and environmental protection.
