What Are the Disadvantages of Ocean Reverse Osmosis (ORO)?
In recent years, seawater reverse osmosis (RO) technology has been widely used in the field of seawater desalination and has become one of the important solutions to freshwater shortages in coastal and water-scarce regions.
It can effectively remove salts and impurities from seawater, producing freshwater suitable for drinking and industrial use.
However, despite its clear advantages, this technology is not without drawbacks.
There is no doubt that seawater reverse osmosis has transformed the desalination industry and provided a stable and safe freshwater source for many water-scarce regions.
However, no technology is perfect, and seawater reverse osmosis also has several drawbacks that cannot be ignored.
This article will comprehensively analyze the main disadvantages of seawater reverse osmosis from several aspects, including energy consumption, capital cost, environmental impact, membrane fouling, water recovery rate, and regulatory requirements.
One of the biggest disadvantages of seawater reverse osmosis is its high energy consumption.Because seawater typically contains around 35,000 ppm of dissolved salts, the system must rely on high-pressure pumps to force water through the RO membrane and separate the salts, usually requiring an operating pressure of 55–80 bar (about 800–1200 psi).
As a result, the entire system continuously consumes a large amount of electricity.
Many studies have shown that seawater desalination plants using reverse osmosis typically consume about 3–10 kilowatt-hours (kWh) of electricity to produce 1 cubic meter of freshwater.This energy demand is significantly higher than many conventional water treatment processes and keeps operating costs high over the long term.
High energy consumption not only increases operating expenses but also creates environmental pressure.At present, most of the electricity used by desalination plants still comes from fossil fuels, which means higher carbon emissions and greenhouse gas emissions, contributing to global climate change.
Building a seawater reverse osmosis desalination plant requires a substantial amount of capital.
In addition to RO membrane elements, the plant must also be equipped with high-pressure pumps, energy recovery devices, pretreatment systems, membrane housings, control systems, and supporting infrastructure, along with land acquisition, plant construction, installation and commissioning, and related permitting costs.
Among these, RO membranes themselves are relatively expensive.For example, the 8040 RO membranes widely used in large desalination projects require multiple membrane elements to form a system, and procurement costs rise rapidly as treatment capacity increases.In addition, the system requires professional technicians for operation, maintenance, and management, including equipment inspection, water quality monitoring, chemical management, and automation control, which further increases long-term operating costs.
While seawater reverse osmosis helps solve freshwater shortages, it may also have certain impacts on marine ecosystems.
First, during water intake, large volumes of seawater enter the intake system, and small fish, plankton, fish eggs, larvae, and other marine organisms may be drawn into the intake structure; some are intercepted by filtration devices, while others may die due to the action of high-pressure pumps, thereby affecting the local marine ecological balance.
Second, after desalination, seawater produces a large amount of highly concentrated brine.This brine has a much higher salinity than natural seawater. If discharged directly back into the ocean, it can raise the salinity of local waters and affect marine organisms that are sensitive to salinity changes, such as seagrass, coral, and shellfish.
In addition, the brine may contain residual chemicals used during pretreatment, such as antiscalants, flocculants, disinfectants, and membrane cleaning agents.If not properly managed, these substances may also cause some pollution to the surrounding marine environment.Therefore, more and more desalination projects are adopting diffuser discharge systems, brine resource recovery, and zero liquid discharge (ZLD) technologies to reduce environmental impacts.
The RO membrane is the core component of the entire seawater reverse osmosis system and also the part most susceptible to fouling.
As the system operates over time, suspended solids, organic matter, colloids, bacteria, and microorganisms in seawater gradually accumulate on the membrane surface, causing membrane fouling, which leads to reduced flux, increased operating pressure, and lower salt rejection.
To restore membrane performance, chemical cleaning must be carried out regularly, including acid cleaning, alkaline cleaning, and sterilization cleaning, which increases chemical consumption as well as maintenance costs and downtime.Even with regular cleaning, RO membranes still have a limited service life.
In general, seawater RO membranes last about 3–7 years, depending on feedwater quality, operating conditions, and maintenance practices.In recent years, fouling-resistant RO membranes have been able to effectively slow fouling and reduce cleaning frequency, but they still cannot completely eliminate membrane fouling and aging, so membrane replacement remains one of the major operating expenses of desalination systems.
Seawater reverse osmosis cannot convert all seawater into freshwater.At present, most seawater reverse osmosis systems have a recovery rate of about 30%–50%.In other words, for every 100 liters of seawater treated, only about 30–50 liters of freshwater are typically obtained, while the remaining 50–70 liters become brine and are discharged.
This recovery rate means that if more freshwater is needed, more seawater must be processed, which in turn requires larger equipment, higher energy consumption, and more membrane elements.
For regions with extreme water scarcity, the limited recovery rate also means that larger desalination facilities must be built, further increasing investment and operating costs.
Despite These Drawbacks, Seawater Reverse Osmosis Still Has Great Value
Although seawater reverse osmosis has issues such as high energy consumption, high investment cost, membrane fouling, and environmental impact, it remains the most mature and widely used seawater desalination technology in the world.
For the Middle East, North Africa, coastal islands, and regions with severe freshwater shortages, seawater reverse osmosis has become an important source of freshwater for daily life, industrial production, and urban development.
In recent years, with the development of high-performance RO membranes, energy recovery devices, intelligent control systems, and green energy technologies, the operating cost of seawater reverse osmosis has been steadily decreasing, while system efficiency continues to improve.
In the future, with more energy-efficient membrane materials, better brine treatment solutions, and renewable-energy-powered operation models, seawater reverse osmosis is expected to become a more environmentally friendly, efficient, and sustainable freshwater solution.