The Effectiveness of Reverse Osmosis

Feb 28, 2023
 by Seven Seas News Team

In reverse osmosis, the water to be purified is forced at high pressure through fine-pored semipermeable membranes, often configured in tubes.

Reverse osmosis can be counted on to deliver high-quality water purification

What is the go-to process for direct potable wastewater reuse, a process that can turn even domestic sewage into clean drinking water?

What process is globally the most popular for turning seawater into drinking water?

What process does the pharmaceutical industry trust to make water pure enough for injection into the human body?

What process is found in the production of ultrapure water that meets the exacting standards of the semiconductor industry?

The answer is reverse osmosis.

How effective is reverse osmosis as a water treatment process? Perhaps the most compelling answer is that when water purity matters most, reverse osmosis always seems to be involved.

How Reverse Osmosis Works

Reverse osmosis achieves its high level of effectiveness by forcing water through a semipermeable membrane stippled with microscopic pores that sieve out contaminants.

Among membrane processes — also including microfiltration, nanofiltration, and ultrafiltration — the reverse osmosis membrane has the smallest pore size and generally rejects contaminants more effectively. In desalination, however, the rejection mechanism of the membrane also repels salt ions due to their ionic valence.

Most reverse osmosis membranes are made of cellulose acetate, polysulfonate, and polyamide. They’re composed of a skin approximately 0.25 microns thick that serves as the active barrier, and a supporting layer approximately 100 microns thick. The membrane configurations include hollow fibers and sheets that are spirally wound with mesh spacers in a tube.

Reverse Osmosis Applications

Beyond pharmaceutical manufacturing and semiconductor production, reverse osmosis is also an effective workhorse technology for a wide range of other applications.

While it is well known for seawater desalination, it is even more effective for brackish water desalination. Many industries use reverse osmosis to produce boiler feed water that will not cause scaling. Reverse osmosis is also commonly used to purify municipal drinking water. In wastewater treatment, reverse osmosis is often the final stage, removing chemicals, pathogens, and dissolved impurities. Other industries use reverse osmosis to produce rinse water that will not leave spots.

One aspect of drinking water purification that has been causing concern lately is the question of how to remove emerging contaminants. In a recent study, reverse osmosis outperformed all other processes, achieving greater than 90% removal of all the studied compounds (EDCs, PhACs, and PCPs).

Cost-Effectiveness of Reverse Osmosis

When desalination is necessary, reverse osmosis is by far the most cost-effective technology available, accomplishing desalination at a decisive tenth the energy cost of its competitor, thermal distillation.

There are, however, drawbacks to reverse osmosis, led by its energy requirement. Reverse osmosis requires energy-intensive pressurization to force water through the membrane. Where the highest water quality is not required, other processes may be chosen to keep energy costs down.

Reverse osmosis systems are associated with elevated CAPEX, and as a sophisticated process that requires specialized knowledge and resources for operations and maintenance (O&M), it can be more costly than other processes. A number of financing structures that bundle long-term O&M with reverse osmosis are understandably gaining prominence in the market.

Ideally, under public-private partnerships (P3) — as well as build-own-operate (BOO) and build-own-operate-transfer (BOOT) contract structures — a specialized water company delivers the reverse osmosis system then continues to shepherd it throughout its service life. Such arrangements free clients to focus on their core missions and also can optimize client capital by lowering or eliminating CAPEX.

Seven Seas Water Group’s Water-as-a-Service® is an innovator in the P3 space, offering BOO and BOOT agreements that bring clients the water they need without the complexities they don’t. Contact Seven Seas to find out more about these flexible financing options.

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