A key metric for evaluating reverse osmosis (RO) performance is the system’s recovery rate. The recovery rate is defined as the ratio of permeate flow over the feed (influent) flow. When operating RO systems, most facility managers aim to optimize the recovery rate – balancing the capital costs and operational costs, along with the costs of water sewer, inherent to operating a water treatment program. A higher recovery rate is desirable because it means more purified water is produced from the original feedwater supply for whatever end use the facility manager is responsible.

As EAI water treatment expert Tony Murphy puts it, “We want to design these systems at a high-efficiency rate and a high recovery rate. So, for every thousand gallons of water we’re feeding the RO system, we are aiming for 80% recovery. This goal tends to provide our clients with the highest operational and financial return.”

However, pushing recovery rates too high comes with risks. As the recovery rate increases, the likelihood of fouling and scaling on the membrane surface also increases. When fouling and scaling occur, membranes experience reduced lifespan, and water quality declines. Tony uses an analogy to explain the impact of fouling: “Running an RO with high potential for fouling or scale is kind of like treating a cold. If you don’t treat the symptoms as well as the cause, that system may end up getting the flu. You’re setting yourself up to be down for a long time, and the cost of not treating the original cause for the sickness is going to end up being expensive.”

Optimizing RO recovery rates requires carefully balancing water production efficiency with actions to preserve membrane health and longevity. This article provides best practices for facility managers to achieve high, sustainable recovery rates for their RO systems.

Understanding Recovery Rates

The recovery rate significantly impacts RO performance and economics. As the recovery rate increases, the RO system produces a higher volume of product water from the original feed. Improving the recovery rate can, in many instances, reduce brine/wastewater volumes by over 50% compared to lower recovery rates. However, pushing recovery also concentrates impurities in the remaining feedwater stream. The higher concentrations can lead to fouling and mineral scaling on membrane surfaces.

Typical RO recovery rates range from 50% to 85%, depending on the application:

• Seawater desalination: Approximately 35-50% recovery rate due to high fouling potential and increased salinity
• Brackish water: 60-80% recovery is common
• Industrial process water: 70-85% recovery rates possible with proper pre-treatment
• Food and beverage: Typically around 50-75%, optimized for consistent water quality

In general, higher recovery rates are desirable to improve water efficiency. However, the optimum level should balance productivity gains with membrane performance impacts.

The Benefits of High Recovery Rates

Operating RO systems at higher recovery rates offers several benefits:

Increased water efficiency

Achieving high recovery rates enables an RO system to produce a greater volume of purified water from the given feedwater supply. For example, increasing recovery from 70% to 80% allows 10% more product water to be generated from the feed flow entering the system. It is important to remember that facilities only install ROs to get more, improved feedwater quality – increasing pure water from the RO serves that purpose.

Reduced wastewater volumes

As less feedwater is rejected as concentrate, higher recovery rates significantly reduce wastewater brine discharges from the RO treatment process. The reduced discharge volumes lower costs associated with wastewater handling and disposal.

Lower long-term operating costs

While increasing recovery does concentrate impurities into a smaller volume stream, the savings from extracting more product water and minimizing waste outweigh the additional costs of concentrate disposal. In many cases, high recovery operation reduces overall operating costs significantly over time.

However, to sustain these benefits, the high recovery rates must be balanced with proper RO system design and effective membrane fouling prevention.

The Risks of Pushing Recovery Rates Too High

While high recovery rates can minimize wastewater and costs, pushing rates too high has several risks, including:

Increased fouling and scaling

As recovery increases, impurities become more concentrated in the feedwater stream. The higher concentrations can cause faster fouling and mineral scaling to occur on the membrane surface. This fouling layer reduces membrane performance, which in turn can lead to operational issues.

Reduced membrane life

The increased fouling and scaling damage the membrane’s integrity and shorten its useful operating life, requiring earlier replacement. More frequent cleanings may also be needed, increasing maintenance costs. Membranes are a large cost of the overall system, and replacing them can lead to lower return on investment for end users.

Higher cleaning and replacement costs

With heavier membrane fouling occurring, additional costs are incurred for cleaning chemicals, labor, as well as for new membrane elements to replace damaged ones.

Production interruptions

Severe fouling or scaling can stop production altogether until membranes are cleaned or replaced. These unplanned stoppages are highly detrimental for continuous operations. Oftentimes water availability is most aptly measured in operational downtime, and turning off a critical RO system may be unacceptable.

While wastewater reduction is desirable, the potential downsides of exceeding optimal recovery rates should lead one to ensure that the system is designed properly, balancing the desire for increase recovery with the risks of doing so. Proper pre-treatment and system monitoring help balance recovery versus membrane health (for more, read our article on maintaining reverse osmosis system performance).

Best Practices for Optimization

To achieve high, sustainable recovery rates, RO system owners should adopt these best practices:

Carefully analyze feedwater

Chemistry analyses on the incoming water help RO system designers understand the potential fouling and scaling risks. Work with an experienced engineer to review total dissolved solids (TDS), hardness, iron, and silica levels before determining optimal recovery rates and eventual system design.

Model recovery scenarios

Software tools like Toray’s WAVE, Veolia’s Winflows, or Hydranautics’ IMSDesign predict the target recovery rates achievable for the feed analysis along with membrane type and system configuration.

Install proper pre-treatment

Multi-media filters, ultrafiltration systems, antiscalant dosing, and other pre-treatment methods lower fouling risks and support higher recovery operations.

Monitor differential pressure

Rising differential pressure between the feed and concentrate indicates the early stages of fouling. Installing real time monitoring on RO systems to track for pressure changes enables quick corrective actions.

Adjust concentrate valve

Opening the concentrate valve lowers recovery rates. The valve can optimize recovery if fouling conditions are detected.

Clean and replace membranes

To counteract fouling issues from sustained high recovery operation, regular cleanings, autopsies, and membrane replacements preserve system performance.

Adhering to these guidelines allows RO plant operators to maximize water recovery rates with the system stability and membrane longevity needed for sustainable and economic performance.

The Role of Remote Monitoring

Implementing remote monitoring and control systems greatly assists sustaining high RO recovery rates by:

Enabling close tracking of differential pressure

Remote monitoring systems continuously log differential pressure between the feed and concentrate streams. Rising pressure may indicate the beginning of fouling. Early notification of potential fouling allows operators to promptly clean or adjust the system before recovery rates significantly fall.

Alerting to out-of-spec conditions

Remote monitoring dashboard and alarms notify staff when critical parameters like differential pressure, permeate quality, or recovery rate drift out of specified ranges. Operators can remotely adjust valve openings or flush modes to quickly return the system to target levels.

Providing data for optimization

The historical reports and visual trends generated from remote monitoring data guides appropriate adjustments of recovery rates, backwash triggers, antiscalant dosing, and other setpoints to optimize separation efficiency, water quality, and membrane longevity over time.

The visibility and control enabled by remote systems is essential for early issue detection, prompt response, and sustaining high performance. The capabilities of these systems, despite the increased cost, empower operators to balance high water recovery with membrane health.

Reverse osmosis systems produce purified water critical for many industrial, commercial and municipal processes. To leverage these systems in the most economical way, facility operators aim to maximize the recovery rate to improve water efficiency and minimize discharge volumes.

Following the guidelines above, operators can achieve high sustainable recovery rates, gaining the water productivity and waste reduction benefits without the drawbacks of premature membrane failure. As our expert Tony sums up, “if you really want to save money, you need to spend the time up front to design the right system. You can pay now with time or pay later with money.”

If you would like to improve your recovery rates and reverse osmosis system performance, or need help designing a custom RO system for your facility, EAI is here to help. Contact us today.