Q: Does adjusting the RO recovery rate impact energy consumption?

Yes . Increasing recovery typically requires the system to operate at a higher pressure , which increases energy use. However, the actual impact depends on how the adjustment is made – especially whether you reduce feed flow, how the pump is configured (fixed vs variable speed), and the overall fouling state of the membranes. Good pretreatment and clean membrane surfaces are essential to minimize energy increase when pursuing higher recovery.

Q: Our membranes in wastewater treatment last only two years. Is that normal?

For surfaces waters , a typical RO membrane lifespan is 4 to 5 years , sometimes even longer when well-maintained. For wastewater or landfill leachate, shorter lifetimes are expected due to more challenging feedwater. However, Kurita often extends membrane life through: Detailed foulant analyses Specialist cleaning routines Improved pretreatment Offsite membrane servicing In many cases, a tailored treatment plan can significantly prolong membrane life beyond your current two-year cycle.

Q: Can underperforming RO elements be repurposed or reused?

Potentially yes. Kurita’s offsite membrane service evaluates each element individually, determining: Which membranes can be recovered Which can still operate in less demanding positions Which must be discarded Many customers are surprised by how many elements remain usable after proper cleaning and diagnosis.

Q: What is the recommended cleaning flow velocity for RO membranes?

For most RO systems, the rule of thumb is: ~10 m³/h crossflow per 8-inch pressure vessel during cleaning. Kurita also provides detailed cleaning guidelines to ensure optimal results, including soaking times, flushing sequences, and temperature considerations.

Q: What if different anti-scalants are needed for different types of scaling (e.g., calcium vs silica)?

In most cases, a single well‑designed antiscalant can control multiple scale types simultaneously. Kurita formulates products to handle combinations of: Calcium carbonate Calcium sulfate Silica Metal oxides Mixed salts In extreme cases, pH adjustment or specialized formulations may be required — but 99% of systems can be protected with one optimized product .

Q: What chemicals help reduce biological fouling in RO systems?

Kurita’s preferred solutions are membrane‑compatible biocides , such as: Kuriverter ™ 110 Kuriverter ™ 220 These products: Are effective on existing biofilm (not just microbe killing) Are safer for membranes Do not create downstream nutrient loads Are often NSF‑approved They offer a much better alternative to traditional chlorination.

Q: How can chemical overdosing negatively impact RO operation?

Overdosing can cause several issues: With coagulants: Excess solids accumulate in multimedia filters More frequent backwashing is required Coagulant can carry over to membrane stages Coagulant interferes with anti-scalants With anti-scalants: Very high dosages can cause the anti-scalant itself to precipitate Cost increases without additional benefits Correct dosage is just as important as correct product selection.

Question 1

Does adjusting the RO recovery rate impact energy consumption?

Accepted Answer

Yes. Increasing recovery typically requires the system to operate at a higher pressure, which increases energy use.

However, the actual impact depends on how the adjustment is made – especially whether you reduce feed flow, how the pump is configured (fixed vs variable speed), and the overall fouling state of the membranes.

Good pretreatment and clean membrane surfaces are essential to minimize energy increase when pursuing higher recovery.

Question 2

Our membranes in wastewater treatment last only two years. Is that normal?

Accepted Answer

For surfaces waters, a typical RO membrane lifespan is 4 to 5 years, sometimes even longer when well-maintained.

For wastewater or landfill leachate, shorter lifetimes are expected due to more challenging feedwater.

However, Kurita often extends membrane life through:

Detailed foulant analyses
Specialist cleaning routines
Improved pretreatment
Offsite membrane servicing

In many cases, a tailored treatment plan can significantly prolong membrane life beyond your current two-year cycle.

Question 3

Can underperforming RO elements be repurposed or reused?

Accepted Answer

Potentially yes.

Kurita’s offsite membrane service evaluates each element individually, determining:

Which membranes can be recovered
Which can still operate in less demanding positions
Which must be discarded

Many customers are surprised by how many elements remain usable after proper cleaning and diagnosis.

Question 4

What is the recommended cleaning flow velocity for RO membranes?

Accepted Answer

For most RO systems, the rule of thumb is:

~10 m³/h crossflow per 8-inch pressure vessel during cleaning.

Kurita also provides detailed cleaning guidelines to ensure optimal results, including soaking times, flushing sequences, and temperature considerations.

Question 5

How does membrane length influence cleaning effectiveness?

Accepted Answer

Longer membrane trains (e.g., six elements per pressure vessel) can be harder to clean effectively because:

Fouling can migrate from one element to the next
Crossflow velocity decreases along the length
Early-stage elements receive better cleaning that downstream ones

Offsite cleaning solves this by treating each element individually, achieving much better results.

Question 6

What if different anti-scalants are needed for different types of scaling (e.g., calcium vs silica)?

Accepted Answer

In most cases, a single well‑designed antiscalant can control multiple scale types simultaneously.
Kurita formulates products to handle combinations of:

Calcium carbonate
Calcium sulfate
Silica
Metal oxides
Mixed salts

In extreme cases, pH adjustment or specialized formulations may be required — but 99% of systems can be protected with one optimized product.

Question 7

How do we balance higher RO recovery with the risk of shorter membrane life?

Accepted Answer

Higher recovery = higher stress on membranes.

However, you can mitigate this by:

Improving pretreatment
Adjusting cleaning protocols
Using appropriate anti-scalants at correct dosages
Checking for seasonal water quality changes
Monitoring scaling and fouling margins via software modelling

Moderate increases (e.g., 75% → 80%) are usually safe with proper preparation and monitoring.

Pushing beyond this requires careful engineering.

Question 8

What chemicals help reduce biological fouling in RO systems?

Accepted Answer

Kurita’s preferred solutions are membrane‑compatible biocides, such as:

These products:

Are effective on existing biofilm (not just microbe killing)
Are safer for membranes
Do not create downstream nutrient loads
Are often NSF‑approved

They offer a much better alternative to traditional chlorination.

Question 9

What is included in Kurita’s free plant survey?

Accepted Answer

A Kurita expert will:

Visit your site
Review all pretreatment steps (media filters, UF/MF, chemicals, backwashing, etc.)
Analyze RO performance and fouling behavior
Identify opportunities to save water, reduce energy, or increase production
Provide tailored recommendations for improvement

This holistic approach ensures even subtle inefficiencies are captured.

Question 10

How can chemical overdosing negatively impact RO operation?

Accepted Answer

Overdosing can cause several issues:

With coagulants:

Excess solids accumulate in multimedia filters
More frequent backwashing is required
Coagulant can carry over to membrane stages
Coagulant interferes with anti-scalants

With anti-scalants:

Very high dosages can cause the anti-scalant itself to precipitate
Cost increases without additional benefits

Correct dosage is just as important as correct product selection.

Question 11

How does membrane type (high-rejection vs fouling-resistant) affect lifespan?

Accepted Answer

Fouling-resistant membranes can perform very well under specific conditions, especially with appropriate pretreatment and stable feedwater.

High-rejection membranes generally operate at higher flux, which can increase fouling risk.

Ultimately, performance depends on:

Feedwater quality
Pretreatment efficiency
Biofilm control
Scaling prevention
Cleaning consistency

Membrane selection should be paired with system optimization.

Question 12

Can sodium dioxychloride replace chlorine dioxide for pretreatment?

Accepted Answer

Kurita generally advises caution with both oxidizing biocides upstream of RO.

While they can control microbes, they also:

Break biological matter into nutrients
Fuel downstream regrowth
Promote EPS formation
Increase fouling risks

Safer, membrane‑compatible, non‑oxidizing biocides are usually recommended.

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