Engineered Treatment for PFAS-Contaminated Water

Per- and polyfluoroalkyl substances – PFAS – are a large family of synthetic chemicals used across industrial and consumer applications because of their resistance to heat, water, oil and chemical degradation.

Those same properties make them extremely persistent once they enter the environment.

Often referred to as “forever chemicals”, PFAS can be present in groundwater, surface water, industrial wastewater, contaminated land drainage and process-water sources.

Treating them effectively requires more than simply installing a carbon filter.

At Hydra-Clear, we engineer PFAS treatment systems around the contaminants present, their concentrations, the water chemistry, required treated-water quality and what ultimately happens to the concentrated PFAS after treatment.

Start With the Analysis

PFAS is not one contaminant.

Different PFAS compounds behave differently during treatment.

Important considerations include:

• Individual PFAS compounds detected
• Total PFAS concentration
• Long-chain and short-chain PFAS
• Feedwater flow rate
• Dissolved organic carbon
• pH
• Conductivity
• Competing anions
• Suspended solids
• Hardness
• Other organic contaminants
• Required treated-water concentration
• Final discharge or reuse requirement

A treatment system designed around PFOA or PFOS cannot automatically be assumed to perform identically against every other PFAS compound.

The analytical data needs to drive the treatment process.

Why PFAS Can Be Difficult to Treat

Many conventional water-treatment processes were never designed to remove PFAS.

Processes such as conventional clarification, sand filtration or normal biological wastewater treatment may provide little reliable control over dissolved PFAS.

The challenge is also complicated by the chemistry of individual compounds.

Longer-chain PFAS generally have stronger adsorption characteristics, while some shorter-chain compounds can be considerably more difficult to capture using conventional adsorption media.

Water chemistry matters as well.

Dissolved organic material and competing contaminants can occupy adsorption sites, reduce effective media capacity and change the performance of the treatment system.

PFAS treatment therefore needs to be engineered against the real water matrix, not simply a laboratory removal percentage.

Granular Activated Carbon – GAC

Granular Activated Carbon is one of the most established treatment technologies used for PFAS adsorption.

As contaminated water passes through the carbon bed, PFAS compounds adsorb onto the very large internal surface area of the carbon.

GAC can be particularly effective for many longer-chain PFAS compounds.

Advantages of GAC

Depending on the application, benefits can include:

• Proven water-treatment technology
• Relatively simple operation
• Low electrical energy demand
• Treatment of large continuous flows
• Simultaneous adsorption of some other organic contaminants
• Straightforward integration into existing treatment plants

However, GAC does not have unlimited capacity.

Eventually the media becomes exhausted and PFAS breakthrough begins to occur.

Carbon Contact Time Matters

An activated carbon vessel should not simply be sized around pipe diameter and maximum flow.

One of the important design parameters is Empty Bed Contact Time – EBCT.

The water needs sufficient contact with the carbon for adsorption to take place.

Hydra-Clear considers factors including:

• Flow rate
• Carbon volume
• Vessel configuration
• PFAS concentration
• Organic loading
• Target treated-water quality
• Required run length
• Lead/lag operation

For critical applications, two vessels can be installed in series.

The first acts as the primary treatment vessel while the second provides polishing and protection against breakthrough.

When the lead vessel becomes exhausted, the lag vessel can move into the lead position and fresh media can be installed downstream.

This approach can improve utilisation of the carbon while reducing the risk of PFAS breakthrough reaching the treated-water outlet.

PFAS-Selective Ion Exchange

Specialist anion exchange resins can also be used for PFAS removal.

Many environmentally significant PFAS occur predominantly as negatively charged species in water.

PFAS-selective ion exchange resins are therefore engineered to capture these compounds through a combination of ionic and hydrophobic interactions.

Compared with conventional activated carbon, selective resins can offer:

• High adsorption capacity
• Compact equipment footprint
• High treatment flow rates
• Low treated-water PFAS concentrations
• Long operating run lengths in suitable applications

The performance depends heavily on the water chemistry.

Competing anions and organic material can influence resin capacity and treatment life.

This is why resin selection should be based on analytical data rather than assuming that one PFAS resin is suitable for every contaminated water source.

GAC or Ion Exchange?

There isn't a universal answer.

GAC may provide the most economical treatment for one water source while selective ion exchange may be substantially more effective for another.

Sometimes the best solution uses both.

For example:

Pretreatment → GAC → PFAS-Selective Ion Exchange

can allow the carbon stage to remove a large proportion of the contaminant and organic load while the selective resin provides final polishing.

Alternatively, a lead/lag configuration of identical media may provide the most appropriate process.

Hydra-Clear assesses the treatment train around:

• PFAS profile
• Required outlet concentration
• Water matrix
• Flow rate
• Available footprint
• Media life
• Waste generation
• Operating cost
• Disposal route

The objective is not to select our preferred media.

It is to select the correct treatment process.

Reverse Osmosis

Reverse osmosis provides a different approach.

Instead of adsorbing PFAS onto a media bed, RO uses a semi-permeable membrane to separate contaminants from the water.

RO can provide very high rejection of many PFAS compounds and can be particularly useful where PFAS needs to be removed alongside other dissolved contaminants.

Potential applications include water containing combinations of:

• PFAS
• Dissolved salts
• Hardness
• Nitrate
• Sulphate
• Metals
• Other dissolved contamination

However, the PFAS rejected by the membrane does not disappear.

It becomes concentrated within the RO reject stream.

That concentrate then has to be managed.

Nanofiltration

Nanofiltration can also provide PFAS rejection depending on the membrane selected and the individual PFAS compounds present.

NF operates at lower pressures than many RO applications and can offer advantages where complete demineralisation is not required.

However, rejection can be more variable, particularly for smaller short-chain PFAS, and membrane selection should therefore be based on the actual application rather than assuming a fixed percentage removal.

Where membrane technology is considered, Hydra-Clear evaluates:

• Membrane selection
• Recovery
• Flux
• Feedwater chemistry
• Fouling potential
• Pretreatment
• PFAS rejection
• Concentrate volume
• Concentrate disposal or further treatment

Removal Is Not the Same as Destruction

This is one of the most important principles in PFAS treatment.

Removing PFAS from water does not necessarily destroy PFAS.

Granular activated carbon transfers PFAS from the water onto carbon.

Ion exchange transfers PFAS onto resin.

Reverse osmosis and nanofiltration concentrate PFAS into a smaller liquid reject stream.

The treated water may therefore contain dramatically lower PFAS concentrations, but the captured PFAS still needs to be managed.

The complete treatment philosophy must consider:

Contaminated Water → PFAS Separation → Treated Water + Concentrated PFAS Waste

That waste may be:

• Exhausted activated carbon
• Exhausted ion exchange resin
• Membrane concentrate
• Regeneration waste
• Concentrated process waste

The correct handling and disposal route needs to be established as part of the project.

A PFAS treatment plant that simply moves the problem somewhere else without considering the residual waste stream is not a complete treatment solution.

Concentration Before Destruction

In some applications, separating and concentrating PFAS can form the first stage of a wider remediation strategy.

Treating a large volume of water containing very low PFAS concentrations using an energy-intensive destruction technology may be impractical.

Instead, the process may concentrate the PFAS into a much smaller waste stream.

For example:

Contaminated Water → Membrane Separation → PFAS Concentrate → Specialist Destruction/Disposal

or:

Contaminated Water → Adsorption → Exhausted PFAS Media → Specialist Treatment/Disposal

A number of destructive technologies are being developed and evaluated for PFAS, including electrochemical and advanced thermal processes, but technology maturity and commercial viability vary considerably.

Hydra-Clear therefore focuses on designing the water-treatment and separation process around proven performance while considering the required downstream waste strategy.

Pretreatment

PFAS treatment rarely exists in isolation.

Other contaminants in the water can significantly influence the performance of carbon, ion exchange resin and membranes.

Depending on the source water, pretreatment may include:

• Suspended solids removal
• Multimedia filtration
• Cartridge filtration
• Ultrafiltration
• Iron and manganese removal
• Organic reduction
• pH adjustment
• Water softening
• Chemical conditioning

Removing competing contamination upstream can improve the reliability and operating life of the PFAS treatment stage.

Industrial PFAS Wastewater

Industrial wastewater can present a much more difficult treatment challenge than relatively clean groundwater or drinking-water sources.

PFAS may be present alongside:

• Oils
• Surfactants
• Solvents
• Suspended solids
• High dissolved solids
• Metals
• Organic contamination
• Variable pH
• Variable flow

In these applications, PFAS removal may need to form one stage of a wider wastewater treatment process.

The treatment sequence could therefore involve:

Equalisation → Pretreatment → Solids Removal → Organic Reduction → PFAS Treatment → Final Polishing

The actual sequence depends on the wastewater chemistry.

Groundwater & Contaminated Land

PFAS contamination associated with historic industrial activity, firefighting foams and contaminated land can migrate into groundwater.

Remediation systems may therefore need to treat continuously pumped groundwater over long operating periods.

For these applications, system design needs to consider:

• Variable groundwater chemistry
• Seasonal flow
• Suspended solids
• Iron and manganese
• Organic loading
• PFAS breakthrough
• Media replacement frequency
• Waste handling
• Continuous operation
• Monitoring

Modular and containerised treatment systems can be particularly useful for remediation projects where equipment needs to be installed close to the contaminated source.

Firefighting Foam Contamination

Aqueous Film Forming Foams – AFFF – have historically been an important source of PFAS contamination at locations such as:

• Airports
• Military installations
• Fire training areas
• Petrochemical facilities
• Industrial sites
• Fuel storage facilities

Treatment requirements can include contaminated groundwater, surface water, firewater storage or wastewater generated during remediation activity.

Because the contaminant profile can vary substantially, representative PFAS analysis is essential before the treatment process is selected.

Monitoring for Breakthrough

PFAS adsorption systems do not normally provide a conventional online instrument that directly measures every PFAS compound.

Treatment performance therefore relies on a combination of system design, operating data and laboratory analysis.

Sampling points can be incorporated:

• Before treatment
• Between lead and lag vessels
• After treatment

This allows media breakthrough to be monitored and replacement planned before the final treated-water quality is compromised.

For larger systems, Hydra-Clear can incorporate automated sampling arrangements and operating-data collection into the control philosophy.

Modular PFAS Treatment Systems

Hydra-Clear can design PFAS treatment systems as:

• Skid-mounted packages
• Containerised treatment plants
• Permanent installations
• Temporary remediation systems
• Lead/lag adsorption systems
• Multi-stage treatment trains

Systems can include:

• Granular activated carbon
• Selective ion exchange
• Reverse osmosis
• Nanofiltration
• Pretreatment
• Fine filtration
• Pumps
• Storage
• Flow control
• Pressure monitoring
• Automatic valves
• Sampling points
• Siemens PLC and HMI control

The treatment equipment is engineered around the required hydraulic duty and contaminant loading.

Designing for Media Change

Media replacement is an operating reality of adsorption-based PFAS treatment.

The system should therefore be designed for it.

Hydra-Clear considers:

• Safe vessel isolation
• Media removal
• Media loading
• Drainage
• Backwashing where appropriate
• Sampling
• Lead/lag sequencing
• Waste-media handling
• Equipment access

Designing a vessel that removes PFAS effectively but is unnecessarily difficult to service simply moves the problem from the process engineer to the maintenance engineer.

Treatment Performance Has to Be Demonstrated

PFAS treatment performance should not be based solely on a generic manufacturer's removal claim.

The effectiveness of any treatment technology depends on:

• Which PFAS compounds are present
• Their concentrations
• Water chemistry
• Competing contaminants
• Flow rate
• Contact time
• Membrane selection
• Media condition
• Operating history

For complex applications, pilot testing or treatability testing may be appropriate before committing to a full-scale treatment plant.

The objective is to establish a treatment process capable of reliably achieving the required water specification under real operating conditions.

PFAS Regulation Is Developing

PFAS regulation continues to evolve in the UK and internationally.

Treatment requirements may differ depending on whether the water is intended for:

• Drinking-water supply
• Industrial process reuse
• Groundwater remediation
• Surface-water discharge
• Sewer discharge
• Waste treatment
• Another regulated application

For this reason, the required treated-water specification should be agreed against the applicable regulatory, permit or customer requirement at the beginning of the project.

Hydra-Clear then designs the treatment system around that defined performance target.

PFAS Treatment Should Be a Process, Not a Product

There is no single filter that solves every PFAS problem.

A successful treatment system requires an understanding of:

The PFAS → The Water Chemistry → The Treatment Technology → The Breakthrough Behaviour → The Residual Waste

Only then can the complete treatment process be engineered.

Talk to a PFAS Water Treatment Engineer

If PFAS has been identified within your groundwater, process water or industrial wastewater, send Hydra-Clear:

• The PFAS analytical report
• Full water analysis
• Required treatment flow
• Daily treatment volume
• Required outlet concentration
• Details of the water source
• Proposed discharge or reuse route

Our engineers can review the contamination profile and determine the appropriate treatment philosophy.

PFAS removal isn't about finding a magic filter. It's about engineering where the PFAS goes.

Call 0800 999 6770 or contact Hydra-Clear to discuss your PFAS treatment application.