Sentinel Water Solutions considers the advantages and disadvantages of pilot testing for PFAS removal in water treatment.
Ask most vendors about pilot testing for PFAS removal, and they will point you toward a standard rental skid. The columns have a fixed height. The sample taps are where they have always been. The underdrain is what came with the unit. The pitch is straightforward: here is the equipment, now design your test around it.
The problem is that PFAS treatment is not a standard problem. Every source of water is different, regulatory requirements vary by state, and site flow rates and facility space constraints directly impact vessel sizing and system layout. On top of that, treatment media such as GAC and IX resin carry very different footprints and long-term cost implications depending on the application. Yet, utilities and engineering teams are often forced to accept standard rental pilot equipment and hope it accommodates all these variables.
This article examines the core advantages and disadvantages of pilot testing for PFAS removal, with particular attention to a risk that is frequently overlooked: that a poorly configured pilot test does not just produce imperfect data. It can actively mislead the design decisions that follow.
What is a pilot skid?
At its most basic level, a pilot skid is a compact, rack-mounted system of pipe columns that simulates full-scale treatment vessels at a fraction of the size. These columns are packed with the treatment media under evaluation, and source water is passed through them under controlled conditions to observe performance. A well-designed pilot should help utilities and engineers understand how site-specific water quality affects treatment performance, estimate media life and operating costs, evaluate hydraulic behaviour and vessel sizing, and compare treatment media options.
Pilot testing is not new to the water treatment industry. Surface water treatment plants have long used jar testing for coagulants and powdered activated carbon. Pilot testing for PFAS is, in essence, another form of small-scale testing, though one that the industry is only beginning to embrace fully for PFAS-specific applications, and one where significant knowledge gaps still exist.
The case for pilot testing: Key advantages
1. Media selection and long-term O&M cost
Perhaps the single most impactful benefit of pilot testing is helping project teams select the right media before committing to full-scale treatment. Annual operations and maintenance (O&M) costs, driven heavily by media replacement, typically represent 15-20% of the initial capital outlay. Over a five-to-eight-year window, a facility can expect to have re-spent its original installation cost on O&M alone. Against that backdrop, the difference between selecting media with a six-month lifespan and one with a 12-18-month lifespan is substantial. Pilot testing provides the data needed to make that distinction confidently before a shovel hits the ground.
2. Vessel sizing, footprint, and capital cost
Media selection does not exist in isolation; it directly dictates vessel size, vessel arrangement, and ultimately the physical and financial footprint of the full-scale system. Ion exchange resin vessels, for instance, are roughly one-third to one-quarter the size of equivalent GAC vessels for the same treatment objective. For facilities with constrained site conditions, that difference can determine whether a viable design is even achievable within a given footprint. Pilot testing helps engineering teams understand not only which media performs better chemically, but also whether that media is compatible with the physical constraints of the site, a distinction that can carry seven-figure implications.
3. Regulatory compliance and permitting support
In some states, conducting a pilot test is a regulatory mandate before a full-scale PFAS treatment system can be permitted. Even where it is optional, pilot data often plays a meaningful role in the permitting process. Regulators reviewing atypical treatment configurations (anything outside a standard lead-lag vessel arrangement, for example) frequently request pilot-scale data that validates the proposed approach. Similarly, when a utility is considering a media that reviewers are unfamiliar with, pilot results provide regulators with the assurance they need that the proposed system will perform as intended.
One area of particular concern for regulators involves the potential downstream impacts of PFAS treatment on chlorination and corrosion control. Certain media types can significantly affect pH, which may create simultaneous compliance challenges downstream. A pilot test can demonstrate, prior to permit issuance, that the selected media will not compromise these critical secondary treatment processes.
4. Ongoing process verification
An often-overlooked application of pilot skids is their value as ongoing process verification tools, even after full-scale treatment has been installed. Unlike conventional water quality parameters, PFAS cannot currently be monitored online; no real-time PFAS analyser exists at the concentrations relevant to drinking water or wastewater treatment, and the development of such technology remains distant. In the absence of online monitoring, side-stream pilot skids running parallel to full-scale treatment can provide periodic, two-to-four-week process snapshots that help operators assess media performance, detect early breakthrough, and respond proactively to fluctuations in source water quality. This is especially pertinent for wastewater applications, where influent composition can vary significantly from day to day.
The challenges and limitations of pilot testing
1. Cost and timeline pressures
The most commonly cited objection to pilot testing is the combination of upfront cost and time. An extensive pilot involving multiple media, high media volumes, frequent sampling, and a long duration can cost upward of $200,000. For a small system, that figure could approach the cost of the full-scale treatment system itself. Meanwhile, grant-funded projects frequently operate under rigid timelines that require a fully permitted design before funding can be secured. In that environment, adding weeks or months for a pilot test can feel like, and sometimes genuinely be, an obstacle to project delivery.
However, it is important to recognise that pilot testing is not a binary, all-or-nothing proposition. The scope, duration, and configuration of a pilot test can be scaled to fit a project’s timeline and budget. A well-designed, targeted pilot that asks specific questions about media performance rather than attempting to characterise every variable can be conducted far more economically and quickly than a comprehensive, multi-variable study.
2. The ‘we’ll switch later’ misconception
One of the most problematic rationalisations for skipping a pilot test is the belief that vessel designs can be made media-agnostic, such that a system built around GAC can simply be retrofitted for ion exchange later if performance falls short. In practice, this is rarely achievable without major reconfiguration. GAC and ion exchange vessels operate under fundamentally different hydraulic loading rates, contact times, and regeneration (or replacement) regimens. The differences in vessel size alone, with IX systems requiring only a fraction of the footprint of equivalent GAC systems, make interchangeability far more complex than it appears on paper. Discovering post-installation that a chosen media is underperforming is an expensive and operationally disruptive outcome that a pilot test is specifically designed to prevent.
3. Pilots do not fully replicate full-scale hydraulics
Pilot testing has inherent limitations that practitioners must understand. A pilot skid simulates treatment process performance; it models hydraulic loading rates and empty bed contact times (EBCT) at scales that can be extrapolated to full-scale vessels. What it does not replicate is the complex hydraulic behaviour of full-scale treatment systems: underdrain design, media bed flow distribution, parallel treatment train imbalances, and other real-world factors that only emerge at scale. Engineers should interpret pilot results as process performance indicators, not as perfect predictors of full-scale system behaviour. Careful, experienced design remains essential even with robust pilot data in hand.
4. Poor pilot configuration can produce misleading results
This is the limitation that receives the least attention and arguably poses the greatest risk. A pilot test that is poorly configured for the specific treatment challenge does not simply generate imperfect data. It can generate confidently wrong data, leading engineering teams toward full-scale design decisions that are difficult and costly to reverse.
Consider a straightforward example involving EBCT, one of the most critical parameters in any PFAS pilot. EBCT is a function of both column height and the position of sample taps within that column. A sample tap placed at 13.75 inches represents 25% of bed depth on a 55-inch column, but that same tap represents 30% of bed depth on a 46-inch column. When column geometry is fixed by rental fleet inventory rather than dialled in for the specific test, these discrepancies compound across the dataset, producing results that cannot be cleanly scaled to full-size vessels.
Similar problems arise from inadequate sampling resolution, which can cause teams to miss breakthrough events or draw misleading conclusions about media longevity. Improper media support, whether through incorrect underdrain mesh sizing or inadequate bed support structures, can introduce channelling and media loss that skews performance data in ways that are not always immediately apparent. The downstream consequences range from re-running pilots at additional cost and time, to oversizing or undersizing full-scale systems, to reduced data confidence during permitting review.
5. Standard rental fleet limitations
Most pilot skids available on the market today are offered through fixed rental fleets: standardised units with set column geometry, predetermined sample tap locations, and limited ability to modify internal components. In this model, the utility and its engineering team adapt the test to the equipment, not the other way around. This represents a fundamental inversion of sound engineering practice.
Beyond the data quality implications, rental fleet availability is increasingly becoming a practical bottleneck. As PFAS treatment timelines tighten and more utilities move toward piloting simultaneously, the industry’s fixed rental inventory is being stretched thin. Project teams facing compliance deadlines are, in some cases, accepting suboptimal equipment configurations simply to stay on schedule, compounding the risks described above.
Decision-making: When to pilot and when to proceed
The clearest indicator that a pilot test is warranted is the presence of unresolved questions about media selection at the design stage. If a project team is still uncertain about which media will be used in the full-scale system, a pilot test should be strongly considered. The greater the uncertainty, the greater the justification.
Computational simulation tools offer a partial alternative for systems with better-established performance data. However, current simulation tools for PFAS removal, particularly for GAC, carry wide uncertainty bands that limit their reliability as standalone design inputs. Until more accurate and validated simulation packages are available, physical pilot data remains the gold standard.
Grant timelines, project budgets, and compliance deadlines will always factor into the decision. The key is to treat the pilot programme and the full-scale design as connected, interrelated parts of a single project, rather than as independent phases that compete for resources. A pilot programme structured around the specific questions the full-scale design needs answered, and scaled to fit the project’s economic and schedule constraints, delivers the greatest value at the least cost.
Engineered for the test: The Sentinel Water Solutions approach
Addressing the limitations of standard rental inventory requires a different starting point. Rather than offering fixed configurations and asking project teams to work within them, Sentinel Water Solutions designs pilot skids around the specific objectives of each test. The process begins by understanding what questions the full-scale design needs to answer, then working backward to configure equipment that generates the most relevant data possible.
In practice, this means adjustable column height and diameter to achieve accurate EBCT simulation without approximation. It means customisable sample tap number and placement, including options for remotely located sample valves that improve both safety and sampling consistency. It means media-specific underdrain mesh sizing tailored to the characteristics of GAC versus IX media, preventing channelling, media loss, and the hydraulic inefficiencies that compromise data integrity. And it means a modular rack and panel system designed for upgrades and expansion, so that a skid configured for an initial pilot study can be adapted for ongoing process verification as the full-scale system matures.
Site constraints are treated as engineering inputs, not afterthoughts. Ceiling height limitations, available footprint for the pilot itself, access requirements, and operator skill levels all inform how a skid is designed and dimensioned. When engineering consultants come to Sentinel with a test objective already defined, the team works to configure a skid that achieves it. When they arrive earlier in the process, Sentinel draws on full-scale treatment experience to help define the right questions before configuring the equipment to answer them.
Sentinel offers multiple pilot skid models spanning a range of budgetary and operational profiles, providing a practical starting point that can be configured to fit the demands of each project without the cost or complexity of a fully bespoke build. The result is a pilot programme that is technically sound, economically realistic, and matched to the actual conditions of the site and test.
Looking ahead: The evolving role of pilot testing
In the near term, a wave of PFAS pilot testing activity is anticipated as utilities race to meet EPA and state-level compliance deadlines with full-scale treatment systems. The urgency is real: designing, permitting, and constructing full-scale PFAS treatment is a lengthy process, and the time to gather pilot data is now.
Over a longer horizon, the role of pilot skids is expected to evolve beyond pre-design testing toward a more permanent function as ongoing process verification instruments. As full-scale PFAS treatment systems proliferate and the limitations of current analytical tools, namely the absence of real-time PFAS monitoring, become more consequential, side-stream pilot systems running in parallel with production-scale operations will provide operators with their most practical tool for continuous process assessment.
Conclusion
Pilot testing for PFAS removal is not without its costs and complications, but the risks of proceeding to full-scale treatment without one are substantial. And the risks of proceeding with a poorly configured pilot may be just as significant. Selecting the wrong media because a fixed rental column skewed the EBCT calculation is not a better outcome than skipping the pilot entirely. It may be worse, because it carries the false confidence of having done the work.
The right question to ask at the start of any PFAS pilot programme is not simply whether to run a pilot test. It is whether the pilot is designed to answer the questions that actually matter for the full-scale system that follows. Are you designing your pilot around your treatment challenge, or inheriting someone else’s equipment constraints? Is your pilot skid helping you reduce risk, or quietly introducing it? Are you getting the data you need, or just the data your equipment allows?
A well-configured pilot programme designed with the same rigour and intentionality as the full-scale treatment system it is meant to inform offers an exceptional return on investment. Spend a little money today to answer the right questions, and the full-scale design that follows will be built on a far more solid foundation. If your pilot provider cannot adapt the equipment to your test, it may be time to rethink the partnership.
About the author
Jinlin Tong is a Product Manager at Sentinel Water Solutions, where she leads the development and delivery of PFAS treatment solutions for municipal and industrial clients. She focuses on aligning customer needs, pilot programme strategy, and full-scale system implementation to drive successful treatment outcomes across drinking water, wastewater, and industrial applications.
Please Note: This is a Commercial Profile
This article will feature in our upcoming PFAS Special Focus Publication.
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