When Filter Media Meets Specification… But Commissioning Still Hurts: Lessons from recent GAC and BAC installations

Missed Peta Thiel at WIOA 2026? Here’s what you need to know. Drawing on recent GAC and BAC projects, Peta unpacked why commissioning can still be challenging — even when filter media meets every specification. In this article, we’ve captured the key insights to help operators better understand, interpret, and manage filter performance during those critical early stages.

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Filter media replacement doesn’t happen often but when it does, everything is on the line.

For most water treatment plants, it’s a once-in-a-decade event. And while specifications, standards, and testing frameworks are designed to de-risk the process, recent experiences show something important: Even when media meets specification, commissioning can still be challenging.

This was the core message from a practical, experience-driven presentation by Peta Thiel at WIOA, unpacking what really happens during GAC and BAC commissioning, and why operators can still face uncertainty.

The Expectation vs Reality Gap

On paper, everything checks out.

Granular activated carbon (GAC) and biological activated carbon (BAC) are typically supplied with:

• Certificates of analysis

• Compliance with standards like ANSI/AWWA and NSF

• Verified physical and chemical properties

These frameworks are critical, they confirm the quality and safety of the media.

But here’s the catch: They don’t predict how that media will behave in your plant.

Filter performance is influenced by:

• Hydraulics

• Backwashing conditions

• Underdrain design

• Operational practices

So when new media is installed, operators are often navigating a period of unknown behaviour, even when everything is technically “correct.”

What Actually Happens During Commissioning

Across multiple recent projects, a consistent pattern emerged.

Operators reported:

• Unexpected headloss behaviour

• Difficulty returning filters to service after backwashing

• Carbon fines persisting longer than expected

• Floating or buoyant particles

• Water quality concerns (e.g. leachables like aluminium)

The real challenge wasn’t just the behaviour itself, it was interpreting it.

👉 Is this normal commissioning behaviour? Or a sign something is wrong?

Without clear expectations, that distinction becomes difficult, especially under pressure to keep plants online.

Case Insight: When the Media Isn’t the Problem

One of the most telling examples involved a full filter refurbishment:

• New GAC media installed

• New nozzle system installed

• Limited early verification of the carbon

Soon after commissioning, operators observed instability and high headloss.

The immediate suspicion? The carbon.

But after investigation: The issue was actually the nozzle system — not the media.

Because independent testing hadn’t been completed early, the media remained a “suspect,” slowing down troubleshooting and increasing uncertainty.

https://www.pumiceproducts.com/pumice-water-filtration-media/

Case Insight: The Value of Early Testing

In another project, the approach was different:

• Independent testing conducted before installation 

• Non-conforming batches identified early

• Media replaced before commissioning

Yes — this caused delays.

But it also meant: When commissioning began, operators had confidence in the media

Even more valuable was pilot testing, which revealed:

• Differences between washed vs unwashed carbon

• The importance of proper initial backwashing

• Risks of fines blocking systems if commissioning steps are skipped

This insight allowed procedures to be refined before full-scale operation.

The Bigger Industry Challenge

There’s a deeper issue at play here.

Filter media replacement is:

• Infrequent

• High-risk

• Operationally complex

And because it happens every 10–15 years: Knowledge gets lost.

The people commissioning today may not have been there last time. Lessons learned aren’t always documented. And valuable experience disappears between project cycles.

Key Lessons from the Field

Here’s what stands out from recent commissioning experiences:

1. Compliance Does Not Equal Confidence

Meeting specification doesn’t guarantee smooth commissioning.

2. Timing of Testing Matters

Early verification builds confidence — late testing creates uncertainty.

3. Commissioning Behaviour Isn’t Always Intuitive

New media behaves differently:

• It needs time to stabilise

• Early anomalies can be normal

4. Commissioning Practices Matter

Aggressive backwashing or air scour can:

• Increase fines

• Destabilise media beds

5. Too Many Changes = Too Much Uncertainty

Replacing multiple components at once makes troubleshooting harder.

6. Pilot Testing Is Underrated

Small-scale trials can reveal major insights before full-scale risk.

7. Capture the Knowledge

If you don’t document the experience, you start from zero next time.

So What Should Utilities Do?

Based on these insights, a more confident approach to media replacement looks like:

✔️ Verify media early (where possible)

✔️ Stage commissioning activities to isolate variables

✔️ Allow time for filter stabilisation 

✔️ Review backwashing strategies carefully 

✔️ Use pilot trials to reduce uncertainty 

✔️ Document everything for the future 

Final Thought

Filter media standards and laboratory testing are essential, but they’re only part of the story.

Real-world performance sits at the intersection of:

• Material properties

• Plant design

• Operational practice

• Human judgement

And that’s where commissioning becomes challenging.

The takeaway is simple, but important:

👉 Good data gets you to compliance. Experience gets you to confidence.