Most water treatment programs still find out about biofilm the same way: heat transfer drops, a filter clogs, or someone finally swabs a coupon and sends it to a lab. By then the biofilm is already established and a shock dose is the only way out. The sensors on the market today claim to catch it earlier — but “biofilm sensor” gets used loosely, and not all of them are actually measuring biofilm.
This article compares four systems commonly proposed for cooling towers and process water loops in Malaysia — Alvim, NCH’s bioDART, Solenis’ OnGuard 3B, and Nalco’s 3D TRASAR Bio-Control — and explains what each one is actually measuring before making the case for why Alvim’s approach is the more direct one.
What “Biofilm Sensor” Actually Needs to Measure
Biofilm is a living colony of bacteria embedded in a self-produced polysaccharide (EPS) slime layer, attached to a surface. To catch it early, a sensor needs to detect the biological activity of that attached colony directly — not a downstream symptom like reduced heat transfer, not a bulk-water proxy, and not a composite score built from unrelated system parameters. The four technologies below take four different routes to that goal, and the route matters as much as the result.
Alvim: Direct Bioelectrochemical Detection
Alvim’s biofilm sensor works on electro-biochemical principles. Bacteria growing as a biofilm produce a bioelectrochemical signal as part of their normal respiration and metabolism, and that signal is directly proportional to the surface area actually covered by biofilm on the probe.
Because the sensor is reading the bacteria’s own electrochemical activity rather than a downstream effect, it can detect microbial attachment from the moment colonisation starts — down to around 1% of the probe surface being covered. The probe also separates biofilm signal from conductivity changes, so scale or general fouling doesn’t get mistaken for biological growth. The output is a real-time, direct measurement of biofilm coverage that can be used to trigger and validate a cleaning or biocide dose.
NCH bioDART: A Composite Index, Not a Direct Reading
NCH’s bioDART system reports a Biofilm Formation Index (BFI) rather than a direct biofilm measurement. The BFI is built from a combination of system parameters — bacteria counts, biocide dosing history, system cleanliness, operating conditions, and nutrient load — blended into a single score that’s meant to correlate with biofilm risk.
That approach gives a useful early-warning trend line, but it’s an indirect index: it’s inferring biofilm conditions from a mix of related variables rather than reading biological activity off a surface. If the underlying assumptions behind the index drift from actual site conditions, the BFI score can move without biofilm actually forming, or vice versa.
Solenis OnGuard 3B: Measuring the Consequence, Not the Cause
Solenis’ OnGuard 3B analyzer fires ultrasonic pulses at a heated target assembly inside the probe and measures the change in pulse travel time. A thickening deposit layer on that heated target slows the pulse down, and the system uses the heating element to also estimate the resulting loss in heat transfer efficiency. It’s designed to differentiate soft deposits (biological/organic fouling) from hard deposits (mineral scale).
This is a genuinely useful measurement for quantifying heat transfer impact, but it’s measuring a physical consequence — deposit thickness and its thermal effect on a simulated heat exchanger surface — rather than the biological activity that’s causing it. A thin, early-stage biofilm that hasn’t yet built up measurable thickness or heat transfer loss can be present on real system surfaces before OnGuard 3B registers it.
Nalco 3D TRASAR Bio-Control: A Microbial Activity Sensor, Not a Biofilm Sensor
Nalco’s 3D TRASAR Bio-Control system is explicitly a microbial activity sensor, not a biofilm sensor. It works by dosing a fluorescent indicator — resazurin — into the recirculating water. Resazurin changes its fluorescent signature when respiring, metabolically active microbes interact with it, and the system reads that change to estimate overall microbial activity in the bulk water, covering both planktonic (free-floating) and sessile (surface-attached) bacteria.
This gives a real-time read on how “biologically active” the water is, and it’s genuinely useful for triggering biocide dosing in response to a bacteria bloom. But it’s a bulk-water activity measurement, not a surface-attached biofilm measurement — high planktonic activity doesn’t necessarily mean a biofilm is forming on a given surface, and a slow-growing, low-turnover biofilm can sit on a surface without driving a large bulk-water fluorescence signal.
Why Alvim’s Method Is Superior
Of the four, only Alvim is reading the biofilm itself. NCH’s BFI is an inferred index built from indirect variables. Solenis’ OnGuard 3B measures a downstream physical consequence — deposit thickness and heat transfer loss — that only becomes detectable once the biofilm has already built up. Nalco’s 3D TRASAR reads microbial activity in the bulk water, which is a proxy for bacteria population, not for whether those bacteria have actually attached and colonised a surface.
Alvim’s bioelectrochemical signal comes directly from the attached bacterial colony’s own respiration, scaling with the actual percentage of surface covered. That’s why it can flag biofilm formation at the 1% coverage stage — before there’s any measurable heat transfer loss, before the bulk water shows elevated activity, and before a composite index would have accumulated enough drift to move. For a cooling tower or process loop operator, that earlier, more direct signal means a cleaning or biocide dose can be triggered and confirmed effective before biofilm reaches the stage where it starts costing energy, throughput, or equipment life — a difference that matters just as much in humid, high-fouling-risk conditions typical of Malaysia as anywhere else.
The Bottom Line
All four systems have a place in a water treatment program, but they answer different questions. If the question is “is biofilm actually forming on my surfaces right now,” Alvim is the only one of the four giving a direct answer. Autoflo Technology supports Alvim biofilm sensor deployments across cooling towers and process water systems in Malaysia — reach out to info@autoflotechnology.com to discuss fitting one to your system.
Frequently Asked Questions
What’s the earliest stage of biofilm growth Alvim can detect?
Alvim’s bioelectrochemical signal is proportional to surface coverage, and the sensor can register biofilm formation from roughly 1% of the probe surface being colonised — well before it would show up as measurable heat transfer loss or bulk-water activity change.
Is Nalco’s 3D TRASAR Bio-Control useless for biofilm control?
No — it’s a strong tool for triggering biocide dosing based on bulk microbial activity, which is a real driver of biofilm risk. It just isn’t measuring the biofilm itself, so it should be read as a leading indicator of bacteria population rather than confirmation that a surface is colonised.
Does Solenis’ OnGuard 3B tell you anything a biofilm sensor can’t?
Yes — its unique value is quantifying the actual heat transfer impact of a deposit layer, which a bioelectrochemical sensor doesn’t measure. It’s better suited to tracking established fouling and its energy cost than to catching biofilm at the earliest stage.
Can these sensors replace routine dipslide or lab microbial testing?
Not entirely. Online sensors give continuous, real-time trend data, while dipslide and lab methods give a periodic, quantified CFU count. Most Malaysia-based plants run both — sensors for early warning and trend monitoring, periodic testing for calibration and verification.
Why does distinguishing biofilm from general fouling or scale matter?
Biological fouling and mineral scale need different treatments — biocide and biodispersant for biofilm, scale inhibitor or acid cleaning for mineral deposits. A sensor that can’t tell the two apart risks triggering the wrong chemical response, which wastes cost and doesn’t solve the actual problem.