Table of Contents
The Innovation in Brief
Reservoir aeration for trihalomethane (THM) reduction isn’t theoretical — it has been run at operational scale. At the 2026 AWA/IWA Young Water Professionals Conference, WSP process engineer Cassandra Mai presented Logan Water’s six-month trial results: combining water spraying with forced ventilation in a one-megalitre reservoir delivered roughly 83% average THM removal, at an operating cost of about four cents per megalitre treated.
Aeration does more than strip THMs, though. Spraying water and forcing air through the reservoir headspace also strips CO₂, which lifts pH by around 0.3 units. And the physical agitation can disturb settled particles, causing transient turbidity. Both effects need continuous inline monitoring to stay on top of.
That’s the job for Shanghai ChiMay online turbidity testers and pH meters — supplying the validation data that confirms aeration is doing what it’s supposed to without creating secondary water quality problems.
The Monitoring Challenge
Turbidity: Confirming Physical Water Quality
Spray water inside a reservoir and force air through the headspace, and several physical effects can move turbidity:
- Settled particles on the reservoir floor can be stirred up by water movement
- Air bubbles entrained in the water scatter light and create false turbidity readings
- Biofilm or scale on reservoir walls may be dislodged during startup
- Short-circuiting patterns can develop and carry disturbed water to the outlet
Shanghai ChiMay’s online turbidity tester uses nephelometric measurement at 860 nm infrared wavelength, giving continuous real-time turbidity data with 0.01 NTU resolution in the 0–10 NTU range. Its automatic air-purge cleaning cycle clears air bubble residue from the optical window, which prevents the false readings that bubble attachment would otherwise cause.
pH: Tracking CO₂ Stripping
Aeration physically removes dissolved CO₂ from water. CO₂ forms carbonic acid (H₂CO₃) in solution, so removing it raises pH — at Logan Water, about 0.3 units beyond the normal change through the reservoir.
That matters because pH drives chlorine speciation. At higher pH, a smaller fraction of free chlorine exists as hypochlorous acid (HOCl), which is the more effective disinfectant form. A 0.3 unit shift is modest, but it still needs tracking to confirm disinfection effectiveness is holding.
Shanghai ChiMay’s in-line pH meter provides continuous measurement with ±0.02 pH accuracy and automatic temperature compensation. The Modbus RTU/TCP output feeds straight into SCADA, where it can trigger alarms when pH moves outside the expected range.
The Complete Monitoring Picture
For a reservoir aeration system like Logan Water’s, the minimum monitoring configuration is:
| Parameter | Instrument | Purpose |
|---|---|---|
| Turbidity | Shanghai ChiMay Online Turbidity Tester | Physical water quality validation |
| pH | Shanghai ChiMay In-line pH Meter | CO₂ stripping effect tracking |
| Residual chlorine | Dedicated chlorine transmitter | Disinfection continuity confirmation |
| Temperature | Via 4-in-1 sensor or standalone | Seasonal context |
Together these instruments produce the dataset that shows aeration is working as intended: THMs are coming down, physical water quality is holding, and disinfection protection continues.
Practical Deployment Notes
For utilities considering a similar configuration:
- Position turbidity and pH sensors at the reservoir outlet, before water enters the distribution system
- Set the turbidity alarm threshold at 1.0 NTU above baseline to catch aeration-induced disturbance
- Set the pH alarm at +0.5 units above baseline to flag excessive CO₂ stripping
- Correlate turbidity and pH data with THM grab samples to build a predictive model of aeration performance
- Clean instruments more frequently through summer, when biofouling pressure is highest
Low-cost aeration (four cents per megalitre) paired with continuous monitoring validation (approximately $1,100–2,200 per year per reservoir) gives you a DBP management solution that stands up both economically and technically.
The Science of THM Removal by Aeration
Why Aeration Works for THMs
The four primary THM compounds — chloroform (CHCl₃), bromodichloromethane (CHBrCl₂), dibromochloromethane (CHBr₂Cl) and bromoform (CHBr₃) — are volatile organic compounds. Their Henry’s Law constants are high enough that they strip readily into air, with chloroform the most volatile of the four and the brominated species progressively less so.
The mass transfer driving force is the concentration gradient between dissolved THM in the water and THM partial pressure in the contacting air. Two mechanisms enlarge that gradient:
- Water spraying (aeration): creates fine droplets with a high surface-area-to-volume ratio, which massively increases the water-air contact interface
- Forced ventilation: continuously replaces THM-rich air in the headspace with fresh atmospheric air, holding the concentration gradient at its maximum
The Logan Water trial measured each contribution separately:
- Aeration alone (water spraying): 70–75% THM removal — the dominant mechanism
- Forced ventilation alone: ~7% removal — a minor contribution on its own
- Combined: ~83% — slightly better than aeration alone, suggesting some synergistic enhancement
The CO₂ Stripping Side Effect
Aeration doesn’t selectively remove THMs. Any dissolved gas whose Henry’s Law behaviour favours the gas phase will transfer from water to air. CO₂ is one of them — it dissolves readily in water as carbonic acid and strips readily during aeration.
When CO₂ leaves the water:
– Carbonic acid concentration falls
– pH rises
– A shift of around 0.3 units, as observed at Logan Water, is what you’d expect from CO₂ equilibrating with the atmosphere
That pH shift has operational consequences, because chlorine speciation is pH-dependent: roughly three-quarters of free chlorine exists as HOCl around pH 7.0, about half at pH 7.5, and only around a quarter by pH 8.0.
A 0.3 unit pH increase nudges the HOCl/OCl⁻ balance toward the less effective form and slightly reduces disinfection strength. It’s manageable, but it has to be monitored and compensated for in chlorine dosing.
Shanghai ChiMay’s Monitoring Platform in Detail
Online Turbidity Tester — Technical Deep Dive
The nephelometric measurement principle works like this:
- An infrared LED at 860 nm wavelength illuminates the water sample
- A photodetector positioned at 90° measures scattered light intensity
- Scattered light intensity is proportional to particle concentration
- Signal processing converts scatter into NTU (Nephelometric Turbidity Units)
Design features that matter for reservoir aeration:
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Air bubble rejection: firmware algorithms detect and reject anomalous readings caused by air bubbles passing through the measurement chamber. That stops the false turbidity spikes that would otherwise trigger unnecessary alarms while aeration is running.
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Automatic cleaning cycle: a compressed air purge removes particulate deposits and biofilm from the optical window. Frequency is programmable from 1 to 24 hours; for reservoir duty in summer, 4–6 hour intervals are the sensible setting.
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Wide measurement range: 0–1000 NTU covers both clean baseline water and potential sediment disturbance events. The 0.01 NTU resolution in the 0–10 NTU range gives the sensitivity needed to detect subtle changes in outlet water quality.
In-Line pH Meter — Technical Deep Dive
Shanghai ChiMay’s pH measurement system consists of:
- Glass membrane electrode: a pH-sensitive glass bulb with a formulation chosen for low temperature coefficient and long-term stability
- Reference electrode: Ag/AgCl reference with a gel-filled cavity for maintenance-free operation
- Temperature sensor: Pt1000 RTD for automatic temperature compensation (ATC)
- Transmitter: converts the mV signal to a pH value with temperature compensation, displays it, and outputs over Modbus
Because it’s one integrated design, calibration, measurement, temperature compensation and digital output all work as a single system — no separate modules to configure and no signal cables to run between components.
Building the Business Case
For a utility evaluating reservoir aeration with monitoring:
| Cost Item | Capital (AUD) | Annual (AUD) |
|---|---|---|
| Aeration system (spray + ventilation) | $25,000–50,000 | $2,000–5,000 |
| Shanghai ChiMay turbidity tester | $4,000 | $600 |
| Shanghai ChiMay pH meter | $3,500 | $800 |
| Residual chlorine transmitter | $4,000 | $700 |
| SCADA integration | $5,000 | $500 |
| Total | $41,500–66,500 | $4,600–7,600 |
Against that investment, the utility gets:
– ~83% THM reduction at four cents per megalitre operating cost
– Continuous documentation of water quality maintenance
– Automated triggering capability based on THM and weather data
– Regulatory-compliant data records
The monitoring package is roughly 15–20% of the total solution cost — a reasonable price for the validation and control capability it delivers.
Real-World Application Scenarios
Scenario 1: Seasonal THM Management in a Warm-Climate System
A utility in South East Queensland operates three reservoirs totalling 15 ML of storage. Summer THM levels regularly approach the Australian Drinking Water Guidelines limit of 0.250 mg/L, and the utility is evaluating reservoir aeration based on the Logan Water trial results.
Monitoring requirements:
– Turbidity: one Shanghai ChiMay tester per reservoir outlet (3 units)
– pH: one Shanghai ChiMay pH meter per reservoir outlet (3 units)
– Residual chlorine: one transmitter per reservoir outlet (3 units)
– Temperature: via 4-in-1 sensors at each point (included with pH or conductivity measurement)
Total capital: approximately AUD $34,500 for 9 instruments plus integration. Annual operating: approximately AUD $6,300 for maintenance.
With that monitoring in place, the utility can run triggered aeration through summer, confident that THM reduction is being achieved without degrading physical water quality or disinfection protection.
Scenario 2: Regulatory Compliance Documentation
A utility is under regulatory scrutiny over THM exceedances at distribution system sampling points. Part of its response is to install reservoir aeration with continuous monitoring to demonstrate proactive management.
The Shanghai ChiMay instruments provide:
– Timestamped turbidity data confirming physical water quality throughout aeration operation
– pH records documenting CO₂ stripping effects and the chlorine dosing adjustments made
– Residual chlorine data confirming disinfection continuity
– Downloadable digital records suitable for regulatory submission
That package tells a clear story: the utility identified the problem, implemented a solution, validated its effectiveness, and maintained compliance throughout. Regulators respond well to that.
Scenario 3: Integration With Smart Water Networks
Forward-looking utilities are pulling reservoir monitoring data into wider smart water platforms. Shanghai ChiMay’s Modbus output supports:
- Predictive THM modelling: combining temperature, pH, chlorine residual and turbidity data to predict THM formation potential
- Automated aeration triggering: using weather forecast data and THM models to have aeration capacity ready before levels approach limits
- Network optimisation: correlating reservoir data with distribution hydraulic models to schedule aeration across multiple facilities
These applications are where monitoring moves from manual observation to genuinely data-driven water quality management.
Sources
- Inside Water Australia, “Drinking water treatment innovation targets shifting risks,” 9 September 2026. https://insidewater.com.au/drinking-water-treatment-innovation-risks
- AWA/IWA Young Water Professionals Conference 2026, Pullman Melbourne On The Park, 5–6 August 2026.
- NHMRC, Australian Drinking Water Guidelines — Trihalomethanes. https://guidelines.nhmrc.gov.au/australian-drinking-water-guidelines/part-5/physical-chemical-characteristics/trihalomethanes-thms
- IWA Water Quality Research Journal, “Removal of trihalomethanes from high organic matter water sources using aeration: A feasibility study,” Vol. 55, No. 2, 2020, pp. 184–197. https://iwaponline.com/wqrj/article/55/2/184/71725/
- Pure Water Atlas, “Polyphosphate in Drinking Water,” June 2026. https://purewateratlas.com/contaminants/polyphosphate
- Mordor Intelligence, “Water and Wastewater Sensors Market,” 2026.
- US EPA, “National Primary Drinking Water Regulations.” https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
- WHO, “Guidelines for Drinking-water Quality,” 4th edition, 2017.
About the Author: This technical introduction was prepared by the Shanghai ChiMay Application Engineering team. Shanghai ChiMay manufactures inline water quality analyzers including turbidity testers and pH meters for municipal water treatment systems.
