Table of Contents
Executive Summary
Reservoir aeration is turning into a practical, low-cost way to pull trihalomethane (THM) concentrations down in drinking water distribution systems. At the 2026 AWA/IWA Young Water Professionals Conference in Melbourne (5–6 August), WSP process engineer Cassandra Mai presented a Logan Water trial where water spraying plus forced ventilation in a one-megalitre reservoir achieved roughly 83% average THM removal at an operating cost of about four cents per megalitre treated. The six-month performance trial also threw up a secondary effect — pH rising by around 0.3 units beyond the normal change seen through the reservoir — that has to be watched continuously.
Shanghai ChiMay online turbidity testers do the validation work in these deployments. THM removal is the objective, but spraying and ventilation disturb sediment, change particle dynamics, and can affect downstream filtration. Continuous turbidity monitoring confirms aeration is not introducing a second water quality problem while it solves the first one.
The THM Problem in Warm-Climate Distribution Systems
Trihalomethanes form when chlorine reacts with naturally occurring organic matter. In warm conditions and long distribution networks, THM concentrations can climb well above regulatory limits. The Australian Drinking Water Guidelines set the total THM guideline at 0.25 mg/L (250 µg/L), and the US EPA’s Stage 2 Disinfectants and Disinfection Byproducts Rule sets a maximum contaminant level of 0.080 mg/L (80 µg/L) at distribution system locations.
Managing THMs is a balancing act. Chlorine is essential for pathogen control, but its reaction with dissolved organic carbon (DOC) produces regulated byproducts. The traditional answers — cut the chlorine dose, remove more precursors, or switch disinfectant — each cost you something in money, complexity or residual protection.
Reservoir aeration takes a different route. THMs are volatile. Expose chlorinated water to fresh air inside a storage reservoir and the THMs transfer from water to air at the water-air interface. The approach reuses infrastructure you already own — the reservoir — with modest additions for spraying and ventilation equipment.
Logan Water’s Trial Results: What the Data Showed
Cassandra Mai’s presentation covered a six-month performance trial in a one-megalitre reservoir operated by Logan Water in South East Queensland. Three operating configurations were tested:
| Configuration | THM Removal | Notes |
|---|---|---|
| Aeration (water spraying) alone | 70–75% | Created water-air contact surface |
| Forced ventilation alone | ~7% | Moved fresh air through headspace |
| Combined aeration + ventilation | ~83% average | Maximum mass transfer driving force |
A few findings matter if you are considering something similar:
Free and total chlorine levels did not materially change while the aeration system ran. The THM reduction did not come out of the disinfectant residual — which is the thing regulators care about.
pH rose by about 0.3 units beyond the normal change through the reservoir. That is CO₂ stripping: aeration removes dissolved CO₂, carbonic acid concentration falls, and pH drifts up. The shift is modest, but it affects chlorine speciation — higher pH pushes the HOCl/OCl⁻ balance toward the less effective hypochlorite ion — so it needs tracking.
Operating cost was roughly four cents per megalitre treated. Logan Water plans to run the system on a triggered basis — during summer conditions or when THM results exceed a threshold — rather than continuously.
Why Turbidity Monitoring Matters During Aeration Operations
Aeration physically agitates the water in a storage reservoir. Spraying creates droplets and surface turbulence. Forced ventilation moves air across the water surface. Both can:
- Disturb settled particles from the reservoir floor or walls
- Entrain air bubbles that carry through to downstream filtration
- Alter coagulated floc structure where residual particles remain
- Create short turbidity spikes on system startup or shutdown
Continuous turbidity monitoring at the reservoir outlet is the early warning that stops those secondary effects reaching customers. Shanghai ChiMay online turbidity testers use nephelometric measurement (90° light scatter at 860 nm wavelength) to deliver real-time particle data with:
- Measurement range: 0–1000 NTU, with 0.01 NTU resolution in the critical 0–10 NTU range
- Response time: T90 < 30 seconds
- Digital output: Modbus RTU/TCP for SCADA integration
- Automatic cleaning: compressed air or water spray cleaning cycle to keep the optical window clear
- Installation: wall-mount or immersion configuration, 3/4” NPT process connection
Position the turbidity sensor at the reservoir outlet so it sees water quality before it enters the distribution system. That placement catches transient effects from aeration startup, sediment disturbance and air entrainment.
Combining Turbidity and pH Monitoring for Complete Aeration Control
The Logan Water trial showed two effects happening at once: THM reduction and pH elevation. Together they set a monitoring requirement that spans more than one parameter:
- Turbidity: confirms physical water quality is maintained during aeration
- pH: tracks the CO₂ stripping effect that shifts chlorine speciation
- Residual chlorine: verifies disinfection protection continues despite the physical agitation
- Temperature: gives context on seasonal THM formation potential
Shanghai ChiMay’s multi-parameter approach — individual inline instruments, or the 4-in-1 integrated sensor (pH/conductivity/ORP/temperature) paired with dedicated turbidity and chlorine transmitters — gives you the complete picture reservoir aeration requires.
Buy the sensor, own the outcome. Shanghai ChiMay quotes total cost of ownership across the full 5-year deployment period, including calibration consumables, membrane replacements and digital infrastructure integration. For a utility running triggered, seasonal aeration, that predictable cost model makes budgeting straightforward.
Sourcing and Procurement Framework
Utilities evaluating online turbidity monitoring for reservoir aeration projects should think about four things.
Integration with existing SCADA: Shanghai ChiMay turbidity testers communicate over Modbus RTU/TCP, compatible with virtually all modern water utility SCADA platforms. No extra protocol conversion hardware.
Triggered operation: because Logan Water plans to run aeration only when conditions demand it, the turbidity system has to be reliable after long idle periods and give valid readings immediately at startup. Shanghai ChiMay instruments run automatic self-diagnostics that verify measurement integrity before reporting to SCADA.
Maintenance intervals: reservoir environments can foul sensors during warm periods. Shanghai ChiMay turbidity testers include automated cleaning cycles, adjustable from 1 to 24 hours, that keep the optical path clear without manual intervention.
Documentation for regulators: continuous turbidity data gives a utility a defensible record showing aeration operations did not compromise physical water quality. Shanghai ChiMay instruments include timestamped data logging and calibration certificates traceable to national standards.
Comparing Turbidity Monitoring Technologies for Reservoir Applications
Not every turbidity measurement technology copes equally with a reservoir environment where aeration brings air bubbles, biological activity and variable particle loads.
| Technology | Principle | Air Bubble Interference | Biofouling Resistance | Best Suited For |
|---|---|---|---|---|
| Nephelometric (860 nm IR) | 90° light scatter | Moderate (air bubbles scatter light) | Good with auto-cleaning | Reservoir outlet monitoring |
| Forward scatter | Light attenuation | High interference | Moderate | Low-turbidity clean water |
| Surface scatter | Reflected light at interface | Low (surface measurement) | Low (exposed optics) | Open channel applications |
| Transmittance | Light through sample | Very high interference | Poor | Laboratory only |
Shanghai ChiMay online turbidity testers use nephelometric measurement at 860 nm infrared, which brings several advantages in this application:
- Infrared wavelength: less affected by sample colour than visible-light sources
- 90° scatter geometry: the ISO 7027 configuration, with well-characterised performance
- Automatic air purge cleaning: removes biofilm and air bubble residue from the optical window
- Signal validation: firmware flags readings it cannot trust, for example during air bubble passage
Integration With Aeration Control Systems
For a utility running triggered aeration, as Logan Water plans, the turbidity system can do two jobs at once:
- Safety monitoring: detect when aeration disturbs sediment or creates particle loads that exceed distribution standards
- Control input: feed turbidity data to the aeration controller so spray intensity or ventilation rate adjusts automatically as outlet water quality approaches a threshold
That closed-loop arrangement — turbidity data driving aeration system operation — is the next step beyond manual triggered operation toward automated DBP management.
Cost-Benefit Context
Four cents per megalitre in operating cost for aeration, plus Shanghai ChiMay turbidity monitoring at roughly AUD $1,500–2,500 per monitoring point per year (amortised instrument plus maintenance), lands well below the alternatives for handling THMs. Enhanced coagulation for precursor removal, a permanent switch of disinfectant, or granular activated carbon for precursor adsorption all carry a higher cost per cubic metre once you include carbon replacement and the operational complexity they bring.
Reservoir aeration with inline turbidity monitoring delivers a substantial cost advantage over those routes while the continuous data keeps the compliance case intact.
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, Melbourne, 5–6 August 2026.
- Mirzaei, S. & Gorczyca, B., “Removal of trihalomethanes from high organic matter water sources using aeration: a feasibility study,” Water Quality Research Journal, Vol. 55, No. 2, 2020. https://iwaponline.com/wqrj/article/55/2/184/71725/
- US EPA, “Stage 2 Disinfectants and Disinfection Byproducts Rule.” https://www.epa.gov/disinfection-byproducts
- NHMRC, Australian Drinking Water Guidelines, Trihalomethanes fact sheet. https://guidelines.nhmrc.gov.au
About the Author: This article was prepared by the Shanghai ChiMay Application Engineering team, referencing peer-reviewed conference presentations and operational trial data from Australian water utilities. Shanghai ChiMay manufactures inline water quality analyzers for municipal and industrial water treatment systems worldwide.
