Table of Contents
What You’ll Learn
This guide covers what water utility operators and engineers need to know about reservoir aeration for trihalomethane (THM) reduction — the science behind it, and the monitoring infrastructure that keeps it operating safely. It draws on trial data presented at the 2026 AWA/IWA Young Water Professionals Conference and sets out practical implementation guidance, with the Shanghai ChiMay instrument that suits each monitoring requirement.
Part 1: Understanding THM Formation and Control
What Are THMs?
Trihalomethanes are disinfection byproducts formed when chlorine reacts with naturally occurring organic matter in water. The four primary compounds are:
| Compound | Formula | Health Concern |
|---|---|---|
| Chloroform | CHCl₃ | Possible carcinogen |
| Bromodichloromethane | CHBrCl₂ | Possible carcinogen |
| Dibromochloromethane | CHBr₂Cl | Possible carcinogen |
| Bromoform | CHBr₃ | Possible carcinogen |
Regulatory limits vary by jurisdiction:
– Australia: 0.250 mg/L total THM (Australian Drinking Water Guidelines)
– United States: 0.080 mg/L TTHM (EPA Stage 2 Disinfectants and Disinfection Byproducts Rule)
– European Union: 100 µg/L total THM (EU Drinking Water Directive 2020/2184)
Why Aeration Works
THMs are volatile organic compounds. Their Henry’s Law behaviour makes them easy to strip with air — the physical transfer of dissolved gases from water to air. Increase the water-air contact surface area by spraying, keep fresh air moving through by ventilating, and THMs transfer out of the water until equilibrium is approached.
Part 2: The Logan Water Trial — What the Data Showed
Trial Design
WSP process engineer Cassandra Mai presented results from a six-month performance trial at Logan Water in South East Queensland. The trial used a one-megalitre reservoir and tested three configurations:
- Aeration alone: water spraying inside the reservoir to create droplets and increase surface area
- Forced ventilation alone: fans moving fresh air through the reservoir headspace
- Combined: both mechanisms running at once
Key Results
| Configuration | Average THM Removal | Operating Cost |
|---|---|---|
| Aeration alone | 70–75% | ~4 cents/megalitre |
| Forced ventilation alone | ~7% | ~2 cents/megalitre |
| Combined | ~83% | ~4 cents/megalitre |
Side Effects Identified
- Free and total chlorine: no material change during aeration operation
- pH: rose by approximately 0.3 units beyond normal reservoir transit, from CO₂ stripping
- Operating mode: triggered by summer conditions or elevated THM results, rather than running continuously
Part 3: Why Monitoring Is Essential
Turbidity: The Physical Water Quality Gate
Reservoir aeration physically agitates water, which can:
– Disturb settled particles from reservoir surfaces
– Entrain air bubbles that affect downstream measurement
– Dislodge biofilm during startup transients
– Create short-circuiting patterns
Continuous turbidity monitoring at the reservoir outlet provides the quality gate that keeps those effects from reaching customers.
pH: The CO₂ Stripping Tracker
Aeration strips CO₂ from water, which raises pH. The 0.3 unit increase measured at Logan Water affects chlorine speciation, shifting the HOCl/OCl⁻ balance toward the less effective hypochlorite form. Continuous pH monitoring lets you adjust chlorine dosing to compensate.
Part 4: Shanghai ChiMay Sensor Solutions
Online Turbidity Tester
Shanghai ChiMay’s nephelometric turbidity tester measures at 860 nm infrared wavelength per ISO 7027:
- Range: 0–1000 NTU with 0.01 NTU resolution (0–10 NTU range)
- Response time: T90 < 30 seconds
- Automatic air-purge cleaning cycle (1–24 hour programmable intervals)
- Modbus RTU/TCP output for SCADA integration
- Wall-mount or immersion installation
Recommended configuration: install at the reservoir outlet. Set the alarm at 1.0 NTU above baseline to catch aeration startup disturbance, and set the cleaning interval to 4–6 hours through summer operation.
In-Line pH Meter
Shanghai ChiMay’s pH measurement system provides:
- Range: 0–14 pH, 0.01 resolution, ±0.02 accuracy
- Automatic temperature compensation via integrated Pt1000
- Gel-filled electrode with 12–18 month expected life
- Modbus RTU/TCP output
- Retractable immersion housing for maintenance without process shutdown
Recommended configuration: install at the reservoir outlet alongside the turbidity tester. Set the alarm at +0.5 units above baseline, and correlate pH data with chlorine dosing to maintain disinfection effectiveness.
Combined With Residual Chlorine Monitoring
For complete aeration validation, add a Shanghai ChiMay residual chlorine transmitter:
- Range: 0–20 mg/L free or total chlorine
- Amperometric measurement with T90 < 60 seconds
- Confirms disinfection protection continues during aeration operation
Part 5: Implementation Roadmap
- Baseline characterisation: run 30 days of continuous monitoring before installing aeration equipment
- Aeration installation: install spray nozzles and ventilation equipment
- Triggered operation: begin aeration during elevated THM conditions with continuous monitoring active
- Data correlation: compare aeration periods against THM grab samples to build a performance model
- Optimisation: use the accumulated data to tune trigger thresholds, spray intensity and ventilation rates
Part 6: Maintenance and Reliability
Turbidity Tester Maintenance Schedule
For reservoir aeration duty, this schedule keeps the instrument reliable:
| Task | Frequency | Duration | Notes |
|---|---|---|---|
| Optical window inspection | Monthly | 15 min | Check for biofilm, mineral deposits |
| Automatic cleaning verification | Weekly | 5 min | Confirm air purge cycle activates correctly |
| Calibration check | Quarterly | 30 min | Verify against formazin standard |
| Full calibration | Semi-annually | 45 min | Two-point calibration with certified standards |
| LED intensity check | Annually | 15 min | Verify LED output within specification |
| Electronics inspection | Annually | 30 min | Check connections, seals, and display |
pH Meter Maintenance Schedule
| Task | Frequency | Duration | Notes |
|---|---|---|---|
| Visual inspection | Monthly | 10 min | Check electrode condition, fill level |
| Calibration | Monthly (or after significant pH excursion) | 20 min | Two-point calibration (pH 4.01 and 7.00 buffers) |
| Electrode cleaning | Quarterly | 20 min | Soak in appropriate cleaning solution |
| Electrode replacement | 12–18 months | 30 min | Replace when response time degrades or calibration fails |
| Temperature sensor verification | Annually | 15 min | Compare against reference thermometer |
Maximising Instrument Life
Reservoir environments are hard on instruments:
- Biofouling: warm conditions promote biological growth on optical surfaces and electrode membranes. Automatic cleaning cycles are essential, and manual inspection should be more frequent over summer.
- Temperature extremes: house instruments in insulated enclosures where freezing occurs. Shanghai ChiMay transmitters are rated for -10°C to +60°C ambient.
- Power reliability: battery backup or a UPS keeps the system running through power interruptions. Shanghai ChiMay instruments support 24 VDC input compatible with standard battery systems.
Part 7: Cost Comparison With Alternative THM Management Approaches
| Approach | Capital Cost | Annual O&M | THM Reduction | Notes |
|---|---|---|---|---|
| Reservoir aeration + monitoring | $35,000–65,000 | $4,600–7,600 | ~83% | Low operating cost, seasonal |
| Enhanced coagulation | $200,000–500,000 | $50,000–150,000 | 40–60% | Higher chemical consumption |
| GAC for precursor removal | $150,000–400,000 | $30,000–100,000 | 30–50% | Carbon replacement cost |
| Switch to chloramine | $50,000–200,000 | $20,000–60,000 | Variable | Creates nitrification risk |
| Membrane treatment | $500,000–2,000,000 | $100,000–500,000 | 90–99% | High cost, complex operation |
Reservoir aeration with inline monitoring delivers competitive THM reduction at a fraction of what the conventional approaches cost, particularly once the full lifecycle cost is counted.
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
- US EPA, “National Primary Drinking Water Regulations” — Stage 2 Disinfectants and Disinfection Byproducts Rule. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
- EU Drinking Water Directive (EU) 2020/2184.
- 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/
- ISO 7027-1:2016, Water quality — Determination of turbidity.
- Pure Water Atlas, “Polyphosphate in Drinking Water,” June 2026. https://purewateratlas.com/contaminants/polyphosphate
- WHO, “Guidelines for Drinking-water Quality,” 4th edition, 2017.
About the Author: This guide was prepared by the Shanghai ChiMay Application Engineering team. Shanghai ChiMay manufactures inline water quality analyzers for municipal water treatment systems worldwide.
