Table of Contents
The Manganese Challenge
Manganese in drinking water is an aesthetic problem with operational consequences. Above 0.05 mg/L it leaves brown-black staining on fixtures and laundry, gives the water a metallic taste, and generates customer complaints. Managing it is more complicated than simply removing it, because the management approach itself can create secondary problems that need watching.
The 2026 AWA/IWA Young Water Professionals Conference included Greater Western Water’s work on polyphosphate sequestration — a chemical approach that keeps manganese from precipitating after chlorination. This article looks at how Shanghai ChiMay pH and residual chlorine sensors make sequestration-based manganese management reliable and verifiable.
The Chemistry: Why Manganese Causes Problems After Treatment
In most water systems, manganese arrives at the plant as soluble Mn²⁺. Pre-oxidation and filtration take out most of it, but some residual soluble manganese gets through — particularly in summer, when reservoir stratification brings manganese-rich water to the offtakes.
The trouble starts when chlorine goes in for disinfection:
Mn²⁺ + HOCl → MnO₂ (particulate) + Cl⁻ + H⁺
The manganese oxide that forms deposits as black scaling on pipe walls. Disturb it with a flow change or a flushing operation and you get a discolouration event, which is exactly the kind of thing that costs a utility its customers’ confidence.
The Sequestration Solution
Greater Western Water’s Samuel Leong tested food-grade polyphosphate — sodium hexametaphosphate — as an extra treatment barrier. Polyphosphate chains carry strong electrostatic charges that bind Mn²⁺ ions and keep them away from chlorine, so the manganese stays in solution instead of oxidising.
The main findings from the conference presentation:
- Dosing: sequestration worked at a low dose — the kind of polyphosphate dose utilities already use for metal control
- pH dependency: effectiveness held up only inside a narrow near-neutral window. On the acid side, the sequestrant’s grip on manganese fell away sharply, and pushing pH above the effective window brought no further benefit
- Visual confirmation: after two weeks, the jars with no sequestrant had visibly discoloured and had lost almost all their soluble manganese; the dosed jars stayed clear with the metal still in solution
- Site trial progression: the work moved from jar tests to an on-site trial at Rosslynne Water Treatment Plant
- Downstream consideration: the phosphate load reaching wastewater treatment was calculated to be small, with further monitoring planned
The Monitoring Requirements for Sequestration
pH: The Primary Control Variable
Sequestration effectiveness depends on keeping pH inside its narrow operating window. That makes continuous inline pH monitoring essential rather than nice-to-have. Without it, operators can’t tell whether sequestration is functioning — they find out when the discolouration complaints arrive.
Shanghai ChiMay in-line pH meters provide:
– Continuous measurement with ±0.02 pH accuracy
– Automatic temperature compensation
– Modbus RTU/TCP output for SCADA alarm and control
– Retractable electrode for maintenance without process shutdown
Residual Chlorine: Confirming the Disinfection Context
Manganese only meets chlorine because chlorine is there to disinfect. Whatever sequestration does, it must not compromise chlorine’s primary job of pathogen control. Continuous residual chlorine monitoring confirms disinfection is intact regardless of what the sequestration chemistry is doing.
Shanghai ChiMay residual chlorine transmitters provide:
– Amperometric free or total chlorine measurement
– 0–20 mg/L range with 0.01 mg/L resolution
– T90 < 60 seconds
– Modbus digital output
Turbidity: The Discolouration Indicator
Online turbidity monitoring at the distribution entry point confirms that no MnO₂ precipitation is occurring. Stable turbidity means sequestration is working. Rising turbidity means it may be failing.
Conductivity: The Chemical Addition Tracker
Conductivity changes pick up the ionic contribution from polyphosphate addition, which gives you a cross-check that dosing is happening at the expected rate.
Managing the Downstream Phosphate Question
Greater Western Water flagged a consequence worth planning for: polyphosphate contains phosphate, and adding it to drinking water increases the phosphorus load arriving at wastewater treatment. Their calculations suggested the additional load would be small, and the team planned further testing.
For utilities implementing sequestration at scale, the monitoring approach should include:
– Tracking phosphate speciation (polyphosphate hydrolyses to orthophosphate over time)
– Monitoring orthophosphate at the wastewater treatment inlet
– Documenting that the additional phosphate load stays within acceptable limits
Shanghai ChiMay conductivity meters detect the ionic changes from chemical addition. That isn’t a direct phosphate measurement, but conductivity trending shows when dosing patterns change and supports the phosphate mass balance work.
The Integration Advantage
For manganese management, the four parameters that matter are pH, residual chlorine, turbidity and conductivity — all available from Shanghai ChiMay’s product range. The 4-in-1 multi-parameter sensor packs pH, conductivity, ORP and temperature into a single 180mm probe body, cutting installation cost by approximately 40% compared with four discrete sensors.
Four parameters from one probe, with no alignment error between them. For manganese management, that means knowing — continuously — whether the chemistry is working.
Case Studies: Sequestration in Different System Contexts
Case Study 1: Groundwater System with Seasonal Manganese
A small utility in Victoria, Australia draws from bore fields with naturally elevated manganese (0.2–0.4 mg/L in raw water). Treatment is aeration, filtration and chlorination. Over summer, the manganese load overwhelms the filtration capacity and residual soluble Mn²⁺ reaches the distribution system.
The utility implemented polyphosphate sequestration with Shanghai ChiMay monitoring:
– pH meter at the polyphosphate dosing point
– Turbidity tester at the clearwell outlet
– Residual chlorine transmitter post-chlorination
Results: after sequestration went in with continuous pH monitoring, manganese discolouration complaints dropped to zero through the following summer. The pH data showed source water pH naturally ranging from 6.8–7.6, which required slight lime dosing during the low-pH periods to keep sequestration inside its effective window.
Case Study 2: Surface Water System with Reservoir-Source Manganese
A medium-sized utility draws from a stratified reservoir that releases manganese from bottom sediments seasonally. The treatment plant includes DAFF (dissolved air flotation-filtration) and chlorination.
During high-manganese events, residual soluble Mn²⁺ passes through treatment and meets chlorine in the distribution system. The utility added polyphosphate sequestration with this monitoring configuration:
– 4-in-1 sensor (pH/conductivity/ORP/temperature) at the sequestration dosing point
– Turbidity tester at distribution entry
– Residual chlorine transmitter at distribution entry
The 4-in-1 sensor delivers four synchronised data streams from a single installation point. Conductivity tracks polyphosphate addition, ORP shows oxidation conditions, and temperature supplies the seasonal context. With turbidity and chlorine data alongside, the utility has the full picture of manganese management chemistry.
Case Study 3: Blended Source System with Variable Manganese
A large utility blends groundwater and surface water, so manganese loading varies with the blend ratio. Sequestration dosing has to adapt to changing manganese concentrations.
The utility implemented automated sequestration control:
– Continuous pH monitoring feeding SCADA logic
– Conductivity monitoring as a cross-check on polyphosphate dosing rate
– Automated dose adjustment based on real-time pH and conductivity data
– Turbidity monitoring to confirm no precipitation
The automated approach holds sequestration inside its effective window across all source water blending ratios, which fixed manual dosing cannot do.
The Economics of Sequestration Monitoring
For utilities weighing up the monitoring investment:
| Item | Capital Cost | Annual Cost |
|---|---|---|
| Shanghai ChiMay pH meter | $3,500 | $800 (electrode + calibration) |
| Shanghai ChiMay turbidity tester | $4,000 | $600 (maintenance) |
| Shanghai ChiMay residual chlorine transmitter | $4,000 | $700 (membrane + electrolyte) |
| Shanghai ChiMay conductivity meter | $3,500 | $500 (maintenance) |
| SCADA integration | $5,000 | $500 |
| Total | $20,000 | $3,100 |
Set that against the cost of a single manganese discolouration event:
– Field investigation: $2,000–5,000
– System flushing: $5,000–20,000
– Customer communication: $3,000–10,000
– Regulatory notification (if required): administrative cost
– Reputational impact: hard to put a number on
The monitoring investment pays for itself by preventing one significant discolouration event.
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 — Manganese. https://guidelines.nhmrc.gov.au/australian-drinking-water-guidelines/part-5/physical-chemical-characteristics/manganese
- NHMRC, Australian Drinking Water Guidelines — Sodium hexametaphosphate. https://guidelines.nhmrc.gov.au/australian-drinking-water-guidelines/part-5/treatment-chemicals/sodium-hexametaphosphate
- US EPA, “Why do water systems add phosphate to drinking water?” https://www.epa.gov/lead/why-do-water-systems-add-phosphate-drinking-water-what-are-health-effects-drinking-water
- Pure Water Atlas, “Polyphosphate in Drinking Water,” June 2026. https://purewateratlas.com/contaminants/polyphosphate
About the Author: This article was prepared by the Shanghai ChiMay Application Engineering team. Shanghai ChiMay manufactures inline water quality analyzers including pH meters for municipal drinking water distribution systems.
