In tap water treatment processes, chlorine dioxide is widely adopted thanks to its powerful disinfection performance. It barely produces disinfection by-products such as trihalomethanes, making it a preferred disinfectant for water treatment plants.Chlorine dioxide travels through pipelines, safeguarding clean water from water plants along extensive pipe networks all the way to household taps. Significant consumption takes place during this long transportation. Hence, pump stations serving the "last mile" of water delivery deserve close attention. Secondary dosing of chlorine dioxide is often required at these facilities to maintain residual chlorine levels at pipe network endpoints.Still, operation and maintenance staff at water plants frequently face a dilemma. Even when residual chlorine test results within the pipe network meet standards, excessively high chemical concentrations often emerge locally on pipelines after terminal pumps, which frequently triggers pipeline corrosion.Today we will break down how to carry out this delicate dosing operation properly.I. Supplementary dosing is not blind over-dosing; uniform concentration is the top priorityMany practitioners hold a misunderstanding: to sustain residual chlorine in remote pipeline sections, adding more chlorine dioxide at pump rooms will always work. Nevertheless, chlorine dioxide is a strong oxidant. If it accumulates locally inside pipelines, it will continuously oxidize metal inner surfaces. Relevant research proves chlorine dioxide can alter the surface chemical properties of metal pipelines, and prolonged exposure to high concentrations accelerates pipe wall corrosion.Our core target is even distribution instead of localized high concentrations. Ideal supplementary dosing enables chlorine dioxide to blend into water smoothly, much like snowflakes melting gradually, rather than forming concentrated hotspots as if explosives were dropped locally.II. Three core measures for precise concentration controlHow can operators strike the proper balance in water supply pump rooms? Three practical field tips are shared below:

Dynamic follow-up: Match dosing rate to fluctuating water flow

Water flow inside pump rooms varies drastically between peak hours and off-peak periods and never stays constant. If the dosing pump runs at a fixed output rate, chlorine dioxide concentration will surge when flow drops. Flow-proportional dosing is strongly recommended to link chemical dosage in real time with pump outlet flow. Flowmeter data can be transmitted directly to the dosing controller to realize automatic adjustment — deliver more chemical with higher water flow, and less chemical with lower flow. This prevents dramatic concentration fluctuations from the source.

Set up a mixing buffer zone: Deploy inline static mixers

Many operators tend to arrange dosing points directly on pipelines downstream of pumps, yet this practice is inadvisable. Direct injection into the main water stream allows the chemical to creep along pipe walls before thorough diffusion. The proper approach is installing static inline mixers immediately after dosing points. Specially designed baffles inside the mixers continuously shear and swirl the water flow. This structure evenly disperses chlorine dioxide within tens of meters and prevents localized over-concentration.

Closed-loop verification: Online residual chlorine analyzers act as monitoring sentinels

Dosing effects must be judged based on real measured data. Operators can install online residual chlorine analyzers at suitable positions downstream of dosing points (ensuring full mixing of disinfectant and water) to supervise the whole dosing system. Set a target residual chlorine value (e.g. 0.5 mg/L). Once readings exceed the threshold, the system automatically cuts down dosing volume and avoids blind manual operation.

III. Hidden hazards to watch out for: Disinfection by-products and under-deposit corrosionStable concentration control is only fundamental. Operators also need to watch for oxygen-corrosion risks that may arise during chlorine dioxide preparation. Iron will be oxidized into ferric ions, which further combine with carbonate ions in water to form ferrous carbonate scale. Continuous buildup of iron scale leads to repeated localized corrosion, and may eventually cause pipeline perforation.Therefore, alongside residual chlorine monitoring, regular testing of dissolved oxygen levels and pipeline corrosion potential is essential. Moderate addition of corrosion inhibitors or appropriate pH adjustment often delivers unexpected pipeline protection effects.Uniform mixing of injected disinfectant, accurate dosing regulated via intelligent monitoring, and reduced local sedimentation through optimized hydraulic conditions — all these coordinated steps support systematic and stable water quality control. Proper management stops chlorine dioxide from triggering unintended damage to terminal water supply facilities.After all, disinfection is a long-term systematic task. The whole water supply system needs coordinated operation. We must avoid protecting water quality at the cost of damaging pipelines and auxiliary equipment, so every drop of supplied water can serve residents reliably.