A coagulant dosing pump at a wastewater treatment plant is set to 45 L/h based on the average flow the plant sees on a normal day. At 6 a.m., as the morning peak arrives and influent flow climbs to nearly double the overnight rate, the pump keeps dosing at 45 L/h. Nobody changes the setting, because nothing tells the pump, or the operator, that the ratio of chemical to flow has just been cut in half.
Coagulant and polymer dosing only works as intended when the chemical dose scales with the volume of water actually being treated. A fixed flow rate can only ever be correct at one specific influent flow, and influent flow at a wastewater treatment plant is never fixed.
The Mismatch Between a Fixed Rate and a Moving Target
Influent flow follows a predictable daily pattern in most plants, a morning peak and a lower overnight trough, and an unpredictable one during storm events, industrial batch discharges, and infiltration. A pump dosing at a constant rate is only matched to the process during the narrow window when actual flow happens to equal the flow the pump was set for. Outside that window, every litre dosed is either too much or too little relative to what is actually arriving.
What Happens When Dosing Doesn’t Track Flow
Overdosing coagulant or polymer during low-flow periods isn’t just a chemical cost problem, though it is that too. Excess polymer in particular can overload downstream filtration, increasing sludge volume and, in some cases, actively working against the settling process it’s meant to support. Underdosing during high-flow periods has the opposite but equally damaging effect: incomplete coagulation and flocculation let turbidity and suspended solids carry through the clarifier, which shows up downstream as a compliance risk rather than a dosing pump problem.
Because the pump itself gives no indication that its rate no longer matches demand, this mismatch typically isn’t caught by watching the pump. It’s caught, much later, by watching effluent quality.
How ppm Mode Ties Dosing to Actual Metered Flow
The Injecta Atlanta’s ppm Mode is built specifically to close this gap. Instead of running at a flow rate the operator sets once, the pump calculates its dosing frequency continuously from an incoming pulse signal from a flow meter, using three programmed inputs: the desired dosing concentration in ppm, from 0.1 to 60,000.0 ppm, the flow meter’s pulse relationship, set as either pulses per litre or litres per pulse, and the concentration of the chemical product actually being dosed, as a percentage. With these three values programmed, every pulse the flow meter sends translates directly into a proportional dosing command, so the pump’s output rises and falls with the metered flow rather than sitting at whatever value was last entered manually.
Handling Flow Spikes Beyond the Pump’s Own Capacity
Every dosing pump has a maximum output, and a large enough flow spike can ask for more than the pump can physically deliver. The Atlanta’s Memory function is the setting that decides what happens in that situation. With Memory switched on, pulses received while the pump is already running at its maximum are not discarded, the pump keeps track of the shortfall and continues dosing at maximum until it has caught up, which the display flags with a MEM indicator whenever the incoming signal exceeds the pump’s rated flow rate. With Memory switched off, any demand above the pump’s maximum is simply not serviced, and the pump doses at its ceiling for the duration of the spike without attempting to make up the difference afterwards.
Neither setting is universally correct, it depends on whether a plant would rather risk a brief window of under-dosing during a spike, or a period of catch-up dosing once the spike subsides. The Atlanta gives the operator that choice rather than making the decision silently.
Setting It Up
Configuring ppm Mode on the Atlanta follows a fixed sequence: set the target ppm value, choose whether the flow meter reports in pulses per litre or litres per pulse and enter that quantity, set the concentration of the product being dosed, and switch Memory on or off depending on how flow spikes should be handled. Once configured, the display shows the current calculated flow rate alongside the programmed ppm value, so the operator can see at a glance that the pump is tracking rather than guessing.
Where This Fits
ppm Mode is the right tool wherever coagulant, polymer, or any other chemical needs to scale directly with a metered process flow, inlet works dosing ahead of primary treatment, polymer dosing ahead of a belt press or centrifuge, or any point in the plant where a flow meter already exists and the dosing pump has simply never been connected to it.
Autoflo Technology is the authorised distributor of the Injecta Atlanta series in Malaysia. For help configuring ppm Mode against your plant’s existing flow metering, contact us at info@autoflotechnology.com.