Use dry solids as the denominator
Dry-solids flow equals wet sludge flow multiplied by solids concentration, with density and unit conversions applied correctly. Use measured feed solids from the test period.
A fixed liters-per-hour polymer setting becomes a different dose when sludge flow or solids changes.
Convert product to active mass
For a liquid emulsion or dispersion, multiply product mass flow by declared active fraction. For dry powder, use the applicable product solids or assay basis from its technical record.
Do not compare neat product volumes across forms or active contents. State the assumptions and units beside the calculation.
Example calculation
If 20 cubic metres per hour of sludge at 2.5 percent solids is approximated at 1,000 kilograms per cubic metre, dry-solids flow is 500 kilograms per hour. A feed of 3 kilograms per hour active polymer equals 6 kilograms active per dry tonne.
This is an arithmetic example, not a recommended dose. Real demand depends on sludge and equipment and must be determined by testing.
Measure actual pump delivery
Collect or weigh pump output over a timed interval at operating backpressure. For prepared solutions, distinguish neat product feed from solution flow and dilution water.
Calibration curves should cover the working range. Recheck after maintenance, viscosity change or a blocked line.
Pair dose with outcomes
At every active dose, record capture, liquid solids, cake solids, throughput and operating stability. Repeat promising points instead of fitting a conclusion to one run.
The useful output is a performance curve and acceptable window, not an isolated number.
Use the calculation in procurement
Normalize trial products to active polymer and include transport, preparation and disposal consequences. Preserve active-content documentation with the quotation.
If a supplier changes product form or active basis, recalculate before comparing price or plant settings.
Control units and sampling time
Use one unit system throughout the calculation and label whether concentration is mass fraction, volume fraction or laboratory percent solids. Match the solids sample to the same period used for sludge and polymer flow.
Short-term feed variation can distort a calculation built from unrelated averages. For a trial, use synchronized readings or a documented time-weighted value and retain the underlying measurements.
Create an operator conversion sheet
Translate the approved active dose into pump settings for several realistic combinations of sludge flow and feed solids. Include the product active fraction and prepared-solution concentration used in the conversion.
The sheet should prompt recalculation after a product-form change, calibration change or solids shift. It is a control aid, not permission to operate outside the tested performance window.
Check uncertainty before comparing small differences
Feed-solids testing, flow measurement, product concentration and pump calibration each contribute uncertainty to the calculated active dose. When two products appear close, repeat measurements and avoid treating a small calculated difference as exact.
Use the same laboratory method, sampling point and calculation workbook throughout a trial. Note whether product feed is measured by mass, calibrated volume or control-system indication. If density is assumed for a liquid product, state the source and temperature basis. Transparent assumptions allow another engineer to reproduce the result and prevent a conversion error from becoming a purchasing conclusion.