Sludge dewatering solids capture describes how much incoming dry matter leaves in the cake rather than returning in liquid streams. It is a different measurement from cake solids. A dry cake can coexist with poor capture, and clear-looking filtrate can carry a significant daily solids load when its volume is large. Polymer trials need both measures to avoid transferring costs back to the liquid treatment process.
Choose a calculation boundary
Draw a boundary around one machine and list every stream crossing it. Include sludge feed, added wash or dilution water, cake, centrate or filtrate, and any separate drain that carries solids. A shared sump collecting several machines cannot automatically represent the performance of one trial line. Either measure the relevant streams separately or explicitly limit what the combined result can establish.
For a measured liquid-loss approach, dry-solids feed rate is feed flow multiplied by feed solids concentration. Dry-solids loss rate is the sum of each outgoing liquid flow multiplied by its measured suspended-solids concentration. Capture is 100 multiplied by one minus the loss-to-feed ratio. Keep mass and volume units consistent, and check whether the chosen laboratory methods represent the fractions being balanced.
Work through an illustrative example
Suppose the measured feed contains 200 kg of dry solids per hour, while all included liquid outlets together carry 10 kg per hour. The calculated capture is 95 percent. These numbers are illustrative, not a performance target. If an unmeasured bypass carries another 10 kg per hour, the apparent result overstates actual capture. Measurement completeness matters more than reporting an extra decimal place.
The dewatering overview provides the equipment context for this calculation. When Xinqi Polymer or another sludge polymer supplier evaluates trial data, provide the boundary and raw measurements with the headline percentage. Without them, two apparently comparable trials may include different loss streams.
Align samples with material travel time
A feed sample and a discharge sample taken at the same clock time may represent different sludge when operation is changing. Establish the approximate transit and hold-up behaviour before organising paired samples. Use a stable observation period or an approved composite approach that accounts for the process. Log machine starts, wash cycles and interruptions that could distort an average.
Mix and handle samples using the laboratory's procedure. Settling in a sample container can make the aliquot unrepresentative, while a grab taken during a wash event may look unusually dilute. Where measurement uncertainty is large, report a range or qualification rather than treating a small difference between polymer products as a real improvement.
Make the purchasing decision on the whole result
Compare capture with cake solids, dry-solids throughput, polymer consumption and liquid return load. A candidate that slightly improves cake dryness but doubles returned solids may be the more expensive operating choice. Keep the raw worksheet in the trial report so later reviewers can recalculate it. The objective is an auditable balance that explains where the solids went, not a favourable percentage detached from the plant.