Residuals handling calculator

Sludge Production & Dewatering Calculator

Extend an MBR excess-solids estimate into a transparent residuals-handling screen for dewatering feed, captured cake, liquor return, polymer demand, operating duty, annual cake, and preliminary cake storage.

Screening tool only. Use the excess biological dry-solids result from the Solids Balance & SRT Calculator where applicable. Confirm feed solids, capture, cake solids, polymer demand, equipment capacity, recycle-stream loads, and disposal arrangements through laboratory, pilot, full-scale, and vendor testing.

Currency labelUsed only to label direct polymer-cost outputs; no conversion is applied.

Residuals and dewatering inputs

All solids values are dry solids unless stated otherwise.

Dry solids production

Excess biological dry solidskg DS/d; hand off from solids balance

Additional chemical dry solidskg DS/d; coagulant/lime residuals etc.

Dewatering operating daysdays/year; use the actual operating programme

Feed, capture, and cake

Dewatering feed total solidspercent TS by mass

Expected solids capturepercent of feed DS retained in cake

Expected cake total solidspercent TS by mass; must not be below feed TS

Equipment and storage screen

Dewatering capacitykg DS/h feed capacity

Cake storage perioddays of cake production

Cake storage marginpercent above calculated storage

Dry-solids densitykg/m³; screening density

Polymer conditioning screen

Dry active polymer dosageg active polymer/kg DS feed

Polymer make-up concentrationpercent active by mass

Polymer solution densitykg/L; screen as water-like if unknown

Active polymer costcurrency/kg dry active polymer

Mass balance and handling results

Calculated from dry-solids conservation and explicit water/solids-density terms.

Governing formulas

Solids and cake mass balance

Dry solids to dewatering = Excess biological DS + Additional chemical DS
Captured cake DS = Feed DS × Solids-capture fraction
Liquor solids loss = Feed DS − Captured cake DS
Feed wet mass = Feed DS ÷ Feed-TS fraction
Cake wet mass = Captured cake DS ÷ Cake-TS fraction

Two-component volume and liquor balance

Feed volume = (Feed DS ÷ Dry-solids density) + (Feed water ÷ Water density)
Cake volume = (Cake DS ÷ Dry-solids density) + (Cake water ÷ Water density)
Released liquor = (Feed water − Cake water) ÷ Water density

Polymer, duty, and storage

Dewatering duty = Feed DS ÷ Dewatering capacity
Dry active polymer = Feed DS × Polymer dose ÷ 1,000
Polymer make-up solution = Dry active polymer ÷ Polymer-solution fraction ÷ Solution density
Nominal cake storage = Cake volume × Storage days × (1 + storage margin)

The two-component density expression avoids relying only on a total-solids ratio when estimating volume at higher cake solids. Treat every performance input as site-specific.[1] [2]

Screening assumptions

Item	Default	Interpretation
Feed total solids	2.0%	Laboratory value required for design.
Solids capture	95%	Process- and sludge-specific.
Cake total solids	20%	Confirm by bench/pilot and vendor testing.
Active polymer	5 g/kg DS	Editable screening input; not a chemistry recommendation.
Dry-solids density	1,400 kg/m³	Volume-screening assumption.
Water density	1,000 kg/m³	Water-like liquor approximation.

Design cautions

Assess the returned centrate/filtrate at the actual dewatering schedule, not solely as a 24-hour average. Dewatering chemistry and performance must be confirmed by testing.[2]

References

Sludge production and dewatering basis

Documentation revision: 2026-10-02. This page documents the calculation basis so an engineer can trace the inputs, units, assumptions, and review needs. Results are preliminary screening estimates; they are not a permit determination, OEM guarantee, or construction/procurement approval.

Method and source basis

The page starts with externally supplied dry-solids loads, applies capture and cake-TS assumptions, estimates cake and liquor mass/volume using dry-solids and water-density terms, and estimates polymer and storage quantities. It is a one-pass screening mass balance.

The sources below provide technical context or analytical/design methodology. They do not endorse this calculator's defaults, and any jurisdiction-specific requirement applies only where that authority has jurisdiction.

U.S. EPA, Design Manual: Dewatering Municipal Wastewater Sludges (EPA 625/1-87/014)
Government of Ontario, Design Guidelines for Sewage Works: Sludge Thickening and Dewatering
U.S. EPA, Biosolids regulatory and technical resources
Metcalf & Eddy/AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.

Assumptions, limitations, and review actions

Capture, cake TS, polymer dose, capacity, sludge density, and operating days are empirical inputs. Confirm them with representative sampling, bench/pilot testing, and equipment/vendor testing; defaults are not universal targets.
The model does not include a complete plant solids balance, recycle nitrogen/phosphorus loads, inert/chemical solids, upstream thickening, wash water, downtime, standby/firm capacity, hauling, disposal, labour, energy, or maintenance.
The output is direct active-polymer cost only. Review cake handling, returned-liquor loading, storage, conveyance, and jurisdictional biosolids/disposal requirements separately.

Professional review checkpoint

Before using the result for specification or operation, reconcile it with representative site data, the applicable permit and design standard, the selected equipment or membrane supplier's current data, and a qualified wastewater/process engineer. Record the input basis, date, units, and any pilot, bench-test, or comparable full-scale evidence used to select the assumptions.