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Sludge Retention Time Scenario Calculator

Nominal solids retention time in days = solids inventory in kilograms ÷ (external wasted solids + external effluent solids in kg/day).

214 / SLUDGE RETENTION TIME SCENARIO

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Starting values are illustrative. Use your own costs, rates and assumptions.

INPUT GROUP 01

Entered quantities and model assumptions

Illustrative defaults are examples. Replace them with matching measurements, reviewed properties and actual quote terms.

Check the assumptions before acting on a result.

Read the method and example

YOUR CALCULATION

Divide matching solids inventory by external solids outflow.

Total counted external solids outflow · kg/day

50

Nominal solids retention time · days

20

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Illustrative inputs loaded. Replace them with your own assumptions.

How the sludge retention time scenario calculator works

Nominal solids retention time in days = solids inventory in kilograms ÷ (external wasted solids + external effluent solids in kg/day). The outflows are summed before division. Zero total outflow has no calculated finite retention; zero inventory with positive outflow gives zero days.

Inventory and outflow must share a system boundary and solids definition, such as a consistent TSS or volatile-solids basis. Internal recycle is not an external solids loss. This differs from liquid hydraulic retention and does not establish a solids-age target, wasting setting, treatment performance or permit compliance.

Quantities use the stated units and finite bounded inputs. Whole purchases round up under the documented model; cost components round half-up to cents before totals are summed. Undefined ratios stay unavailable. π and logarithms use normal numeric precision. Display rounding does not alter the entered assumptions.

Worked example

1,000 kg inventory divided by 40 kg/day waste plus 10 kg/day effluent gives 20 days. Increasing waste solids to 90 kg/day gives 1,000/100 = ten days.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

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