RAS Water Balance

Solve steady RAS purge/makeup from nitrate production, nitrate-bearing makeup and solute-free evaporation; distinguishes internal circulation from boundary replacement and excludes denitrification.

Description

A steady RAS dissolved-nitrogen balance links production, purge and makeup.

A steady RAS dissolved-nitrogen balance links production, purge and makeup. Evaporation removes water without carrying the modeled dissolved nitrogen, while makeup introduces its own nitrogen.^[1]

Solve steady RAS purge/makeup from nitrate production, nitrate-bearing makeup and solute-free evaporation; distinguishes internal circulation from boundary replacement and excludes denitrification.

When to use RAS Water Balance

Use this tool to solve steady RAS purge/makeup from nitrate production, nitrate-bearing makeup and solute-free evaporation; distinguishes internal circulation from boundary replacement and excludes denitrification.

Prepare the cohort, water, feed or equipment measurements for one consistent operating period. Confirm nitrogen reporting bases, dry/wet masses, flow units and supplied design assumptions.

How to use RAS Water Balance and understand its results

Prepare the cohort, water, feed or equipment measurements for one consistent operating period. Confirm nitrogen reporting bases, dry/wet masses, flow units and supplied design assumptions.
Enter nitrateProductionKgNPerDay, makeupNitrateMgNPerLiter, targetNitrateMgNPerLiter, evaporativeLossM3PerDay, internalRecirculationM3PerDay using the field table and calculation rules, then run the tool.
Read requiredPurgeM3PerDay, requiredMakeupM3PerDay, internalRecirculationFractionOfTotalFlow. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
nitrateProductionKgNPerDay	Nitrate production kg n per day	number	Required
makeupNitrateMgNPerLiter	Makeup nitrate mg n per liter	number	Required
targetNitrateMgNPerLiter	Target nitrate mg n per liter	number	Required
evaporativeLossM3PerDay	Evaporative loss m3 per day	number	Required
internalRecirculationM3PerDay	Internal recirculation m3 per day	number	Required

Supply nonnegative production, makeup concentration, evaporation and internal recirculation. Target concentration must exceed makeup concentration. Calculate purge and makeup m³/day, then internal flow divided by internal flow plus makeup. That denominator must be positive even when production is zero.

purge=(1000 nitrogenKgPerDay+makeupConcentration×evaporation)/(targetConcentration−makeupConcentration); makeup=purge+evaporation

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
requiredPurgeM3PerDay	Required purge m3 per day	number
requiredMakeupM3PerDay	Required makeup m3 per day	number
internalRecirculationFractionOfTotalFlow	Internal recirculation fraction of total flow	number

json

{
  "input": {
    "nitrateProductionKgNPerDay": 0.1,
    "makeupNitrateMgNPerLiter": 0,
    "targetNitrateMgNPerLiter": 10,
    "evaporativeLossM3PerDay": 2,
    "internalRecirculationM3PerDay": 1000
  },
  "output": {
    "requiredPurgeM3PerDay": 10,
    "requiredMakeupM3PerDay": 12,
    "internalRecirculationFractionOfTotalFlow": 0.9881422924901185
  }
}

Limitations and assumptions

This steady balance excludes denitrification, other nitrogen sinks and time variation. The recirculation fraction is a flow ratio, not a nitrogen-removal efficiency.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Denitrification Rate: Screen denitrification capacity against kinetic volume, biodegradable carbon and nitrate load with caller rates; does not infer carbon bioavailability or recommend dosing. For a complementary task, use Nitrification Rate: Measure net TAN disappearance and active-area-normalized rate across parallel streams; negative net removal is preserved and TAN disappearance alone does not prove nitrification.

References

RAS Water Balance — tool.io

Similar or alternative tools

Denitrification Rate
Screen denitrification capacity against kinetic volume, biodegradable carbon and nitrate load with caller rates; does not infer carbon bioavailability or recommend dosing.
Nitrification Rate
Measure net TAN disappearance and active-area-normalized rate across parallel streams; negative net removal is preserved and TAN disappearance alone does not prove nitrification.