Effluent Permeate BOD & COD Calculator
Estimate preliminary MBR permeate BOD5 from soluble and particulate fractions, or use the alternative SRT-based kinetic equation to estimate permeate COD.
Preliminary mass-balance tool: In an MBR, membrane separation strongly controls the particulate portion of permeate BOD, while biological treatment is critical to residual soluble BOD. Enter representative, site-specific fractions and removal assumptions; this calculator does not replace pilot testing or calibrated process modelling.
Enter values and select Calculate to view the permeate-BOD estimate.
Kinetic Permeate COD Estimate
Use the user-specified SRT-based equation as an alternative preliminary estimate of permeate COD: S = Ks × (1 + kd) × SRT ÷ [SRT(μm − kd) − 1].
Enter kinetic values and select Calculate COD.
Interpretation: This is an alternative kinetic estimate, not a conversion between BOD and COD and not a replacement for measured permeate COD. The denominator must remain positive for the formula to be valid.
Equations used
The calculation separates total influent BOD into soluble and particulate fractions. Biological removal is applied to both fractions; membrane retention is applied only to the residual particulate fraction.
Alternative kinetic COD equation
Scope and interpretation
MBR treatment combines biological treatment with membrane separation. The membrane acts as the solids-separation barrier, but soluble BOD performance depends primarily on the biological process and wastewater characteristics. This calculator deliberately exposes these distinct assumptions. U.S. Bureau of Reclamation MBR technical report [1] MBR review article [2]
Permeate BOD and COD calculation 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 BOD screen partitions total influent BOD5 into soluble and particulate fractions, applies entered biological removal to both, applies membrane retention to residual particulate BOD, and reports the resulting permeate concentration and load. The optional COD equation is a separate kinetic screen.
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, Membrane Bioreactors Wastewater Management Fact Sheet (2007)
- WEF Manual of Practice No. 36, Membrane Bioreactors
- Standard Methods 5210B or ISO 5815-1 for BOD5 measurement
- Iorhemen et al., Membrane Bioreactor Technology for Wastewater Treatment (2016)
Assumptions, limitations, and review actions
- Define BOD5, COD, soluble/filtered fraction, sample timing, and laboratory method. Fractional removals are simplified screening assumptions, not independently guaranteed sequential removals.
- The page does not model peak/seasonal flow, biodegradability, inhibition, temperature, HRT/SRT, MLSS, oxygen/nutrients, fouling/TMP, integrity, bypass, or upset conditions.
- Meets target means only that the entered assumptions produce a value below the user-entered screening target; it is not a permit or compliance result.
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.