Water tools

Influent nitrogen fractionation for nutrient removal design

Nutrient removal models do not run on TKN alone. From routine measurements and the unbiodegradable particulate COD this tool derives the five nitrogen fractions, and tells you how low the effluent TKN can go.

Total TKNmg N/L

Free and saline ammoniamg N/L

Soluble (filtered) TKNmg N/L

Unbiodegradable soluble organic Nmg N/LMeasured or assumed; typically about 0.5.

Unbiodegradable particulate CODmg COD/L

N content of VSSmg N/mg VSS

COD/VSS ratio of organicsmg COD/mg VSS

Fractions

Ammonia

29.10mg N/L

Biodegradable soluble organic N

3.51mg N/L

Unbiodegradable soluble organic N

0.49mg N/L

Biodegradable particulate organic N

1.54mg N/L

Unbiodegradable particulate organic N

9.86mg N/L

Total organic N

15.40mg N/L

What it means

Nitrogen available to the process

34.15mg N/L

Lowest effluent TKN an ideal plant reaches

0.49mg N/L

Unbiodegradable soluble organic N passes through untouched; everything else is synthesised or nitrified.

How it works

The five fractions follow from routine measurements and the unbiodegradable particulate COD:

N_{o r g} = T K N - N H_{4} N_{o b s} = T K N_{s o l} - N H_{4} - N_{o u s}

(1)

T K N_{p a r t} = T K N - T K N_{s o l} N_{o u p} = \frac{f_{n} X_{U}}{f_{c v}} N_{o b p} = T K N_{p a r t} - N_{o u p}

(2)

where

$T K N$: total Kjeldahl nitrogen, mg N/L
$N H_{4}$: free and saline ammonia, mg N/L
$T K N_{s o l}$: soluble Kjeldahl nitrogen, mg N/L
$N_{o r g}$: total organic nitrogen, mg N/L
$N_{o b s}$: biodegradable soluble organic nitrogen, mg N/L
$N_{o u s}$: unbiodegradable soluble organic nitrogen, mg N/L
$T K N_{p a r t}$: particulate Kjeldahl nitrogen, mg N/L
$N_{o u p}$: unbiodegradable particulate organic nitrogen, mg N/L
$N_{o b p}$: biodegradable particulate organic nitrogen, mg N/L
$f_{n}$: nitrogen content of volatile solids, mg N per mg VSS
$f_{c v}$: COD to VSS ratio, mg COD per mg VSS
$X_{U}$: unbiodegradable particulate COD, mg/L

where f_n is the nitrogen content of VSS, f_cv the COD to VSS ratio and X_U the unbiodegradable particulate COD. The fractions sum back to TKN. Assumes no nitrate or nitrite in the influent. The unbiodegradable particulate nitrogen leaves with the waste sludge; only the unbiodegradable soluble organic nitrogen remains in the effluent of an ideal plant.

Influent nitrogen fractionation for nutrient removal design

How it works

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