Water tools

High-rate trickling filter sizing

Trickling filters are sized on organic loading and checked on hydraulic loading. The NRC relation then predicts the removal, which you compare with the effluent target.

Average flowm³/d

Maximum daily flowm³/d

Maximum hourly flow (as m³/d)m³/d

Influent BOD₅ to the filtermg/LKeep below about 100 to 150 mg/L for stone media (oxygen limitation).

Volumetric organic loadingkg BOD₅/m³·dHigh rate after an anaerobic reactor: 0.5 to 1.0.

Packing depthmStone 2 to 3 m; plastic media up to 6 m.

Number of filters

Recycle ratio0 to 2.

Sludge yieldkg TSS/kg BOD₅ removed0.8 to 1.0 high rate without nitrification.

Volatile fraction of sludge

Settled sludge solids%

Filter

Media volume

371m³

Total area

185m²

Diameter per unit

10.9m

Hydraulic loading, average

16.2m³/m²·d

Hydraulic loading, max day

19.4m³/m²·d

Hydraulic loading, max hour

29.1m³/m²·d

Performance

BOD₅ removal (NRC)

71%

Effluent BOD₅

30mg/L

Sludge

Sludge produced

168kg TSS/d

Volatile sludge

126kg VSS/d

Sludge volume

16.4m³/d

How it works

Media volume from the organic loading, area from the depth, then hydraulic loading as a check:

V = \frac{Q S_{o}}{L_{v}} A = \frac{V}{H} L_{h} = \frac{Q}{A}

(1)

Removal by the NRC relation with the recirculation factor:

E = \frac{100}{1 + 0.443 \sqrt{L_{v} / F}} F = \frac{1 + R}{(1 + R / 10)^{2}}

(2)

S_{e} = S_{o} (1 - E / 100) P_{s l u d g e} = Y Q (S_{o} - S_{e}) V_{s l u d g e} = \frac{P_{s l u d g e}}{γ C_{s l u d g e}}

(3)

where

$V$: media volume, m³
$Q$: flow, m³/d
$S_{o}$: influent BOD₅, kg/m³
$L_{v}$: volumetric organic loading, kg BOD₅/m³·d
$A$: filter area, m²
$H$: packing depth, m
$L_{h}$: hydraulic loading, m³/m²·d
$E$: BOD₅ removal, %
$F$: recirculation factor
$R$: recycle ratio
$S_{e}$: effluent BOD₅, mg/L
$P_{s l u d g e}$: sludge produced, kg TSS/d
$Y$: sludge yield, kg TSS per kg BOD₅ removed
$V_{s l u d g e}$: sludge volume, m³/d
$γ$: sludge density, about 1,020 kg/m³
$C_{s l u d g e}$: settled sludge solids, fraction

The NRC relation was developed for stone beds fed settled wastewater; for anaerobic effluents it should be used with caution. Stone media clog at high organic loads; plastic media allow deeper beds and higher loadings. Add a secondary settler at 16 to 32 m³/m²·d average surface loading.

High-rate trickling filter sizing

How it works

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