Water tools

Granular activated carbon: EBCT, carbon mass, usage rate and bed life

At best, every gram of carbon leaves the bed loaded to equilibrium with the influent. That sets a floor on carbon usage and a ceiling on bed life; competition and the mass transfer zone only make it worse.

Flowm³/h

Empty-bed contact timemin5 to 30 min for synthetic organics.

Bed densitykg/m³350 to 550.

Freundlich K(mg/g)(L/mg)^(1/n)

Freundlich 1/n

Influent concentrationmg/L

Approach velocitym/h5 to 15 m/h.

Bed life at the exhaustion limit

175d

A maximum for a single solute with a short mass transfer zone. Natural organic matter shortens it substantially.

Minimum carbon usage rate

17.9g/m³

Maximum specific throughput

55.9L/g

Equilibrium loading at influent

55.9mg/g

Bed

Carbon mass in the bed

1,702kg

Bed volume

3.78m³

Bed depth at the approach velocity

1.67m

Bed area

2.27m²

How it works

E B C T = \frac{V_{F}}{Q} = \frac{L}{v} M_{G A C} = E B C T Q ρ_{F}

(1)

If every grain reaches equilibrium with the influent before the bed is exhausted, the carbon usage rate and the throughput per gram are

C U R_{m i n} = \frac{C_{i n f}}{q_{e} (C_{i n f})} = \frac{C_{i n f}}{K C_{i n f}^{1 / n}} {throughput}_{m a x} = \frac{1}{C U R_{m i n}}

(2)

t_{b e d} = \frac{M_{G A C}}{C U R_{m i n} Q}

(3)

where

$E B C T$: empty-bed contact time, min
$V_{F}$: bed volume, m³
$Q$: flow
$L$: bed depth, m
$v$: approach velocity, m/h
$M_{G A C}$: carbon mass in the bed, g
$ρ_{F}$: bed density, kg/m³
$C U R_{m i n}$: minimum carbon usage rate, g per L treated
$C_{i n f}$: influent concentration, mg/L
$q_{e}$: equilibrium loading at the influent concentration, mg/g
$K, 1 / n$: Freundlich constants
$t_{b e d}$: bed life, d

The treatment objective does not enter this limit. The real usage rate comes from pilot or rapid small-scale column tests; the bed must be longer than its mass transfer zone or breakthrough is immediate. Beds in series recover 25 to 50% of the carbon when bed life is under three to six months.

Granular activated carbon: EBCT, carbon mass, usage rate and bed life

How it works

Related reading