Annual report Chair on Drinking Water Engineering 2008 - TU Delft

Modeling of biological activated carbon filtration
Research objectives
The research objective is to develop a quantitative simulation model for biological activated (BAC) filtration in
drinking water treatment. The model includes adsorption and biodegradation processes and should be able to
predict the removal of natural organic matter (NOM) and pesticides.
Project outline
Introduction
Pre-oxidation prior to granular activated carbon (GAC) filtration enhances biological activity, resulting in NOM
removal. Oxidation also reduces adsorbability of NOM. Both phenomena result in lower solid-phase concentrations
of NOM on activated carbon. The reduced solid-phase concentrations causes less competition between
pesticides and NOM, resulting in longer filter run times for pesticides.
Approach
Based on literature review a white box simulation model for BAC filtration was developed. In an other work
package of the project a biomass quantification method based on adeninotriphosphate (ATP) was developed
and the dominant bacteria species in BAC filters were determined and characterized. Laboratory experiments
were performed to determine the effect of oxidation on the adsorption characteristics of the NOM. This provided
data for model calibration. Pilot plant experiments for both ground and surface water were used for
model validation.
Results
Laboratory experiments showed that due to oxidation and biodegradation the solid-phase concentrations of
NOM reduce to 50% of the original values. Pesticide spiking experiments in a pilot plant at concentrations of
2 µg/l showed that BAC filter run times are up to two times longer than GAC filter run times (see figure 1). In
the pilot plant biomass profiles were determined with the ATP on carbon method. Surprisingly ATP on carbon
concentrations peak in spring and not in summer when temperatures are maximal.
atrazine [µg C/l]
2,5
2
1,5
1
TW-BAC1:
0.7 g O3 ·g C
influent
0,5
0
EBCT 5 min
EBCT 10 min
EBCT 20 min
0 100 200 300 400 500 600 700
Time [days]
Figure 1 - Atrazine breakthrough in GAC and BAC at empty bed contact times of 5 min and 10 min
-1
0-12 g H2O2 ·m-3 44 <strong>Annual</strong> <strong>report</strong> DWE 2008
TW-GAC1:
0 g O 3 ·m -3
0 g H 2 O 2 ·m -3
influent
EBCT 5 min
EBCT 10 min
EBCT 20 min