Summary Adsorption - Drinking Water Treatment 1, TU Delft
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Module
Water Treatment
Institution
Water Treatment
Drinking Water Treatment 1
The course gives the technological backgrounds of treatment processes applied for production of drinking water. The treatment processes are demonstrated with laboratory experiments. Study goals: Knowledge of technological basics and design parameters of drinking water tr...
0
0 10,000 20,000 30,000
bed volumes (m3/m3)
influent
effluent
,adsorption water treatment
Framework
This module explains adsorption.
Contents
This module has the following contents:
1. Introduction
2. Theory
2.1 Equilibrium
2.2 Kinetics
2.3 Mass balance
2.4 Solutions for the basic equations
3. Practice
3.1 Pseudo-moving-bed filtration
3.2 Pressure filtration
3.3 Powdered activated carbon
104
, water treatment adsorption
1 Introduction The activated carbon filters of the drinking water
production plant at Kralingen have the objective
Water contains dissolved organic matter that can- to improve the taste of the water, to reduce the
not be removed with floc formation, floc removal regrowth of bacteria in the piped network, and
or sand filtration. These dissolved organic com- to remove toxic substances from the water.
pounds are: The carbon filters are placed after the floc for-
- odor-, taste- and color-producing compounds mation, sedimentation and rapid sand filtration
- organic micropollutants (pesticides, hydrocar- to avoid rapid clogging.
bon compounds)
Activated carbon adsorbs (part of) the organic The installation is based on pressure filters, so
matter and is mainly used to treat drinking water the construction height can be limited and only
produced from surface water. an extra pumping phase (middle pressure) is
needed.
In the past, d������������������������������������
rinking water produced from surface
water would pass through the following steps: floc The installation has the following characteris-
formation, floc removal (sedimentation and filtra- tics:
tion) and disinfection with chlorine. Filter bed height: 4m
This was sufficient to comply with the drinking Filtration surface area: 28 m2
water guidelines for turbidity, odor, taste and hygi- Number of filters: 12
enic reliability. Contact time (EBCT): 12 min
Type of carbon: Norit ROW 0.95
In 1987 Amsterdam Water Supply discovered Regeneration frequency: 1.5 year
the presence of pesticides (Bentazon) in drinking
water. Due to this discovery, the traditional treat-
ment of surface water was no longer satisfac- Under high temperatures this material becomes
tory and an extension with activated carbon was carbonated, meaning that the carbon partly trans-
required. forms into carbon monoxide and water. This is how
the carbon gets its open structure (Figure 1).
In addition, chlorine can react with organic matter The internal surface area of the activated carbon is
(precursor), and trihalomethanes (THMs) can be several times larger than the external surface area.
formed. These THMs are toxic.
To reduce the concentration, the formed THMs can
be removed with activated carbon. The problem, pesticides
however, is that carbon is rapidly saturated with
THMs and has to be regenerated frequently. It is
preferable to prevent the THMs from being formed. micro pores
This can be done by reducing the concentration of
macro pore
the precursor before adding chlorine.
meso pore
Precursors cannot be measured directly, but the
concentration of organic matter, expressed as TOC
or DOC, is an indication.
The best way to prevent THM formation is to avoid
the dosing of chlorine, but this requires another
treatment setup.
macro pores > 25 nm
meso pores 1 - 25 nm
Activated carbon is a substance with a high carbon micro pores < 1 nm
concentration (e.g., pit-coal, turf). Figure 1 - The open structure of activated carbon
105
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