D10: Impact of Contaminants - Hydromod

Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas
EUROLAKES
D10: Impact of Contaminants
FP5_Contract No.: EVK1-CT1999-00004
Version: 4.0
Date: 25/07/01
File: D10-vers.4.0.doc
Page 107 of 136
clog the filter creating the need for frequent washing. It is therefore essential to provide
a floc separation stage that uses settling or flotation techniques prior to filtration (Line
4).
The floc formed after addition of coagulant clarifies the water. This floc also has adsorbent
qualities allowing a number of pollutants to be adsorbed on its surface. However,
if the concentration of pollutant organic matter is too high, it may be necessary to
include additional treatments, such as oxidation (Line 6) or adsorption (Line 5), which
are used together with one or other of the clarification processes.
Some of the above treatment stages have a biological effect (Line 7). Whenever a
treatment process involves a solid liquid interface, the latter encourages the development
of micro-organisms, which may have a positive effect on the treated water. This is
true of filter stages (sand or GAC) and, to a lesser extent, the sludge bed employed in
settling tanks.
Figure 11-5 Basic processes in Drinking Water Treatment according to [DEGREMONT, Water
Treatment Handbook, 1991]
The traditionally applied processes in rendering surface waters suitable for drinking are:
1. Mechanical treatment (screening, straining, sand removal, etc.)
2. Aeration
3. Sedimentation of suspended solids, mostly in combination with coagulation and
flocculation