Biology Reference
In-Depth Information
4.3.4. Flocculation
Flocculation is a process by which a chemical coagulant added to the water
acts to facilitate bonding between particles, creating larger aggregates which
are easier to separate. The method is widely used in water treatment plants
and can also be applied to sample processing for monitoring applications.
A review of flocculation for bacteria using polymers also provides a good
overview of the mechanisms.
41
In 2006, Ferrari and colleagues presented a calcium carbonate
flocculation method for concentration of pathogens from industrial
wastewaters.
42
They stressed the need for internal controls given the
highly variable recovery rates observed. Additionally, the authors con-
sidered it essential to improve our understanding of the factors which
lead to poor recovery rates when adapting techniques developed for
drinking water to more complex matrices. Previous studies on the effect
of turbidity on recovery rates have been contradictory. Recently, it has
been shown that addition of small silica particles improves
Cryptosporid-
ium
oocyst recovery, whereas particles greater than around 50 µm reduce
oocyst recovery.
In 2008, Calgua presented a method for one-step concentration
of viruses from seawater, using preflocculated milk proteins (e.g. 10g of
skimmed milk powder dissolved in the 1 L sample).
43
The technique was
applied to a study of adenoviruses in seawater samples, although the method
could be adapted for other water types.
In 2012 Zhang et al. reported the use of a new coagulant for the
concentration of
Escherichia coli
and
Heliobacter pylori
from raw and fin-
ished waters.
44
The study built on earlier work which had shown that
lanthanum chloride was more effective as a sample concentration method
than iron chloride or aluminum sulfate together with a microrespiromet-
ric detection method. However, this technique was not quantifiable for
specific bacteria and so the process was adapted for molecular detection.
The disadvantage of using iron coagulents is that the iron is known to
interfere with DNA extraction, lowering the yield. This was not found
for lanthanum. EDTA was employed as an elution agent, operating as a
metal ion chelator and successfully dissolved lanthanum flocs in less than
a minute, although it performed less well with flocs of the other coagu-
lant chemicals. A concentration of 10 times was reported which could be
improved to 500 times by performing a two-step process and including a
centrifugation stage.
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