ZPM: Zeta potential mixer
ZPM stands for Zeta Potential Mixer. They are manu-
factured from 316 grade stainless steel for freshwa-
ter and a combination of plastic and titanium for
marine applications. The ZPM is flanged into the
pipework and as the water passes through the ZPM,
it is violently mixed and cavitated.
A ZPM is essential for the APF coagulation reactions
but it also has other benefits. The ZPM splits the wa-
ter molecule as well as dissolved oxygen to generate
free radicals and to increase the redox potential. The
Dryden Aqua ZPM therefore increases the oxidation
potential and drops the zeta potential of the water.
The net effect is that it promotes coagulation and
disinfection. The violent mixing action also stresses
cryptosporidium oocysts and renders them suscep-
tible to oxidation by chlorine or it simply kills them
directly. All of the above benefits make the Dryden
Aqua ZPM an essential part of the DAISY system.
How does a ZPM work?
Installed upstream of the filter, the ZPM amplifies
the coagulation and flocculation reactions for the
conversion and precipitation of dissolved compo-
nents into small particles. The cavitation reactions
provide the perfect mixing and turbulent environ-
ment necessary for coagulation using APF. The ZPM
neutralises the electrical charge (Zeta Potential) on
dissolved chemicals and small particles to make
some positively and some negatively charged. The
opposite charges attract and this causes coagu-
lation and flocculation. As the electrical potential
drops to neutral, the redox oxidation potential of
the water increases.
DAISY filter circulation for private pools
2
3
1
AFM ®
ZPM
APF
Variable frequency pump
DRYDEN AQUA
Enhanced oxidation with ACO
and ZPM after AFM ® filtration
Sand filters incubate and generate colonies of
bacteria called bacteria floc. Indeed the primary
source of bacteria in a swimming pool is actually
the sand filter as opposed to the bathers. Just like
biofilm, bacterial floc are large colonies of several
million bacteria held together by an alginate glue.
The alginate protects the bacteria from chlorine
for several minutes to several hours. AFM ® does
not incubate bacteria but bacteria can still grow
on the inside of the filter shell, nozzles and in the
pipework. A ZPM after the filters will smash bacte-
ria floc into individual bacteria which then allows
the chlorine to kill the bacteria before the water
reaches the pool.
ZPM for disinfection and
cryptosporidium control
The ZPM downstream of the filter is installed for
mechanical disinfection and barrier against bac-
teria. The Nano bubbles created by the cavitation
are of most use here. They will be attracted to the
surface of solids such as bacteria, viruses, spores
and protozoa. Nano bubbles adhere to the surface
where they then implode. The energy released
blows a hole through the cell membrane of the
pathogen. The bacteria or parasite will be killed
or the hole formed allows chlorine to enter.
Bacteria and other pathogens are incubated on
the surface of sand in the sand filters, on the walls
of the balance tank and any surface in contact
with the water. The slippery surface on tiles is not
body-fat but a thin invisible film of bacteria. Some
pathogens (e.g. Cryptosporidium) as well as bio-
film protected colonies of bacteria are extremely
resistant to chlorine. The ZPM breaks these colonies
apart and allows chlorine to disinfect the water
before the water reaches the pool. Bacterial floc
can survive for a few minutes to several hours,
bacteria from ZPM shattered floc can only survive
for about 30 seconds.
ACO
ZPM
1 Filtration with AFM ®
2 Coagulation and flocculation with APF and ZPM
3 Catalytic oxidation with ACO and ZPM
10
Step 3:
Nano-bubble implosion process