IDM | Technology/IT
Figure 1: Process combination of the Daireuse process.
Therefore they had to start new ways of water
management.
Condensates from evaporation of milk and
whey contain low molar mass organic molecules,
traces of lactic acid, alcohols, acetoines,
non-protein-nitrogen etc. Those components
enhance microbiological growth (often associated
with slimy by-products), create odors and
cannot be removed completely just by a reverse
osmosis process. These very small organic
molecules are biodegraded by the innovative BiopROtector
technology (carrier-based biological
process) and converted to other components
which then are separated easily by downstream
membrane systems.
This allows a high water quality to be achieved
with a very low content of TOC, comparable to
drinking water also regarding the low potential
for microbiological growth. In the present
case the treated water is blended with drinking
water, standardized and fed into the common
dairy network for potable water.
2 Process Overview
For upgrading of the condensates the
Daireuse process has been applied, consisting
of the following main process steps:
• BiopROtector: biological fluidized bed reactor
and fixed bed reactor
• Ultrafiltration (UF)
• Reverse Osmosis (RO)
2.1 BiopRO tector
The BiopROtector not only prevents biofouling
in downstream membrane units but in combination
16 · 9 2017 | international-dairy.com
with UF and RO it is also a key technology
for producing high quality process water from
evaporator condensates which is contaminated
with dissolved organic molecules.
The BiopROtector for this application is designed
as a two-step process (see figure 1)
• Fluidized bed BiopROtector (A), to remove the
bulk of nutrients (>75%) present in the feed
water
• Fixed bed BiopROtector (B), a polishing step for
further removal of remaining nutrients and reducing
the biological activity of the feed water
In case of low contaminated water at typically
COD (=RBOC**) levels < 10 mg/l and NH4-N < 1
mg/l, the fixed bed BiopROtector (B) is applied
directly without pretreatment (A). It is able to
reduce the concentrations COD and NH4-N to
levels where growth of a biofilm is minimized,
thus producing high quality process water
Backwash of the fixed bed BiopROtector is done
typically once per month to get rid of surplus
biomass and to keep the BiopROtector vital. The
backwash procedure takes approx. 15-20 minutes.
In case of high contaminated water (this is the
case here) the amount of oxygen in the water is
insufficient to oxidize the COD and ammonia in
the fixed bed BiopROtector. For those situations
a two stage BiopROtector is designed, a fluidized
bed with coarse bubble aeration (A) followed by a
fixed bed unit (B).
With high amounts of nutrients in the condensate
the bulk of the COD and ammonia is
oxidized in the fluidized BiopROtector. The carriers
are kept constantly in suspension by coarse
bubble aeration.
Ultrafiltration
The BiopROtector converts very small organic molecules
into gases and microorganisms which can be
separated easily with ultrafiltration technology. UF
membranes separate quantitatively components
with particle sizes > 0.05 μm. High quality hollow
fibre UF membrane modules with certification for
drinking water production are used.
In order to control membrane fouling a
regular (typically daily) chemical enhanced
backwash (CEB) cycle with low concentrations
of chemicals is performed.
In addition to the CEB mentioned above, a
recovery clean is applied from time to time
(typically every 6 – 8 weeks) to fully recover
the permeability of the membranes.
2.2 Reverse Osmosis
For double security and for elimination of
dissolved, non-biodegradable components a
reverse osmosis unit is finally installed.
The RO permeate is similar to DI water (conductivity
<< 50 μS/cm). Usually it is stabilized by
addition of small amounts (0.3 mg/l) of chlorine
dioxide and – depending on the application –
blended with other water sources and standardized
prior to reuse.
The RO concentrate (approx. 15 – 20% of
the feed flow to RO) is still of high quality (COD
lower than in RO Polisher permeate) and is
typically utilized as process water for less critical
applications (e.g. water for cooling towers).
The RO unit includes a cleaning-in place
(CIP-) system for regular rinsing or service
cleaning of the unit.
3 Economics
The Daireuse process is a combination of standardized
units which are also used in other drinking water
applications. To achieve a long service life pipework
and tanks are made from corrosion resistant,
high quality plastics. That’s why the equipment can
be offered quite cost-efficiently. Also the operation
costs for Daireuse systems are relatively low:
• Chemical cleanings are required only occasionally
and are mainly performed by using cheap
basic chemicals (e.g. NaOH, H2SO4). Costs for
cleaning chemicals are therefore quite low
• Due to the low cleaning frequency a long
membrane lifetime is achieved. The membranes
used for UF and RO are drinking water
membranes which are manufactured in
large quantities. Membrane replacement
costs are therefore relatively low.
** Readily Biodegradable Organic Carbon: the fraction of organic components, in most cases present as volatile fatty acids, like acetic acid and
propionic acid, alcohols, acetoins, amino acids etc.