Prevention of Biofouling in Industrial RO Systems: Experiences with Peracetic Acid

Prevention of Biofouling in Industrial RO Systems:
Experiences with Peracetic Acid
W.B.P. van den Broek*, M.J. Boorsma **, H. Huiting***, M.G. Dusamos **** and
S. van Agtmaal*
* Evides Industriewater, Evides B.V., PO Box 4472, 3006 AL Rotterdam, The Netherlands
(E-mail: [email protected])
** WLN, PO Box 26, 9470 AA Zuidlaren, The Netherlands (E-mail: [email protected])
*** KWR Industry & Water, KWR Watercycle Research Institute, PO Box 1072, 3430 BB Nieuwegein,
The Netherlands (E-mail: [email protected])
**** JohnsonDiversey B.V., PO Box 40441, 3504AE Utrecht, The Netherlands
(E-mail: [email protected])
Abstract: Biofouling is the major fouling type occurring in reverse osmosis (RO) plants treating
surface water or effluent from a waste water treatment plant. Severe biofouling can result in
operational problems, higher energy and chemical consumption and premature membrane
replacement. There are different methods to control biofouling. One method is removal of
nutrients in the pre-treatment of the membrane filtration plant, another method is periodic
removal of biofouling by chemical cleanings or the use of chemicals to prevent biological growth
in the RO systems. In this paper the results of experiments with peracetic acid on three different
full scale plants are presented. Two of the plants are operated by Evides Industriewater, the
third one by Bètawater, a subsidiary company for industry water of Waterleidingmaatschappij
Drenthe (WMD).
One of the main outcomes is that biofouling can be controlled fully on reverse osmosis (RO)
plants with the applied method with a peracetic acid based product (Divosan Activ). If the proper
measures are taken to avoid oxidation damage due to transition metals, this method with the
environmental friendly product results in a stable process and savings by a significantly reduced
CIP interval.
Keywords Biofouling, Peracetic Acid, Reverse Osmosis, Prevention, Biofouling Control,
Pre-treatment, Operational Experience.
INTRODUCTION
A major problem in RO systems is fouling of the membrane elements. Severe fouling
will cause serious operational problems, like loss of productivity, increased pressure
drop, loss of retention, frequent chemical cleanings and premature RO element and
cartridge filter replacement. All these problems result in higher operation costs.
The major fouling mechanisms of RO systems are biofouling, scaling, inorganic
colloids and organic fouling. Different types of fouling can occur simultaneously,
influencing each other. In practice it is difficult to find out which fouling occurs first
and which fouling is the result from the initial fouling. Biofouling is the most occurring
fouling in reverse osmosis systems for desalination (Khedr, 2000), specifically in
systems with surface water or effluent from Waste Water Treatment Plants (WWTP) as
raw water source. These water sources contain Natural Organic Matter (NOM). Part of
the NOM is present as low concentration easily biodegradable compounds, which can
be used by micro organisms as a carbon source for their growth and reproduction. In the
presence of easily assimilable carbon and sufficient nutrients (typical Phosphor and
Nitrogen containing sources) biological growth will occur as a biofilm on all kind of
surfaces. Excessive biological growth will result in biofouling: accumulation of biomass
on a surface by growth and/or deposition to a level causing operational problems
(Vrouwenvelder, 2001).
Water Practice & Technology Vol 5 No 2 © IWA Publishing 2010 doi: 10.2166/WPT.2010.042
Controlling Biofouling in membrane filtration systems
Based on the above considerations, controlling biofouling is considered to be the major
challenge when operating a membrane filtration installation. There are different options
to control biofouling in membrane filtration installations.
An option often applied for industrial membrane applications is curative; the
biofouling is removed by chemical cleanings via the Cleaning In Place (CIP) method. In
industrial membrane applications with little biofouling the CIP is applied as generic
cleaning method typically once each or every second month. The CIP systems for
industrial membrane applications are commonly designed for this usage frequency and
not fully automated. In installations with severe biofouling a significantly increased CIP
frequency is required (e.g. twice a week). On sites with multiple RO trains this is not a
practical solution for the operational staff.
Another option is the prevention of the biofouling. This can be achieved by
preventing the growth by removal of the nutrients and easily assimilable carbon in an
extensive pre-treatment system or by inhibiting the growth by the use of (biocidal)
chemicals. Usable pre-treatment processes to reduce the biofouling are processes that
reduce the compounds that micro organisms need to grow on. As a result the biofouling
in the adjacent membrane system is strongly reduced. Examples of these pre-treatment
processes are:
• Flocculation/coagulation/sedimentation and filtration
• (Biological) activated carbon filtration
• Denutritor technology (Jansen, 2007)
• Scavenging with ion exchange resins
In many recent RO installations the pre-treatment contains an Ultrafiltration system.
This pre-treatment is very effective in removal of particles, suspended matter and
colloids, but not sufficient to remove low molecular NOM or ammonium and thus not
sufficient to prevent biofouling growth in piping, storage tanks and downstream RO
system.
The use of chemicals to control biofouling can be based on either the principle to
prevent or limit the growth of micro organism with non oxidising chemicals or by
destroying the biofouling with weak oxidizing agents. In general the application of
strong oxidants is not recommended because of the poor chemical resistance of the
reverse osmosis membranes for those chemicals. However, under specific conditions
some of these chemicals can be applied. Possible chemicals or combinations of
chemicals to control biofouling are:
non oxidizing:
•
DBNPA (2,2-dibromo-3-nitrilopropionamide)
•
Isothiazolones
•
Sodium bisulphite (reducing)
mildly oxidizing:
•
Monochloramines
strong oxidizing:
•
Peracetic acid (PAA) and hydrogen peroxide
•
Chlorine dioxide
•
Hydrogen peroxide silver blend
2
PERACETIC ACID
Peracetic acid is an unstable molecule formed by the reaction of acetic acid with
hydrogen peroxide at a low pH.
CH3COOH + H2O2 ÅÆ CH3COOOH + H2O
The oxidation potential of PAA (1.81 eV) lies between ozone (2.07 eV) and chlorine
dioxide (1.57) (OMRI, 2008). The oxidative effect is besides the oxidation potential
dependent on the applied concentration, the dissociation state (pH dependent),
temperature and (cumulative) contact time. Although PAA has a considerable oxidation
potential and herewith the potential to degrade the RO membrane, in the recommended
concentrations and environment it is expected to be insufficient to attack most
polyamide thin-film RO membranes. This expectation is based on the allowance stated
by the membrane manufacturers for the use of PAA at certain concentrations and under
certain conditions, as shown in Table 1.
Table 1: Guidelines for the use of peracetic acid or hydrogen peroxide
Maximum concentrations
DOW Technical
Manual 2005
0.2% H2O2
Hydranautics
TSB110.08 2006
<0.2% H2O2 + PAA
Maximum temperature
Compatibility
<25°C
0.5%, 96 h
<25°C
Other mentioned aspects
remove Fe
CSM Technical
Manual 2006
0.2% H2O2 +
400 mg/l PAA
<25°C
no transition metals transition metals can
(Fe, Mn) in feed
cause damage
water
The PAA used in the experiments described in this article is the commercially
available product Divosan Activ (JohnsonDiversey), this is a stabilised mixture of
hydrogen peroxide, acetic acid and peracetic acid.
PAA based products are used since decades in Food & Beverage and Laundry
applications as halogen free oxidiser, bleaching agent and/or disinfectant. In many
applications it is used as an alternative to hypochlorite. The PAA based product used in
the tests described in this paper is used over many years in Dairy (RO) membrane
filtration plants in case disinfection is required. Advantage of PAA based products in
industrial RO membrane filtration systems is the effectiveness and rapid action at low to
moderate temperatures (5 – 40 ºC), the very good rinsability, and the effectiveness in
systems with some (mineral or organic) fouling.
To minimise potential impact on the membranes and operation costs, intermittent
dosage is an interesting concept compared to the continuous application of a biofouling
control agent. This also allows to apply a different water source during the application.
Recently the improved effectiveness of the intermittent application of biocides
(in general) versus continuous application has been reported by a model study
(Szomolay, 2006).
PAA based products need to be handled with care by trained staff only. Operational
safety is to be ensured by using the proper chemical storage, handling and dosing
systems. The application has to be applied according the valid local legislation. As of
the degassing nature of PAA, low dosages and long dosing idle periods, operational
reliability requires the usage of a suitable dosing system. PAA is a halogen free
oxidiser, this prevents the formation of halogenated organic compounds or trihalogen
compounds (THC) as with halogen comprising oxidation agents. PAA will break down
3
via acetic acid and hydrogen peroxide to the environmentally safe and natural
compounds carbon dioxide, oxygen and water.
In general, oxidative agents used for cleaning polyamide RO membranes can cause
oxidative membrane degradation. Membrane manufacturers give guidelines for the use
of these chemicals. In table 1 the guidelines of the manufacturers of the membranes
used in the described experiments are given.
The guidelines of these manufacturers are almost the same. The DOW Technical
manual mentions only H2O2, Hydranautics only the mixture with PAA (without exact
concentration) and CSM the complete mixture with concentrations. Temperature, pH
and the presence of transition metals are critical aspects when using PAA. Therefore
measures should be taken to prevent transition metals, more specifically manganese and
iron, presence during the application of PAA on polymeric RO membranes. The
concentrations of H2O2 used in the described experiments are 25-50 times lower than
the guidelines in table 1. The described experiments are all executed with Divosan Activ
with a ratio PAA: H2O2 being 5.5:24. Usage of products with a different PAA: H2O2
ratio can influence the results.
OPERATIONAL EXPERIENCES IN INDUSTRIAL RO PLANTS
Evides Industriewater owns and operates a number of industrial membrane filtration
plants, that have (had) problems with biofouling. Implementing an additional pretreatment in the existing plants to prevent the biofouling would require large
investments and retrofits of the plants. Therefore Evides Industriewater decided to
research the control of biofouling by the application of chemicals. For the same reason
WLN and Bètawater, a subsidiary company for industry water of N.V.
Waterleidingmaatschappij Drenthe (WMD) investigated this subject. The experiments
with PAA (Divosan Active) were tested in cooperation with JohnsonDiversey, the
supplier of this product. Tests were carried out during the normal operation of the
membrane filtration plants.
Demin water plant Baanhoek
At the industrial water plant Baanhoek surface water (Biesboschwater) is treated with
ultrafiltration – antiscalant dosing – reverse osmosis – degasifier – mixed bed ion
exchange to demin water. Membranes in this plant are from Dow FilmTec. Due to
biofouling the RO systems had to be chemically cleaned once a week in summer time,
resulting in a stressed operation of the plant. To control biofouling the following
chemicals have been tested:
• Intermittent dosage of peracetic acid /hydrogen peroxide
• Off line dosage of chlorine dioxide
• Off line shock treatment with sodium bisulphite
In this paper only the results of the test with PAA are illustrated.
The feed water for the RO is ultrafiltrated surface water from the Biesbosch
reservoirs. Before the UF 0.5 mg/l Fe is dosed as flocculant, but the removal of this iron
is very good. (Table 2) Just before the RO 3 mg/l antiscalant (Permatreat 191T) is
dosed. This antiscalant prevents also iron fouling on the membrane. Normally the CIP
frequency in winter and early spring is low. In April the pressure drop of the 1st stage
RO membranes starts to increase, resulting in a higher cleaning frequency. The
intermittent dosage of PAA was started early April 2006 just after a CIP of the RO
trains.
4
Table 2: Water quality feed water RO
Temperature (°C)
Iron (mg/L)
TOC (mg/L C)
pH
Min
3.0
<0.005
3.0
Avg
13
0.005
3.3
7.5
Max
24
0.016
3.5
Tests were performed on one line and another line was operated under normal
condition to compare the efficiency. The PAA was dosed inline before the cartridge
filters in a concentration of 10-15 mg/l for 5 min every 3 hours. There was almost no
consumption of PAA during passage of the RO-modules. The concentration of PAA in
the permeate was less than in de concentrate but still about 10 mg/l was found in the
permeate.
The results are shown in figure 1. The normalized pressure drop of the RO train
without the dosage of PAA (blue dots) starts to increase and therefore requiring
chemical cleanings. With warmer feed water in early summer the pressure drop
increases more rapidly. The pressure drop of the RO train with the PAA dosage (red
dots) remains low.
4.5
Normalized Pressure Drop [bar]
4.0
Dosage stopped
June 21, 2006
RO without Peracetic acid
RO with Peracetic acid
3.5
3.0
2.5
2.0
1.5
1.0
0.5
6/
30
/2
00
6
6/
20
/2
00
6
6/
10
/2
00
6
5/
31
/2
00
6
5/
21
/2
00
6
5/
11
/2
00
6
5/
1/
20
06
4/
21
/2
00
6
4/
11
/2
00
6
4/
1/
20
06
0.0
Date
Figure 1: Efficiency of peracetic acid/hydrogen peroxide on biofouling control
The normalized pressure drop is calculated as follows:
NPD = Tcf x Qcf x dP
where
Tcf = (viscosity at T=25°C/viscosity at T=T)^N
Qcf= (Q ref/Qavg)^M
Tcf = Temperature correction factor
Qcf = Flow correction factor
Qref= Reference flow
dP= differential pressure (Pconcentrate –Pfeed)
M and N are membrane specific parameters
5
June 21, 2006 the intermittent dosage of peracetic acid/hydrogen peroxide had to be
stopped due to a permeate quality problem. In the period thereafter the pressure drop of
that RO system also started to increase rapidly with the same rate as the other unit. In
the two and a half months period the RO system without the application of PAA had to
be cleaned 9 times, while the train with PAA did not require any cleaning. Also the
cartridge filters of the RO without PAA had to be changed several times per month
while the system with PAA didn’t need replacements. During the dosage of PAA the
normalized salt passage (NSP) dropped slightly as can be seen in Figure 2. The decline
of the NSP indicates that there was no degradation of the RO membrane during this
experiment.
NSP RO with PAA
4,0
Dosage stopped
June 21, 2006
3,5
Normalized Salt Passage [%]
3,0
2,5
2,0
1,5
1,0
0,5
Date
Figure 2: Normalized Salt Passage RO with PAA
The normalized salt passage is calculated as follows:
NSP = ECpas x Tcf,sp x Qcf,sp
ECpas = 100 x ECp /(ECf x ln(1/(1-R/100))/(R/100))
Tcf,sp = e^(U x (1/(Tf + 273,15)-1/(273,15+25°C))
R =100 x Qp/Qf
Qcf,sp = Qp/Qp,ref
where
ECpas = passage of electrical conductivity
ECp = electrical conductivity permeate
ECf = electrical conductivity feed water
Tcf,sp = temperature correction factor for the salt passage
Tf = temperature feed water
U = membrane specific parameter
Qcf,sp = flow correction factor for the salt passage
Qp = flow permeate
Qf = flow feed water
Qp,ref = reference flow permeate
R = recovery
6
710
-2
00
6
630
-2
00
6
20
06
620
-
610
-2
00
6
531
-2
00
6
521
-2
00
6
511
-2
00
6
5120
06
20
06
421
-
411
-2
00
6
4120
06
0,0
Demin water plant Sas van Gent
The raw water source for the plant in Sas van Gent is effluent from an industrial waste
water treatment plant at a starch producing plant. The treatment consists of an inline
flocculation with iron, dual media filtration, ultrafiltration, antiscalant dosing, first pass
RO system, degasifiers and a second pass RO system. In times when the effluent water
can not be used due to quality issues drinking water is used as feed water for the RO.
The water treatment plant produces demineralised water for the starch producing plant.
Initially (December 2006 – February 2007) the dosing of PAA was done at one RO
system (RO1A) on already fouled ESPA2 membranes (from Hydranautics) with a very
high pressure drop. The other RO, with the same fouled membranes, was kept as a
reference. The dosage was 18 mg/l inline for 5 minutes every 3 to 6 hours with the
permeate to waste. In a month time the normalized pressure drop (NPD) of the ROsystem (1st array) with PAA dosing was down by 0.4 bar while the NPD of the reference
system was up by 0.5 bar. Meanwhile the mass transfer coefficient (MTC) and NSP did
not change in either system. Due to these promising results after two months a PAA
dosing was started on the other RO line too. In the following months the pressure drop
could not be kept stable (also not with an increased dosing frequency of every 4 hours)
and in June/July 2007 membranes for both RO lines were replaced by new membranes:
Dow FilmTec for RO1A and Saehan membranes for RO1B.
Table 3: Water quality feed water RO (when effluent is used)
Temperature (°C)
Iron (mg/L)
TOC (mg/L C)
pH
Min
25
0.05
15
Avg
30
0.16
20
7.2
Max
35
0.32
25
When effluent is used as source water the temperature is high and also the iron
concentration (permeate of the UF-system) is high due to colloidal particles not held
back by the UF-system. The required antiscalant level for water with, - besides ionic
iron -, also colloidal iron is unclear and can be a cause for iron deposit formation on the
membranes. These are two risk factors for damaging the membranes. For minimising
this risk the dosing frequency was lowered to every 6 hours and from November 2007
to every 24 hours with effluent and no dosing with drinking water. Also the dosage was
adjusted to obtain a concentration of 1-2 mg/l of PAA in the concentrate after the 1st
array. The alternative for preventing the iron risk is to dose the PAA in a flush with
demin water. Technically this was more difficult to establish and this would result in
more water loss and downtime of the system. Furthermore it would still be possible that
colloidal iron deposit is present on the membrane surface. This can be removed only
periodically with a proper CIP and can not be prevented by applying an antiscalant.
Figure 3 shows that the NPD is kept stable for the whole period of dosing (more
than 8 months) with about every 6 weeks a preventive CIP. In November 2007 an
evaluation was made of the first dosing period. At that time it became clear that there
was a steady increase in NSP (figure 4). The yellow line is the temperature and an
indicator for the type of water source: above 22°C it is effluent else it is drinking water.
Then, the dosing frequency was lowered strongly. But as the graph shows, even in the
period of decreased dosing frequency the NSP looks to increase further. Only after
stopping the dosage the NSP seems to stabilize or even slightly to decrease.
7
NPD (Normalised Pressure Drop) RO1B
NPD array 1
NPD array 2
CIP
Temperature
Saehane RE 8040FE (7-25-2007)
4,00
dosing every 24 h (effluent); no
dosing on drinking water
dosing every 6 h (effluent and
drinking water
40
35
Normalised Pressure Drop [Bar]
25
20
2,00
15
Temperature (°C)
30
3,00
10
1,00
5
0
716
-2
00
8
527
-2
00
8
-2
00
8
47
217
-2
00
8
12
-2
920
07
11
-9
-2
00
7
920
-2
00
7
81
-2
00
7
0,00
Date
Figure 3: Normalized pressure drop RO1B demin water plant Sas van Gent
NSP (Normalised Salt Passage) RO1B
Saehane RE 8040FE
CIP
2,00
20
1,50
15
1,00
10
0,50
5
0,00
0
716
-2
00
8
25
527
-2
00
8
2,50
4720
08
30
217
-2
00
8
3,00
12
-2
920
07
35
11
-9
-2
00
7
3,50
920
-2
00
7
40
Temperature (°C)
Temperature
4,00
8120
07
Normalised Salt Passage [%]
EGV passage
dosing every 24 h (effluent); no
dosing on drinking water
dosing every 6 h (effluent and
drinking water
Date
Figure 4: Normalized Salt Passage RO1B demin water plant Sas van Gent
The other RO line with Dow FilmTec membranes operated under the same conditions
showed similar results. This increase of the NSP seems to be the result of the
degradation of the RO membrane due to the combination of dosing PAA, relatively high
temperature of the water and the presence of iron in the feedwater.
In April 2008 the dosing of PAA was ended because of the risk of too high salt
passage. Now a periodic (once every 1-2 days) conservation with sodium bisulphite is
applied with a concentration of 0.9%.
8
Demin water plant Klazienaveen
At the site in Klazienaveen (in the province of Drenthe, The Netherlands) boiler feed
water is produced from surface water with ultrafiltration and reverse osmosis (with
antiscalant dose). Since the surface water contains high levels of organic matter a
coagulation with poly aluminium chloride (PAC) and continuous sand filtration is used
as pre-treatment. Experiments with PAA and DBNPA carried out on this plant were
technologically supported by WLN and financially by InnoWATER (a Dutch subsidy
scheme for innovative water technology). In this paper only the results of the test with
PAA are illustrated.
Table 4: Water quality feed water RO
Temperature (°C)
Iron (mg/L)
Manganese (mg/L)
DOC (mg/L C)
pH
Min
1.0
< 0.005
< 0.005
3.0
Avg
12
0.018
0.12
8.1
6.8
Max
25
0.13
0.34
14.2
The RO system consists of 3 lines (RO1, RO2 and RO3); RO1 contains
Hydranautics ESPA2-membranes, intensively used since 2004; RO2 new ESPA2membranes (March 2007) and RO3 new Trisep LF membranes (March 2007).
The dosage of PAA was only applied to RO1. The dosage took place in the period
from 30th May till 13th November 2007 and as from April 2008. Historically, only
during this period with a higher feed water temperature biofouling occurs. Before the
start of the experiment the feed piping is internally hydraulically cleaned and also the
RO membranes were intensively cleaned by CIP to remove any transition metals from
the membranes in case these would be present as surface foulant. PAA was dosed
during 5 minutes in RO-permeate during a flush (total flush time: 15 minutes). RO
permeate is used to ensure transition metal free water. At normal operation the
antiscalant is used to avoid any new deposits from transition metals. During 2007
10 mg/l PAA (first few weeks 5 mg/l) was dosed every 3 to 4 hours. In April 2008 the
dosing of PAA was started again, now with a six hours interval. Since the beginning of
July 2008 the dosing frequency is further reduced to three times a day.
In figure 5 the normalized pressure drop is shown for the 3 different RO-lines. The
purple line is from RO1 with the PAA-dosing, the brown line is from RO2 and the
green line from RO3. As can be seen the purple line is stable in time.
Since the experiment on RO1 started (May 2007) until July 2008, RO1 has been cleaned
4 times preventively whereas the reference (RO2) had to be cleaned 14 times (together
with replacements of cartridge filters) curatively due to the increased NPD.
Figure 6 shows that the NSP of the 1st stage of RO1 (purple line) is stable during the
period of dosing (June-October 2007 and since April 2008). The reference RO2 (brown
line) is slightly decreasing probably due to fouling of the membranes. No negative
effect has been observed on the salt passage using this dosing protocol on these
membranes. In the first weeks of dosing PAA (5 mg/l) there was no residual PAA found
after the cartridge filter. However even then there was a positive effect on the
development of the NPD. The benefits of the PAA usage in this experiment (1 RO line
over a period of 14-15 months) are the saving of cartridge filters, 20 man-days (often
unplanned and during holiday season) to execute RO CIP cleanings, less usage of CIP
chemicals and waste, energy saving as of reduced operational pressure and possibly
longer life time of the membranes (as a result of little to none biofouling growth and
9
less chemical cleaning). Dosing during a flush with RO-permeate has a small
disadvantage as well, that is loss of product and production time. In general it resulted
in a far more stable and thus better manageable process.
Figure 5: Normalized pressure drop first stage RO’s Klazienaveen
NSP (Normalised Salt Passage) 1st stages RO 1, 2 en 3
4
No PAA dosing PAA
Dosing PAA on RO 1; every 3 - 4 h
No PAA dosing PAA
Dosing PAA on RO 1; every 6 - 8 h
3.5
3
EC passage [%]
2.5
2
1.5
1
0.5
0
Mar-07
May-07
Jul-07
Sep-07
Nov-07
Jan-08
Mar-08
Date
Tref: 20 °C
RO1 1e trap
RO2 1e trap
Figure 6: Normalized Salt Passage first stage RO’s Klazienaveen
10
RO3 1e trap
May-08
Jul-08
The positive results have led to the extension of this experiment this year (2008)
with a lower frequency of once every 6 to 8 hours. The results are obtained with 3 year
old membranes and a point of research is the effect (salt passage) on new membranes
after an initial period of operation without the usage of PAA to allow to rinse out any
residual (production) material.
The results of these three cases show that the use of PAA for biofouling control is
possible (without negative side effects) under specific conditions. The increase of the
NSP at the Sas van Gent plant can be the result of the high temperature in combination
with the iron present in the feedwater (and maybe also on the membranes). These are
also the restrictions made by the membrane manufacturers (see table 1) for using PAA.
It seems that these restrictions also have to be applied when using PAA in a periodic
inline dosing at a low concentration.
CONCLUSIONS
The following conclusions can be drawn.
• periodic (intermittent) inline dosing of low concentration of PAA (Divosan Active)
appeared to be very effective in preventing biofouling of RO membranes
• part of the PAA (and H2O2) will be found in the permeate when the RO is online
during dosage and possible restrictions regarding to following treatment steps or
application of the demin water have to be taken into account
• inline dosage of PAA on iron containing water (0.2 mg/l) with a temperature of
about 30°C on new membranes can result in an increased salt passage within a few
months
• the damaging effect of the presence of iron (and/or manganese) can be effectively
minimized by a proper and regularly executed preventive RO cleaning scheme,
dosing the PAA in a flush with demin water and applying an antiscalant as required
by the water specifications.
References
CSM Technical Manual (2006), 91,11.
Dow Liquid Separations FilmTec Reverse Osmosis Membranes technical manual (2005),
133-134.
Hydranautics Technical Service Bulletin (2006) TSB110.08, 4.
Jansen, A.E. (2007) Tecnología de tratamiento del agua en procesos industriales. Expo Agua,
Buenos Aires, Argentina.
Khedr, M. (2000) Membrane fouling problems in reverse-osmosis desalination applications.
Desalination and Water Reuse Quarterly Volume 10/ no. 3, 8–17.
OMRI (2000), Peracetic Acid, NOSB TAP Materials Database Compiled by OMRI,
www.omri.org/peracetic_acid3.pdf (accessed 11 July 08)
Szomolay, B. (2006), “Analysis and control of a biofilm disinfection model”, Dissertation,
Montana State University, Bozeman, Montana
Vrouwenvelder, J.S. and Kooij, D. van der (2001) Diagnosis, prediction and prevention of
biofouling in NF and RO membranes. Desalination 139, 65-71.
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