Boron is a chemical element commonly found in the environment in compounds called borates. It is difficult to remove boron from seawater using reverse osmosis (RO) due to its uncharged and nonpolar nature. Multiple configurations can be used to effectively remove boron including double-pass RO systems, single-pass RO combined with ion exchange resins, and multistage RO systems sometimes incorporating ion exchange or acidification steps. The specific configuration used depends on factors like feed water chemistry and the desired permeate quality.

2. Boron
 Boron is a chemical element with
symbol B and atomic number 5.
Boron, an inorganic compound, is
a non-volatile metalloid that is
ubiquitous in the environment in
compounds called borates.
Common borates include boron
oxide, boric acid, and borax.


3. Boron properties

4. Boron properties

5. Boron properties

6. Boron properties

7. Natural weathering processes are largely
responsible for the presence of boron in seawater.
Also, boron can be found naturally in ground water,
but its presence in surface water is a consequence
of the discharge of treated sewage effluent, in
which arises from use in some detergents, to
surface waters.
Boron Sources

8. Anthropogenic Sources
 Glass and ceramics and porcelain,
 detergents and soaps , cosmetics, bleaching agents
 coal burning power plants
 Insecticides
 High-hardness and abrasive compounds
 Shielding in nuclear reactors
 Pharmaceutical and biological applications
 fire retardants, glazes and agricultural products
 food preservatives

10.  For humans boron can represent reproductive
dangers and has suspected teratogenetic properties.
 A major limiting factor is the possible damage to plants
and crops. Excess boron also reduces fruit yield and
induces premature ripening on other species such as
kiwi
two predominant reasons for
limiting boron in water:

11.  Intakes of more than 0.5 grams per day for 50 days cause
minor digestive and Boron toxicity symptoms in humans
include diarrhea, nausea, vomiting, lethargy, dermatitis,
poor appetite, weight loss, and decreased sexual activity
Health issues and toxicity

12.  In seawater sources, the typical boron concentration in
the raw water is in the range of 4.6 mg/l while in confined
ocean bodies boron concentration can deviate
substantially from this average value, for example, boron
concentration in the Mediterranean Sea can be as high
as 9.6 mg/l Depending on location and seasonal effects,
the boron concentration can exceed 7 mg/l, e. g. in the
persian Gulf
Boron

14. Boron removal processes

15. Unlike most of the elements in seawater, boron is not ionized (i.e. it
has no charge)
Boron takes two forms in drinking water (or seawater):
Boric Acid: H3BO3
Borate Ion: H3BO2-
RO is much better at removing charged ions. Hence the removal of
borate ion is much better than the removal of boric acid.The dominant
form (borate or boric acid) depends on the pH:H3BO3=H++H3BO2-
Why is Boron Hard to Remove?

16. Boric acid is uncharged and has trigonal structure.
Therefore, boric acid is nonpolar, which causes it to
interact very differently with membrane materials relative
to charged salt ions and polar water molecules. RO
membranes that permit high boron rejection along with
high salt rejection and high water permeation might be
manufactured through careful consideration of physical
structure and chemical composition.
Why is Boron Hard to Remove?

17.  .

18. RO
 RO processes have been
widely used for seawater
desalination. Despite high
removal (>99%) of other
ionic species from seawater,
the removal of boron by RO
has proven challenging.
Due to the recent
improvement of membrane
performance, seawater RO
(SWRO) membranes, which
achieve up to 95% rejection
of boron in the
manufacturer’s testing
condition, have been
commercialized.

19.  It is difficult for a single-stage RO process to
achieve an average rejection over 90% and to
produce permeate that meets the provisional WHO
boron guideline.
RO

20.  Generally, the rejection of boron has been lower than
90% and has been reported to be as low as 40% with
low-pressure brackish water RO membranes.
 Previous studies have shown that boron rejection by
RO membranes improves as pH increases (i.e., as
major species shift toward increasingly deprotonated
forms), as operating temperature decreases, and as
transmembrane pressure increases
RO

21. Chemistry of boron
 Boron is usually present in water
as boric acid, a weak acid which
dissociates according to:In the
usual pH operating range of
reverse osmosis elements, Eq.
(1) is the one with the highest
importance. We thus have a
presence of both dissociated and
non-dissociated boric acid
 species in the water


22.  There are several methods applied in seawater
desalination and they can also be implemented for
removal of boron
 1. Use of improved RO membranes with higher B-
rejection
 2. Increasing the pH of the water to be treated by
caustic soda (or other base) prior to RO membrane,
and reacidifying the treated water after the membrane
to bring it to the desired acidity
 3. Passing the desalinated water through two extra
passages of RO treatment
 4. Adding an electrodialysis stage after RO treatment
 5. decreasing the tempreture
AMENDMENT

24. 
 3233 BOHHBOH
Not
rejected
Well
rejected

27.  ln practice, RO seawater desalination consist of
two or more passes with natural pH (pH 6 to 7)
at the first pass and elevated pH up to 11 at the
second pass to effectively remove boron to
acceptable levels (usually less than 0.5 mg/L)
Boron Removal

28.  Furthermore, already at pH higher than 9, calcium
carbonate (CaCO3) and magnesium hydroxide
(Mg(OH)2) salts can crystallize on the membrane surface,
leading to fouling problems. For these reasons, several
RO desalination plants have been designed with more
stages in series operating at different pH values. In order
to obtain boron concentrations 0.4 ppm often boron
selective resins are coupled to the RO units
Solve Problem!

29.  Single-Pass RO System
 Double-Pass RO System
 Single-Pass RO with Boron Specific Ion Exchange Resin
 Multistage RO Systems
Configurations of different process
options for boron removal.

30.  For the treatment of seawaters, a typical single-pass process
would operate at a recovery from 40 to 50% and a permeate
flux of 7 to 9 gfd (12 to 15 L/m2-hr).Typical feed pH for these
systems ranges from 6.0 to7.5 (acidified) or 7.8 to 8.2. Under
these conditions, the single-pass SWRO membrane unit
generally produced permeate with salinity within the potable
limits (i.e., less than 500 mg/L TDS) from the simulation data.
However, boron concentrations in the permeate were likely to
be much higher than 0.5 mg/L.
Single-Pass RO System

31.  the rejection of boron in a single-pass configuration
can be significantly enhanced by increasing the
feed pH. Figure (b) shows a single-pass RO
process with feed pH adjustment. In this
configuration, an antiscalant must be used if the pH
is increased above 9.5.
Single-Pass RO System

32.  The double-pass process typically consists of a leading SWRO
unit (RO1) operating at a recovery of 40 to 50% followed by a
brackish RO unit (RO2) operating at a recovery of 85 to 90%.
Since the feed to the RO2 process is the RO1 permeate (i.e.,
RO2 feed has low salinity), the RO2 unit operates at a
relatively high flux (typically 20 gfd). Therefore, the number of
elements required in the RO2 unit would be relatively small,
thereby lowering marginal capital costs.
Double-Pass RO System

33. Capacity: 136,000m3/d
Membrane Type
1st Pass: TM820H-400B
2nd Pass: TM720-430
Boron regulation : <0.5mg/l
Recovery Rate
1st Pass: 45%,
2nd Pass: 90%,
Pass 1
Permeate
Tank
Post
Treatment
Energy Recovery
(DWEER : Calder)
Pass 1 : SWRO
Recovery : 45%
Pass 2 : BWRO
Recovery : 90%
pH : 10.0 – 10.4
RO Feed
Water
Tank
Bypass
Scale
inhibitor
NaOH
RO section Detail
Low Pressure
Pump (VFD)
High Pressure
Pump
Booster
Pump (VFD)
Low Pressure
Pump
2-pass system with alkaline dosing is applied for Boron removal
High Boron Rejection Seawater
Desalination Plant in Singapore

34.  does not require a pH adjustment of the RO permeate.
Recovery rates for ion exchange systems are typically
very high (~98%). However, O&M costs of ion exchange
systems tend to be high due to the expense of specialty
resins required for removing boron and the need for resin
regeneration.. For the cost analysis, it was assumed that
the ion exchange unit treated 16% of RO permeate.
Single-Pass RO with Boron
Specific Ion Exchange Resin

36. Dual-Pass RO with Boron Specific
Ion Exchange Resin

37.  the low recovery and scale formation potential problems
associated with double-pass systems might be effectively
avoided by multistage configurations without requiring the costly
ion exchange process. In both configurations, additional RO units
are employed to further treat the concentrate produced from the
second pass RO unit. in figure 5.1-(e), the concentrate from the
second-pass RO is treated by an ion exchange softening
process to remove divalent cations. The effluent from the
softener is further treated by RO (RO3). Since there is little
calcium and magnesium present in the effluent from the softener,
risk of scale formation in the RO3 unit is minimal, regardless of
pH. In addition, the concentrate from the RO3 unit is essentially
a pure NaCl solution.
Multistage RO Systems

38. In this configuration, the concentrate from the second pass RO
(RO2) is directly treated with another RO unit (RO3). To
prevent scale formation, pH of the RO2 concentrate is reduced
by acidification, prior to processing by the RO3 unit. The
permeate from RO3, which has a very low concentration of
divalent cations, is further processed with an additional RO unit
(RO4) at an elevated pH.
Multistage RO Systems

39. Estimated water production cost for each
configuration.

40. Feed water: pH, temperature, TDS
Membrane element: membrane chemistry, element
efficiency
 System design and operation: average permeate
flux (APF), system recovery, concentration
polarization, cleanings
FACTORS INFLUENCING BORON REJECTION

41.  . In the case of seawater desalination by reverse
osmosis, (RO) the boron rejection is usually
insufficient to obtain desalinated water (RO
permeate) that can meet drinking water quality
requirements.
 Multi-step RO systems or RO-IE (ionic exchange)
combinations are then applied.
Conclusions

42.  Surface analyses showed that all membranes
tested had a negative surface charge and a ridge
and valley structure. The negative charge of the
membrane played an important role in boron
removal, since charge repulsion is one of the
important mechanisms of boron rejection..
Conclusions