Pretreatments
Demineralisers. Critical issue: contamination of membranes
Membranes, Getting dirty and obturation
Biological
Organic
Inorganic
Incrustation
Bacteria
Hydrocarbon
Silica
Calcium carbonate,
Fungus and yeast
Humic acids and
fulvics
Clays
Magnesium carbonate,
Aluminium
Calcium phosphate,
Iron
Magnesium phosphate
Manganese
Barium or Calcium
phosphate
Polymer extracellular
Cationic
Polielectrolite
Calcium fluoride
Disinfection or
Bacteriostatic
Active carbon
absorption
Different
previous filters
Antiscalant or
Water softener
Prevention or process delay
Water Treatment Division
Pretreatments
Demineralisers. Critical issue: contamination of membranes
The membranes are contaminated by several causes:
Collodial Material
Iron
Compaction
Chemical oxidation
damage
Biological Pollution
Scaling by silica
Biological
Pollution
Excess pressure
damage
Water Treatment Division
Pretreatments
Demineralisers. Pretreatments to remove Chlorine
Chlorine remover
Chlorine changes the membrane properties, allowing the salts to
pass through the membranes easily, therefore chlorine must be
removed before the RO treatment.
The filtering material is coconut shell carbon, with a particle size
distribution of 1,2-2,5 mm. Chlorine with carbon leads to a
chemical reaction producing CO2 (carbon dioxide) and chloride,
both don’t damage the membrane. At the backwash stage, the
particles settled in the filtering material are removed, and the
carbon layer is rearranged (since the water goes through it)
compressing the material and creating preferential channels that
decreases the surface contact area between water and carbon.
The active carbon must be replaced within 12-24 months. In
addition to the consumption due to the chlorine removal reaction,
the continued water flow with salts will lead to a decreased
contact area due to the formation of scales on the carbon
surface, delaying the chlorine removal process.
Water Treatment Division
Pretreatments
Demineralisers. Examples of contamination of the membranes
Iron
Water Treatment Division
Pretreatments
Demineraliser. Pretreatment to remove Iron
Iron remover
The iron in water is usually found as Fe(II), highly soluble and not
capable of being filtered.
Iron, as Fe(II), is not a problem for the membrane task,
nevertheless, after its oxidation (due to the oxygen contact, or
after being chlorinated) changes to Fe(III) form that is a solid in
suspension, it will plug the mesh spacer and the membrane will
get dirty.
The iron removal treatment lies in transforming the Fe(II) into
Fe(III) form and its filtration. When Fe(II) has contact with the
BIRM (manganese dioxide) it becomes oxidized, turning into
Fe(III). Under this form the iron is not soluble, forming a
granulated that can be sieved.
In order to make this possible, the water must have a pH between
7 and 8,5, in addition to an oxygen concentration higher than 15%
in relation to the iron or manganese concentration.
We should take into account these premises at the start up stage,
so if they are not fulfilled, it will be compulsory to check with our
Central SAT.
Water Treatment Division
Pretreatments
Demineralisers. Examples of contamination of the membranes
Solids in suspension
Water Treatment Division
Pretreatments
Demineraliser. Pretreatments to remove solids in suspension
Silex Filter – Anthracite
Solids in suspension. The solid presents a low inertia in its capacity of
flotation/decantation, remaining suspended. It is normal not to distinguish the
particles individually if their sizes are about the micrometer magnitude. The
smallest particles (0,2-1 microns) are named as colloidal particles or colloids.
It is needed to eliminate the solids in suspension, which plugged the mesh
spacer. The silex is silica sand, similar to beach sand, but with a particle size
distribution of 0,7-1,3 mm. The anthracite is a heavy mineral carbon, with a
particle size of 1,2-2,5 mm. We take materials with different densities in order to
increase the filtration capacity and its quality.
The backwash is used as cleaning method, causing a mechanical rub. This rub
releases and removes the filtered particles. The three materials, contained in the
filter, are mixed after the backwash, coming apart again in the right order due to
the density difference, just as it appears in the drawing.
Water Treatment Division
Pretreatments
Demineralisers. Examples of contamination of the membranes
Organic material
Water Treatment Division
Pretreatments
Demineraliser. Pretreatments to remove the Organic Material
Organic Material filter
Organic material: All substance or molecule containing carbon (except
carbonates). The carbon is in any molecule that belongs or was a part of
a living creature.
The organic material plugs the membrane, blocking it, and therefore
decreasing its efficiency.
The filtering material has the same characteristics as in the chlorine
remover.
The organic material, in contact with the carbon, sticks to the granulate
due to molecular attraction forces.
We have to take into account that both the organic material filter and the
chlorine remover, are units that enhance the bacterium growth, because
the carbon granulates offer a wide contact surface with the water due to
its “spongy” form, therefore we should control the likely bacteriological
contamination.
If we have chlorine and organic material in the same water, IT WILL
NOT BE NECESSARY to install a chlorine remover and an organic
material filter, just placing the organic material filter will be enough (not
the chlorine remover).
Water Treatment Division
Pretreatments
Demineralisers. Examples of contamination of the membranes
Biofilm
Water Treatment Division
Pretreatments
Demineraliser. Pretreatments to remove the Biofilm
The microorganisms (bacterium) can survive inside the water pipes of the equipments, excreting a
jelly film (biofilm) that can block the membranes. To avoid this problem, we have two methods
available, both exclusive among them.
Bisulfite
The product is sodium bisulfite. The solution to inject is prepared at a
maximum concentration of 10 g/l.
It is dosed diluted in water, and after a period of 3-4 weeks, the content of
the feeder drum must be renewed, even if the volume prepared is not yet
finished, therefore the quantity of product to be prepared must be
calculated.
The control of the dosage pump is included in the electric panel of the
demineraliser, in this way it will be dosed automatically in the water flow,
before the demineraliser inlet.
Water Treatment Division
Pretreatments
Demineraliser. Pretreatments to remove the Biofilm
Biocide
It is an organo-bromine compound (Genesol-30) with a wide bactericidal
range (aerobic & anaerobic), suitable for all kind of membranes. It is
acid and causes a partial dilution and the drag of the biofilm that could
be settled in the membrane.
A 400 ppm concentration must be added for 20-30 minutes once a
week. The dosage is done by the automatic program, starting the pump
after one week and there is water demand. The product is corrosive and
is NOT suitable for food applications.
Water Treatment Division
Pretreatments
Biocide vs Bisulfite
Biocide (Mod. 4069200)
Bisulfite (Mod. 4044000)
Consumible: Product available in 5 l drum , more expensive (Mod.
52418 228 €)
Consumible: Product available in 25 l drum (Mod. 5241700 53 €)
Cost of optionals: Cheaper optional doser: pump, support to the
demineraliser or wall mounted and level sensor for the drum (Mod.
4069200 425€)
Cost of optionals: More expensive optional doser: pump, support,
dilution deposit and level sensor for the drum (Mod. 4044000 460 €)
Preparation: No need for preparation before the dosage, the product is
used pure.
PreparationTo prepare 100 litres of dilution following the start up tables,
mixing the product and demineralised or tap water.:
Dosage: It is dosed automatically for 20 minutes once a week,
meanwhile the equipment is working. The repercussion in the quality of
the demineralised water is insignificant.
Dosage: It is dosed simultaneously with the antiscalant, this means,
always that the equipment is producing demineralised water. It has not
effect at all in the demineralised water quality.
Application Range It is effective for all kind of aerobic and anaerobic
bacteria, killing them. It is not dosed continuously because the product,
in a long-term, causing a damage in the membranes.
Application Range: It removes the oxygen from water and avoids the
growth of the aerobic bacteria, which are the most common.
Room requirements. Only the size of the 5 litres drum and the doser
pump, easy to mount in a cabinet.
Room requirements. It requires a 120 litres tank, included in the
optional, besides the doser pump.
Maintenance. To prime the pump after every drum change. The primed
can be avoided if the content of a new drum is flowed into the drum just
finished.
Maintenance. If the product has not been consumed in 3-4 weeks we
have to renew it, emptied completely and filling it up with the mixture
required.
Water Treatment Division
Pretreatments
Demineralisers. Examples of contamination of the membranes
Lime
Water Treatment Division
Pretreatmentss
Crystal of Calcium Carbonate (lime)
Water Treatment Division
Demineralisers
Demineralisers. Examples of contamination of the membranes
Scalant process. How are the crystals formed?.
IONES
ION
PROTONUCLEUS
GROUP FORMATION
ARRANGEMENT
NUCLEUS
CRYSTALS
GROWTH
1000 atoms
Water Treatment Division
Pretreatments
Demineralizer. Pretreatment against lime
Water Softener
Resin
The Calcium and Magnesium are the elements with
the most scalant power. It is not used as pretreatment
stage for the demineraliser, but it is suitable for water
treatment before the boiler inlet.
Antiscalant dossing
The Calcium and Magnesium are the elements with the
most scalant power. The dosage of this element avoids the
lime crystal formation.
Water Treatment Division
Demineralisers
Demineralisers. Examples of contamination of the membranes
Difference between antiscalant and water softener
Antiscalant effect
THRESHOLD EFFECT AGENT
(Antiscalant)
IONS
IONS
GROUP FORMATION
NUCLEUS
ARRANGEMENT
CRYSTALS
GROWTH
Avoids the
crystal
formation
Water Softener effect
Ca2+ (H2O) + R-Na+ ---- Na+ (H2O) + R-Ca
Water Treatment Division
Demineralisers
Difference between antiscalant and water softener.
Antiscalant doser
system
+
Antiscalant drum
Water softener
+
Salt
Water Treatment Division
Demineralisers
Difference between antiscalant and water softener.
Antiscalant dosage
Water softener 2x100 litres
Consumption of antiscalant product:
Salt Consumption:
– Daily need of water: 21 m3 at 70 ºHF.
– Necessary regeneration of the water softener
every 9 m3
– Number of regenerations per day: (21m3/day)
/ (9m3/ regeneration) = 2.3 regenerations /day
– Consumption of salt per litre of resin in every
regeneration: 0,2 kg/Litres of resin
– Consumption of salt in every regeneration: 0,2
kg/Litre of resin x 100 Litres of resin = 20 kg of
salt per regeneration
– Salt consumption per day: 2.3 regenerations /
day x 20 kg of salt/regeneration = 46 kg/day
– Salt consumption in the same period of
time (124 days): 46 kg/day x 124 days =
5. 704 kg = 228 sacks of 25 kg
– Daily need of water: 21 m3 at 70 ºHF.
– “High” dosage of product: 5 mg/L = 5 g/m3
– Daily product consumption: 21m3 x 5 g/m3 =
105 g/day = 0.105 kg/day
– 1 drum of 10 L = 13 kg
– So 1 carafe of 10 litres of antiscalant will
last: 13 kg / 0.105 kg/day = 124 days
Water Treatment Division
Demineralisers
Difference between antiscalant and water softener.
Example of calculation
Conclusion: In 124 days of use:
5.704 Kg of salt
=
1 bottle of 10 L (13 Kg)
Make yourself your calculations:
Price/kg Salt x 5.700 kg salt = EUR spent on salt
versus
RRP 10 L Antiscalant drum = 189,00 EUR
Water Treatment Division
Pretreatments
Selection of the pretreatment for demineralizer.
Water sample
IT- 11-56 Test
IT- 11-55 Chlorine
Identification and
Delivery
Laboratory
Results of Analysis
Advantage:
- Less maintenance
- Long lasting components
- Efficiency
- Better water quality
Recommended Configuration
Introduction of Analysis results
Water Treatment Division
Pretreatments
Mantenimiento Filtros de Pretratamiento
1. Maintenance each 12 months
1.
2.
3.
Checking of conditions of the filter carried out by TAS Istobal
Replacement (if is necessary) of the content of the filter carried out by TAS
Istobal
Collecting the used filter material by an authorized manager of waste, paid
by the customer.
Water Treatment Division