SIST EN 17818:2024

SLOVENSKI STANDARD
01-marec-2024
Naprave za proizvodnjo biocidov na kraju samem - Aktivni klor, pridobljen iz
natrijevega klorida z elektrolizo
Devices for in-situ generation of biocides - Active chlorine generated from sodium
chloride by electrolysis
Anlagen zur In-Situ-Erzeugung von Bioziden - Aktives Chlor hergestellt aus
Natriumchlorid durch Elektrolyse
Équipements pour le production in situ de biocides - Chlore actif produit à partir de
chlorure de sodium par électrolyse
Ta slovenski standard je istoveten z: EN 17818:2023
ICS:
13.060.20 Pitna voda Drinking water
71.100.80 Kemikalije za čiščenje vode Chemicals for purification of
water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 17818
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2023
EUROPÄISCHE NORM
ICS 13.060.20
English Version
Devices for in-situ generation of biocides - Active chlorine
generated from sodium chloride by electrolysis
Équipements pour le production in situ de biocides - Anlagen zur In-Situ-Erzeugung von Bioziden - Aktives
Chlore actif produit à partir de chlorure de sodium par Chlor hergestellt aus Natriumchlorid durch Elektrolyse
électrolyse
This European Standard was approved by CEN on 27 November 2023.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATIO N

EUROPÄISCHES KOMITEE FÜR NORMUN G

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 17818:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Requirements . 10
4.1 General. 10
4.2 Design . 10
4.2.1 Temperature. 10
4.2.2 Backflow prevention. 10
4.2.3 Safety . 10
4.3 Performance . 10
4.4 Instructions . 10
5 Electrolysis system and components . 10
5.1 General. 10
5.2 Electrolysis cell . 10
5.3 Control unit . 11
5.4 Optional items . 11
5.4.1 Flow detector . 11
5.4.2 System for dissipating stray electrical currents . 11
5.4.3 Chlorine production adjustment feature . 11
5.4.4 Temperature probe . 12
5.4.5 Conductivity / TDS probe . 12
5.4.6 Buffer tank . 12
6 Process variants . 12
6.1 Overview of process variants . 12
6.2 Electrolysis systems with non-divided electrolysis cell . 14
6.2.1 General. 14
6.2.2 Processes with lower generation capacity and short-term operation . 14
6.2.3 Processes with high generation capacity and/or long-term operation . 17
6.3 Electrolysis system with divided electrolysis cell (membrane or diaphragm) . 19
6.3.1 General. 19
6.3.2 Process with acidic chlorine solution . 20
6.3.3 Process with neutral chlorine solution . 22
6.3.4 Process with alkaline chlorine solution . 24
7 Safety requirements . 25
7.1 General requirements . 25
7.2 Hydrogen. 25
7.3 Chlorine gas . 26
7.4 Excess products and solutions . 26
7.5 Buffer tank . 26
7.6 Safety bunds . 27
7.7 Prevention against backflow . 27
8 Equipment of the room or area for installation of the electrolysis system . 27
9 Operation and maintenance . 28
10 Test requirements . 28
10.1 General . 28
10.2 Scope of testing . 29
10.2.1 General . 29
10.2.2 System documentation . 29
10.2.3 Chemical characterization. 29
10.2.4 Determination of the active chlorine content (main constituent). 33
−
10.2.5 Determination of the chlorate content (ClO ). 35
−
10.2.6 Determination of the bromate content (BrO ) . 36
−
10.2.7 Determination of the chloride content (Cl ) . 36
Annex A (informative) Natural decay of stored hypochlorite solutions . 38
A.1 General . 38
A.2 Decay reactions . 38
A.3 Factors influencing chlorine decay and chlorate formation . 39
A.3.1 Influence of temperature and storage time . 39
A.3.2 Chlorate formation vs. time and temperature . 40
A.3.3 Influence of initial concentration vs. days of storage . 41
A.4 Influence of pH . 41
A.5 Influence of decay catalysers (pollutants) and prevention . 42
Bibliography . 43

European foreword
This document (EN 17818:2023) has been prepared by Technical Committee CEN/TC 164 “Water
supply”, the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2024, and conflicting national standards shall be
withdrawn at the latest by June 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Devices according to this document may be used in different fields of application, e.g. drinking water,
swimming pool water, wastewater, air treatment, surface disinfection, etc. Additional requirements to
this document shall be observed, where appropriate for the specific application.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Introduction
In respect of potential adverse effects on human and animal health and the environment, caused by the
product covered by this document:
a) this document provides no information as to whether the product may be used without restriction
in any of the Member States of the EU or EFTA;
b) note that, while awaiting the adoption of verifiable European criteria, existing national regulations
concerning the use and/or the characteristics of this product remain in force.

1 Scope
This document defines the minimum requirements for treatment systems, which generate the active
substance - “Active chlorine” - from sodium chloride by electrolysis for on-site (in situ) operation.
The in situ generated active substance (IGAS), in this case active chlorine, may be put into a solution (“off-
line”) or directly generated in the pipes (“in-line”).
This document specifies the device construction, and test methods for the equipment used for in situ
generation of active chlorine. It specifies requirements for instructions for installation, operation,
maintenance, safety and for documentation to be provided with the product.
The in situ generation of active substances and the placing of their precursors on the EU market are
subject to the specifications of the Biocidal Products Regulation (EU) 528/2012 [“Biocidal products”].
Active substances, generated by devices, which are claiming compliance with this document, shall comply
with the BPR for both the registered active chlorine, quality standards and the precursor in accordance
with appropriate application and “Product Type” as listed in the BPR.
This standard does not identify applications for in situ devices for generation of active chlorine. The range
of applications for in situ generation of chlorine is diverse. It is the responsibility of the economic
operator/product supplier, claiming compliance with this standard, to identify the appropriate system
type and operating conditions for the specific application and to:
— specify the quality of the biocide appropriate to the application. This may be defined in national or
international standards;
— specify the appropriate product type and operating conditions (concentration, dosage rate and
quality of the active chlorine);
— specify any other regulatory requirements relevant to the specific application;
— specify the appropriate precursor sodium chloride, for the application;
— and to label the product accordingly.
2 Normative references
The following documents are referenced in the text in such a way that some parts of these or their entire
contents constitute requirements of this document. With dated references, only the referenced issue is
applicable. With undated references, the last issue of the referenced document is applicable (including all
changes).
EN 1717, Protection against pollution of potable water in water installations and general requirements of
devices to prevent pollution by backflow
EN IEC 60751, Industrial platinum resistance thermometers and platinum temperature sensors (IEC 60751)
EN ISO 7393-1, Water quality — Determination of free chlorine and total chlorine — Part 1: Titrimetric
method using N,N-diethyl-1,4-phenylenediamine(ISO 7393-1)
EN ISO 7393-2, Water quality — Determination of free chlorine and total chlorine — Part 2: Colorimetric
method using N,N-dialkyl-1,4-phenylenediamine, for routine control purposes (ISO 7393-2)
EN ISO 10304-1, Water quality — Determination of dissolved anions by liquid chromatography of ions —
Part 1: Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate (ISO 10304-1)
EN ISO 10304-4, Water quality — Determination of dissolved anions by liquid chromatography of ions —
Part 4: Determination of chlorate, chloride and chlorite in water with low contamination (ISO 10304-4)
EN ISO 15061, Water quality — Determination of dissolved bromate — Method by liquid chromatography
of ions (ISO 15061)
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
In addition, the terminology contained in Article 3 of the BPR is to be included in the application for this
document.
3.1
biocidal active substances
substance or microorganism that has an action on or against harmful organisms
[SOURCE: (Definition of active substance in BPR Article 3 (1) (c).)]
3.1.1
technical active substance (TAS)
active substance produced including minor constituents and any contaminants produced during the
process
3.1.2
IGAS – in situ generated active substance
biocidal active substances, when they are generated from one or more precursors at the place of use
3.2
anolyte
medium output from the anode compartment
3.3
buffer tank
one or several tanks separate from the electrolysis cell or the reactor for temporary provision of the
generated chlorine solution that is intended for the application
3.4
diaphragm
porous barrier in a divided electrolysis cell without ion selectivity between the anode and cathode
compartment of the electrolysis cell
Note 1 to entry: In contrast to the membrane, the diaphragm permits the passage of a limited quantity of hydroxide
ions from the cathode compartment to the anode compartment. This reduces the pH-value in the cathode
compartment, while the pH-value in the anode compartment increases at the same time.
3.5
electrochlorination system
device that uses the principle of electrolysis to produce active chlorine excluding additional equipment
3.6
electrolysis cell
system in which positively charged electrodes (anodes) and negatively charged electrodes (cathodes) are
positioned face to face
3.6.1
divided electrolysis cell
electrolysis cell in which the anode and cathode compartments are divided by a membrane or diaphragm
3.6.2
non-divided electrolysis cell
electrolysis cell in which the anode and cathode compartments are not divided, therefore enabling
unimpeded liquid, ion and gas transport in the space between the electrode pairs
3.7
expert
person who, due to their technical scientific training, work experience and knowledge of applicable
standards and regulations, is able to assess an electrolysis system with regard to functions and safety
Note 1 to entry: This person can be from the manufacturer or an independent third-party organization (such as a
test institution) without limitations, an inspector according to EN ISO/IEC 17020 Type C [8], fulfils this criterion.
3.8
feed water
water in accordance with the chemical requirements of the corresponding manufacturer’s specifications
for the production of sodium chloride solution and/or operation of the electrolysis system
3.9
gas separator
system for the physical separation of gases (in this case: hydrogen/chlorine) from liquids
3.10
injector
component that enables the flow of the sodium chloride solution, the active chlorine solution, the chlorine
gas or their mixtures into a water flow, typically employing the venturi principle
3.11
in-line electrolysis
process in which the water to be treated is the operating medium and fed directly into the electrolysis
cell
3.12
in-situ generation
reaction of at least one precursor to generate the technical active substance on site
3.13
membrane
cation-selective barrier in a divided electrolysis cell between the anode and cathode compartment
Note 1 to entry: This prevents the reaction between the chlorine gas and hydroxide ions (OH−), by allowing
monovalent cations and inhibiting anions (chloride and hydroxide) to permeate through the membrane.
3.14
nominal capacity
maximum production rate of active chlorine as specified by the manufacturer
3.15
operating media
artificial or natural sodium chloride solutions that are used for electrolysis
3.16
precursor
substance that is fed to the in-situ device for production of the biocide active substance, independent of
its disinfection or biocide-law related properties substance or mixture (formulation containing the
precursor(s)), from which an active substance (including free radicals) is generated in situ
3.17
product range
systems that operate according to the same functional principle but with different capacities
3.18
reactor
system for converting chlorine gas and sodium hydroxide into a sodium hypochlorite solution
3.19
sodium chloride solution
3.19.1
artificial sodium chloride solution
solution produced using manufactured sodium chloride
Note 1 to entry: E.g. in accordance with EN 14805, EN 973, EN 16370 or EN 16401.
3.19.2
natural sodium chloride solution
naturally occurring sodium chloride containing solution, such as sea water and brackish water
3.20
stability curve
representation of the chlorine content and by-products at the specified temperature over time
Note 1 to entry: In systems with buffer tanks, this forms a basis in order to ensure that the active substance content
and the amount of by-products such as chlorate in the generated chlorine solution in the buffer tank do not change
unacceptably during the time between generation and metering the chlorine solution.
3.21
system type
system in a product range with a representative capacity
Note 1 to entry: Production capacity in kg/h chlorine.
4 Requirements
4.1 General
The manufacturer/supplier, claiming compliance with this standard, shall fulfil the following
requirements:
4.2 Design
4.2.1 Temperature
The equipment shall be designed to operate to the requirements of this standard with water
temperatures between 5 °C and 25 °C and with ambient temperatures between 5 °C and 35 °C minimum.
For higher temperatures, the device shall be designed accordingly.
4.2.2 Backflow prevention
If connected to a drinking water supply, the device shall be fitted with a backflow prevention device
appropriate to the application in accordance with EN 1717.
4.2.3 Safety
System design shall include appropriate measures for management of release potentially hazardous
hydrogen gas, excess chlorine and surplus production (see Clause 7). It shall include protection against
stray electrical discharge and compliance with relevant standards to the application.
4.3 Performance
The device shall be tested at the highest active chlorine concentration and maximum production rate as
specified by the manufacturer and appropriate to the requirements of the end user application.
This test may be conducted on the manufacturer’s premises or on the installed system.
4.4 Instructions
The manufacturer/supplier of the device shall provide detailed instructions for installation (see
Clause 8), operation and maintenance for the complete system, including appropriate safety procedures
(see Clause 7).
5 Electrolysis system and components
5.1 General
Electrochlorination systems shall include, as a minimum, an electrolysis cell and control unit. Optional
items may also be included (see 6.3).
5.2 Electrolysis cell
The electrolysis cell comprises a vessel into which positive (anode) and negative (cathode) electrodes are
appropriately located.
The electrodes, which can vary in number, shape, material and dimensions, produce the disinfectant and
oxidizing agent under the action of the electric current.
NOTE Depending on its chemical composition the feed water supply might increase mineral deposits
precipitating on the cathodes. The higher the total hardness of the water, the greater the scaling, thereby
significantly reducing the production of disinfectant and possibly also the flow through the electrolysis cell in the
case of inline electrolysis. To reduce these effects, the electrolysis cells can function with polarity reversal,
automatic/semi-automatic acid washing systems or alternatively, the water supply can be (softened) treated
appropriately.
Sufficiently resistant materials shall be used for all parts of the systems and devices that come into contact
with the chemicals and their solutions that are utilized and generated.
The electrochlorination system should be assembled and installed in accordance with the manufacturer's
instructions and in compliance with the requirements of applicable standards – e.g. electrical.
5.3 Control unit
The control unit can be built into or independent of the electrochlorination device.
The control unit integrates the components that control the cell power supply and therefore the
production of disinfectant. The control unit shall deliver a Safety Extra-Low Voltage (SELV) supply.
Where the control unit is not included in the device, it shall bear a manufacturer's plate indicating the
data, in particular:
— the identification of the distributor (commercial name or logo, etc.);
— the power supply voltage in Volt;
— the frequency in Hertz;
— the power input in Watt;
— the current in Ampere;
— the protection index (IP);
— and the insulation class if necessary.
The control unit shall be installed in accordance with:
— the information indicated on this plate;
— the manufacturer's requirements and recommendations;
— applicable standards.
5.4 Optional items
5.4.1 Flow detector
This component informs the electrochlorination system of an adequate flow, required for the electrolysis
process. This flow can be used to control or shut down the chlorine production.
5.4.2 System for dissipating stray electrical currents
This system enables the safe dissipation of stray currents of all origins present.
5.4.3 Chlorine production adjustment feature
This feature allows the level of production of disinfectant and oxidizing agent chlorine by the
electrochlorination system to be adjusted according to one or more predetermined parameters set by the
manufacturer (operating time, production power, etc.) independently of the actual needs of the
application or depending on external signals, such as redox measurement, chlorine level measurement
by amperometric sensors or colorimetric methods, etc.
5.4.4 Temperature probe
This probe measures the water temperature and displays it on the control unit. Examples of use:
Production temperature monitoring, protection of the cell, estimation of the salt level, display the water
temperature, etc.
5.4.5 Conductivity / TDS probe
This component serves to determine the concentration of the sodium chloride solution fed into the
electrolysis cell.
5.4.6 Buffer tank
Systems with a buffer tank can be sized with lower nominal capacity in order to serve the maximum
chlorine demand than systems without a buffer tank.
The buffer capacity shall be designed so that the chlorate concentration can be minimized according to
the corresponding application. The possible influences on the installation location shall also be
considered (sunlight, temperature, contamination, etc.).
Storage over a period of longer than 24 h should be avoided. The operator should be able to adjust the
level in the buffer tank, but should not be able to exceed the maximum level specified by the
manufacturer. The manufacturer shall provide suitable instructions.
For systems without a buffer tank, the nominal capacity of the electrolysis system shall cover the intended
maximum chlorine demand.
6 Process variants
6.1 Overview of process variants
There are various processes available to generate the active substance “Active chlorine, generated from
sodium chloride by electrolysis” on site (in situ) and put it into a solution. One feature that all processes
have in common is the use of artificial sodium chloride solution (produced using marketable sodium
chloride, e.g. in accordance with EN 14805, EN 973, EN 16370 or EN 16401) or sea water/brackish water
as the precursor.
This section specifies the two main product variants – non-divided electrolysis variants and divided
electrolysis cell (membrane or diaphragm) – see Figure 1. Non-divided cell variants produce alkaline
hypochlorite solution at 2 alternative levels of production capacity and dosing duration. Divided cell
variants operate on the higher production capacity/duration but can be adapted to produce either
alkaline, acidic, or neutral chlorine solution.

Figure 1 — Overview of process variants

6.2 Electrolysis systems with non-divided electrolysis cell
6.2.1 General
In the case of electrolysis systems with non-divided electrolysis cells, the cell is fed with an aqueous
sodium chloride solution. The electrolysis process results in chlorine gas at the anode, while hydrogen,
hydroxide ions and consequently also sodium hydroxide are produced at the cathode. Due to the
unimpeded transport of liquid and gas, the chlorine and alkali react in the cell to produce sodium
hypochlorite (see Figure 2). Part of the chloride used is not converted in the cell and remains in the
hypochlorite solution generated.

Key
1 anode
2 cathode
Figure 2 — Non-divided electrolysis cell

6.2.2 Processes with lower generation capacity and short-term operation
Processes with lower generation capacity and short-term operation are those that comply with all of the
following criteria:
— the maximum production quantity is less than 10 g of chlorine per day and
— the intended, cumulated operating duration is less than one hour per day and
— the application or the disinfection requirement only requires a certain (minimum) chlorine value in
the water to be maintained for a short time.
In electrolysis systems with low generation capacity and short-term operation, the electrolysis cell has a
continuous flow of water containing chloride. Generation of active chlorine by electrolysis is performed
periodically. The solution generated in situ is of an alkaline nature (Hypochlorite solution).
After disinfection, the residual disinfectant shall be flushed out of the system and discarded to drain.
Structurally, the electrolysis cell is to be installed between the supply of the water containing chloride
(e.g. from a salt solution container) and the system to be disinfected (for a schematic illustration see
Figure 3). The electrolysis cell is operated in the salt solution container (installation example I) and in the
sodium chloride solution suction line (installation example II) with saturated sodium chloride solution
or after the injector (installation example III) with diluted sodium chloride solution.
The system shall be self-venting during operation, so that any potential accumulation of hydrogen gas is
prevented. Due to the mode of operation of the electrolysis cell, no safety-relevant quantities of hydrogen
gas are produced per disinfection process.
Key
A feed water supply
B artificial (saturated) sodium chloride solution
C diluted sodium chloride solution
D-I active chlorine solution in installation example I
D-II active chlorine solution in installation example II
D-III active chlorine solution in installation example III
E suction line for sodium chloride solution
1 salt solution container with artificial sodium chloride solution
2 injector
3 anode
4 non-divided electrolysis cell
5 cathode
6 water to be disinfected
7 drain or further use
I installation example: salt solution container
II installation example: sodium chloride solution suction line
III installation example: diluted sodium chloride solution
Figure 3 — Use of non-divided electrolysis cells with installation examples

6.2.3 Processes with high generation capacity and/or long-term operation
Processes with high generation capacity and/or long-term operation are those that meet at least one of
the following criteria:
— the maximum production quantity is more than 10 g of chlorine per day and/or
— the sum of the designated operating time is more than one hour per day and/or
— the disinfection requires a continuous (minimum) chlorine concentration in the water to be
maintained.
The hypochlorite solution is fed into a buffer tank (see Figure 4) or used directly (see Figure 5).
The hydrogen gas that incidentally occurs shall be safely discharged with consideration to its
explosiveness.
In the non-divided cell for direct use, a hypochlorite solution is generated with a concentration of > 2 g/l
active chlorine.
A special case of non-divided electrolysis cells is such, where the electrolysis cell is part of the water flow
to be treated (“in-line”, see Figure 6). In this case the reaction between the generated chlorine gas and
the water takes place more rapidly than the reaction between chlorine gas and sodium hydroxide. Thus,
a chlorine solution of hypochlorous acid and sodium hypochlorite is formed instead of a sodium
hypochlorite solution in a higher concentration. The resulting solution is therefore nearly neutral/slightly
alkaline, depending on the pH of the feed water, the ability to buffer the pH (alkalinity) and the ratio
between the generated solution and the feed water (flow of the feed water). The water shall have a
sufficient chloride concentration. The hydrogen that incidentally occurs shall be safely discharged with
consideration to its explosiveness.
NOTE This might take place, for example, via the surface of the water into rooms of sufficient size and/or with
good ventilation.
Key
1 anode
2 cathode
3 buffer tank
Figure 4 — Process with alkaline hypochlorite solution with buffer tank
Key
1 anode
2 cathode
Figure 5 — Process with alkaline hypochlorite solution for direct use

Key
1 anode
2 cathode
NOTE In electrolysis system with non-divided electrolysis cells (“inline” according to Figure 6), the pH value
can also be mainly determined by the feed water for operational reasons.
Figure 6 — Process with alkaline hypochlorite solution, where the electrolysis cell is part of the
flow of the water to be treated (“in-line”)

6.3 Electrolysis system with divided electrolysis cell (membrane or diaphragm)
6.3.1 General
Electrolysis systems with divided electrolysis cells are those with high generation capacity and/or long-
term operation that meet at least one of the following criteria:
— the maximum production quantity is more than 10 g of chlorine per day and/or
— the intended, cumulated operating duration is more than one hour per day and/or
— the disinfection requires a continuous (minimum) chlorine concentration in the water to be
maintained.
The anode compartment is supplied with artificial sodium chloride solution, produced from feed water
and sodium chloride (e.g. in accordance with EN 16370 or EN 16401) as the operating media, whereby
+
the chloride (Cl−) is oxidized to chlorine (Cl ) at the anode. The sodium cation (Na ) passes through the
semipermeable membrane to the cathode compartment (see Figure 7).
With the diaphragm-electrolysis process, a diaphragm is used instead of a membrane. In contrast to the
membrane, the diaphragm permits the passage of hydroxide ions from the cathode compartment to the
anode compartment. This reduces the pH-value of the cathodically formed sodium hydroxide in the
cathode compartment, while the pH-value of the anolytes in the anode compartment increases at the
same time (see Figure 8).
Key
1 anode compartment
2 cathode compartment
3 anode
4 cathode
5 membrane
Figure 7 — Membrane cell
Key
1 anode compartment
2 cathode compartment
3 anode
4 cathode
5 diaphragm permeable for monovalent ions
Figure 8 — Diaphragm cell
The quantity of chloride used, which is dissolved in water, is not fully converted in the electrolysis cell.
The solution from the anode chamber can be used, discarded or fed directly into the anode compartment
through recirculation. Alternatively, this can also be fed back into the salt solution tank. In this case,
additional equipment or functions shall be used to avoid a release of the chlorine gas, e.g. by increasing
the pH or dechlorination, e.g. by means of active carbon treatment.
Feed water is fed to the cathode compartment and is reduced to hydrogen (H ) at the cathode. The
− +
remaining hydroxide ions (OH ) together with the sodium-(Na )-cations form sodium hydroxide (NaOH).
The hydrogen is separated from the alkaline solution in a gas separator. The hydrogen gas that
incidentally occurs shall be safely discharged with consideration of its explosiveness.
6.3.2 Process with acidic chlorine solution
The chlorine gas that is generated in the electrolysis cell is separated from the anolyte and fed directly in
a vacuum process to the water to be treated, extracted either as chlorine gas or as a chlorine solution (see
Figure 9 and Figure 10).
Key
1 anode
2 cathode
3 injector
Figure 9 — Process with acidic chlorine solution (extracted as chlorine gas)
Key
1 anode
2 cathode
3 injector
Figure 10 — Process with acidic chlorine solution (extracted as chlorine solution)
6.3.3 Process with neutral chlorine solution
The chlorine gas separated from the anode side is dissolved in water, after which the pH value is adjusted
to between 6,5 and 7,5 using the separately collected alkali (see Figure 11).
Key
1 anode
2 cathode
3 injector
4 buffer tank
Figure 11 — Process with neutral chlorine solution
In an alternative process, the sodium chloride solution is alkalised in the cathode compartment. With the
possible discarding of a pre-set quantity of the alkaline sodium chloride solution, this is transferred to
the anode compartment, where the elementary chlorine generated on the anode is converted into neutral
chlorine solution in the alkaline sodium chloride solution (see Figure 12).
Key
1 anode
2 cathode
3 buffer tank
Figure 12 — Process with neutral chlorine solution (alkaline sodium chloride solution
recirculation)
6.3.4 Process with alkaline chlorine solution
The chlorine gas that is generated in the electrolysis cell is separated from the anolyte and converted into
a hypochlorite solution in a separate reactor with the sodium hydroxide produced in the cathode
compartment (see Figure 13).
Key
1 anode
2 cathode
3 injector
4 buffer tank
Figure 13 — Process with alkaline chlorine solution and divided cell (conversion of chlorine gas
and sodium hydroxide)
7 Safety requirements
7.1 General requirements
Electrolysis systems shall be operated properly with consideration of the requirements applicable to the
corresponding system type, e.g. regarding handling chemicals and electrical systems. Note that
precursors that are harmless from a hazardous substance perspective can produce aqueous solutions and
gases that can have specific hazardous properties. The safety requirements shall be configured so that
hazard prevention is ensured.
7.2 Hydrogen
With all electrolysis systems, hydrogen is produced as a by-product of the process. The electrolysis
system shall be designed for safe dilution and discharge of the hydrogen, this shall be specified in the
system documentation described in 10.2.1.
In all electrolysis systems with divided electrolysis cells, as well as electrolysis systems with non-divided
electrolysis cells operated with buffer tank (see Figure 4), the following applies for diluting and
discharging the hydrogen:
— the hydrogen produced is to be diluted with air to a safe hydrogen concentration at the site of
generation with a fan (see safety concept, 10.2.1). The discharge and flow rate of the dilution air shall
be monitored by a flow monitor;
— the electrolysis system shall be designed to switch off automatically in case the quantity of dilution
air is insufficient;
— the diluted hydrogen is to be fed into the open air via a dedicated
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