Water Treatment for Electrolysis

In addition to electrical energy, ultrapure water is also required to operate an electrolyzer in order to produce hydrogen. The purer the water, the longer the service life of the PEM stack used.

This guide from Batarow Hydrogen GmbH focuses exclusively on the production of ultrapure water from tap water or rainwater using reverse osmosis and full desalination resin. All components used can be replaced by comparable devices.

In conjunction with the “ELY 17” or “ELY 22” electrolyzer, the following schematic concepts for water supply can be used

Connection concepts with tap water

If the system is to be operated with tap water, the following concept can be applied:

Figure 1: Schematic diagram of tap water treatment

The tap water is fed into a storage tank and sucked in by a pump. This pump increases the water pressure to at least 2 bar and feeds the water into the osmosis system. The osmosis system requires a minimum inlet pressure of 1 bar. Alternatively, it can also be connected directly to the water supply. Reverse osmosis removes ions from the water. This produces usable osmosis water and waste water in a ratio of 1:1. The waste water transports the removed ions out of the system. The osmosis water is stored in a storage tank, from which it is later fed into the electrolyzer. Before entering the electrolyzer, it undergoes a final cleaning process using a full desalination cartridge.

Example figures for conductivity reduction:

Typically, the conductivity of tap water is 300 µS/cm. The osmosis system can reduce this to below 50 µS/cm. The deionization cartridge further reduces the value to below 0.5 µS/cm. The resulting wastewater has a conductivity of at least 600 µS/cm.

A deionization cartridge with 10 liters of mixed bed resin can demineralize approximately 1,250 liters of water with a conductivity of 300 µS/cm. However, if pre-purified osmosis water is used, the capacity of the cartridge increases significantly – up to 7,000 liters before a replacement is necessary.

With approximately 9 liters of ultrapure water per 1 kg of hydrogen, approximately 780 kg of hydrogen could be produced before the deionization cartridge needs to be replaced.

In order to ensure the function and service life of the osmosis membrane as well as the quality of the ultrapure water in the long term, it is recommended that the manufacturer’s instructions for maintenance and filter replacement be strictly observed.

Recommended components::

• Water tank: 1000-Liter-IBC-Container
• Ultra pure water tank: 1000-Liter-IBC-Container (food approval recommended)
• Osmosis system: Proline X3-600 GPD (Osmofresh)
• Pump: Circulation pump: 24V, 2,4 bar delivery hight
• full desalination cartride: GFK VE-2800 (Aqmos)

Connection concept with rainwater

If the system is to be operated with rainwater, a pre-filter must also be installed to remove organic components such as leaves, twigs, or moss from the water. Only then can the water be further treated as follows:

Figure 2: Schematic diagram of rainwater treatment

After this coarse filtration, the pre-filtered rainwater is sucked in by a pump, which feeds the water into the osmosis system at a pressure of at least 2 bar. The osmosis system requires a minimum inlet pressure of 1 bar.

Filter elements in the osmosis system:
The osmosis unit also contains fine filters, such as:

• Sediment filter for removing fine suspended solids up to a particle size of 1 µm,
• Activated carbon filter for reducing organic compounds, odors, and chlorine.

These elements provide an additional purification step before the water is pressed through the osmosis membrane.

Reverse osmosis then removes most of the dissolved salts and ions from the water. This produces a 1:1 ratio of osmosis water to wastewater. The osmosis water is temporarily stored in a ultrapure water tank. Before the water is fed into the electrolyzer, it undergoes final complete desalination with a deionization cartridge.

Figure 3: Water treatment system setup

The possible setup of the water treatment system shown in Figure 2 is intended as a practical example. It shows a typical installation for operation with rainwater.

In addition to the electrical supply for the pre-pump and pressure booster pump of the osmosis system, the rainwater is fed into the system via a white hose. The wastewater produced during reverse osmosis is discharged via a black hose. The purified osmosis water is fed into the osmosis water tank via a blue hose.

Depending on the model selected, the following aspects may differ:

• The ratio of wastewater to osmosis water,
• The number and type of pre-filters,
• The hose or pipe colors used.

The color coding of the cables is manufacturer-specific and may vary depending on the application. Deviations from the color selection shown here are therefore possible.

Example figures for conductivity reduction:

Typically, the conductivity of rainwater is around 45 to 60 µS/cm. The osmosis system reduces this value to below 3 µS/cm. Subsequent treatment with the deionization cartridge reduces it further to below 0.5 µS/cm. The wastewater has a conductivity of around 100 µS/cm.

A deionization cartridge with 10 liters of mixed bed resin can demineralize approximately 1,250 liters of water with a conductivity of 300 µS/cm. By using pre-purified osmosis water from rainwater, the capacity can be increased to up to 125,000 liters before the cartridge needs to be replaced.

With approximately 9 liters of ultrapure water per 1 kg of hydrogen, approximately 14,000 kg of hydrogen could be produced before the deionization cartridge needs to be replaced.

The replacement of filter elements (e.g., sediment or activated carbon filters) in the osmosis system is manufacturer-specific and depends on the specifications of the respective manufacturer.

As a general rule of thumb, filters should be replaced every 1 to 2 years, depending on the duration of use, water quality, and system load.

In order to ensure the function and service life of the osmosis membrane as well as the quality of the ultrapure water in the long term, it is recommended that the manufacturer’s instructions for maintenance and filter replacement be strictly observed.

Recommended components::

• Water tank: 1000-Liter-IBC-Container
• Ultra pure water tank: 1000-Liter-IBC-Container (food approval recommended)
• Osmosis system: Proline X3-600 GPD (Osmofresh)
• Pump: Circulation pump: 24V, 2,4 bar delivery hight
• full desalination cartride: GFK VE-2800 (Aqmos)