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F r a u n h o F E r I n s t I t u t E F o r I n t E r F a C I a l E n G I n E E r I n G a n d B I o t E C h n o l o G y I G B

Process water treatment by oxidative and electrolytic Processes

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the Challenge

Nowadays, the recirculation of water in industrial production

processes is recognized as a necessity. In order to re-use wa-

ter sensibly, the undesired substances that build up have to

be removed with as little expenditure of time and money as

possible. With the development of new products and materi-

als as well as the introduction of new production methods

and techniques, new issues arise for the treatment of the re-

spective process waters. Examples of this problem:

New complex dyestuffs, pesticides, tensides and

pharmaceuticals

The use of nanoparticles

Varying wastewater contamination resulting from rapid

product change

There are new challenges concerning the treatment of raw

water as well. The pollution of the past now affects natural

water sources, surface waters, and groundwater.

The build-up of pesticides and pharmaceuticals in rivers,

lakes, and groundwater is an example of this. Systematically

detecting these micropollutants and their decomposition and

reaction products has only recently become possible with im-

proved methods of analysis.

In many cases the currently established processes and systems

cannot do the job without adaptation and support from new,

selective systems. The Fraunhofer IGB has recognized this ne-

cessity and is working on the improvement of existing pro-

cesses such as adsorption, filtration, flocculation/precipitation,

electrodialysis, homogenization and disinfection as well as on

new approaches in process and unit operations. The use of

oxidative and electrolytic processes for water treatment is one

of our main fields of research. Together with industrial part-

ners, new concepts and technologies are being developed at

the Fraunhofer IGB up to industrial scale. Water treatment and

the circulation of process water can thus be carried out eco-

nomically and sustainably.

In numerous production processes water is used as a solvent or means of conveyance, as cooling water or washing water. In-

creasing costs for the purification and disposal of wastewater, regional or seasonal shortage of water, and a growing awareness

of environmental issues within companies have increased water recycling. Water is used several times and impurities have to be

removed selectively.

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aoP – advanced oxidation Processes

Oxidative water treatment (AOP, advanced oxidation process-

es) is understood as processes for chemical treatment in

which hydroxyl radicals are formed. These highly reactive radi-

cals are available for chemical decomposition reactions and

also react with organic or inorganic substances that are not

easy to break down biologically. They can be formed by add-

ing oxidative substances such as ozone (O3) and hydrogen

peroxide (H2O2), or by introducing energy by means of UV ra-

diation, ultrasound or electric current via inert electrodes as

well as by a combination of these processes.

At present, catalytic, photochemical, and electrochemical pro-

cesses as well as plasma processes for oxidative water treat-

ment are investigated at the Fraunhofer IGB. Various experi-

mental set-ups for continuous, semi-continuous and batch

trials are available for this purpose. Among other equipment,

the Fraunhofer IGB has an AOP plant, with which all the well-

established processes can be tested individually or in combina-

tion. Due to comprehensive sensing and automation, the test

parameters can be adapted and varied automatically.

oxidative and electrolytic Processes

advanced oxidation Processes and technologies: technologies: taoPs, aotsaotsaot

Photochemical processes Super critical water

oxidation (SUWOX)

Electron beamirradiation

Sonolysis

Non-thermal plasma processes

Electrochemicalprocesses

Catalytic processes

Solar processesphotocatalysis

X-ray irradiation

Gamma-Radiolysis

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1 Pilot plant for the development of Advanced Oxidation

Processes (AOP) at the Fraunhofer IGB.

2 Oxidation processes for water treatment.

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Electro-physical precipitation

Another process established at the Fraunhofer IGB is electro-

physical precipitation (EpF). Here the water to be treated is

passed through a reactor, in which an electric current flows

through sacrificial electrodes. This results in electrochemical

reactions; the sacrificial electrodes dissolve, releasing their

metal ions. Besides reactive radicals (AOP process), metal hy-

droxide flocs are produced in the process. These electrolyti-

cally generated metal hydroxide flocs have a high adsorption

capability and can thus bind to finely dispersed particles. In

addition, there are coprecipitation and occlusion precipitation

reactions, in which dissolved organic and inorganic substanc-

es are precipitated. The precipitated substances can then be

separated mechanically.

Electro-physical precipitation replaces conventional chemical

flocculation techniques with the advantage that the floccu-

lants are made available electrolytically from solid state elec-

trodes where they are required in dissolved molecular form.

Iron or aluminium can be used as electrode material; these

are inexpensive, readily available, and easy to handle. The

metal ion is specifically added only to the water to be treated;

an increase in the salt content does not occur. Using this pro-

cess there are no costs for the purchase, handling, and dis-

persal of flocculants and flocculating additives.

The Fraunhofer IGB has an extensive range of laboratory and

pilot plant equipment with plants of up to 500 l/h flow rate.

We can therefore treat greatly differing volumes of process

water – from general feasibility studies to continuous extend-

ed-time trials. Optimal infrastructure at the Fraunhofer IGB en-

ables quick analysis of water samples as well as quick process

adaptation to varying requirements.

Combination and integration of oxidative and

electrolytic processes

Oxidative and adsorptive processes such as EpF can be com-

bined, depending on the problems to be solved. By doing this,

results can be achieved that exceed the sum of the results of

the individual processes. A further advantage of these pro-

cesses is that they are suited to standby operation and can be

switched on or off at any time. Integration into existing plants

and automation including autonomous operation or remote

control are feasible without any problems. Continuous online

logging of organic carbon (TOC, total organic carbon) can be

effected, enabling requirement-based and thus energy-opti-

mized treatment.

However, not only oxidative and adsorptive processes can be

combined advantageously. The combination with aerobic

and anaerobic biological treatment stages can also be real-

ized at the Fraunhofer IGB in laboratory scale and pilot plant

demonstrations.

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In general, electrolytic and oxidative processes have the

following advantages:

Complete mineralization of pollutants possible

No increase in salinity, which enables recirculation

Less handling of hazardous chemical agents

No disinfection by-products – in particular no halogenated

compounds

Little or no sludge formed

Hygienic outflow water

Robust process – discharge criteria can be met reliably

Available quickly – standby operation possible

Suitable for varying quantities and qualities of wastewater

Staff savings and increased reliability

Electrolytic and oxidative processes offer economically attrac-Electrolytic and oxidative processes offer economically attrac-Electrolytic and oxidative processes offer economically attrac

tive and sustainable solutions for the purification of industrial,

process waters, and wastewaters. They are a good alternative

for substances that cannot be broken down conventionally or

that are only degradable at great expense.

With oxidative and electrolytic processes, it is possible to oxi-

dize dissolved contaminants or pollutants that are difficult to

break down. Pollutants are either directly oxidized or precipi-

tated by way of hydroxide flocs. Electrogenerated hydroxide

flocs are extremely well suited for removing the finest particle

contaminants. The proposed oxidative and electrolytic pro-

cesses do not increase water salinity, and the maintenance re-

quired is minimal. By process combination full treatment can

be guaranteed even for varying pollutant load.

Electrolytic and oxidative processes can be integrated advan-

tageously in a treatment chain with biological processes, for

example to remove substances that cannot be broken down

biologically. Furthermore, oxidative methods are effective in

treating toxic, carcinogenic, or mutagenic (TCM) substances,

pharmaceuticals, and hormonally active substances.

advantages

1 Electrolytically generated iron hydroxide. Removal of particle

contaminants by means of an electro-physical process.

2 Continuously operating reactor for the removal of color particles

from 5 m3/h process wastewater.

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Halving the treatment costs for paper mill wastewater

by means of electro-physical precipitation

For a paper manufacturer we optimized an existing process

water treatment plant by increasing its capacity. We replaced

conventional flocculation with a plant using the principle of

electro-physical precipitation. Savings on chemicals, floccu-

lants, polyelectrolytes, and sodium hydroxide reduced the

treatment cost by half.

Removal of finely suspended substances from paint

wastewater by electro-physical precipitation

In a feasibility study for an aircraft manufacturer we success-

fully treated paint wastewater from the painting systems by

means of electro-physical precipitation. The turbidity of the

wastewater was reduced by 95 % and the chemical oxygen

demand (COD) by 75 %. Similar studies were carried out for

paint manufacturers. Here too, we were able to show that it

is possible to reduce the turbidity, the COD, and the smell

significantly.

Decoloration of organic dyes by UV / H2O2 and anodic

oxidation using iridium oxide electrodes

As models for real wastewater from the textile industry, a dis-

solved organic dye and a particulate organic dye were discol-

ored by more than 90 % – until the liquids were transparent

to the human eye. The study also served to determine the

most energy-efficient process parameters and compared the

decomposition products produced by each method.

Reduction of the biological contamination of cooling

lubricant with ultrasound / ozone

In a publicly funded project we investigated whether the effi-

cient reduction of microbial contamination in cooling lubricant

emulsions can be achieved by means of ultrasound or ultra-

sound in combination with specific AOP processes. Depending

on the type and concentration of the microbial contamination

we were able to achieve a sustained reduction, without im-

pairing the quality of the cooling lubricant.

Electrolytic ozone production on laboratory and

pilot plant scale

We have investigated electrolytic ozone production on the

laboratory and pilot plant scale. Ozone was produced using

boron-doped diamond electrodes in divided and undivided

cells. Cell geometry, electrode materials and shapes, solid

electrolyte and connecting material, as well as the operational

parameters were optimized in cooperation with our industrial

partners. Up to 5 g ozone/h and up to 22 vol% ozone can be

produced in the gas phase.

aPPlications and references

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Further projects

In a number of publicly funded projects, we are developing

technologies, components, and systems for specific water

treatment tasks in co-operation with our European project

partners.

A good example is our development of a new type of high-

performance UV light source for the sterilization of water. It

was effected in co-operation with a European industrial part-

ner. The UV light in this application is emitted by a plasma,

which is stimulated by microwaves. Unlike conventional mer-

cury discharge lamps, the resulting UV light has a broad

range of different wavelengths. The UV-spectrum was tai-

lored to reach maximal germicidal effect.

In another project funded by the EU we are developing, to-

gether with the consortium, a new type of AOP-system to

break down complex organic pollutants in wastewater into

harmless compounds. This goal is reached by using multi-

chromatic UV light without adding any chemicals.

For the production of ozone we have developed an electro-

chemical cell, with which ozone can be generated efficiently

and inexpensively for environmentally compatible disinfection.

The Fraunhofer Institute for Interfacial Engineering and Bio-

technology IGB develops and optimizes processes and plants

for water treatment and adapts these to the requirements of

industrial practice. The services provided include:

Scientific assessment, technical advice, studies on electro-

lytic and oxidative processes for water treatment

Market and technology studies for process water treatment

Comprehensive chemical and physical analyses to charac-

terize process water

Laboratory plants for customized pre-trials relating to floc-

culation and oxidation characteristics of the process water

Pilot plants for:

Electro-physical precipitation

Ozone + / - hydrogen peroxide + / - catalysts

UV irradiation

Ultrasound

Anodic oxidation (direct / indirect), cathode reactions

Mobile prototype plants for on-site studies and trials

Development of plant technology including automation

and scaling up to industrial size in cooperation with indus-

trial partners

Process optimization for the treatment of water as well as

viscous media, such as cooling lubricants, foodstuffs, slud-

ges, and pastes

Integrated solutions by means of combination with aerobic

and anaerobic biological processes

Combination with processes for desalination or the recov-

ery of acids and bases

services Provided

Fraunhofer Institute for

Interfacial Engineering

and Biotechnology IGB

(Fraunhofer-Institut für

Grenzflächen- und

Bioverfahrenstechnik IGB)

Nobelstrasse 12

70569 Stuttgart

Germany

Phone +49 711 970-4401

Fax +49 711 970-4200

info@igb.fraunhofer.de

Director

Prof. Dr. Thomas Hirth

Phone +49 711 970-4400

thomas.hirth@igb.fraunhofer.de

www.igb.fraunhofer.de

Fraunhofer IGB brief profile

The Fraunhofer IGB develops and optimizes processes and products in the fields of medicine,

pharmacy, chemistry, the environment and energy. We combine the highest scientific quality

with professional expertise in our fields of competence – Interfacial Engineering and Materials

Science, Molecular Biotechnology, Physical Process Technology, Environmental Biotechnology

and Bioprocess Engineering, as well as Cell and Tissue Engineering – always with a view to eco-

nomic efficiency and sustainability. Our strength lies in offering complete solutions from labo-

ratory scale to pilot plant. Customers benefit from the constructive cooperation of the various

disciplines at our institute, which is opening up novel approaches in fields such as medical en-

gineering, nanotechnology, industrial biotechnology, and wastewater purification. The Fraun-

hofer IGB is one of more than 80 research units of the Fraunhofer-Gesellschaft, Europe’s larg-

est organization for application-oriented research.

www.igb.fraunhofer.de

Contact

Dipl.-Ing. Christiane Chaumette

Phone +49 711 970-4131

christiane.chaumette@igb.fraunhofer.de

Alexander Karos, M. Sc.

Phone +49 711 970-3564

alexander.karos@igb.fraunhofer.de

Dipl.-Ing. Siegfried Egner

Head of Department

Physical Process Technology

Phone +49 711 970-3643

siegfried.egner@igb.fraunhofer.de