Process water treatment by oxidative and electrolytic

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1 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 1

2 In numerous production processes water is used as a solvent or means of conveyance, as cooling water or washing water. Increasing 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. The Challenge Nowadays, the recirculation of water in industrial production processes is recognized as a necessity. In order to re-use water 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 materials as well as the introduction of new production methods and techniques, new issues arise for the treatment of the respective 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 improved 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 necessity and is working on the improvement of existing processes 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 partners, 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 economically and sustainably. 2

3 1 oxidative and electrolytic Processes aop advanced oxidation Processes Oxidative water treatment (AOP, advanced oxidation processes) is understood as processes for chemical treatment in which hydroxyl radicals are formed. These highly reactive radicals 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 adding oxidative substances such as ozone (O 3) and hydrogen peroxide (H 2O 2), or by introducing energy by means of UV radiation, ultrasound or electric current via inert electrodes as well as by a combination of these processes. At present, catalytic, photochemical, and electrochemical processes as well as plasma processes for oxidative water treatment are investigated at the Fraunhofer IGB. Various experimental 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 wellestablished processes can be tested individually or in combination. Due to comprehensive sensing and automation, the test parameters can be adapted and varied automatically. 1 Pilot plant for the development of Advanced Oxidation Processes (AOP) at the Fraunhofer IGB. 2 Oxidation processes for water treatment. 2 Solar processes photocatalysis Photochemical processes Super critical water oxidation (SUWOX) Catalytic processes Electrochemical processes advanced oxidation Processes and technologies: aops, aots Electron beam irradiation Gamma-Radiolysis Non-thermal plasma processes Sonolysis X-ray irradiation 3

4 1 1 Electro-physical precipitation Another process established at the Fraunhofer IGB is electrophysical 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 hydroxide flocs are produced in the process. These electrolytically 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 substances are precipitated. The precipitated substances can then be separated mechanically. Electro-physical precipitation replaces conventional chemical flocculation techniques with the advantage that the flocculants are made available electrolytically from solid state electrodes 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 process there are no costs for the purchase, handling, and dispersal 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 extended-time trials. Optimal infrastructure at the Fraunhofer IGB enables 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 combined, 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 processes 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-optimized treatment. However, not only oxidative and adsorptive processes can be combined advantageously. The combination with aerobic and anaerobic biological treatment stages can also be realized at the Fraunhofer IGB in laboratory scale and pilot plant demonstrations. 4

5 2 advantages With oxidative and electrolytic processes, it is possible to oxidize dissolved contaminants or pollutants that are difficult to break down. Pollutants are either directly oxidized or precipitated by way of hydroxide flocs. Electrogenerated hydroxide flocs are extremely well suited for removing the finest particle contaminants. The proposed oxidative and electrolytic processes do not increase water salinity, and the maintenance required is minimal. By process combination full treatment can be guaranteed even for varying pollutant load. Electrolytic and oxidative processes can be integrated advantageously 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. 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- 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. 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 m 3 /h process wastewater. 5

6 Applications and references 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, flocculants, 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 successfully 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 / H 2O 2 and anodic oxidation using iridium oxide electrodes As models for real wastewater from the textile industry, a dissolved organic dye and a particulate organic dye were discolored 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 efficient reduction of microbial contamination in cooling lubricant emulsions can be achieved by means of ultrasound or ultrasound 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 impairing 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. 6

7 Services provided 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 highperformance UV light source for the sterilization of water. It was effected in co-operation with a European industrial partner. The UV light in this application is emitted by a plasma, which is stimulated by microwaves. Unlike conventional mercury discharge lamps, the resulting UV light has a broad range of different wavelengths. The UV-spectrum was tailored to reach maximal germicidal effect. In another project funded by the EU we are developing, together 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 multichromatic UV light without adding any chemicals. For the production of ozone we have developed an electrochemical cell, with which ozone can be generated efficiently and inexpensively for environmentally compatible disinfection. The Fraunhofer Institute for Interfacial Engineering and Biotechnology 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 electrolytic and oxidative processes for water treatment Market and technology studies for process water treatment Comprehensive chemical and physical analyses to characterize process water Laboratory plants for customized pre-trials relating to flocculation 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 industrial partners Process optimization for the treatment of water as well as viscous media, such as cooling lubricants, foodstuffs, sludges, and pastes Integrated solutions by means of combination with aerobic and anaerobic biological processes Combination with processes for desalination or the recovery of acids and bases 7

8 Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB (Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB) Nobelstrasse Stuttgart Germany Phone Fax Director Prof. Dr. Thomas Hirth Phone Contact Dipl.-Ing. Christiane Chaumette Phone Alexander Karos, M. Sc. Phone Dipl.-Ing. Siegfried Egner Head of Department Physical Process Technology Phone 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 economic efficiency and sustainability. Our strength lies in offering complete solutions from laboratory 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 engineering, nanotechnology, industrial biotechnology, and wastewater purification. The Fraunhofer IGB is one of more than 80 research units of the Fraunhofer-Gesellschaft, Europe s largest organization for application-oriented research.