September 9, 2024. DAS Environmental Experts offers customized, sustainable wastewater solutions and recycling concepts for the semiconductor industry. With high quality standards and individual project management, we are your reliable partner.
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Water is a vital resource for humans, animals and plants, but only just under three percent of the world’s water reserves are freshwater. Large parts of this usable freshwater are inaccessible due to natural conditions and anthropogenic influences. The latter include water pollution, overuse, loss of forests and peatlands as important water reservoirs and increasing urbanization. These man-made changes affect the natural water cycle and have far-reaching consequences, including river changes, land use change and climate impacts. At the same time, the demand for freshwater is continuously increasing worldwide, particularly due to population growth, industrial development and climate change. According to UN forecasts, the world’s population will grow to around 9.7 billion people by 2025.
According to estimates, annual global freshwater consumption is already around 4 – 4.5 trillion cubic meters (4000 – 4500 cubic kilometers) per year. Germany alone has an annual water consumption of around 219 billion cubic meters, with industry, agriculture and private households being the main consumers. At the same time, the water infrastructure in many parts of the world is outdated and urgently requires investment.
As a major consumer of water resources, the semiconductor industry faces the global challenge of optimizing its water requirements and using innovative wastewater treatment technologies to reduce the strain on freshwater resources and ensure sustainable use of this vital resource.
The production of microprocessors on silicon wafers is energy-intensive and consumes large quantities of water, chemicals and gases. In addition, hazardous waste such as heavy metals, acids and solvents are produced, which can cause environmental damage if they are not disposed of properly. In the production process, the silicon wafers pass through more than 1000 individual process steps in the clean room and must be cleaned regularly. Ultrapure water (UPW) is used for these cleaning processes.
In addition, ultrapure water is used in etching processes to remove excess etchant and neutralize any chemical residues. Both in the cleaning processes and in the etching process itself, the water is contaminated by various chemicals and process gases such as nitric acid, sulphuric acid, hydrogen fluoride, ammonia, hydrogen peroxide, isopropanol and particles from the various phases of chip production and must be purified at great expense.
With over 30 years of experience in industrial wastewater and waste gas purification, DAS Environmental Experts is the epitome of German engineering and quality manufacturing. Our proven and scalable solutions provide reliable wastewater treatment for the specific requirements of high-tech manufacturing as well as numerous other industries such as food and beverage, chemical, pharmaceutical and cosmetics.
Our project approach encompasses the individual requirements of our customers from wastewater volume and composition to specific requirements for energy and chemical use as well as footprint and other design requirements to effluent quality for recycling, indirect as well as direct discharge. By prefabricating the plant components in Dresden, we guarantee the highest quality and efficiency.
Our comprehensive range of services covers all areas: from consulting (including laboratory and pilot tests) to planning, plant construction, commissioning, optimization and maintenance of wastewater treatment plants. Our versatile range of biological, mechanical and chemical-physical processes enables us to reduce the specific pollutants in our customers’ process, industrial and waste water to the permissible limits for discharge or recycling.
This includes, among other things:
A moving bed biofilm reactor (MBBR) is a biological reactor, capable of removing a wide range of organic contaminants from industrial wastewater due to its flexibility and efficiency. It offers good performance in the removal of nitrogen and phosphorus compounds as well as in the removal of organic compounds represented as COD/BOD/TOC. The process is robust, user-friendly and easily scalable, making it highly adaptable to specific customer requirements. The use of carrier material and the associated very high sludge age is ideal for adapting to a wide range of organic substances, including those that are difficult to degrade. As it is not activated sludge, less excess sludge is also formed, which reduces operating costs.
The MBBR contains loosely packed plastic support material, which serves as a surface for the colonization of specialized microorganisms. These free-floating carrier materials have a large surface area to enable a high biomass concentration. The microorganisms are responsible for the degradation of both organic wastewater constituents and nitrogen compounds and ensure that the MBBR process is much more stable and adaptive than other biological treatment technologies due to the very long residence time in the wastewater and the resulting selective specialization as well as the protected space in the growth bodies.
Air is blown into the reactor to provide oxygen and supply the microorganisms with nutrients. Due to the lower solids content compared to activated sludge processes, the oxygen input is very efficient. At the same time, aeration ensures mixing of the wastewater and the carrier materials in the reactor.
Microorganisms in the wastewater, such as bacteria, attach themselves to the surface of the carrier materials and form a biofilm. This biofilm contains a variety of organisms that can break down organic compounds in the wastewater.
The microorganisms in the biofilm break down organic compounds and other pollutants in the wastewater by using them as a food source. This degradation takes place through biochemical processes such as aerobic and anaerobic respiration and denitrification.
After the microorganisms have broken down the pollutants, the purified water flows out of the reactor. Most of the biomass remains in the reactor and can be used for the biodegradation of further pollutants. As the biomass is not present as activated sludge, there is also less excess sludge at the end.
The EE has many years of experience with MBBR in various industries.
For the use of this technology in the semiconductor industry, we recommend the following technological process combination as an example:
Another wastewater treatment method, that can be used in the semiconductor industry is the Membrane Bio Reactor (MBR). Here, the activated sludge process is combined with membrane filtration to retain particles and activated sludge before the biologically treated wastewater is discharged.
The wastewater is first fed into a biological reactor with microorganisms. These organisms play a decisive role in the degradation of organic contaminants in the wastewater and, in contrast to the MBBR, are not present as a biofilm but as activated sludge and therefore in the form of flocs suspended in the wastewater. Here too, anaerobic, anoxic and aerobic basins or zones are used in order to utilize the properties of different microorganisms in the biocenosis. In contrast to the MBBR, however, these pass through all stages and do not remain in one zone.
In order to maintain the activity of aerobic organisms, air is blown into the reactor, which enables their aerobic growth and accelerates the degradation of impurities. Anaerobic or anoxic zones are mixed without the introduction of air. The treated wastewater then passes through membrane filtration in the MBR system. Special membranes are used to effectively retain particles and activated sludge.
Periodic backwashing of the membranes is required to remove deposits and blockages, which is usually done by reversing the water flow or chemical cleaning methods. Depending on the level of contamination, alkaline solutions, acids or enzymatic cleaners and hypochlorite containing chlorine are used. The activated sludge is recirculated into the upstream parts of the plant in order to avoid a critical concentration in the membrane chamber. The excess sludge produced during the process is also removed from this recirculation. Finally, depending on the application, the purified water can be reused or fed into the central wastewater disposal system.
Alternatively, it can be subjected to further purification processes in order to achieve higher purity levels. The advantages of this process are, for example, the absence of solids in the effluent, potentially lower reactor volumes due to higher activated sludge concentrations, simple increase in filtration capacity in stages and lower footprint of solids separation compared to gravity sedimentation.
Chemical-physical wastewater treatment is a combination of different processes to remove heavy metals, organic compounds, acids and bases as well as particles from the process water. Depending on customer requirements, our team of experts decides which of the processes to combine in order to achieve optimum results.
Filtration is a mechanical process for separating solids from liquids. Membrane filtration in the form of microfiltration, ultrafiltration, nanofiltration and reverse osmosis, which can retain particles and molecules of a defined size, is particularly suitable for use in the semiconductor industry. This process can also be used to remove colloidal substances and bacteria and to desalinate the water.
Flotation removes dispersed or suspended substances from liquids using coagulants such as aluminum sulfate or ferric chloride as well as flocculants. The process effectively contributes to the removal of particulate impurities from other treatment steps such as activated sludge separation from the MBBR before the water is subjected to further purification processes.
Sedimentation is used to separate solid particles by gravity in shallow, virtually flow-free tanks. The tanks are usually designed according to residence time, i.e. the water must remain in the tank until the particles have sunk. Depending on the particle size, sedimentation is a robust, low-energy and simple process for separating solids by using gravity. It can be spatially optimized using lamella lamella separators.
Oxidation processes are used, among other things, to remove organic compounds that are difficult to biodegrade, particularly effectively through photochemical purification with hydroxyl radicals from hydrogen peroxide or ozone using UV light. These Advanced Oxidation Processes (AOP) reliably destroy trace substances. This process can also be used to break down so-called heavy metal complexes.
Adsorption is the accumulation of substances on the surface of a solid by van der Waals forces. The adsorbent activated carbon can bind a variety of substances to its porous surface. This effectively binds organic compounds such as PFAS and other dissolved substances from wastewater. Doped activated carbon and iron hydroxide granules are used to remove arsenic and heavy metals. Chemisorption, in which substances are bound to the surface by chemical bonds, is often irreversible in contrast to adsorption.
Neutralization is used to adjust the pH value. Acids or bases are added as required, particularly after processes such as precipitation and flocculation. It can also be used before the biological process to set a neutral pH value so that the bacteria are not destroyed.
Precipitation is a chemical process for separating a previously dissolved substance from a solution. Heavy metals are precipitated by adding suitable substances to convert them into sparingly soluble metal hydroxides. Anions such as fluoride ions can be precipitated by reactions with calcium, iron or aluminum salts. Iron and aluminum salts can be used for phosphate precipitation.
Flocculation removes the finest particles from the water, which are present in suspension or as colloidal solutions. Using suitable chemicals called flocculants and flocculation aids, these particles can be agglomerated to form macro-flocs that sediment. This improves the settling properties and dewatering of residues.
Ion exchangers are materials that can replace ions in a solution with other ions. For example, calcium ions can be replaced by sodium ions. When the ion exchanger is exhausted, it must be regenerated. Ion exchangers are used for the targeted removal of heavy metals and ions, e.g. as a “police filter” after precipitation/flocculation. They are also used for softening, resalination and desalination of water. In the semiconductor industry, they are crucial for the production of extremely pure, demineralized water (ultrapure water).
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👉 MBBR wastewater treatment plant for the multi-stage biological treatment of wastewater from etching processes (YouTube)
Photo: DAS Environmental Experts
