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[...]Grit Traps and Classifiers The best solution for any grit separation application Grit Trap and Classifier Product Groups Longitudinal Grit Trap Lamella Grit Trap Circular Grit Traps Complete Plants Grit Classifier For reasons of operating reliability of wastewater treatment plants it is necessary to separate grit, gravel and other mineral materials transported with the wastewater (an average of 60 l from 1000 m³ of wastewater according to DWA Work Sheet M369) from the digestable organic material. Good grit separation prevents operational problems, such as grit sedimentation in aeration tanks and digestors, reduces wear of subsequent equipment, such as pumps or stirrers, and avoids clogging of sludge hoppers and sludge lines. While as much as possible of the mineral matter should be removed, as much organic matter as possible should remain in the wastewater. Testing of the grit capture rate is usually done with a grit particle size of 0.2 mm. The most common grit separating systems in use are grit channels, circular grit traps and vortex grit traps. Grit is either separated by gravity sedimentation (grit channels) or centrifugal force (circular and vortex grit traps). FAQ Frequently Asked Questions What are the different types of grit chambers? Depending on the type of grit trap, they separate the grit either by gravity (grit channels, lamellae separators) or centrifugal force (circular and vortex grit traps). Scraper blades or screw conveyors are often used to clear a grit channel. Solids removal in the further course of the process is effected by pump, grit classifier or integrated grit classifying screw. HUBER grit traps are available in many different designs. How are grit chambers designed and dimensioned? According to Kalbskopf, the design of aerated grit chambers is always based on the retention time of the wastewater in the grit chamber. Unaerated grit chamber systems are always dimensioned according to the surface loading rate. What is the quantity of grit in municipal wastewater? The DWA Code of Practice M369 specifies an average amount of grit trap material of 60 l per 1000 m ³ of wastewater.[...]

[...]Emschermündung, Germany The hydraulic capacity of the wastewater treatment plant Emschermündung is 30 m³/s. This is a gigantic flow, larger than of any other German, perhaps even European, wastewater treatment plant. The wastewater arrives at the plant not via conventional sewers, but its inflow is the river Emscher. The treated effluent of the plant enters the river Rhine. This is the reason why the plant’s name is Emschermündung, meaning “mouth of the Emscher”. The river Emscher flows through the northern part of the old industrial heartland of Germany, the Ruhr region. The Emscher river is in fact used as an open sewer, serving several big cities and many towns located along this river. The Emschergenossenschaft (Emscher River Wastewater Association) has started a giant renaturization project by constructing sewers parallel to the river Emscher, starting upstream down, but it will take many years to complete this project down to the Emschermündung plant. Since the plant’s inflow is an open river, it has to treat a storm water flow of up to 30 m³/s. And one can easily imagine the huge freight of debris, leaves and grit arriving within a few hours after storm events. Giant bar screens are provided at the plant’s headworks. The first stage screens have a bar spacing of 60 mm, that of the second stage screens is 20 mm. The screened inflow enters a very large settling basin with a surface area that easily exceeds that of a sport stadium. Then the wastewater flow is distributed to several smaller parallel settling tanks with a length of 50 m. Bottom scrapers push the sediment back into the large basin. The combination of these basins serves as a giant grit trap. The large basin is provided with a pair of bottom scrapers, each provided with four air-lift pumps. The total grit slurry flow from the basin is 400 m³/h. Of course, this flow does not only contain grit, but also rocks, debris, silt, sludge and much water. Pair of 20 m³ slurry receiving tanks with HUBER Screw Conveyors Ro8 Two RoSF9 Wash Drums with WAP® screenings presses for the removed and washed coarse solids One of two big HUBER Coanda Grit Washing Plants RoSF 4, size 3 Video: HUBER Grit Treatment System RoSF5 at major WWTP "Emschermündung" One of two big HUBER Coanda Grit Washing Plants RoSF 4, size 3 The management of the Emschergenossenschaft decided to provide a grit treatment system They want to recycle their large amount of grit as construction material, e.g. for pipe or road bedding. This is only possible if the grit is washed, its organic content reduced to well below 5 % and dewatered. The problem was that such a giant grit treatment system, removing such huge freights of debris and sludge, has never been built before. No standard grit treatment system was available in the market for this purpose. In addition, the Emschergenossenschaft wanted to add some more grit slurry from other wastewater treatment plants, sewer flushing and gully cleaning. Planning of the entire grit treatment system was commissioned to the consulting engineering firm Dr. Sixt. As the result of a public tendering procedure, the Emschergenossenschaft selected the HUBER concept because of its obvious advantages in respect of functionality, operational reliability and cost effectiveness. Detailed design of the system began during autumn 2004, after we were awarded the contract for the supply of the system’s core equipment. For operational reliability our grit treatment and recycling concept includes redundant key components. It comprises the following main process steps: Up to 400 m³/h grit/sludge slurry flows through a channel to screw pumps with 540 m³/h capacity. After the slurry is lifted, it flows by gravity through the entire treatment system. First the slurry flows through a DN 800 channel to a pair of HUBER Wash Drums RoSF9 . Additional slurry from other plants, sewer flushing and gully cleaning is lifted from 20 m³ slurry receiving tanks into this channel by means of HUBER Screw Conveyors Ro8 . Course solids > 10 mm are retained and washed in the ROTAMAT® wash drums RoSF9, while the finer slurry drains through the drums’ perforations. The washed course solids drop at the end of the wash drum into WAP screenings presses where they are dewatered, compacted and discharged onto belt conveyors for discharge into containers. The screened slurry drains from the wash drums into an aerated concrete grit chamber underneath. The grit settles while most of the organic solids and silt is returned into the wastewater treatment plant for further treatment. The settled grit is removed with an air-lift pump that forwards a flow of about 60 m³/h grit slurry through an elevated channel. At the end of the channel the flow is distributed to a pair of HUBER Coanda Grit Washers RoSF4 . We provided our largest size grit washers that can each handle a 30 m³/h flow with 1.5 t/h of grit. Within the grit washer tanks, in a fluidized bed, the grit is washed from organic solids. The organics in the wash water overflow at the top and are returned to the plant. The washed grit is removed at the bottom of the grit washer tanks and dewatered in an inclined screw. At the end of the screw the clean grit, containing less than 3 % organics and less than 10 % water, is discharged into a container. The clean grit product is then reused as construction material. The grit treatment and recycle system was started up during fall 2005. During the following weeks we had to do some optimization work. In the meantime, the system operates reliably and to the customer’s satisfaction. It has proven well capable to handle even the extreme grit freights that the Emscher river carries into the plant.[...]

[...]Dublin, Ireland HUBER Technology UK was chosen as supplier of seven bar screens and seven screenings wash-presses for the Dublin Bay Inlet Works at Ringsend. The order also included supply of all control panels for all our machines. The plant’s management selected our multi-rake bar screens RakeMax® because of their low head loss during peak flow, in spite of their small bar spacing. Another selection criterion was their great screenings removal capacity. It also helped that our super-launder screenings presses WAP® SL provide superior washing intensity and compaction capability, resulting in a reduction of screenings disposal costs that are well beyond the reach of our competition. We supplied seven units of our multi-rake bar screens RakeMax® with a nominal length of 6,300 mm and a bar spacing of 6 mm together with seven units of our super-launder wash press WAP® SL size 12. Each RakeMax® screen feeds screenings through launder chutes to a dedicated WAP® SL. The RakeMax® screens replaced existing escalator type perforated plate screens (also called perforated band screens) with 6 mm diameter perforations. These prior screens were no longer capable to handle the increased peak flows and peak solids loads to the plant. Our equipment was installed in a rolling program, one unit after the other, with the treatment plant remaining in continuous operation. The RakeMax® units have a 6mm bar spacing and the bars do not have a rectangular or trapezoidal shape, but cross section with the shape of a tear drop. A tear drop shape causes little flow restriction and thus low head loss, or the other way round, the tear drop shape guarantees high flow capacities. The supplied screens handle a peak flow of 4.7 m³/s (75,000 GPM). Several rakes per screen are mounted between a pair of chains. The chains are driven by a variable frequency drive (VFD) and are moved at a faster speed when the hydraulic head rises beyond a certain set point. This head is monitored in each of the seven channels with a Pulsar Ultra 5 differential ultrasonic level sensor. This means: if the screens become blinded, the raking process is automatically accelerated and the degree of blinding and the head loss are thus reduced again. The WAP® SL units are designed for high-intensity washing of the screenings. Well washed screenings can be better compressed and compacted. The washed-out BOD is returned into the treatment plant and remains available for the denitrification process that operates more effectively the higher the BOD/N ratio is. The regular wet screenings processing capacity per WAP® SL unit is 8 m³/h. At peak times, when all screens are operating fast, the WAP® unit’s operating cycle is automatically modified to allow each unit to process 12 m³/h. This operating cycle is even further accelerated as the conveyor sections of the machines are also driven with variable frequency drives to permit even more feeding of the WAP® SL units in case that the screenings load should rise further to 15 m³/h. This unique throughput versatility is only available with HUBER wash presses. Installation of our entire equipment was supervised and supported by Huber engineers to ensure that progress of this large and important project was smooth. All Huber machines were supplied with control panels designed, built and programmed by Huber engineers. Each contains an Allen Bradley PLC & HMI system with variable speed drives. Compact Block I/O units are used to communicate with the customers DeviceNet site network for the transmission of telemetry status signals and remote enable signals. The successful completion of this project has demonstrated our ability to provide the right solution for our customers’ needs and requirements thanks to our wide product range. And it has also demonstrated the ability of our HUBER UK engineering team to develop intelligent control solutions in compliance with customers’ specifications.[...]

[...]Every wastewater regulation specifies a limit value for ‘lipophilic substances’, which in practice are referred to as grease. As a rule, more than 90 per cent of the total grease concentration is often present as dispersed grease particles and emulsified grease. Conventional grit and grease traps at sewage treatment works can only retain non-dispersed, floatable grease (DWA M760). The remaining dispersed substances are separated in the biological treatment section of the sewage treatment works. Various grit chamber solutions Factory-built grit chambers are often combined with grease traps (floating-material separators) (DIN 19569-13). According to DWA, factory-built and cast-in-situ aerated long grit chambers – i.e. grit channels with a specific length-to-width ratio – can be supplemented with a grease trap (grease trap pocket) by means of a slotted partition wall. The HUBER Complete Plant ROTAMAT ® Ro5 has been manufactured for over 30 years using state-of-the-art technology with a separate grease trap, as shown in Figure 1. Factory-built, manufacturer-specific grit chambers do not usually have a separate grease trap pocket, but instead separate the floating matter by means of a submerged baffle at the outlet of the grit chamber. Effective grease separation requires large, calm surfaces to ensure that the floating matter accumulated on the liquid surface is not resuspended. In the case of aerated DWA grit channels with a side-mounted grease trap, the non-dispersed, floatable fats are transferred into the grease trap by the resulting laminar flow and remain there until removal. Factory-manufactured, customised grit chambers which operate without a grease collection trap despite being aerated can only retain non-dispersed, floatable fats to a limited extent due to the very turbulent surface. One exception is the HUBER Complete Plant Hydro Duct ROTAMAT ® Ro5 HD system, as this machine features a non-aerated section with a calm surface. Removal and disposal of floating matter The removal and disposal of retained floating matter are handled in different ways. HUBER grit chambers use automatically operated paddle scrapers without exception (see Figure 2). The accumulated floating matter is pushed along the grease trap pocket or a baffle wall and, at the end, is discharged into a grease collection shaft via an inclined ramp (see Figure 3), having been partially dewatered. A level-controlled screw pump conveys the moist solids, where possible, into a raw sludge shaft (digestion) or into a separate container. Other systems attempt to remove the accumulated floating matter using fixed, height-adjustable pumping equipment, or flush the floating matter into a channel using a large volume of wastewater by raising the water level. In both cases, solid–liquid separation must take place in an external, additional unit to avoid problems in the digester or during disposal by third parties. As a general rule, returning the grease–water mixture to the wastewater stream (upstream of the screen) or feeding it into a wash press should be avoided.[...]

[...]In Germany, Austria and Switzerland, enough water of high quality is naturally available at any time. One could almost forget that our most important resource is highly sensitive and gives life not only to humans and animals but also to germs and microorganisms. There are therefore good reasons to protect our water resources and use air filters in drinking water reservoirs. “We have never always built water reservoirs without air filters. Why should we use air filters now?” You may have heard this provocative counter-question sometimes from a customer when you recommended that he should improve his reservoir and try something new. If you sometimes do not have the time and patience or the right arguments in such a case to counter such a question, frequently asked by a person with “experience”, we explain in the following several good reasons why to use air filters in water reservoirs: Water comes clean from a spring or well and is intermediately stored in a "clean" reservoir before it is distributed to the consumers via pipelines. Even if the operators of public water supply facilities are well familiar with germ numbers, they often do not consider that the source of germs can be dust in the air which the water reservoir sucks and releases. The long established practice of using ventilation chimneys in water reservoirs is still very common, frequently with “diagonal” supply and exhaust air streams. Many operators think it is enough to have an insect screen with 1 mm mesh or perforation. They think everything is all right with some air draft. Basically, air exchange is the right idea but only as long as the air is very clean. We all tend to forget that dust is always present in the air. We only remember it in spring, during the blossoming of the trees, when a yellow dust layer covers our cars we have cleaned the day before, or once a year when the wind brings dust from Africa and colours the sky in ochre creating exceptionally beautiful red sunsets. We should then be aware that also our water reservoirs ‘breath in’ this dust and the undesired germs contained if the air remains unfiltered. We want to explain below how much dust and germs are present in the ambient air which stream into the water reservoir with the unfiltered air and settle on the water surface and the reservoir walls and ceiling. Due to their huge volume water reservoirs are ideal ‘dust settlement chambers’ where the air is cleaned like in a wet scrubber. But the problem is that the scrubbing water is our drinking water. We should therefore think twice and better filter the air before we say: “We have never used air filters. Why do we need them now?” The HUBER catalogue "Innovative Solutions for Potable Water" and our PG8 brochure “Hygiene in Drinking Water Reservoirs” explain the fundamentals of air filtering for water reservoirs. An annual amount of 21,000 mg dust and 1680 billion germs pass into a 500 m³ water reservoir. This figures can be explained: If you search the internet to find the 'average dust content', you will find 0.05 mg/m³ (after rain events) or 0.1 mg/m³ (dry weather) in rural areas and 0.1 to 0.45 mg/m³ in urban areas (source: ikz.de). This is not much, one may think at first glance. But we should look at these figures in more detail: If we assume a ventilation number of only 1.2 per day, due to the varying water level, and multiply it with the a.m. 0.1. mg/m³ and 365 days, the result is 500*1.2*0.1*365 = 21,900 mg or 21.9 g per year, which is not a small amount. We offer our HUBER air filter plants L251, L252, L361 and L661 especially for the use in water supply facilities. Air throughput capacity is specified for a pressure difference of 120 pascal. In order to dimension the filter plant to suit the individual water reservoir, we use the formula “reservoir volume divided by 2.0 to 2.5”. The water reservoir either breathes the air in and out automatically as the water level falls and increases, or an additional ventilator is installed upstream of the filter (and operated with overpressure!). An additional ventilator is recommended where condensation is expected to occur and needs to be reduced. In this case, it must also be provided for an outlet air duct with a flap closing without current. For applications with an additional ventilator we recommend to use the type L 361 filter plant if there is sufficient space. Our L 361 filter plants have a class F6 fine filter upstream of the class H13 filter for suspended matter. The fine filter retains already approximately 95% to 99% of the dust (depending on particle sizes), with the result of a significantly longer life of the class H13 filter with a gravimetric separation efficiency of 99.95%. H13 filters are used in clean rooms, semiconductor production, sterile bottling plants of the pharmaceutical industry, or to filter the exhaust air from nuclear-technical plants. The costs of a HUBER air filter plant are in the parts per thousand range of a complete new building project or complete refurbishment of a water reservoir. The budget for an air filter plant without pipelines and additional ventilator is 1,500 to 3,000 €, depending on the range of equipment features. No chimneys are required if a lateral safety louvre with insect screen and wall connection plate is used.[...]

[...]India The joint venture A.T.E. HUBER Envirotech continues to grow in the field of sludge dewatering, achieving considerable success with the HUBER Screw Press Q-PRESS®. To provide optimal support for the first commissioning projects in India, twelve of the partner’s service technicians completed two intensive online training courses delivered by the HUBER Service Academy. This laid an important foundation for a smooth project start and the sustainable transfer of knowledge. Deepening technical and process knowledge The first training module focused on the technical fundamentals of the supplied machinery. The participants gained structured insights into the design and operation of the Q-PRESS®, specific installation guidelines and systematic commissioning preparation and execution. Thanks to the practical approach, the colleagues developed a solid understanding of mechanical processes and the relevant control functions. The second training module deepened the process-related know-how that is crucial for stable and efficient operation. Topics covered included design guidelines for peripheral plant components, such as polymer preparation and mixing technology and pumps, as well as setting key control parameters correctly. The participants also learnt how to interpret key performance indicators, optimise processes in a targeted manner, and reliably resolve typical faults. This provided the service technicians with both theoretical knowledge and concrete recommendations for action in the field. Successful application and strengthened collaboration The compact training course had an immediate impact: Shortly after it concluded, A.T.E. HUBER Envirotech reported the successful commissioning of a project involving three HUBER Screw Press Q-PRESS® 440.2 units, leaving the customer highly satisfied. This outcome highlights the importance of joint knowledge transfer and the high quality of the training provided. The training programme strengthened the technical expertise of our Indian colleagues and also furthered international cooperation. The HUBER Service Academy is thus making an important contribution to global quality assurance and the successful implementation of future projects.[...]

[...]Uhldingen-Mühlhofen, Germany In August 2023, after more than two years of construction, one of the most cutting-edge systems for the removal of trace substances was successfully put into operation at the Uhldingen-Mühlhofen association sewage treatment plant. At the heart of the new treatment stage is a combined process of ozonation and activated carbon filtration on a technical scale that had not yet been implemented to date. 24 HUBER CONTIFLOW® GAC activated carbon filters and HUBER TT7 pressure door HUBER supplied the two-lane activated carbon stage with a total of 24 CONTIFLOW® GAC activated carbon filters for reliable biological post-filtration and adsorption. In addition, the upstream ozone reactor was equipped with the proven HUBER TT7 pressure door. As part of ozonation, trace substances are initially oxidised and converted into various transformation products. In the downstream activated carbon filter stage, these products are partly biodegraded and partly adsorbed. Reliable separation of persistent and hazardous trace substances With this additional treatment stage, the largest sewage treatment plant of the Lake Überlingen Wastewater Association now treats up to 230 l/s. Persistent and hazardous trace substances such as medication residue, hormones and flame retardants are reliably separated even before they enter Lake Überlingen. This part of Lake Constance supplies around four million people in large parts of Baden-Württemberg with around 135 million m³ of drinking water each year.[...]

[...]The wastewater expert Hans G. Huber receives the highest endowed European environmental award The Deutsche Bundesstiftung Umwelt (DBU), one of Europe's largest foundations that promotes innovative and exemplary environmental projects, awards the Deutschen Umweltpreis 2006 (German Environmental Award 2006) to Hans G. Huber, member of the board of directors of the Hans Huber AG, for his innovative decentralised wastewater treatment technology. The wastewater expert Hans G. Huber receives the highest endowed European environmental award for outstanding achievements in global environmental protection for his great commitment to developing and successfully promoting high-quality, reliable technologies for fresh water and wastewater treatment, especially also in emerging and developing countries. The Deutsche Bundesstiftung Umwelt (DBU), one of Europe's largest foundations that promotes innovative and exemplary environmental projects, has awarded this highest endowed European environmental award to Hans G. Huber, member of the board of directors of the Hans Huber AG, for his innovative decentralised wastewater treatment technology. “As a visionary businessman Hans Huber is searching for technical solutions to our global water problems. He sees wastewater as a resource and has committed himself to the reuse of this valuable product.” – With these words Dr. Fritz Brickwedde, secretary general of the Deutsche Bundesstiftung Umwelt (DBU), honoured today the sixty-four-years-old Bavarian businessman. He said Hans G. Huber had developed reliable, high-quality technologies for fresh water and wastewater treatment that are applicable also in emerging and developing countries. In this way he contributes to achieving a millennium goal of the United Nations. His successful marketing shows that ecology and economy can be combined. A commitment that pays off: Hans G. Huber receives DBU’s German Environmental Award 2006. The award was handed over by the German Federal President, Horst Köhler, in Dresden on 29 October 2006.[...]

[...]After 41 years, Hans Huber and Karl-Josef Huber retire from their position as managing directors. Dr.-Ing. E.h. Hans Huber and his brother Karl-Josef Huber have given up their position as CEOs but will stay with the company as members of the supervisory board. With Hans Huber’s son Georg Huber and Dr.-Ing. Oliver Rong, son-in-law of Karl-Josef Huber, the sixth Huber generation has taken over the management of the company that has been family owned for 175 years. With effect from 1st January 2010 Georg Huber is CEO of HUBER SE and further in charge of finances and personnel. Dr.-Ing. Oliver Rong is Vice CEO and in addition in charge of production, engineering/design and purchasing. Dr.-Ing. Johann Grienberger (in charge of technology) and Rainer Köhler (in charge of sales) complete the board of directors. In 1968, when the two brothers Hans and Karl-Josef Huber took over the former Hans Huber GmbH from their father, the company counted just about 25 employees. By focusing on the material stainless steel and the water sector they managed to develop the locally acting company into a global player. Today, with 500 employees at its headquarters in Berching, HUBER manufactures more than 2000 machines each year in its state-of-the-art factory that is highly specialised on processing stainless steel. Over 25,000 HUBER machines have been sold worldwide since the nineteen eighties. HUBER's global presence in over 60 countries consists of 25 subsidiary offices and numerous agencies throughout the international market for wastewater treatment, sludge treatment and process technology. In total, about 900 employees worldwide work for the HUBER group. The young generation of the Huber family with Georg Huber and Dr. Rong emphasize they will continue to pursue the policy Hans Huber and Karl-Josef Huber have felt committed to. It is also their goal to develop and produce in Berching innovative products and solutions for the international markets and sell them all over the world via HUBER’s worldwide network of subsidiaries, agencies and representative offices. As supervisory board members, Hans and Karl-Josef Huber will certainly also in the future contribute their valuable expertise that is backed by decades of experience.[...]

[...]Summary The HUBER Disc Dryer RotaDry® is a robust and compact dryer design with a high water evaporation capacity in relation to volume and footprint. It is ideally suited for the partial drying of sewage sludge and for the interaction with a fluidised bed mono-incineration plant. Fully automated, it contributes to a relief of the operating personnel and an optimisation of the combustion of sewage sludge. Effective disc drying supports sewage sludge mono-incineration. A high percentage of phosphorus can be recovered relatively easily from the ashes produced by acid hydroloysis. This is of great importance with regard to the future phosphorus recovery obligation for medium and large wastewater treatment plants. Disc drying technology has proven itself over decades for the partial and full drying of sewage sludge. For an effective application of disc drying systems and the use of waste heat, certain basic conditions must be taken into account. The basic concept of disc drying technology dates back to the 1960s, and was initially developed for drying fish meal. In the 1970s and 1980s, this contact drying system found a new area of application in the field of sewage sludge drying on large sewage treatment plants or fluidised bed mono-incineration plants. For more than 40 years, disc drying of sludge has proven itself in practice. Usual water evaporation capacities per unit are in the range of 2,000 to 6,000 kg/h. Description of the dryer and its operation The disc dryer consists of a heated rotor fitted with hollow discs, which rotates in a housing. It belongs to the category of indirect contact dryers. The material to be dried touches the heated discs, is heated up and dried. To increase performance, additionally the housing can be equipped with a heated double jacket. The heating media are usually saturated steam in the pressure range of 6 to 10 bar(a) and temperatures of 158 to 180 °C as well as thermal oil in the temperature range of 180 to 220 °C. For an effective utilisation of the contact heating surface, the use of saturated steam is advantageous compared to superheated steam. The pressure drop in steam pressure control should be kept as low as possible to maximise the effective pressure difference of the steam turbine for power generation. The sludge is fed at one end of the dryer via a screw or a thick sludge pump and moves through the dryer. Due to the rotation of the discs, the sludge is mixed and transported further by conveying elements attached to the disc peripheries. The dried sludge is discharged via a screw mounted at right angles to the discharge end of the dryer. Fixed scrapers are mounted between the discs, which prevent the sludge from sticking to the discs. The rotor speed ranges from 8 to 11 revolutions per minute depending on the disc diameter. Figs. 2 and 3 show the view and the internal structure of a HUBER Disc Dryer RotaDry®. The discs are usually made of stainless steel 1.4307 or, if there is a higher risk of corrosion, 1.4571. If increased wear and tear due to special sewage sludge contents such as sand or crystals of magnesium-ammonium-phosphate is to be expected, the discs can optionally be designed in duplex steel. Field of application of the HUBER Disc Dryer RotaDry® Partial drying One of the main applications of the disc dryer is the partial drying of sewage sludge for a self-sustaining fluidised bed mono-incineration. In this process, the energy content of the partially dried sewage sludge must be adjusted to approximately 4,000 to 4,200 kJ/kg of original substance, whereby preheating of the combustion air is assumed. Depending on the type of sewage sludge and its degree of stabilisation, this means drying to a dry residue content (DR) of ~ 35 to 45%. In any case, the DR of the partially dried sewage sludge must remain below a critical dry residue level, which is characterised by the glue phase in a DR range of 40 to 60%. The sludge becomes sticky, pasty and difficult to convey. With low stabilised sludge the phase starts in the range of 40 to 45% DR, with well stabilised sludge the glue phase is only reached above a DR of 45 to 50%. The partially dried sludge is then conveyed to the incinerator and shredded and fed into the fluidised bed of the incinerator via a throw-wheel feeder or steam lances. In mono-incineration plants, two disc dryers are usually used in parallel for redundancy reasons. In this case, each dryer is designed to handle about 50% of the total water evaporation volume. In extreme cases, however, one dryer must be capable of handling up to 70% of the total drying capacity even if the steam pressure increases, in order to maintain combustion in partial load operation. For redundancy reasons, each dryer is equipped with its own sludge feeding system. As a result of the AbfallKlärV ordinance, which was passed at the end of 2017, more and more projects for partial drying and mono-incineration of sewage sludge are being planned and implemented. An economical operation with a corresponding size of the mono-incineration system can be more easily implemented through the delivery and acceptance of foreign sludge from the region. This has certain consequences for the operation of the plant. On the one hand, the problem of foreign matter must be taken into account. Frequent transshipment processes during the sludge transport increase the risk that foreign matter such as stones, metal or wooden parts are mixed into the sludge and can possibly cause blockages or damage to the plant. If necessary, foreign matter separation in the form of a double-shaft roller separator or a screen for impurities must be provided in the sludge transport line. On the other hand, dewatered sludge with widely varying dry residues and properties is delivered to the sites. When drying and incinerating on large sewage treatment plants with mainly own sludge, the sludge properties vary only to a limited extent between summer and winter operation. With a high proportion of foreign sludge, the operation of the sewage sludge mono-incineration plant is made considerably more difficult because the throughput of dewatered sludge must often be adjusted depending on the DR content of the sludge at the dryer inlet. Each drying plant is designed for water evaporation capacity and not for sewage sludge throughput. A lower DR content of the dewatered sludge causes a reduction in throughput for the same water evaporation rate and vice versa. In this context it is advantageous for the operator to be able to rely on a DR measurement of the dewatered sludge and the partially dried sludge. In order to relieve the operating personnel, the throughput adjustment on the disc dryer should be fully automatic by means of a control system. This also improves the interaction with the downstream combustion, which requires partially dried sludge with a heating value that is as constant as possible for long-term stable operation. The incineration of the partially dried sludge provides sufficient thermal energy in the form of steam for disc drying. From a thermal capacity of the incineration plant of around 3 MW, the use of a steam turbine for electricity generation can also become economical. Full drying In the 1990s, disc dryers for full drying to over 90% DR were installed at larger sewage treatment plants without their own incineration. In this case, however, part of the dried material must be mixed back into the dewatered sewage sludge to avoid passing through the critical glue phase in the dryer. This gives the mixed sludge a dry residue of 60 to 65% and it can be conveyed through the dryer without mechanical problems and dried in the usual way. Due to a lack of waste heat, however, primary energy in the form of oil or gas often has to be used for steam generation or for heating thermal oil. In the case of full drying, a dust separator must be connected between the dryer and the condensation stage, otherwise there is a risk of the condenser blocking and the condenser must be cleaned more frequently in any case. Vapour condensation The condensation of the vapours containing water vapour is carried out either directly by spraying vapour condensate or indirectly via a tube bundle heat exchanger. There is also the possibility of multi-stage condensation, in which, for example, thin sludge can be preheated in the first stage and used to increase the degree of dewatering of internal sludge. The second case of indirect heat exchange has the great advantage that waste heat can be used at a higher temperature level of up to 90 °C, e.g. for an external local heating supply. The heat transfer during vapour condensation is significantly influenced by the leakage air portion in the vapours. The lower the leakage air mass flow, the more effective the condensation. The non-condensable parts of the vapour flow are generally used as secondary combustion air in partial drying with downstream fluidised bed combustion due to the high odour load. The vapour condensate is polluted with ammonium and COD-bearing substances such as fats, white oils or organic acids and must be treated before indirect discharge to the sewerage system.[...]