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      Aggregate Washing | Water Treatment

      Water Treatment

      Traditionally lagoons have been used to settle the silt (- 63 micron) and reuse the water in the washing process. However, nowadays due to environmental, planning or space restrictions, new solutions have to be required.

      Duo is recognised as the market leader in the quarrying and aggregate recycling industries for water and silt management systems. We are able offer bespoke solutions for individual applications using the very best technology from the leading manufacturers in Europe together with our own products and processing experience.

      At Duo we pride ourselves on meeting the exact requirements of our customers rather than offering from a limited range of standardised products.

      Filter Press

      Filter presses are used to dewater sludge from the underflow of thickener tanks. Filter presses operate on a batch process and produce a dry silt cake that is typically between 20% and 30% moisture.

      The basic principle involves thickened sludge being pumped under pressure in to the chambers within the press. Each filter plate is covered by a filter cloth and as the sludge is pumped in, the water drains through the filter cloth and exits the plates. When the water has sufficiently drained to the required moisture content, the press automatically opens and discharges the dry cakes into a stocking bay below.

      Side Beam

      The sidebar filter press is the cost-effective solution for producing high solids filter cake with extremely high clarity in the liquid effluent. It combines rugged construction, precision engineering, ease of operation and a wide range of features and options to tackle the most difficult dewatering problems.

      It produces consistent results under varying influent conditions.

      Sidebar construction, filter plate size range available from 250 mm x 250 mm to 1500 mm x 2000 mm.


      Model No.Plate Size Volume (L)
      1800 x 800272
      21000 x 1000567
      31000 x 1000432
      41000 x 1000810
      51000 x 10001012
      61000 x 1000675
      71300 x 13001350
      81300 x 13002700
      91300 x 13001125
      101300 x 13002025
      111300 x 13001575
      121300 x 13002070
      131300 x 13003510
      141300 x 13002520
      151300 x 13003015


      • Operating Pressures 6 bar to 16 bar 
      • Versatility of plates, manifolds, automation levels and optional equipment
      • Electric hydraulic closure systems.

      Features & Benefits:

      • World Class engineering standards
      • Specifically designed to cope with abrasive slurry
      • Production of a very dry, manageable cake. Typical moisture content less than 30%
      • Wide range of sizes and configurations
      • Optional expansion piece
      • Different cake thickness available for different sludges
      • Automatic Operation
      • Dewatering solution to most process flows
      • Long service life

      Overhead Beam

      The overhead filter press represents the state-of-the-art in filter press design and is available in a variety of sizes and styles to suit the most rigorous applications. The filter plates are suspended from the top which allows for excellent access and all the working mechanisms are protected. The continuously revolving chain mechanism allows for very quick discharge of the filter cakes.


      Model No.Plate Size Volume (L)
      11000 x 10003248
      21200 x 12005423
      31300 x 13006287
      41500 x 15009190
      51500 x 200012211
      62000 x 200017283
      • Overhead construction size range available from 1200mm to 2000mm
      • Operating pressures 6 bar or 16 bar
      • Versatile selection of plates, manifolds, automation levels and optional equipment
      • Electric hydraulic closures systems
      • Single ram compression closure available in all sizes up to 1500mm
      • Four ram tension closure available in 2000mm

      Features & Benefits:

      • Very fast opening time 
      • High throughput capacity
      • Wide range of sizes and configurations 
      • Optional expansion piece 
      • Automatic operation 
      • Rugged construction 
      • Extensive aftermarket services available 
      • Dewatering solution to most process flows 
      • Future expandability 
      • Easy access to filter plates and cloths
      • Reduced labor 
      • Long service life 
      • Convenience and reliability


      Centrifuges dewater sludge on a continuous process using the principle of centrifugal force. Centrifuges are becoming more popular in the aggregates industry due to their compact size relative to the production levels, their lower capital cost and their lower operating costs. They produce a dry silt cake typically ranging from 35% to 45% moisture. 

      The basic principle involves pumping thickened sludge into a rotating drum. Flocculent is added prior to the feed point to create strong bonds between the silt particles. The rotating drum causes the solids to settle on the drum and the water is discharged by gravity. A rotating screw conveys the dewatered solids to the discharge end of the centrifuge for stockpiling.

      We work with our Italian partner, Gennaretti, who are experts in this method of dewatering. Gennaretti have built up extensive knowledge in the last 10 years of processing silts from aggregates. They are market leaders in this field due to their focus in this area and ongoing research and development program.


      ModelHydraulic CapacityMotor Power (Kw)Dry Solid reject (m³/h)Dimensions LxDxH (mm)
      GHT 1026110.51575 x 690 x 1348
      GHT 2021518.522170 x 880 x 1755
      GHT 302202232510 x 880 x 1755
      GHT 302-410303052510 x 880 x 1755
      GHT 40245457.52960 x 1300 x 2000
      GHT 5026055123330 x 1300 x 2067
      GHT 502-6009075183330 x 1300 x 2067
      GHT 60220016035.54850 x 2000 x 2750

      Features & Benefits:

      • Specifically designed to cope with abrasive slurry
      • 5000 hours’ warranty on the main wear part of the machines
      • Compact size relative to production levels.
      • Production of a dry, manageable cake
      • Very successful at processing silts from Recycled Aggregates, Sand & Gravel, Limestone
      • Continuous automatic adjustment of scroll speed to maintain cake dryness and throughput
      • Touch screen PLC electric panel
      • Simple rotor pump to feed centrifuge
      • Very fast installation time
      • Highly mobile


      Decanter GHT P
      The scroll and the bowl drive of these machines is driven by a single electric motor operated by an inverter that enables a proportional differential speed variation. This model is suitable for processes with constant inlet characteristics and with a fixed outlet result.

      Decanter GHT V
      The bowl drive is given by an electric motor while the scroll is operated by a hydraulic system. The rpm speed variation is continuous and automatic and takes place in two manners: by means of adjusting a constant rotation (the drive coupling changes according to the dry solid), or a constant coupling (the rotations vary according to the dry solid value). This line is suitable when the product to be treated has variable inlet characteristics and a high dry solid outlet value is requested.


      Deep Cone Thickeners

      Deep Cone Thickeners are an effective alternative to traditional thickener tanks. Deep Cone Thickeners hold many advantages over traditional thickeners. Some of these advantages include no moving mechanical parts, lower flocculent consumption, smaller footprint and large storage area for sludge in the conical section. Due to their steep conical sides, higher densities of sludge can be achieved and gravity is utilised to transfer the sludge to the outlet. High density sludge means there is less dewatering required downstream.

      Duo initially introduced Deep Cone Thickeners to the quarry industry in 2004 and due to their numerous advantages we have supplied more than 50 of these units to date.

      Our range includes:

      CapacityFlow rate
      4m Diameter190m3/hr
      5m Diameter300m3/hr
      6m Diameter425m3/hr
      7m Diameter550m3/hr
      8m Diameter750m3/hr

      Features & Benefits:

      • Small foot print
      • No moving parts
      • Easy and affordable maintenance 
      • Reduced Flocculent consumption
      • Large storage area for sludge in cone
      • Consistent sludge density 
      • Automatic density control 
      • Automatic sludge discharge


      Duo can supply a range of deep cone thickeners to suit the individual requirements of each application.

      Dynamic Thickeners

      Dynamic Thickeners are commonly used for the separation of silt and water from sludge. They are circular tanks with a shallow cone section and internal rake. The sludge is fed into the top of the thickener where flocculent is added. The rake rotates slowly and gradually pulls the settled silt towards the central discharge port. By monitoring the torque level on the rake we can control the density at which the sludge is discharged.

      The tanks are manufactured in sections and bolted together on site for ease of transport and their low level design is beneficial where height restrictions apply to a site.


      Duo offers two types of Dynamic Thickener to meet the individual requirements of each application. They in range in size from the 4m dynamic cone capable of processing 120m3/hr to the dynamic rake capable of processing over 3000m3/hr.

      Dynamic ConeDynamic Rake
      DC 4mDR 8m
      DC 6mDR 10m
      DC 8mDR 12m
      DC 10mDR 16m
      DC 20m

      Features & Benefits:

      • Low level design 
      • Internal rake mechanism 
      • Torque monitor
      • Suitable were there are height restrictions on site
      • Suitable for feeding by gravity
      • Easily assembled on site

      Lamella Thickeners

      The lamella principle uses several parallel inclined plates to create the maximum settling area possible given the space restrictions.

      Conventional clarification equipment requires a much larger surface footprint in order to match the solids removal capacity of a lamella clarifier. Loading rates normally used for the design of conventional settlers can be applied to the sizing of a Lamella clarifier/settler by substituting the single-surface settling area of a conventional clarifier with the multi-surface settling are of a Lamella Plate.

      The casing is typically made of coated or stainless steel and the lamellas are made of propylene. The effluent enters the lamella separator through the inlet channel on the top and flows to the bottom of the separator. The water is led back to the top, on its way the water flows through the lamellas, onto which the solid particles settle. The purified water flows to the top and reaches the outlet by passing a weir. The sludge slides down the lamellas and is collected in the sludge funnel. A rabble rake can be installed to prevent caking of the sludge. The sludge is discharged at intervals when the required density is achieved. Our Lamella Separators are manufactured in a wide range of sizes to suit all applications.


      Features & Benefits:

      • Multi-surface settling area
      • The compact design enables high thickening capacity relative to footprint
      • Easy and affordable maintenance as there are few moving parts
      • Balanced flow distribution ensures equal flow to each plate and across the plate surface area
      • One piece construction reduces installation time and lowers installation costs
      • Available in a range of sizes to suit a variety of installations. 3000m3/hr

      Flocculent Systems

      Flocculent Mixing Systems

      Flocculent is used in the water treatment process to initially separate solids (- 63 micron) from water.

      Flocculation occurs when destabilised particles are brought together by high molecular weight polymers such as Polyacrylamides. These polymers physically form a bridge between two or more particles, uniting the solids into loose three-dimensional structures. These structures are both denser and more porous than the untreated solids and so help in the typical/common forms of mechanical dewatering employed.

      Duo offers a range of Flocculent Mixing Systems that automatically prepare a batch of flocculent by mixing the flocculent powder with water to achieve the required concentration. Our systems are size specific to each application to ensure the flocculent has sufficient time to mix prior to being dosed, ensuring the best results and minimising the amount of flocculent required in the process.

      Features & Benefits:

      • Automatic mixing of the flocculent and water
      • Easily adjustable concentration levels
      • Manufactured from stainless steel
      • Complete with electrical control panel
      • Produces thoroughly mixed flocculent
      • Makes consistent production of dry cake achievable
      • Minimises flocculent waste

      Automatic Flocculent Dosing Systems

      Automatic flocculent dosing systems are metering systems that determine the consumption of the chemicals in the thickener process. Metering of the chemicals is achieved by precisely adjusting the flow of flocculent depending upon the level of silt in the in the sludge. The level of slit is continuously monitored.

      The continuous monitoring of silt levels ensures the correct level of flocculent consumption resulting in economic savings as there is no overuse and the desired quality of filter cake is also guaranteed. Underuse of flocculent is also avoided which ensures clean reusable water at all times.

      Features & Benefits:

      • Automatic dosing of the flocculent
      • Compact size
      • Complete with electrical control panel
      • No operator monitoring required
      • Makes consistent production of dry cake achievable
      • Minimises flocculent wastes
      • Avoids problems caused by either over or under flocculation
      • Can be retro fitted to existing water treatment plants

      Speak to an expert

      Call us now on +44 (0) 2476 405 100 or request a call back

      John Bracken
      Sales Director – Duo Equipment