Progressive cavity pumps: a solution for industrial sludge treatment
The industrial sludge treatment process
The treatment and disposal of industrial sludge represent one of the most complex challenges in wastewater treatment plants. Modern facilities must handle semi-solid materials with high dry matter content, viscous fluids prone to plasticization, and substances with adhesive properties that require reliable, high-performance pumping solutions. Nova Rotors progressive cavity pumps have established themselves as the reference technology for sludge treatment, offering superior performance compared to traditional systems.
Wastewater treatment plants have been developed to remove harmful substances contained in wastewater through biological processes that use activated or activated sludge. These processes inevitably generate semi-solid waste known as thickened sludge, which must be treated and disposed of in accordance with strict environmental regulations. Over the years, scientific research and the use of new technologies have made it possible not only to safely dispose of these materials, but also to repurpose them beneficially across various industrial sectors — from biogas production to reintegration into nature as agricultural fertilizers.
The sludge treatment cycle typically consists of several successive stages: the collection of primary sludge from sedimentation tanks, thickening to reduce water content, mechanical dewatering via centrifuges or filter presses, temporary storage in silos, and finally definitive disposal through drying, incineration, or energy recovery. At each stage, the physical characteristics of the sludge change significantly: the dry matter percentage increases progressively from values of 2–5% up to 20–40% in dewatered sludge, while viscosity and the tendency toward plasticization make the material increasingly difficult to handle.
Progressive cavity pumps: the challenges of sludge pumping
The pumping of sewage sludge presents specific challenges that require specialized technologies. Thickened sludge contains high percentages of suspended solids and tends to plasticize, forming accumulations and blockages in pipelines. The adhesive properties of the material can cause bridging in feed hoppers, while the presence of fibres, abrasive particles and foreign bodies subjects pumps to intense mechanical stress. Furthermore, the need to ensure operational continuity in wastewater treatment plants, which typically operate 24 hours a day, requires extremely reliable pumping solutions with minimal downtime for maintenance.
Progressive cavity pumps, also known as single-screw pumps or eccentric screw pumps, represent the most effective technology for industrial sludge treatment. The operating principle is based on a helical steel rotor that rotates eccentrically within an elastomeric stator, creating a series of sealed chambers that move progressively from the suction to the discharge port. This mechanism ensures continuous and uniform fluid transfer, free of pulsations and with a gentle action that does not damage the structure of the biological flocs present in activated sludge.
The Diamond single-screw pumps from Nova Rotors stand out for their superior performance in sludge treatment. Their ability to pump materials with dry matter content of up to 40% makes them ideal for all stages of the treatment process. The robust design and high-quality materials ensure exceptional operational longevity even under the most demanding conditions, while the patented pin joint guarantees high reliability and reduced maintenance costs compared to other pumping technologies.
Advantages of progressive cavity pumps for sludge
- Handling of complex fluids: ability to pump high-viscosity sludge with suspended solids and a tendency to plasticize
- Constant flow rate: uniform flow independent of operating pressure, essential for precise dosing of polyelectrolytes and additives
- Low hydraulic shear: reduced mechanical stress that preserves floc structure and optimizes dewatering processes
- Self-priming capability: ability to draw in fluid even in the presence of air, reducing priming issues
- Operational reversibility: ability to reverse the direction of rotation to clear any blockages
Single-screw pumps for sludge disposal: series and applications
Nova Rotors has developed a comprehensive range of single-screw pumps specifically designed for the various stages of sludge treatment. Each series has been optimized to meet the specific handling requirements, from managing liquid primary sludge to transferring dewatered sludge with high dry matter content. The modular design allows for customized configurations based on the characteristics of the sludge to be processed and the operating conditions of the plant.
DN Series: flanged industrial pumps for heavy-duty applications
The DN series represents the reference solution for pumping thickened sludge in large wastewater treatment plants. These flanged industrial pumps are designed for intensive use and ensure reliability in continuous applications. Available with UNI, DIN, ANSI flanged and BSP threaded connections, DN pumps cover a wide range of flow rates and pressures, adapting perfectly to plant requirements. They are typically used for transferring sludge from the collection tank to mechanical dewatering systems such as centrifuges, filter presses and belt presses.
The robust construction featuring a cast iron or stainless steel pump body, hardened and tempered steel rotor, and wear-resistant elastomer stator ensures superior operational longevity even with sludge containing abrasive particles. The Diamond series patented pin joint allows for optimal distribution of axial loads and torques, reducing stress on the bearings and extending maintenance intervals.
DH and DHS Series: hopper pumps for dewatered sludge
Hopper pumps with feed augers represent the ideal solution for transferring dewatered sludge with high dry matter content. The DH series is equipped with a hopper and auger that feeds directly into the hydraulic section of the pump, ensuring continuous transfer even of poorly flowing and viscous substances. These pumps are particularly suited for pumping from centrifuges or filter presses to storage silos, collection skips or final drying systems.
The DHS series with standard hopper and the DHB series with dual-shaft bridge-breaking hopper have been developed specifically to prevent the formation of bridges and accumulations that could block the feed. The wide infeed auger ensures continuous conveyance of material towards the pump, while the joint protection guarantees resistance to mechanical stress. Available in various configurations with hoppers of different sizes, these pumps can be customized to meet the specific requirements of each plant.
Sludge treatment pumps: complete solutions for purification
Nova Rotors has been operating in the sludge treatment and disposal sector for many years, providing complete solutions ranging from single-screw pumps to industrial macerators, from dosing systems to complementary accessories. The references accumulated at national and international level attest to the company's commitment to supplying reliable technologies for a sector that demands absolute operational continuity and compliance with the most stringent environmental regulations.
Integration with industrial macerators
To optimise the efficiency of sludge treatment, Nova Rotors offers the TG Terminator series of industrial macerators. These devices, installed upstream of the pumps, reduce the size of solid particles and foreign bodies present in the sludge, protecting the pumps from blockages and damage. Pre-maceration significantly improves flow management, reduces plant downtime and extends the operational life of transfer pumps.
Dosing pumps for chemical additives
In the sludge treatment process, the precise dosing of polyelectrolytes, flocculant polymers and other chemical additives is essential for optimising dewatering and reducing the volumes to be disposed of. The Diamond series single-screw dosing pumps ensure accurate flow rate control, enabling the consistent dosing of additives in line with the sludge load to be treated. Precise dosing translates into improved performance of dewatering systems, reducing operating costs and enhancing the quality of the dewatered sludge.
Floating stator pumps for the environmental sector
The Wobble floating stator pumps represent a particularly interesting alternative solution for certain applications in wastewater treatment. This technology is distinguished by its innovative design in which the stator can move freely within the pumping chamber, dynamically adapting to operating conditions. The R and RL series pumps are extremely compact and versatile, offering an excellent cost-to-performance ratio for medium-intensity applications.
Maintenance of floating stator pumps is particularly straightforward and cost-effective thanks to the reduced number of components. Pumping is free of pulsations and the centrifugal effect is virtually absent even at high rotational speeds. These characteristics make them suitable for the for low-volume wastewater handling and polyelectrolyte dosing applications, and fluids containing suspended solid particles. The self-priming capacity of up to 4 metres and the wide flow passages reduce head losses and improve operational efficiency.
Applications of Wobble pumps in water treatment
Floating stator pumps are used for transferring incoming wastewater to treatment plants, for recirculating activated sludge in biological oxidation tanks, and for handling liquid primary sludge. The AISI 304 or 316 stainless steel version ensures corrosion resistance and compliance with environmental regulations. Certified elastomers (NBR, EPDM, FPM) can be selected based on the chemical characteristics of the fluid to be pumped, ensuring durability and reliability even in the presence of aggressive substances.
Comparative table: pumps for sludge treatment
| Pump series | Sludge type | % dry matter | Typical application |
| DN/JN | Thickened sludge | 5–15% | Transfer from collection tanks to dewatering systems (centrifuges, filter presses) |
| DH/JH | Dewatered sludge | 15–30% | Hopper feed to storage silo, handling of poorly flowing sludge |
| DHS/JHS | Dewatered sludge | 20–35% | Transfer from centrifuges/belt presses to silos, skips or collection tanks |
| DHB/JHB | High dry matter sludge | 25–40% | Pumping sludge from filter press to skips, dual-shaft bridge-breaking hopper |
| DV (Vertical) | Liquid/thickened sludge | 3–12% | Direct suction from wells, cisterns or deep tanks, customisable length |
| R/RL Wobble | Liquid primary sludge | 2–8% | Wastewater transfer, activated sludge recirculation, low dry matter applications |
| M Dosing | Polymers/additives | Variable | Precise dosing of polyelectrolytes, flocculants and chemical additives for dewatering |
Materials and configurations for demanding environments
The sludge treatment sector requires pumps built with high-quality materials capable of withstanding wear and intense mechanical stress. Nova Rotors offers a wide choice of materials for pump bodies, rotors and stators, enabling the optimal configuration based on the specific characteristics of the sludge to be treated. Pump bodies are available in GG25 cast iron for standard applications, carbon steel for intensive industrial use, and AISI 304 or AISI 316 stainless steel for corrosive environments or where high hygiene standards are required.
Rotors can be manufactured in hardened and tempered steel to resist abrasion, with surface treatments such as hard chrome plating HCP, nitriding or ceramic coatings for particularly demanding applications. Stators are available in various elastomeric compounds: NBR (nitrile) for standard use, EPDM for superior chemical resistance, and FPM (Viton) for high temperatures and aggressive fluids. The appropriate selection of materials, supported by Nova Rotors' technical expertise, is essential for ensuring operational longevity and reducing maintenance costs.
Mechanical seal systems
Pumps for sludge treatment are equipped with mechanical seals designed to prevent leaks and contamination. Single mechanical seals are available for standard applications, and pressurised double seals with a flushing system are available for critical environments. Seal materials (silicon carbide, tungsten carbide, ceramic) are selected based on the characteristics of the fluid and operating conditions. For applications in potentially explosive atmospheres, Nova Rotors offers ATEX-certified pumps in compliance with Directive 94/9/EC.
Operational efficiency and environmental sustainability
The use of Nova Rotors progressive cavity pumps in sludge treatment contributes significantly to the overall efficiency of wastewater treatment plants. Superior performance in terms of operational reliability translates into reduced plant downtime, optimised energy consumption and minimised maintenance interventions. The ability to handle sludge with high dry matter content makes it possible to reduce the volumes to be disposed of, with a consequent reduction in transport costs and associated emissions.
Nova Rotors supports its customers in the environmental sector with a comprehensive after-sales service, which includes specialist technical consultancy, immediate availability of original spare parts and process optimisation support. The company, certified to ISO 9001:2015 and ISO 45001:2018, guarantees consistent quality and regulatory compliance across all products supplied. The hydraulic testing facility allows each pump to be tested before delivery, verifying flow rate, pressure, power consumption and NPSH through computerised data acquisition systems.
Nova Rotors: your partner in sludge treatment
Nova Rotors progressive cavity pumps represent the most reliable and efficient technology for the treatment and disposal of industrial sludge. The comprehensive range of solutions, from high-performance Diamond single-screw pumps to cost-effective and versatile Wobble floating stator pumps, makes it possible to meet any plant requirement. Thirty years of experience in the wastewater treatment sector, combined with continuous technological innovation and superior build quality, position Nova Rotors as the ideal partner for civil and industrial wastewater treatment plants.
Founded in 1990 and located in Sossano at the foot of the Colli Berici, Nova Rotors has built its reputation by supplying robust, reliable and high-performing pumps for the most demanding applications. The ability to customise pumps to meet specific customer requirements, supported by a computerised production process and highly qualified technical staff, ensures optimal solutions for every type of sludge and operating condition. The hundreds of installations completed in Italy and around the world bear witness to the effectiveness of Nova Rotors technologies in ensuring operational continuity, reducing management costs and contributing to the environmental sustainability of wastewater treatment plants.
Investing in Nova Rotors single-screw and progressive cavity pumps means choosing quality, reliability and innovation to optimise sludge treatment, minimise environmental impact and ensure compliance with the increasingly stringent regulations of the environmental sector. With flow rates of up to 420 m³/h, pressures of up to 48 bar and the capacity to handle sludge with dry matter content of up to 40%, Nova Rotors pumps are the complete solution for the challenges of industrial sludge treatment — today and in the future.