Top OEMs for Solids Conveyance Systems

1. INTRODUCTION

In the hierarchy of unit processes within municipal and industrial wastewater treatment facilities, solids conveyance systems often receive less design scrutiny than liquid stream biological processes. However, the mechanical transport of dewatered biosolids, screenings, and grit represents one of the most mechanically intensive and maintenance-critical operations in a treatment plant. The failure of a conveyance system creates an immediate bottleneck, potentially forcing the shutdown of dewatering equipment (centrifuges, belt filter presses, screw presses) and necessitating expensive emergency hauling or manual handling of hazardous waste.

Solids conveyance encompasses the movement of non-liquid materials generated during the treatment process. This includes raw screenings captured at the headworks, grit removed from detritors and vortex chambers, and, most significantly, the dewatered sludge cake produced at the solids handling facility. The rheology of these materials varies drastically. Screenings are often fibrous, wet, and laden with inorganic debris. Grit is abrasive and heavy. Dewatered biosolids are thixotropic, sticky, and viscous, presenting unique challenges regarding friction, adhesion, and odor generation.

The primary applications for these systems include transporting material from the discharge of dewatering equipment to storage silos, truck loading bays, incinerator feed points, or thermal dryers. In modern facility design, regulatory drivers heavily influence equipment selection. Odor control requirements mandate fully enclosed systems to prevent the escape of hydrogen sulfide (H2S) and volatile organic compounds (VOCs). Additionally, the push for beneficial reuse (Class A biosolids) requires conveyance systems that maintain hygiene standards and integrate seamlessly with pasteurization or drying technologies.

For the consulting engineer and plant manager, OEM selection is not merely about finding a machine that moves material from Point A to Point B. It is about selecting a system architecture—whether shaftless screw, belt, or high-pressure piston pump—that aligns with the specific material characteristics, facility layout, and long-term maintenance resources. The integration of these systems requires a comprehensive understanding of mass balance, bulk density fluctuations, and the physical constraints of retrofitting equipment into existing concrete structures.

2. HOW TO SELECT THIS PROCESS EQUIPMENT

Selecting the appropriate solids conveyance technology requires a rigorous engineering analysis of process variables, material properties, and operational constraints. Unlike liquid pumping, where head and flow define the selection, solids handling requires an understanding of non-Newtonian flow behavior and bulk material mechanics. The following sections detail the critical engineering criteria for specification and selection.

Process Function and Performance Requirements

The first step in selection is defining the conveyance objective. Is the system intended for batch loading of trucks, continuous feed to a thermal dryer, or intermittent transport of screenings?
Capacity and Redundancy: Engineers must calculate the peak wet tons per hour (WTPH) output of upstream dewatering equipment. Conveyors are typically sized with a safety factor of 1.25 to 1.5 times the peak discharge rate of the dewatering unit to prevent bottlenecks. Redundancy is critical; a common design standard is N+1 configuration, where a reversible distribution conveyor or redundant pump allows for continuous operation during maintenance intervals.

Hydraulic and Process Loading Considerations (Rheology)

The physical characteristics of the material dictate the technology.
Percent Solids (%TS): A centrifuge producing 25-30% dry solids creates a cake that behaves differently than a belt press producing 18% solids. Higher solids content generally increases shear strength and viscosity, requiring higher torque for screw conveyors or higher hydraulic pressure for piston pumps.
Stickiness and Thixotropy: Wastewater sludge is thixotropic—its viscosity decreases under shear stress but returns to a gel-like state when static. “Stickiness” is a major failure mode for belt conveyors (carryback) and shafted screws (clogging). Shaftless screw conveyors and hydraulic piston pumps are generally preferred for sticky, cohesive sludges because they lack central shafts or complex return idlers where material can accumulate.

Materials of Construction

Corrosion and abrasion are the primary enemies of conveyance longevity.
Metallurgy: For municipal sludge, 304 Stainless Steel is the industry baseline. However, in applications with high septicity or industrial contributions, 316 or 316L Stainless Steel is required to resist pitting corrosion from chlorides and hydrogen sulfide. For shaftless screw spirals, high-tensile micro-alloy steel (HTMAS) or special carbon steel alloys are often used to provide the necessary spring tension and torsional strength, which stainless steel often lacks in high-torque applications.
Liners: Shaftless screw conveyors rely on trough liners. Ultra-High Molecular Weight Polyethylene (UHMWPE) is the standard for biosolids due to its low coefficient of friction. For grit or screenings applications, where abrasion is severe, Hardox wear bars or basalt liners may be specified to prevent rapid degradation of the trough.

Integration with Upstream and Downstream Processes

The conveyor is the handshake between unit processes.
Infeed Geometry: The transition from a centrifuge discharge chute to a conveyor requires careful geometric design to prevent bridging. Vertical drops should be minimized or tapered to prevent impact damage to liners.
Discharge Points: Systems feeding silos or trucks often require motorized slide gates or diverter valves. These components must be designed to cut through a column of solids and seal tightly to prevent drippage. Pneumatically actuated knife gates are common, but they require reliable instrument air and heat tracing in cold climates.

Footprint and Layout Constraints

Incline Limitations: Different technologies have different incline limits. Belt conveyors are typically limited to 15-20 degrees before material rollout occurs (unless cleated). Shaftless screws can operate up to 30 degrees efficiently, but efficiency drops significantly above that. For vertical transport, vertical screw conveyors or hydraulic piston pumps are required.
Flexibility: In retrofit applications with complex routings, hydraulic piston pumps offer the advantage of piping flexibility—sludge can be pumped through elbows and vertical rises similar to liquids, albeit at much higher pressures. Mechanical conveyors are generally rigid and require straight-line runs.

Operations and Maintenance Impacts

Cleaning: Enclosed systems control odor but complicate cleaning. Engineers should specify oversized inspection hatches with safety grates at regular intervals. Belt conveyors require wash boxes and scraper systems to remove carryback, which generates a washwater stream that must be piped back to the plant drain system.
Wear Components: Design for maintainability means positioning drive motors and bearings in accessible locations, not against walls or ceilings. For shaftless screws, the liner is a sacrificial wear part; the design must allow for liner replacement without removing the spiral if possible, or provide a clear pull-space for spiral removal.

Lifecycle Cost Considerations

Initial capital cost is often misleading. A belt conveyor may be cheaper to buy but requires more operator attention (cleaning, tracking) and generates washwater costs. Hydraulic piston pumps have high capital and energy costs but offer the lowest maintenance requirement for long-distance transport and completely contain odors. Engineers must evaluate the Total Cost of Ownership (TCO) over 20 years, factoring in energy, wear parts (liners, belts, stators), and operator labor hours.

3. COMPARISON TABLE

The following table compares the top OEMs in the solids conveyance sector based on their primary technological focus. Engineers should use this to align project constraints (e.g., vertical lift requirements, distance, material type) with the specific engineering strengths of each manufacturer.

OEM Name	Primary Technology	Typical Applications	Engineering Strengths	Limitations	Maintenance Considerations
Schwing Bioset	Hydraulic Piston Pumps / Sliding Frames	Long-distance biosolids transport, silo feeding, thermal dryer feed, high-pressure applications.	Can transport high-solids cake over long distances (1,000+ ft) and vertical lifts; fully enclosed piping; handles thixotropic material well.	High initial capital cost; significant footprint for hydraulic power units; high energy consumption relative to mechanical screws.	Hydraulic system maintenance (oil, filters, valves); poppet valve seat replacement; relatively low mechanical wear on piping.
SPIRAC	Shaftless Screw Conveyors	Dewatered sludge transport, screenings handling, grit conveyance, truck loading bins.	Originators of shaftless technology; handles sticky, fibrous, and variable size materials without clogging; fully enclosed for odor control.	Limited transport distance per single unit; incline limitations (efficiency drops steeply >30 degrees); spiral weight limits length.	Liner replacement (sacrificial UHMWPE or multi-color wear indicators); gear reducer maintenance; zero-speed switch monitoring.
Serpentix	3D Continuous Path Belt Conveyors	Complex layouts requiring horizontal and vertical curves, climbing steep inclines, sticky sludge handling.	Unique convoluted belt allows for turning corners and climbing steep angles (up to 90 degrees) in a single drive system; scrapes clean easily.	Open or semi-open design can make odor containment more challenging than piped systems; many moving parts (chain, rollers).	Chain lubrication and tensioning; belt repair/replacement; roller bearing maintenance; cleaning of the pan/belt interface.
Jim Myers & Sons (JMS)	Screw Conveyors / Belt Conveyors / Diverters	General biosolids handling, truck loading, silo systems, distribution conveyors.	Robust structural fabrication; offers both shafted and shaftless options; “Bio-Handling” specific designs for sludge; versatile customization.	Traditional screw/belt limitations regarding incline and distance; belt systems require washwater and tracking.	Standard mechanical maintenance (bearings, drives); belt tracking adjustments; seal and gasket replacement for odor control.
JWC Environmental	Screenings Conveyance / Washer Compactors	Headworks screenings transport, washing, and compacting.	Specializes in the “Monster” series for screenings; integrates grinding/washing with conveyance; extremely robust against debris.	Focused primarily on screenings/grit rather than long-distance biosolids transport; specialized niche application.	Cutter stack maintenance (if grinder integrated); brush replacement; auger wear monitoring in abrasive grit applications.

4. TOP OEM MANUFACTURERS

The following manufacturers represent the industry standard for solids conveyance in water and wastewater applications. Each has a distinct technological philosophy and area of expertise.

Schwing Bioset

Core Technology: Hydraulic Piston Pumps and Sliding Frame Silos.

Schwing Bioset is widely recognized for adapting concrete pumping technology to the wastewater sector. Their primary conveyance solution is the KSP Piston Pump. Unlike screw or belt conveyors, which are mechanical transport devices, the KSP is a positive displacement pump capable of generating pressures exceeding 1,000 psi. This allows dewatered cake (even with high solids content) to be pushed through hard piping for long distances, up vertical risers, and around complex geometries.

Engineering Focus: The system consists of a hydraulic power unit driving reciprocating material cylinders. A poppet valve housing directs the flow of material. From an engineering perspective, this solution is ideal for “Class A” biosolids or thermal hydrolysis processes where the material must be kept in a completely closed loop to maintain temperature or sterility. The friction loss calculations for these systems are complex, involving the shear stress of the sludge against the pipe wall and the formation of a boundary layer. Schwing also manufactures sliding frame silos, which solve the problem of “rat-holing” and bridging in sludge storage by using a hydraulic frame to break bridges and feed extraction screws.

Serpentix

Core Technology: Three-Dimensional Continuous Path Conveyors.

Serpentix offers a unique mechanical solution that differentiates itself from standard flat belt or screw conveyors. Their design utilizes a convoluted belt (pan) system driven by a high-strength chain. The belt creates a “trough” that can negotiate horizontal turns and vertical climbs within a single continuous run, powered by a single drive motor.

Engineering Focus: The primary advantage of the Serpentix system is layout flexibility. In retrofit applications where a conveyor must navigate around existing pillars, piping, or tanks, a Serpentix unit can snake through the facility without the need for multiple transfer points (which are common sources of spillage and maintenance). The belt design is also self-cleaning to a degree, as the convolutions flatten out at the discharge point, allowing scrapers to effectively remove sticky sludge. They are particularly effective for climbing steep inclines (up to 45 degrees or more depending on the model) without material rollback, a common failure mode in standard belt conveyors.

JWC Environmental

Core Technology: Screenings Handling and Augers.

While JWC Environmental is most famous for the “Muffin Monster” grinders, they are a critical OEM in the conveyance of headworks solids. Their conveyance solutions are typically integrated into screenings washer/compactors (the Screenings Washer Monster). These systems do not just convey; they wash organic fecal matter out of the screenings, compact the material to reduce volume and water weight, and then transport the dry plug to a dumpster.

Engineering Focus: The engineering challenge here is handling wet, stringy, and heterogeneous material (rags, plastics, wipes). JWC utilizes shaftless auger technology within these systems to prevent ragging (wrapping of debris around a shaft). Their systems are typically constructed of stainless steel with heavy-duty spirals designed to withstand the torque required to compact screenings against a discharge resistance. For engineers designing headworks, JWC provides a single-source solution for grinding, screening, and conveying, simplifying the interface between the channel and the dumpster.

Jim Myers & Sons (JMS)

Core Technology: Screw Conveyors, Belt Conveyors, and Diverters.

JMS is a major fabricator known for robust, American-made material handling systems. They do not rely on a single technology but offer a portfolio including shafted screws, shaftless screws, and belt conveyors. Their “Bio-BELT” and “Bio-SCREW” lines are specifically engineered for the wastewater sector, distinguishing them from agricultural or aggregate conveyor manufacturers.

Engineering Focus: JMS excels in the structural integration of conveyance systems. They design and fabricate the complete support structures, catwalks, and chutes. A key strength is their diverter gate technology. Properly diverting sticky sludge from one screw to another or into a silo is mechanically difficult; JMS utilizes robust knife gates and ploughs designed to slice through heavy sludge cake. Their shaftless screws feature heavy-duty hold-downs to prevent the spiral from rising out of the trough under load (“climbing”), a necessary safety and performance feature for high-torque applications.

SPIRAC

Core Technology: Shaftless Spiral Conveyors.

SPIRAC is arguably the global leader in shaftless screw conveyor technology. They pioneered the concept of removing the central shaft to allow for a higher fill rate and the passage of large or fibrous objects without clogging. Their systems utilize a high-tensile micro-alloy steel (HTMAS) spiral that rests on a sacrificial liner (typically UHMWPE) at the bottom of the trough.

Engineering Focus: The absence of a center shaft and intermediate bearings eliminates the primary maintenance points of traditional screw conveyors. For engineers, SPIRAC systems offer a fully enclosed, odor-tight solution. They are modular, allowing for relatively easy installation in tight spaces. SPIRAC also engineers the “live bottom” silo, where multiple shaftless screws cover the floor of a rectangular bin to provide mass-flow discharge of sludge, preventing arching. Their engineering expertise lies in the metallurgy of the spiral—balancing hardness for wear resistance with the elasticity required to handle fatigue cycles from the screw’s rotation.

5. APPLICATION FIT GUIDANCE

Choosing the right OEM often depends on the specific domain of the plant and the material being handled.

Municipal Wastewater (Biosolids/Sludge)

For transporting dewatered cake from centrifuges or presses to silos:
SPIRAC and JMS are the standard choices for short-to-medium distances with linear layouts. Their enclosed screw designs manage odors effectively and handle the sticky nature of polymer-dosed sludge.
Schwing Bioset is the preferred choice for large facilities requiring transport over long distances (e.g., >100 feet), vertical lifts exceeding 30 feet, or where the sludge must be fed into a pressurized process (like an incinerator or dryer).

Headworks (Screenings and Grit)

JWC Environmental is the dominant fit here. Their equipment is specifically hardened to handle the rags, rocks, and inorganic debris found in headworks. Using a standard sludge screw for grit often leads to premature failure due to abrasion; JWC and SPIRAC (with specialized grit liners) are better suited for this abrasive duty.

Complex Retrofits

Serpentix shines in older plants where new dewatering equipment is being shoehorned into an existing building. If the conveyance path requires navigating around pillars, turning 90 degrees, and then climbing at a 40-degree angle, a single Serpentix belt can replace what would otherwise be three separate screw conveyors and two transfer chutes.

Silo and Storage Discharge

For truck loading stations, JMS and SPIRAC provide excellent live-bottom bin solutions. For large cylindrical silos where bridging is a major concern, Schwing Bioset’s sliding frame technology provides a distinct advantage in ensuring consistent material feed to the extraction screws.

6. ENGINEER & OPERATOR CONSIDERATIONS

Beyond the equipment spec, several practical factors influence the success of a conveyance project.

Installation and Commissioning

Alignment is Critical: Particularly for long screw conveyors, trough alignment must be precise. Misalignment causes uneven liner wear and can lead to spiral fatigue failure. Laser alignment during installation is recommended.
Anchoring: Piston pumps (Schwing) generate significant dynamic loads and vibration. Reaction forces must be calculated and transferred to the concrete pad; inadequate grouting or anchoring can lead to pipe rupture or structural damage.

Maintenance Access

Engineers often design conveyors high in the air to clear trucks or other equipment. However, operators must access these units to change liners, grease bearings, or clear blockages.
Catwalks: Mandatory for any conveyor elevated more than 6 feet. Relying on ladders for maintenance is a safety hazard and ensures maintenance will be deferred.
Liner Replacement: For shaftless screws, the liner will wear out. Designs must allow the liner to be slid out from one end, or the trough must be accessible to lift the spiral. If piping or ductwork blocks the trough covers, liner replacement becomes a major demolition project.

Operational Lessons Learned

Cold Weather: In northern climates, sludge left static in a conveyor or pipe can freeze. Heat tracing and insulation are mandatory for outdoor runs. Piston pump pipelines are easier to trace than screw conveyor troughs.
Start-up Under Load: Power outages happen. When power returns, the conveyor is full of heavy, settled sludge. Motors must be sized with high starting torque (NEMA Design C or premium efficiency with VFD torque boost) to restart under full load conditions. Hydraulic pumps naturally excel here; screw conveyors may require manual digging out if not oversized.

Safety

Conveyors are responsible for many severe injuries in heavy industry.
Nip Points: Belt conveyors have dangerous nip points at the drive and tail pulleys. Guards must be OSHA compliant and require tools to remove.
Emergency Stops: Pull-cord E-stops should run the entire length of any open or accessible conveyor.
Zero Speed Switches: These are critical for fire prevention and spill protection. If a motor is running but the shaft isn’t turning (due to a sheared key or broken coupling), the switch must trip the motor to prevent heat buildup and alert the SCADA system to stop upstream feeds.

7. CONCLUSION

Selecting the correct solids conveyance system is a balance of rheology, geometry, and lifecycle philosophy. There is no single “best” OEM; rather, there is a best fit for the specific hydraulic and physical constraints of the treatment plant.

For high-pressure, long-distance, or hygienic enclosed transport, Schwing Bioset defines the standard. For versatile, enclosed, and odor-controlled transport of sticky sludge within a building, SPIRAC and JMS offer robust shaftless and shafted screw solutions. When facility geometry is complex and requires 3D routing, Serpentix provides unique problem-solving capabilities. Finally, for the rugged demands of headworks screenings, JWC Environmental delivers specialized, integrated processing and transport.

Engineers must look beyond the initial price tag. The cost of a conveyance failure—measured in downtime, emergency hauling fees, and operator labor—far exceeds the premium paid for properly sized, heavy-duty equipment. Specifications should prioritize liner longevity, serviceability (access), redundant drive capacity, and materials of construction capable of withstanding the corrosive and abrasive nature of wastewater solids.

source https://www.waterandwastewater.com/top-oems-for-solids-conveyance-systems/