Top OEMs for Trickling Filter Systems

1. INTRODUCTION

The trickling filter is one of the oldest and most established biological treatment processes in municipal and industrial wastewater applications. Classified as an attached-growth (or fixed-film) process, a trickling filter operates by passing wastewater over a stationary medium—historically rock or slag, but increasingly structured plastic modules—where a biofilm establishes itself. This biomass metabolizes organic matter and nitrogenous compounds from the liquid stream. While activated sludge systems often dominate the conversation regarding secondary treatment, trickling filters remain a critical unit process due to their resilience, energy efficiency, and operational stability under varying load conditions.

In modern wastewater treatment facilities, trickling filters are utilized in various configurations. They serve as roughing filters to reduce high Biological Oxygen Demand (BOD) loads prior to downstream aeration basins, as the primary secondary treatment step for BOD removal, or as tertiary nitrification towers designed specifically to convert ammonia to nitrate. The fundamental mechanism involves the distribution of wastewater over the media surface, typically via a rotary distributor, allowing the liquid to trickle through the void spaces. Air circulates through the media (either via natural draft or forced ventilation), providing the oxygen required for the aerobic respiration of the biofilm.

From a regulatory perspective, the resurgence of interest in trickling filters is driven by two main factors: energy neutrality and nutrient limits. Trickling filters consume significantly less energy than suspended growth systems because oxygen transfer occurs passively through natural draft ventilation rather than through energy-intensive mechanical aeration. For utilities facing strict operating expenditure (OPEX) constraints or net-zero energy mandates, the trickling filter presents a favorable thermodynamic profile. Furthermore, the decoupling of hydraulic retention time (HRT) and solids retention time (SRT) in fixed-film systems allows for stable nitrification even in colder climates, provided the media surface area is sized correctly.

However, the apparent simplicity of the trickling filter belies the complexity of its design and equipment selection. The efficiency of the process is contingent upon the uniform distribution of influent over the media bed and the structural integrity of the media itself. Poor distribution leads to short-circuiting, dry spots, and reduced treatment capacity. Mechanical failure of the rotary distributor—specifically the center bearing or the seal assembly—can render a treatment train offline for extended periods. Consequently, the selection of Original Equipment Manufacturers (OEMs) for the rotary distributor mechanisms and the media packs is a critical engineering task.

Engineers must evaluate OEMs based not on marketing claims, but on hydraulic engineering capabilities, bearing life calculations, structural materials, and the long-term mechanical reliability of the center column assemblies. The distinction between a high-performing trickling filter and a maintenance burden often lies in the precision of the distributor arm design and the quality of the support systems. This article provides a comprehensive technical analysis of the leading OEMs in this sector, focusing on the engineering criteria essential for municipal and industrial specifications.

2. HOW TO SELECT THIS PROCESS EQUIPMENT

Selecting the correct equipment for a trickling filter system involves a multi-disciplinary approach, integrating process engineering, hydraulics, and structural design. Unlike packaged systems where the unit comes pre-assembled, trickling filters are often constructed systems where the rotary distributor and the media are specified components installed within a concrete or steel containment structure.

Process Function and Performance Requirements

The first step in equipment selection is defining the process objective. High-rate trickling filters function differently from low-rate or roughing filters.
BOD Removal vs. Nitrification: Equipment selection changes based on the target pollutant. For carbonaceous BOD removal, the focus is on handling higher organic loading rates (typically 15 to 100 lbs BOD/1,000 ft³/day). This requires robust distribution systems capable of handling heavy biomass sloughing without clogging. For nitrification, the organic load is lower, but the hydraulic wetting rate (SK value) becomes critical to maintain biofilm thickness and prevent predation by filter flies or snails.
Spülkraft (Flushing Intensity): A critical performance metric is the flushing intensity, or Spülkraft. This is the hydraulic force applied to the biofilm as the distributor arm passes. Engineers must select distributors capable of modulating rotational speed to achieve the necessary flushing intensity to shear off excess biomass and prevent ponding, while ensuring the wetting rate remains adequate for treatment.

Hydraulic Considerations and the Rotary Distributor

The rotary distributor is the mechanical heart of the system. Its selection is governed by flow ranges and head requirements.
Hydraulic vs. Motorized Drive: Standard distributors are hydraulically propelled by the reaction force of the wastewater exiting the nozzles. This requires a minimum hydraulic head (typically 24 to 36 inches above the media surface). For facilities with low flows or highly variable diurnal peaks, a hydraulically driven arm may stall. In these cases, engineers must specify electrically driven distributors to ensure constant rotation and uniform dosing regardless of influent flow.
Flow Turn-Down Ratio: Municipal systems experience significant flow variations. The distributor center assembly and arm design must accommodate these fluctuations. A common design includes a dual-compartment arm or a vari-gate nozzle system that opens additional orifices as flow increases. The OEM’s ability to model these hydraulic profiles is essential to prevent “weeping” at low flows or overflow at peak wet weather events.

Materials of Construction

The environment within a trickling filter is highly corrosive due to the release of hydrogen sulfide and the constant humidity.
Distributor Mechanisms: Standard specifications call for hot-dip galvanized steel or Type 304/316 stainless steel for the arms and center column. In coastal or severe industrial applications, duplex stainless steel may be warranted. The guy rods (tension supports) are particularly vulnerable to corrosion fatigue and should be oversized and corrosion-resistant.
Media: Historically, rock was used, but it is limited by low void space and weight. Modern selection favors structured PVC or polypropylene media. The material selection must account for UV stability (for top layers) and chemical resistance to the specific industrial wastewater profile.

Integration with Upstream and Downstream Processes

Primary Clarification: Effective grit and solids removal upstream is non-negotiable. Distributors with fine nozzles will clog if primary treatment is inadequate. Engineers should specify nozzle diameters (typically > 1 inch) that align with the screening capture ratio of the headworks.
Recirculation Pumping: Trickling filters often require recirculation of effluent to maintain wetting rates during low flow or to dilute high-strength influent. The distributor selection must account for total hydraulic throughput, including the recirculation ratio (typically 1:1 to 4:1).

Footprint and Structural Layout

Tower Height vs. Pumping Cost: Plastic media allows for biotowers up to 30 feet high, reducing the footprint compared to shallow rock filters. However, taller towers increase the static head requirement for influent pumps. The equipment selection involves a trade-off analysis between civil construction costs (footprint) and long-term energy costs (pumping head).
Media Support Systems: For plastic media, a specialized grating system is required at the bottom of the tank. This support grid must handle the wet weight of the biomass-laden media and allow unrestricted airflow. OEMs for media often supply these integrated support systems.

Operations and Maintenance Impacts

Bearing Systems: The turntable bearing is the single most critical failure point. A failed bearing requires lifting the entire center column, a massive maintenance undertaking. Engineers should specify heavy-duty, turntable-style bearings with calculated L-10 lives exceeding 100,000 hours.
Seal Design: Older designs used mercury seals, which are now environmental hazards. Modern specifications should mandate mechanical seals or oil-filled contactless seals. The ease of replacing these seals without completely dismantling the distributor is a key selection criterion.

Lifecycle Cost Considerations

While trickling filters have low energy costs, the capital cost of media is significant. Lifecycle analysis must compare the durability of the media (20+ years for high-quality PVC) against cheaper alternatives that may become brittle or crush under the biofilm load. Additionally, the energy cost of pumping against the static head of the tower should be factored into the Net Present Value (NPV) calculation when comparing OEM designs for hydraulic efficiency.

3. COMPARISON TABLE

The following table outlines the primary engineering characteristics of the top OEMs in the trickling filter market. Engineers should use this data to align specific project constraints—such as high hydraulic variability, media retrofit needs, or heavy-duty industrial loadings—with the manufacturer’s core competencies.

OEM Name	Typical Applications	Engineering Strengths	Limitations	Best-Fit Scenarios
WesTech Engineering	Municipal secondary treatment, Industrial roughing filters, Biotowers.	Robust center column design; wide range of arm configurations (2-4 arms); excellent hydraulic seal options.	Premium pricing for custom metallurgy; longer lead times for large-diameter units.	Large municipal plants requiring high reliability and longevity; custom retrofit of existing basins.
Evoqua (Xylem)	Municipal wastewater, Nitrification towers, Upgrades of legacy Envirex installations.	Extensive installed base (Envirex lineage); advanced nozzle designs for uniform spreading; deep process knowledge.	Can be complex to navigate legacy product lines; integration with non-standard controls may require coordination.	Standard municipal applications; projects valuing established brand heritage and parts availability.
Ovivo	General municipal, Industrial high-strength waste, Retrofits.	Eimco heritage; strong expertise in hydraulically driven mechanisms; durable structural designs.	May have limited options for ultra-specialized small-scale industrial units compared to niche fabricators.	Public works projects requiring specification-compliant, durable mechanical distributors.
Walker Process Equipment	Municipal trickling filters, Rotary distributors for circular tanks.	Simple, heavy-duty mechanical design; focus on ease of maintenance and long bearing life.	Less focus on the biological process media itself compared to integrated suppliers.	Standard municipal designs prioritizing mechanical simplicity and ease of operator maintenance.
Brentwood Industries	Plastic media supply, Trickling filter retrofits, Biotowers.	Industry leader in structured sheet media; integrated support grids and drift eliminators; process modeling support.	Does not manufacture the rotary distributor mechanisms (focus is strictly on media and internals).	Projects requiring media replacement, capacity upgrades via vertical media, or new biotower internals.

4. TOP OEM MANUFACTURERS

WesTech Engineering

WesTech Engineering has established itself as a premier manufacturer of rotary distributors for trickling filter systems, emphasizing structural durability and hydraulic precision. Their equipment is widely recognized in the municipal sector for handling both standard and high-rate filtration processes.

Engineering & Technology:
WesTech’s distributors are designed with a focus on the center assembly, which is the pivot point of the entire mechanism. They utilize high-grade turntable bearings that are calculated for substantial radial and thrust loads, ensuring stability even under uneven arm loading conditions. Their hydraulic designs incorporate features to manage wide flow ranges. For variable flow conditions, WesTech employs distinct arm configurations, such as the use of weir boxes or variable-gate nozzles that maintain rotation speed and distribution uniformity when flows drop below the design average. This is critical for preventing “stall” in hydraulically driven systems.

Maintenance & Lifecycle:
From an operator’s perspective, WesTech units are designed for accessibility. The center columns often feature mechanical seals that eliminate the environmental liabilities associated with legacy mercury seals. Lubrication points are generally accessible from the walkway or bridge. The arms are constructed with clean-out ports at the ends, allowing operators to easily flush accumulated solids that might bypass primary screens.

Evoqua (Xylem)

Evoqua, now part of Xylem, encompasses several legacy brands, most notably Envirex, which has been a staple in wastewater treatment for decades. Their trickling filter portfolio benefits from this deep historical data and immense installed base.

Engineering & Technology:
Evoqua’s strength lies in their distribution nozzle technology and arm geometry. They offer spreaders that are engineered to maximize the wetting of the media surface area, minimizing dry spots where treatment efficiency is lost. Their designs are highly adaptable, offering both tubular and rectangular arm cross-sections depending on the hydraulic head available. For nitrification towers, where hydraulic loads can be high but organic loads low, Evoqua provides specialized braking systems or motor drives to control the rotational speed (SK value), ensuring the biofilm is not sheared off prematurely.

Maintenance & Lifecycle:
Evoqua emphasizes backward compatibility. For municipalities with aging infrastructure, Evoqua can often retrofit modern arms or center columns onto existing piers, saving significant civil costs. Their support network is extensive, providing critical spare parts for systems that may have been installed 30 or 40 years ago.

Ovivo

Ovivo brings the heritage of Eimco and other acquired technologies to the trickling filter market. They are a major player in large-scale municipal infrastructure and offer robust mechanical solutions for biological treatment.

Engineering & Technology:
Ovivo’s rotary distributors are characterized by their heavy-duty construction. They offer reaction-driven units for standard applications and motor-driven units for scenarios requiring precise speed control. Ovivo engineers pay particular attention to the hydraulic profile of the center well, ensuring that the transition of flow from the vertical riser to the horizontal arms minimizes turbulence and head loss. This efficiency is crucial in gravity-fed systems where every inch of hydraulic head is valuable. They also provide comprehensive designs for the underdrain systems, ensuring that air flows freely upwards against the liquid stream (in natural draft applications).

Maintenance & Lifecycle:
The Ovivo design philosophy prioritizes longevity. Their bearings are housed in robust casings designed to protect against the corrosive atmosphere of the filter. They offer various material upgrades, including 316L stainless steel for aggressive industrial wastewaters, extending the lifecycle of the structural components significantly.

Walker Process Equipment

Walker Process Equipment is a respected name in the industry, known for manufacturing reliable, no-nonsense process equipment. Their trickling filter distributors are consistent with this reputation, offering straightforward mechanical designs that perform reliably in harsh environments.

Engineering & Technology:
Walker Process focuses on the fundamentals of rotary distributor design. Their units typically feature a mast-type center assembly which provides excellent stability. The arms are guyed (supported by tension rods) to the center mast, allowing for long span capabilities without excessive deflection. They offer distinct nozzle designs that can be adjusted to tune the flow distribution across the radius of the tank. While they may offer fewer “smart” features than some competitors, their mechanical engineering is conservative and robust, often resulting in equipment that exceeds its design life.

Maintenance & Lifecycle:
Walker units are favored by maintenance superintendents for their simplicity. The mechanisms are easy to understand and service. Parts availability is generally good, and the equipment is designed to be repaired in the field rather than requiring total replacement. The lack of overly complex proprietary components reduces long-term dependency on the OEM for basic service.

Brentwood Industries

Unlike the other OEMs listed, Brentwood Industries focuses primarily on the media and internal support systems rather than the rotary distributor mechanism. However, they are so integral to the modern trickling filter market that they are an essential inclusion for any engineer specifying a system.

Engineering & Technology:
Brentwood is the leader in structured sheet plastic media. They offer various cross-flow and vertical-flow media configurations tailored to specific treatment goals (e.g., BOD removal vs. Nitrification). Their engineering strength lies in process modeling; they assist consulting engineers in sizing the media volume and selecting the specific surface area (ft²/ft³) required to meet permit limits. Furthermore, they engineer the bottom support piers and grating systems, which are critical for structural safety.

Maintenance & Lifecycle:
Brentwood’s PVC media is chemically resistant and structurally stable, capable of supporting the weight of heavy biomass without collapsing—a common failure mode in inferior plastic media. They also supply drift eliminators to prevent aerosol nuisance, a key operational concern for plants located near residential areas. Their focus is on the static assets inside the tank, ensuring they last 20+ years without degradation.

5. APPLICATION FIT GUIDANCE

Selecting the right OEM and configuration depends heavily on the specific wastewater application.

Municipal Water (Wastewater Treatment)

For standard municipal secondary treatment, WesTech and Evoqua are generally the preferred choices due to their ability to handle diurnal flow peaks. Their hydraulic designs prevent the arms from stalling during low night flows, which is a common issue in smaller municipalities. If the facility is a “Roughing Filter” intended to shave peak loads before an aeration basin, a high-rate distributor from Ovivo or Walker Process with large orifices is ideal to prevent clogging from heavy biological sloughing.

Industrial Wastewater

Industrial applications often involve high-strength waste (high BOD/COD) or specific corrosive elements. In these scenarios, the media selection is paramount. Brentwood Industries vertical flow media is often specified here to minimize plugging risk. For the distributor, stainless steel construction (304 or 316) is mandatory. WesTech is often favored here for their ability to customize metallurgy and seal materials to withstand aggressive chemical environments.

Small vs. Large Facilities

For small rural facilities, simplicity is key. A hydraulically driven Walker Process unit is often the best fit due to its low maintenance requirements and lack of electrical components on the bridge. For large regional plants with complex nutrient removal permits, Evoqua or WesTech units with motorized drives and variable frequency drives (VFDs) allow operators to fine-tune the rotational speed for optimal wetting and snail control, providing the process control required for strict permits.

Retrofit vs. Greenfield

In retrofit scenarios—such as converting a rock filter to plastic media—Brentwood Industries is the primary partner for the internals. They can engineer the new support grid to fit existing floor slopes. If the existing center pier is sound, Evoqua specializes in retrofitting new high-efficiency arms onto legacy center columns, saving the cost of demolition and concrete work.

6. ENGINEER & OPERATOR CONSIDERATIONS

Installation and Commissioning

The most critical phase in trickling filter installation is the leveling of the distributor arms and the media placement.
Distributor Leveling: The center column must be perfectly plumb. Even a slight deviation can cause the arms to scrape the media or rotate unevenly, leading to premature bearing failure. Engineers must enforce strict tolerances in the specification (typically 1/8 inch over the tank diameter).
Media Stacking: For plastic media, the blocks must be installed in alternating patterns to ensure structural interlocking. Walking on the media during installation must be strictly controlled to prevent crushing the delicate flute structures before they are fully supported.

Maintenance Access

Operators require safe access to the center column for lubrication and inspection. Specifications should include a robust galvanized or aluminum walkway bridge. The distributor center well should be equipped with drainage valves to allow for seal inspection without flooding the bearing housing. Lubrication lines for the main turntable bearing should be extended to the walkway to allow greasing while the unit is in operation.

Operational Lessons Learned

Snail Control: In nitrifying filters, Physa snails can consume the biofilm faster than it grows. A motorized distributor allows the operator to slow the rotation, increasing the instantaneous hydraulic flush (Spülkraft) to wash snails out of the media. Hydraulically driven arms often lack the power to achieve this flushing intensity.
Cold Weather Operation: In freezing climates, ice formation on the media surface or the distributor arms is a risk. Distributors should be equipped with “ice breaker” splash plates or designed to maintain continuous high flow to prevent freezing. Limiting recirculation during extreme cold to prevent super-cooling the wastewater is a key operational strategy.

Long-Term Reliability Risks

The primary long-term risk is the degradation of the center bearing. Once this bearing fails, the distributor ceases to rotate, and treatment stops. Engineers should specify bearings with a high service factor and ensure the OEM provides a detailed replacement procedure. Another risk is media collapse. While rare with modern PVC, it has occurred with cheaper materials or improper installation. Ensuring the media OEM provides a warranty on structural integrity (crush strength) is a vital risk mitigation step.

7. CONCLUSION

The selection of OEMs for trickling filter systems is a decision that impacts the facility’s biological performance and mechanical availability for decades. While the technology is mature, the engineering nuances between manufacturers—specifically regarding center column hydraulics, bearing design, and arm geometry—are significant.

For the mechanical distributor, WesTech Engineering, Evoqua, Ovivo, and Walker Process Equipment represent the tier-one capabilities required for municipal applications. Each brings distinct strengths, from WesTech’s hydraulic versatility to Walker’s mechanical simplicity. For the media and internal support systems, Brentwood Industries remains the standard-bearer for structured plastic media solutions.

Engineers must look beyond the initial capital cost and evaluate the lifecycle implications of the equipment. A slightly more expensive distributor with a calculated bearing life of 20 years and a mechanical seal offers far greater value than a lower-cost unit that requires a crane mobilization for bearing replacement in five years. By rigorously specifying hydraulic loading capacities, material grades, and maintenance features, engineers can ensure their trickling filter systems remain the reliable, energy-efficient workhorses they are designed to be.

source https://www.waterandwastewater.com/top-oems-for-trickling-filter-systems/