Aqua-Aerobic vs WesTech for Filtration: Pros/Cons & Best-Fit Applications

Introduction to Tertiary Filtration Selection

Tertiary filtration is frequently the final safeguard between regulatory compliance and a permit violation. As discharge permits tighten — particularly on total phosphorus and turbidity for water reuse — the margin for error in equipment selection has narrowed considerably. A common misconception is treating filtration as a commodity unit process, assuming a disk filter is a disk filter, or that deep bed granular media is obsolete. That oversimplification produces hydraulic bottlenecks, excessive backwash waste volumes and unforeseen operating burdens.

Comparing Aqua-Aerobic vs WesTech for Filtration: Pros/Cons & Best-Fit Applications is a genuine decision point. It is rarely about one manufacturer being objectively better; it is an analysis of technology fit. Aqua-Aerobic Systems is recognized for pioneering pile cloth media filtration with the AquaDisk, driving a shift toward low-head, small-footprint solutions. WesTech Engineering competes in cloth media with the SuperDisc while also offering a substantial portfolio of conventional deep bed and continuous backwash media filters.

This article breaks down hydraulic profiles, solids loading capacity, mechanical reliability and lifecycle cost. Comparable evaluations appear in our analysis of Xylem and WesTech filtration equipment.

How to Select and Specify

Duty Conditions & Operating Envelope

Cloth media filters from both manufacturers operate primarily by surface filtration. They handle hydraulic peaks efficiently but have finite solids loading capacity.

• Solids loading: Cloth media handles moderate influent suspended solids effectively. Where secondary clarifiers are prone to bulking or washout producing significant spikes, deep bed granular media offers better depth storage and resistance to blinding.
• Hydraulic throughput: Calculate peak hourly flow. Cloth media operates at higher hydraulic loading rates than deep bed filters, which is why space-constrained sites favor it.
• Variable flow: Both handle intermittent flow, but cloth media filters are generally easier to bring online and offline automatically without the ripening period granular media requires to reach effective filtration.

Materials & Compatibility

• Tankage: Both manufacturers offer stainless steel units or concrete basin retrofits. For high-chloride or industrial service, verify the stainless grade and the passivation process.
• Cloth media: Typically nylon or polyester pile cloth. Verify chemical compatibility with coagulants and polymers. Polyamide materials can degrade under sustained chlorine residual.
• Granular media: Silica sand, anthracite or garnet. Highly resistant to abrasion and chemical attack but susceptible to cementing where calcium carbonate potential is high.

Hydraulics & Process Performance

• Head loss: Cloth media filters are low-head devices, with clean filter head loss measured in inches and terminal head loss typically set around a foot. This often permits gravity flow through the plant without intermediate pumping.
• Deep bed filters: Require substantially more head to drive water through the media and underdrain, frequently necessitating an intermediate lift station that adds both capital and operating cost.
• Backwash hydraulics: Cloth media uses a vacuum backwash shoe, cleaning while the filter remains online, with low reject volume. Granular media requires taking the cell offline with high-rate backwash pumps and air scour, producing higher reject volume that requires equalization capacity.

Installation Environment & Constructability

Retrofit capability is a primary driver for cloth media. The vertical orientation of disks places substantial surface area in existing concrete basins — including abandoned traveling bridge sand filters. Aqua-Aerobic has a long history of custom-fitting AquaDiamond and AquaDisk units into existing rectangular basins, and WesTech offers comparable retrofit capability for the SuperDisc.

Footprint: A cloth media filter station occupies a fraction of the area a conventional rapid sand filter station requires. That constructability advantage is frequently the deciding factor in urban plants with limited real estate.

Reliability & Failure Modes

• Mechanical complexity: Cloth media filters have moving parts submerged in wastewater — center tube, drive, vacuum shoes, rollers. These are reliable but are wear items, and a drive motor failure takes the entire unit offline.
• Static beds: Conventional gravity filters have no moving parts in the cell. Complexity shifts to the gallery — actuated valves, blowers, backwash pumps. A failed valve can often be manually actuated; a failed disk drive stops the process.
• Redundancy: Specify N+1 at peak flow. For cloth filters that means a redundant disk unit; for sand filters, a redundant cell.

Controls & Automation

• Level-based control: Primary control for both. As solids accumulate, water level or differential pressure rises.
• Timer-based backup: Prevents biological fouling during low-flow periods by initiating a wash cycle even without head loss rise.
• Instrumentation: Influent and effluent turbidity meters are mandatory. For phosphorus removal, orthophosphate analyzers typically feed forward to chemical dosing upstream.

Maintainability, Safety & Access

Confined space: Maintenance on submerged disk components often requires tank drainage and confined space entry. Some designs allow individual segment removal without draining, but it remains a wet, labor-intensive task.

Media replacement: Cloth socks and panels are consumables replaced every few years depending on loading and cleaning frequency, through a manual operation. Sand and anthracite last far longer unless upset conditions cause media loss or cementing; topping off is common while full replacement is a major capital project.

Lifecycle Cost Drivers

• Capital: Cloth media generally carries lower capital cost through reduced concrete work and smaller footprint.
• Energy: Cloth media saves energy by eliminating intermediate pumping and using low-horsepower backwash pumps.
• Maintenance: Cloth media requires periodic cloth replacement and chemical cleaning to remove fouling. Granular media has lower material maintenance but higher energy cost for backwash pumping and air scour.

Comparison Tables

Table 1: Technology & Manufacturer Comparison

Table 2: Application Fit Matrix

Engineer & Operator Field Notes

Commissioning & Acceptance Testing

• Solids loading stress test: Do not test hydraulic throughput with clean water alone. Require performance verification at design solids loading. If the unit backwashes continuously at half the design solids loading, either the pore size is too small or the effective filtration area was overestimated.
• Vacuum shoe alignment: A critical punch list item on any cloth filter. If the shoe does not ride flush against the media face, suction is lost and the cloth is not cleaned effectively, producing visible uneven cleaning patterns on the disks.
• Level sensor calibration: Ensure the transducers controlling the backwash trigger are calibrated to the actual weir elevation. Incorrect settings cause short cycling.

Common Specification Mistakes

Over-specifying media life: Specifications often demand a guaranteed cloth life. Manufacturers will agree mechanically, but biological fouling and mineral scaling are process issues, not warranty defects. Specification language should address mechanical integrity, not process-dependent longevity.

Ignoring clarifier performance: Engineers size filters assuming secondary clarifiers always deliver low suspended solids. Real-world upsets happen. If the plant has a history of clarifier washouts, a deep bed filter may survive the event better than a cloth filter, which can plug solidly and bypass.

O&M Burden & Strategy

Algae control: Cloth filters from either manufacturer are susceptible to algae growth on the exposed upper portion of the disks when installed outdoors. Covers are effectively mandatory in most climates to prevent photosynthesis blinding the media. Where covers are value-engineered out, expect increased manual power washing.

Spare parts: For cloth filters, stock spare socks or panels, a vacuum pump rebuild kit and a drive motor. For granular filters, stock valve actuators and limit switches; media is not a shelf spare.

Troubleshooting

Continuous backwashing on cloth media

• High influent solids loading exceeding design
• Biological fouling reducing porosity — perform a chemical clean
• Vacuum pump failure or clogged suction lines — check gauges and clean the manifold

High effluent turbidity on granular media

• Channeling or mudball formation in the bed. Inspect the bed surface during backwash; uneven distribution suggests clogged or broken underdrain nozzles.

Design Details and Calculations

Sizing Logic

Required surface area equals peak flow divided by the surface loading rate. Loading rates differ substantially between deep bed sand and cloth media, and cloth media carries a higher peak rating for wet weather duty, though the applicable value is vendor and regulator specific.

Net versus gross area: For cloth media, manufacturers rate units on submerged effective area. As water level rises during filtration, effective area increases. Specifications must define the loading rate at the average operating level rather than maximum overflow level, to ensure conservative design.

Backwash waste: Cloth media backwash is a small percentage of forward flow, pumped intermittently at high frequency. Granular media backwash is a large slug of water per wash that usually requires an equalization tank before returning to the head of the plant.

Specification Checklist

1. Definition of filtration area: Define explicitly how area is calculated, preventing manufacturers from over-claiming effective area.
2. Material origin: Specify American Iron and Steel compliance where federal funding is involved. Both manufacturers can comply, but it affects lead time and cost.
3. Performance bond: Require a process performance bond tied to effluent turbidity and phosphorus limits based on defined influent conditions.
4. Control system: Specify non-proprietary PLC hardware so plant staff can troubleshoot code. Avoid black box controllers.

Standards

• AWWA B100 for granular filter material. Cloth media is proprietary and not covered by a generic material standard, which is exactly why performance-based specification matters more there.
• Reuse regulations: Verify the specific model proposed carries current acceptance at the loading rate intended. Both manufacturers maintain approved loading rate listings for defined influent turbidities.

Frequently Asked Questions

What is the main difference between AquaDisk and SuperDisc?

Both are cloth media filters. The differences lie in the drive mechanism and cloth attachment — one approach pulls a cloth sock over the disk segments, the other uses panel-based attachment where cloth is mechanically secured to a frame. Backwash shoe mechanics and drive configurations also differ. From a process standpoint both achieve similar effluent quality; the maintenance procedures for changing media differ.

How do you select between cloth media and sand filters for phosphorus removal?

It depends on the limit and chemical usage. Both can achieve low total phosphorus with upstream coagulation. Cloth media suits footprint-constrained sites with lower energy use. Sand filters suit high biological solids potential, or where a polishing step that also provides some denitrification is wanted. Sand generally offers more buffer against chemical overdosing than cloth.

What is the typical lifespan of cloth media?

In municipal service, several years. Lifespan shortens with high influent solids, frequent high-pressure backwashing, abrasive grit, or sustained chlorine residual that degrades the fibers. Budget for replacement on a defined cycle as a baseline planning assumption.

Why does my cloth filter backwash continuously?

The filter cannot process incoming flow at current head loss. Usual causes are influent solids exceeding design, excessive polymer dosing creating sticky floc that blinds the cloth, biological fouling requiring chemical cleaning, or mechanical failure of the backwash pump or shoe.

What does a tertiary filtration system cost?

Costs vary widely with site complexity. Cloth media equipment packages are generally less expensive than deep bed sand systems on an installed project basis, primarily because civil and concrete costs are substantially lower. Obtain current quotes rather than relying on published unit costs, which move with steel and labor markets.

Can one manufacturer’s filters retrofit into the other’s basins?

Generally yes. Since both offer cloth media solutions designed to drop into existing concrete basins, engineers can design a technology-neutral basin accommodating either manufacturer’s equipment with minor modifications to baffle walls and fillets.

Conclusion

The choice between Aqua-Aerobic and WesTech is a selection between filtration philosophies and mechanical executions rather than a brand preference. Aqua-Aerobic is the standard-bearer for cloth media with a large installed base and sustained focus on pile cloth technology. WesTech offers a broader portfolio, supplying cloth media where it fits and deep bed or continuous backwash sand solutions where the application demands robustness over compactness.

The path forward involves rigorous hydraulic modeling and a clear understanding of the facility’s operating capabilities. Related evaluations appear in our comparisons of DuPont Memcor and Aqua-Aerobic and of DuPont Memcor and WesTech.