Automatic Backwash Cloth Filters

Automatic backwash cloth filters remove suspended solids from water or wastewater by passing flow through synthetic fabric media mounted on panels or discs inside a tank. As solids accumulate on the cloth surface, differential pressure across the filter increases until it triggers an automated backwash cycle that reverses flow and uses suction to clean the fabric without taking the unit offline. These filters typically achieve effluent suspended solids concentrations below 10 mg/L when treating secondary effluent. You'll find them in tertiary treatment applications, ahead of membrane systems for pretreatment, and in industrial reuse schemes where consistent low-turbidity water is required. The key trade-off is that cloth media requires periodic replacement (typically every 3-7 years depending on loading), and aggressive chemical cleaning may be needed when biological growth or scaling occurs despite routine backwashing.

• Tertiary Filtration for TSS Polishing: Primary application following secondary clarifiers in 2-25 MGD plants requiring <10 mg/L TSS effluent. Cloth filters achieve 5-8 mg/L TSS consistently with 2-4 gpm/sf loading rates. Selected over sand filters for lower footprint (60% smaller) and reduced backwash water consumption (1-3% vs 5-8%)
• Phosphorus Removal Enhancement: Used downstream of chemical precipitation systems where coagulant addition creates fine floc requiring polishing. Typical installations handle 0.5-15 MGD flows, achieving 0.1-0.3 mg/L total phosphorus when combined with ferric chloride or alum dosing upstream
• Peak Flow Management: Installed parallel to existing filters to handle wet weather flows up to 2x design capacity. Common in 5-50 MGD plants with combined sewer systems, providing consistent effluent quality during storm events when conventional filters become hydraulically limited
• Membrane Pre-treatment: Protects downstream RO/MF systems by removing particles >10 microns. Reduces membrane fouling rates by 40-60% in water reuse applications, extending cleaning cycles from 30 to 45-60 days

Misconception 1: Backwashing completely restores the cloth to like-new condition indefinitely.

​

Reality: Routine backwashing removes bulk solids, but biological growth, chemical scaling, and fiber degradation accumulate over time and reduce filtration performance.

​

Action: Ask your operations team about their chemical cleaning frequency and request manufacturers' recommended cleaning protocols during equipment evaluation.

​

Misconception 2: All cloth filters perform identically since they use similar fabric materials.

​

Reality: Backwash mechanisms, cloth weave specifications, panel configurations, and hydraulic designs vary significantly between manufacturers, affecting solids capture and maintenance requirements.

​

Action: Request side-by-side performance data and observe operating units at similar plants before specifying a particular system.

Filter cloth panels form the primary filtration surface where suspended solids are captured as water passes through. Panels are typically woven polyester or polypropylene fabric stretched over stainless steel frames in modular configurations. The cloth's weave density determines filtration effectiveness—tighter weaves capture more solids but require more frequent backwashing and higher head loss.

​

Backwash spray nozzles direct high-pressure water jets across the cloth surface to dislodge accumulated solids during cleaning cycles. Nozzles are usually stainless steel or polymer with fan-shaped spray patterns that traverse the entire cloth width. Proper nozzle alignment prevents uneven cleaning that leaves residual solids and creates localized blinding on the cloth surface.

​

Drum or disk assembly supports the filter cloth and rotates slowly to present dirty sections to the backwash spray. The drum is typically powder-coated or stainless steel construction with perforated surfaces that allow filtered water to exit. Rotation speed affects backwash efficiency—too fast wastes water while too slow allows excessive buildup between cleaning cycles.

​

Filtrate collection chamber collects clean water that passes through the cloth and directs it to the outlet piping. The chamber is usually concrete or coated steel with internal baffles to prevent short-circuiting and ensure even flow distribution. Poor chamber design causes uneven loading across cloth panels, reducing effective filtration area and increasing backwash frequency.

​

Solids discharge trough captures dislodged solids during backwashing and conveys them to waste handling systems or upstream processes. Troughs are typically stainless steel or fiberglass with sloped bottoms to prevent solids accumulation and plugging. Inadequate trough capacity or slope causes solids to settle and re-enter the filtrate stream, defeating the backwash cycle.

Daily Operations: You'll monitor effluent turbidity and head loss across the cloth to verify filtration performance. Normal operation shows gradual head loss increase between backwash cycles with turbidity remaining below permit limits. Check that backwash cycles initiate automatically at the programmed head loss setpoint and that solids discharge freely to the waste trough. Notify maintenance if backwash frequency increases suddenly or if effluent turbidity rises despite normal head loss.

​

Maintenance: Expect weekly visual inspections of cloth condition for tears or blinding and monthly checks of spray nozzle alignment and flow patterns. Cloth replacement typically occurs annually or when visual inspection shows permanent blinding that backwashing cannot remove. Most cloth changes require two operators and basic hand tools but no specialized training. Budget for vendor service if drum bearings or drive mechanisms fail, as these require alignment expertise beyond typical operator skill sets.

​

Troubleshooting: Rising effluent turbidity with normal head loss suggests cloth tears or bypass around panel seals—inspect cloth visually and check gasket compression. Increasing backwash frequency with clean cloth indicates higher influent solids loading or partially plugged spray nozzles. Cloth typically lasts 12 to 18 months before blinding becomes irreversible. Call for engineering support if backwash cycles fail to restore normal head loss or if you suspect structural issues with the drum assembly.

Selecting an automatic backwash cloth filter requires balancing hydraulic capacity, filtration performance, and operational constraints—each parameter influences the others and affects both capital cost and long-term reliability.

​

Filtration Rate (gpm/sf) determines the cloth surface area needed to handle your plant's flow without excessive headloss. Municipal cloth filters commonly operate between 2 and 10 gpm/sf. Lower rates provide more conservative performance with longer filtration cycles and better solids capture, while higher rates reduce footprint and construction costs but require more frequent backwash cycles and may challenge removal efficiency during peak loading events.

​

Influent Total Suspended Solids (mg/L) drives how quickly the cloth blinds and how often backwash must occur. Municipal applications typically treat influent TSS between 10 and 50 mg/L. Higher solids loading shortens filtration cycles and increases backwash frequency, demanding more robust cloth materials and larger backwash pumps, while lower concentrations allow extended run times and gentler cleaning sequences that preserve cloth integrity over years of service.

​

Headloss at Design Flow (inches of water column) indicates when the cloth needs cleaning and affects upstream hydraulic grade line requirements. Most municipal cloth filters initiate backwash between 6 and 24 inches of headloss. Lower trigger points maintain consistent effluent quality and reduce energy consumption but increase backwash frequency, while higher thresholds extend filtration cycles but risk solids breakthrough and require more available head in your hydraulic profile.

​

Backwash Flow Rate (gpm per disk or panel) determines pump sizing and the volume of filtrate needed for cleaning. Municipal cloth filter backwash systems commonly require between 15 and 40 gpm per disk. Higher flow rates provide more aggressive cleaning that removes deeply embedded solids but consume more filtrate and energy, while lower rates offer gentler cleaning that extends cloth life but may not fully restore capacity after heavy loading periods.

​

Cloth Mesh Size (microns) controls what particle sizes are captured and affects both effluent quality and blinding tendency. Municipal tertiary cloth filters commonly use mesh openings between 10 and 20 microns. Finer mesh captures smaller particles and achieves lower effluent TSS but blinds more rapidly and requires more frequent backwash, while coarser mesh extends filtration cycles and reduces maintenance but may not meet your permit limits during algae blooms or upset conditions.

​

All values are typical ranges—actual selection requires manufacturer consultation and site-specific analysis.

Should you select disk or panel filter configuration?

​

• Why it matters: Configuration affects footprint, backwash effectiveness, and how easily operators access cloth elements.
• What you need to know: Available floor space, headroom constraints, and your team's preference for maintenance access.
• Typical considerations: Disk filters stack elements vertically in cylindrical housings, requiring less floor area but more overhead clearance. Panel filters arrange elements as flat cassettes in rectangular tanks, offering walk-around access but consuming more square footage.
• Ask manufacturer reps: How does element replacement time compare between your disk and panel configurations?
• Ask senior engineers: Which configuration has performed better in plants with similar staff size?
• Ask operations team: Do technicians prefer overhead element removal or side-access cassette replacement during maintenance?

​

How will you integrate backwash waste handling into existing plant hydraulics?

​

• Why it matters: Backwash flow timing and volume can overload existing return streams or require dedicated equalization.
• What you need to know: Peak backwash flow rate, cycle duration, and capacity of receiving process or storage.
• Typical considerations: Backwash cycles generate short-duration high flows that may upset upstream processes if returned directly. Some plants route waste to dedicated equalization basins, others blend returns during low-demand periods to avoid hydraulic spikes.
• Ask manufacturer reps: What is your maximum instantaneous backwash discharge rate for this filter size?
• Ask senior engineers: Where have you successfully routed cloth filter backwash waste in similar plants?
• Ask operations team: Can our existing return pumps handle intermittent backwash flows without process disruption?

​

What level of automation do you need for backwash initiation?

​

• Why it matters: Automation level determines operator workload, response time to fouling, and control system complexity.
• What you need to know: Staffing patterns, existing SCADA capabilities, and tolerance for headloss variation before backwash.
• Typical considerations: Timer-based systems backwash at fixed intervals regardless of actual fouling, while differential pressure triggers respond to real-time loading. Hybrid approaches combine both methods to prevent over-cleaning during low-loading periods and ensure minimum cleaning frequency.
• Ask manufacturer reps: Does your standard control package support both timer and pressure-differential initiation modes?
• Ask senior engineers: Have you seen timer-only systems waste backwash water during low-demand periods?
• Ask operations team: Would you prefer fixed schedules you can predict or automatic response to pressure?

Lead Times: Typically 16-24 weeks from order to delivery; custom configurations or stainless steel construction extend timelines. Important for project scheduling—confirm early.

​

Installation Requirements: Requires reinforced concrete channel or basin with level mounting surface; 480V 3-phase power and backwash water supply from plant effluent or clearwell. Overhead clearance needed for disc/drum removal during maintenance (typically 12-15 feet). Rigging equipment required for setting units.

​

Coordination Needs: Coordinate with structural for basin design and anchor bolt placement; electrical for motor controls and instrumentation wiring; process for backwash water supply piping and waste return routing. Interface with SCADA system for remote monitoring and alarm integration.

Automatic backwash cloth filters are purchased as complete packaged units including filter discs/drums, backwash systems, instrumentation, and controls.

​

Aqua-Aerobic Systems – AquaDisk and AquaDrum cloth media filtration systems. Specializes in both tertiary and primary effluent applications with various media grades.

​

Nordic Water – Discfilter and Drumfilter product lines. Known for compact footprint designs and low backwash water consumption.

​

WesTech Engineering – Cloth media disc filters with integrated backwash systems. Focus on municipal retrofits and capacity expansion projects.

​

This is not an exhaustive list—consult regional representatives and project specifications.

• Traveling bridge sand filters - Better for higher TSS loads (>30 mg/L), roughly 20% higher capital cost but lower O&M
• Membrane bioreactors (MBR) - When space is extremely limited, 3-4x higher cost but superior effluent quality
• Conventional sand filters with polymer - Lower capital cost (40-50% less) but higher chemical costs and larger footprint requirements, suitable for plants with available land