Static wedge-wire screens in Pakistan

Where this equipment fits

Food-process solids recovery and selected industrial pretreatment.

For housing STPs in Lahore and mixed industrial drains, assess the actual rag, plastic and fibre load. Where stormwater can enter the sewer, check the peak hydraulic condition and a safe maintenance bypass. Specify how screenings will be washed, collected and removed from the site.

How to select static wedge-wire screens

Use these inputs to define the equipment duty before comparing proposals.

• 01Slot opening and solids shape
• 02Feed distribution and gravity head
• 03Cleaning method and access

What affects the price in Pakistan?

The quoted price depends on slot opening and solids shape, materials, controls and the agreed supply scope. For a useful comparison, identify freight, taxes, installation, commissioning and initial spares as separate proposal items where applicable.

For replacement equipment, share the existing nameplate, photographs and connection dimensions. For a new installation, share the design flow or loading, site location and available space. Final availability, delivery and performance terms are confirmed with the selected equipment.

Integration with your treatment plant

Peak flow and upstream / downstream channel levels. Required opening and downstream protection duty. Screenings handling, access and standby arrangements. These interfaces should be checked alongside the individual equipment specification.

Worked example: check effective screen area as blinding increases

Illustrative calculation, not a final hydraulic design. Assume a peak feed of 18 m³/hour to a 1.2 m wide screen with 1.5 m of wetted sloping length. Gross wetted area is 1.2 × 1.5 = 1.80 m². If edge seals, supports and non-wetted margins remove 10%, effective clean area is 1.62 m².

The clean surface loading is 18 ÷ 1.62 = 11.1 m³/m²/hour. If representative testing shows that only 60% of the clean area remains available before cleaning, available area becomes 0.972 m² and the instantaneous loading rises to 18.5 m³/m²/hour. Obtain the supplier's capacity and head requirements for the exact wedge-wire profile, slot, curvature, feed box, distribution weir, solids and agreed loaded condition.

Worked example: convert captured solids into handling duty

Illustrative mass balance. At 120 m³/day, assume a representative trial measures 180 mg/L of screenable dry solids retained by the proposed opening. Captured dry solids are 120 × 180 ÷ 1,000 = 21.6 kg/day. If drained screenings leave the chute at 18% dry solids, wet screenings mass is 21.6 ÷ 0.18 = 120 kg/day.

If two equal handling periods are planned, each must receive about 60 kg before allowing for peak production, rainfall, wash water or a missed collection. If spray cleaning uses 0.35 m³/hour for ten minutes, twelve times per day, spray water is 0.35 × 10 ÷ 60 × 12 = 0.70 m³/day. Confirm where free drainage and spray water return without overloading an upstream sump or downstream process.

Define the wastewater and separation duty first

• Record minimum, normal and peak instantaneous flow, batch releases, pump starts, production and washdown schedules, temperature, pH and expected future flow.
• Describe solids by size, shape, density and behaviour, including food pieces, peel, grain, fibres, labels, hair, grease, sticky material and mineral grit.
• Measure what must be protected or recovered downstream. A nominal slot is not a guaranteed particle cut because long, flexible and flat solids can align with an opening.
• Trial representative wastewater across normal and difficult operating periods. Use measured capture, blinding, drainage and cleaning frequency instead of clean-water capacity alone.
• Use an equalization tank where controlled release can reduce a batch peak, but still check the screen against the real instantaneous feed rate.

Choose the screen geometry and feed arrangement together

• State whether the proposal is a curved sieve-bend, parabolic run-down or inclined flat panel. Record the clear slot, profile wire, support spacing, tolerance, flow direction and replaceable panel details.
• Provide a calm feed box, level distribution weir and full-width loading. A good screen panel cannot correct a jet concentrated on one side.
• Check inlet and outlet levels, gravity head, overflow route, freeboard and the head needed to distribute peak flow without flooding the upstream process.
• Confirm how the liquid passes through the slots while retained solids move to the discharge edge. Check that the chute cannot bridge, return solids or direct drainage onto a walkway.
• Use a high-level instrument or switch where ponding or overflow could damage production, flood the room or bypass treatment.

Check blinding, grease, fibres and grit limits

• Grease and sticky organic material can coat wedge wire and reduce drainage. A grease interceptor has a separate retention and cleaning duty and is not replaced by screening.
• Hair, strings and flexible fibres can bridge slots or form a mat. Compare the static screen with a mechanically cleaned fine screen if representative trials show rapid blinding or unsafe cleaning frequency.
• Sand, glass and hard grit can abrade feed points, wire and chutes. Confirm wear allowances and provide separate grit management where required.
• Do not reduce the slot simply to improve capture. A smaller opening may increase blinding, upstream head, cleaning water, labour and uncontrolled bypass.
• If load varies sharply, compare a rotary drum screen with driven cleaning and controlled reject discharge on the same wastewater and peak duty.

Plan cleaning without damaging the wedge wire

• Define normal manual washdown, optional spray cleaning, required water quality, pressure, nozzle coverage, valve and isolation. Confirm the screen supplier's allowable cleaning pressure and tools.
• Do not use metal scrapers, uncontrolled high-pressure jets or chemical cleaners unless the screen supplier has approved them for the wire, welds, seals and frame.
• Provide a safe washdown route and contain aerosols and splash where the wastewater or retained material creates an exposure risk.
• Record flow, upstream level, cleaning time and visual condition before and after cleaning. Rising frequency can indicate changed solids, damaged distribution, grease or an unsuitable opening.
• Keep spare nozzles, seals and any replaceable panel or cleaning accessories identified in the proposal rather than assuming they are included.

Compare static wedge wire with other screening arrangements

Complete the screenings and drainage route

• Define wet mass, loose volume, short peak discharge, chute angle, draining time, bin size, bagging and the authorized collection or disposal route.
• Where odour, insects or putrescible food solids matter, define covered storage and collection frequency rather than relying on daily average mass alone.
• Use a screenings washer or compactor only after trials define the feed, free water, washing objective, compaction duty, drainage return and discharge height.
• Return drainage to a defined hydraulic point. Do not create an unnoticed recycle that repeatedly loads the screen or bypasses flow measurement.
• Provide floor grading, trapped drainage and washdown containment suited to the site's wastewater and housekeeping rules.

Provide standby, bypass and safe access

• Where production or treatment cannot stop, provide duty and standby capacity, a removable spare panel or an isolated alternate flow path that does not become a routine untreated bypass.
• Design gates and isolation so an operator can clean or remove the screen without entering flowing wastewater or reaching across an open channel.
• Use non-slip platforms, handrails, covers and lifting equipment for the heaviest removable item and its clear removal path.
• Define safe access to both sides of the panel, feed box, nozzles, chute and bin. Include lockout for pumps and automated sprays even though the screen itself has no drive.
• Keep overflow and bypass events visible, alarmed and recorded. A dry downstream channel does not prove acceptable screening if wastewater escaped elsewhere.

Specify the complete static-screen package

• Screen panel and frame, feed box, distribution weir, overflow, enclosure or splash guards, screened-liquid outlet, solids chute, drains, supports and anchors.
• Materials and corrosion allowance for measured wastewater chemistry and the room environment, with weld finish, pickling or passivation where specified.
• Spray bar, nozzles, strainer, pressure indication, valve and low-pressure alarm where automated washing is part of the accepted design.
• Instruments, local controls, high-level alarm, upstream pump interlock and power-failure response where relevant.
• Drawings, hydraulic basis, certified dimensions, loads, installation interfaces, operating manual, spare-parts list, warranty limits, commissioning and training.

Commissioning and acceptance checks

• Confirm level, alignment, supports, seals, distribution weir, outlet, overflow, chute, drainage, access and guards before introducing wastewater.
• Use clean water to find obvious leakage or poor distribution, then test representative wastewater at minimum, normal and peak operating periods.
• Record feed flow, upstream and downstream levels, wetted width and length, visual distribution, captured wet mass, samples, cleaning interval, spray flow and any bypass.
• Agree how influent and screened samples will be collected and compared. Capture based on one grab sample or clean water does not establish performance on changing industrial wastewater.
• Accept the complete route, including solids leaving the chute, bin capacity, drainage return, safe cleaning and restart after the loaded condition, not only liquid passing the panel.

Operating and maintenance requirements

• Each shift, check even feed, upstream level, overflow, blinding, chute discharge, bin fill, drainage and housekeeping.
• At the site-defined interval, clean nozzles and strainers, inspect slot damage, welds, seals, corrosion, supports and signs of abrasive wear.
• Trend flow, cleaning time, cleaning-water use, captured mass and unplanned bypass. Investigate changes against production and wastewater records.
• After a panel repair or process change, repeat the relevant hydraulic and capture checks rather than assuming the original duty still applies.

Information needed for a useful quotation

• Site and application, wastewater source, operating schedule, minimum, average and peak instantaneous flow, batch releases and future allowance.
• Representative solids description, samples or photographs, measured screenable solids, TSS, grease, fibres, grit, temperature, pH and cleaning chemicals.
• Required opening and capture basis, downstream equipment protected, inlet and outlet levels, available gravity head, feed pipe or channel and overflow route.
• Required duty and standby arrangement, cleaning method, water pressure and quality, enclosure, chute, bin, compaction, drainage and disposal interface.
• Materials, hazardous or hygienic area needs, access, lifting, electrical supply, instruments, controls, civil limits, installation scope, acceptance test and documentation.

For an existing plant, Aquenvia can review the measured duty through the upgrade and maintenance service. For a new industrial pretreatment train, share the screen duty within the effluent treatment assessment.

Common static wedge-wire screen questions

Does a static screen need electricity?

The separation surface has no drive, but upstream pumps, level alarms, automated sprays or reject equipment may require power and controls. The process also needs enough hydraulic head.

Will the stated slot remove every larger particle?

No. Particle shape, orientation, flexibility, feed distribution, grease and the solids mat affect capture. Prove the required separation with representative wastewater and the proposed screen geometry.

Can static screening replace grease removal?

No. It may remove suitable food pieces or fibres, but free grease, emulsions and dissolved material need their own assessment and treatment route.

When should we consider a driven screen?

Consider an automatically cleaned fine or rotary drum screen when trials show rapid blinding, unsafe manual cleaning, variable peaks, difficult fibres or a continuity requirement that the static arrangement cannot meet.

Compare static wedge wire with a cleaned fine screen

The fine-screen comparison guide helps check feed distribution, surface loading, opening geometry, blinding, grease, fibres, cleaning, drainage and solids collection on representative wastewater.

Compare static wedge wire with a rotary drum

The rotary drum screen comparison guide helps assess feed distribution, active area, opening geometry, blinding, grease, fibres, driven cleaning, wash water and reject discharge on the same wastewater.