Rotary drum screens in Pakistan

Where this equipment fits

Food-processing wastewater, fibre-bearing streams and compact inlet works.

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 rotary drum screens

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

• 01Aperture and feed arrangement
• 02Peak flow and solids characteristics
• 03Spray wash and discharge height

What affects the price in Pakistan?

The quoted price depends on aperture and feed arrangement, 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: estimate active and partially blinded screen area

Illustrative calculation, not a final hydraulic design. Assume peak flow is 90 m³/hour. A 1.0 m diameter drum has 1.2 m of screened length, and the supplier confirms that 40% of the cylindrical surface is active at the design water level. Gross active surface is π × 1.0 × 1.2 × 0.40 = about 1.51 m².

If perforations, supports and structural blockage give a confirmed clean open-area ratio of 35%, net clean open area is 1.51 × 0.35 = about 0.528 m². The simplified clean hydraulic rate is 90 ÷ 0.528 = about 170 m³/m²·hour.

If retained solids block 40% of the clean open area before cleaning restores it, about 0.317 m² remains and the simplified rate rises to about 284 m³/m²·hour. Do not select a drum from this arithmetic alone. Obtain the supplier's clean and loaded curves using the actual inlet, water levels, basket geometry, screen opening, drum speed and cleaning cycle.

Worked example: convert capture and wash water into handling duties

Illustrative mass balance. At 90 m³/hour for 10 hours, daily screened flow is 900 m³. If representative sampling shows 120 mg/L of screenable dry solids and a trial supports 60% capture, retained dry solids are 900 × 120 × 0.60 ÷ 1,000 = 64.8 kg/day.

If discharged screenings contain 25% dry solids, wet screenings mass is 64.8 ÷ 0.25 = about 259 kg/day. If screen and reject washing use an assumed 0.7% of daily flow, wash water is 900 × 0.007 = 6.3 m³/day. If it is used during 1.5 hours of wash cycles, the average while washing is 4.2 m³/hour. Replace every assumed percentage with supplier data, trials and field records before sizing the press, bin, water supply or drainage return.

Define the feed arrangement before selecting a drum

• State whether the screen will sit in a channel, a supplied tank or a pumped package, and whether wastewater enters the open end, outside surface or another manufacturer-defined path.
• Record minimum, normal and peak instantaneous flow, batch duration, pump starts, upstream storage and downstream water-level changes.
• Survey channel or tank dimensions, inlet invert, available head, operating water levels, freeboard, discharge height, drainage and access.
• Prevent jets, uneven distribution or short-circuiting from using only part of the basket. Confirm inlet energy dissipation and the supplier's minimum and maximum water levels.
• For variable industrial discharges, use equalization only where it provides a controlled feed without allowing grease or solids to settle, float or become septic.

Choose opening geometry for the protection duty

• Name the downstream equipment or process to protect and obtain its permitted opening and carryover requirements.
• Distinguish wedge-wire slots, round or square perforations and mesh. The same nominal dimension can produce different capture, open area and blinding behaviour.
• Check plate or wire thickness, support bars, seam details, basket stiffness and the total clean open area after every obstruction is included.
• Use a coarse mechanical screen first where large rags, plastics, stones or wood could damage the drum, screw, brush or spray system.
• For a wider technology review, use the fine-screen selection guide to compare the same hydraulic and downstream protection duty.

Check clean, loaded and one-unit-out hydraulics

• Use the actual submerged or wetted screening surface at each operating level, not the full geometric drum area.
• Request clean and agreed partially blinded flow and headloss curves for the proposed basket, opening, inlet and drum speed.
• Check upstream surcharge, freeboard, overflow and bypass before cleaning starts, while the drum rotates, during a wash cycle and if the drum stops.
• Prove the required peak duty with one screen isolated where continuity is required. Include usable isolation gates or valves and the effect on the remaining channel or tank.
• Use upstream and downstream level instruments where differential level starts the screen, identifies blinding or protects the plant.

Characterize grease, fibres and abrasive solids

• Sample during normal production, cleaning, start-up, shutdown and difficult batches. Record fibres, hair, wipes, plastics, food pieces, grease, grit and temperature.
• Sticky fats can coat a cold basket, brush and chute. Confirm temperature range, spray-water temperature if relevant, cleaning chemicals if allowed and hygienic access.
• For kitchen wastewater, remove gross food solids where justified and retain a correctly sized grease trap or interceptor. A drum screen does not replace grease separation.
• Long fibres can wrap around shafts or screws and bridge the reject chute. Check the actual fibre length, toughness and wet behaviour.
• Grit and hard particles can wear wedge wire, perforated plate, brushes, screws and bearings. Define upstream removal, wear materials and inspection points.
• Do not infer capture from total suspended solids alone. Identify the fraction that the proposed opening and geometry can physically retain.

Match rotation, brushing and spray washing to the wastewater

• Define normal and cleaning drum speed, drive torque, overload protection and whether speed changes affect hydraulic capacity or solids discharge.
• For an external brush, state brush material, contact adjustment, wear allowance, replacement access and the response to wrapped fibres.
• For spray cleaning, state nozzle arrangement, minimum pressure, instantaneous flow, water quality, filtration, isolation and low-pressure alarm.
• Check that the cleaning system reaches the complete active basket and removes solids without forcing unacceptable carryover through the opening.
• Agree start, stop and overrun logic from differential level, upstream level, timer or a justified combination, plus a maximum idle period where deposits may dry.

Complete the screenings and wash-water route

• Measure retained dry solids, wet mass, loose volume, free water and short peak discharge during representative trials or operation.
• State whether the unit only screens or also washes, conveys, compacts and dewaters the reject. Do not assume an integrated press is included.
• Where separate equipment is used, define the interface with screenings washing and compaction, including chute or launder, drop height, drainage and interlocks.
• Define bag or bin capacity, full-container alarm, change frequency, spill control, access, odour control, washdown and the authorized disposal route.
• Return spray water, drainage and separated liquid to a controlled point. Check the short return peak and prevent captured screenings from returning to the inlet.

Compare rotary drum screening with alternatives

Controls, standby and safe failure response

• Coordinate the drum, screw or conveyor, brush, spray valve, washer or compactor, full-bin alarm and upstream pumps through the MCC and control panel.
• Include local and remote modes, emergency stops, guarded isolators, run and fault status, overload, jam, low spray pressure, high level and bypass alarms.
• Prevent automatic feeding when the drum, reject conveyor, press, drainage or collection container is unavailable.
• Define safe power-restoration behaviour. Do not restart into a jam, open guard, full bin or unavailable downstream handling route.
• Record run time, starts, differential level, wash cycles, overloads and bypass events where trends will support maintenance.

Provide safe access and maintainability

• Provide non-slip platforms, gratings, handrails and lifting equipment around the drum, tank, covers, drive and reject equipment.
• Guard the drum, screw, chains, sprockets, brushes and pinch points. Provide lockout points for every moving part and the wash-water pressure source.
• Allow access to inspect both sides of the basket, supports, seals, brush contact, sprays, bearings, gearbox, chute, drainage and level sensors.
• State the heaviest removable component, lifting points, cover or hatch size, clear removal path and laydown area.
• Provide ventilation, lighting, washdown and drainage suitable for sewage, food waste, grease, aerosols and odour.

Specify the complete rotary drum screen package

• Drum basket and supports, frame or tank, shaft, seals, bearings, drive, screw or conveyor, brush, scraper, spray bar, nozzles and discharge chute.
• Inlet distribution, channel or tank connections, anchors, seals, isolation, overflow or protected bypass and upstream and downstream level instruments.
• Wash-water supply, pressure control, filtration where required, valves, piping and drainage to the agreed return point.
• Integrated or separate reject washing, compaction and dewatering, plus bags or bins, enclosure, odour control and disposal interface.
• Control panel, cables, local station, alarms, interlocks, emergency stops, communications, platforms, guards and lifting.
• Installation, dry checks, water testing, representative-wastewater commissioning, training, manuals, initial consumables, recommended spares and special tools.

Commissioning and acceptance checks

• Verify inlet, tank or channel dimensions, anchors, alignment, operating levels, opening geometry, drum clearances, seals, brush contact, spray coverage, guards and lifting.
• Calibrate level instruments and confirm automatic start, stop and overrun, timer backup, alarms, interlocks and emergency stops.
• Observe clean and agreed loaded hydraulic conditions at minimum, normal and peak flow, including one-unit-out duty where specified.
• Use representative wastewater and solids to confirm distribution, capture, cleaning, carryover, reject transport and the complete handling sequence.
• Measure spray pressure and flow, wet screenings mass or volume, drainage and return rate. Test low pressure, jam, high level, full bin, bypass and power restoration safely.
• Accept against agreed opening and geometry, peak flow, water levels, headloss basis, capture evidence, carryover, wash duty, reject condition and stable test duration.

Operating and maintenance requirements

• Trend flow, water levels, differential level, drum run time, starts, wash cycles, spray-water use, overloads, jams, bypass and screenings quantity.
• Inspect the basket, perforations or wedge wire, supports, seams, seals, brush, scraper, sprays, screw or conveyor, bearings, gearbox, fasteners and corrosion.
• Clean nozzles, basket surfaces, ledges, inlet distribution, chute, drainage and level sensors before deposits create false readings or reduce active area.
• Investigate rising levels, longer run time, carryover or wet reject. Causes can include changed solids, grease, damaged basket, poor brush contact, blocked sprays or worn seals.
• Keep critical brushes, nozzles, seals, bearings and drive protection identified from the selected supplier rather than assuming generic spares will fit.

Information needed for a useful quotation

• Minimum, normal and peak instantaneous flow; batch or pump sequence; inlet arrangement; upstream and downstream levels; available head and freeboard.
• Required opening and geometry, downstream protection duty, representative solids, fibres, grease, grit, temperature and capture evidence.
• Clean and loaded hydraulic basis, duty and standby philosophy, one-unit-out requirement, bypass protection, isolation and high-level consequences.
• Channel or tank scope, basket material, cleaning method, wash-water quality and pressure, reject mass and volume, discharge height and handling route.
• Controls, instruments, alarms, pump and handling interlocks, electrical supply, ambient and corrosive conditions, ventilation and data requirements.
• Civil work, access, guards, lifting, installation, commissioning, operator training, manuals, spares and measurable acceptance terms.

For an existing drum with high level, grease coating, wrapped fibres, damaged basket, ineffective sprays or unreliable reject handling, Aquenvia's upgrade and maintenance service can review the feed, hydraulics, screen, controls and access together.

Common rotary drum screen questions

Browse the screening equipment category or review Aquenvia's industrial effluent-treatment service for the complete pretreatment duty.

Compare a rotary drum with other fine-screen arrangements

Use the fine-screen hydraulic and protection guide to compare opening geometry, wetted area, clean and blinded headloss, spray washing, grease and fibres, screenings discharge, standby and acceptance on the same duty.

Compare rotary drum and step screening

The step-screen hydraulic and operating guide helps compare channel geometry, openings, screenings-carpet behaviour, grit exposure, bottom cleaning, discharge height, controls and safe maintenance on the same duty.

Compare rotary drum and screw screening

Use the screw-screen hydraulic and operating guide to compare feed arrangement, active area, opening geometry, brush and spray cleaning, screw wear, lifting, compaction, controls and safe maintenance on the same duty.