Screenings washers & compactors in Pakistan

Where this equipment fits

Mechanically screened headworks with wet screenings.

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 screenings washers & compactors

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

• 01Incoming waste volume
• 02Wash water and return drainage
• 03Discharge container and compaction duty

What affects the price in Pakistan?

The quoted price depends on incoming waste volume, 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: convert screen discharge into the washer duty

Illustrative calculation, not a final equipment selection. Assume a screen produces 400 kg/day of wet screenings at 12% dry solids. Incoming dry solids are 400 × 0.12 = 48 kg/day. If loose wet screenings have a measured bulk density of 180 kg/m³, loose volume is 400 ÷ 180 = 2.22 m³/day.

If the screen and washer run for eight hours per day and the measured short peak is 2.5 times the average operating-hour rate, peak loose feed is 2.22 ÷ 8 × 2.5 = about 0.69 m³/hour. The washer, chute, screw, drain and discharge must all pass that short peak without bridging. Replace the assumed moisture, density, operating hours and peak factor with weighed bins, timed collections and representative site records.

Worked example: washing, dewatering and bin balance

Illustrative mass balance. Continue with 48 kg/day of incoming dry solids. Suppose a representative trial shows that washing returns 20% of that dry mass as biodegradable material with the drain. Dry solids leaving for disposal are then 48 × 0.80 = 38.4 kg/day. If the accepted discharge contains 32% dry solids, wet discharge is 38.4 ÷ 0.32 = 120 kg/day.

If wash water is 1.20 m³/day, and water held in the compacted discharge is 120 - 38.4 = 81.6 kg/day, the simplified liquid return is about 352 + 1,200 - 81.6 = 1,470 kg/day, or approximately 1.47 m³/day at water-like density. This is an estimate for return-flow planning, not a laboratory balance.

At a measured compacted bulk density of 350 kg/m³, discharge occupies 120 ÷ 350 = 0.34 m³/day. Three days of storage plus 30% contingency requires about 1.34 m³ of usable bin volume. Odour, insects, collection access or local disposal practice may require more frequent removal and therefore govern before volume.

Define the incoming screenings before selecting the machine

• Identify every feeding screen and its opening, cleaning cycle, operating hours, normal and short-peak discharge, wash spray and discharge height.
• Measure wet mass, loose volume, free water and dry-solids content during representative dry-weather, wet-weather, production and cleaning periods.
• Describe rags, wipes, plastics, hair, fibres, food material, grease, stones, glass, metal and grit. Hard objects and long fibres affect torque, wear and blockage differently.
• Keep coarse, fine and industrial screenings separate where their handling or disposal duty differs. One average sample can hide the worst feed.
• Use records from the mechanical bar screen, fine screen or other selected screen rather than estimating washer capacity only from wastewater flow.

Choose the collection and feed arrangement

• State whether screenings fall directly, travel by conveyor, or move in a launder. Confirm the short-peak feed, free water and simultaneous discharge from multiple screens.
• Survey chute angle, drop height, clear opening, side walls, access and the points where wet rags or plastics can bridge. A washer cannot recover capacity lost in an undersized chute.
• For a launder, define transport-water flow, slope, gate sequence, overflow, drainage, flushing and the effect of all water on washer and plant hydraulics.
• Prevent a stopped washer from backing screenings into the screen, overflowing the channel or blocking the only treatment route. Provide a safe temporary collection plan.
• Coordinate discharge from rotary drum, step, screw and static wedge-wire screens on their measured reject condition.

Separate washing, dewatering and compaction requirements

• Washing aims to separate suitable attached organic material from retained debris. Dewatering removes free water. Compaction reduces volume. State which duties are required instead of using the terms interchangeably.
• Define acceptance by representative inlet and outlet samples, wet mass, dry-solids mass, dry-solids percentage, volume, drain quality and visible carryover.
• Do not apply a supplier's maximum reduction claim to unrelated screenings. Results depend on opening, rag and plastic content, grit, grease, wash intensity and discharge restriction.
• Confirm whether organics should return to the biological process and where. Washed solid screenings still need an approved off-site route and must not be returned to the wastewater inlet.
• Check that more aggressive washing will not shred plastics or inorganics into material that escapes with the drain.

Complete the wash-water and drain-return design

• State wash-water source, quality, pressure, normal and peak flow, daily volume, strainer, isolation, backflow protection and low-pressure response.
• Show each spray bar and nozzle, cleaning access and the supplier-approved method for removing blockage without exposing operators to moving equipment.
• Size drain screens, pipes and channels for free water, wash water and released organics without standing sewage, sedimentation or repeated blockage.
• Return liquid to a defined point that has hydraulic and organic-loading capacity. Avoid a hidden recycle around flow measurement or into equipment that cannot accept the short peak.
• Where service water is interrupted, define whether the washer stops, continues as a dewatering compactor or diverts screenings to safe storage.

Check screw, press tube, wear and overload protection

• Define screw diameter, shafted or shaftless arrangement, flight material, trough or pipe, screen section, press restriction and discharge elevation.
• Ask for allowable torque, motor rating, gearbox service factor, current or torque monitoring, reverse or clearing sequence and the safe response to repeated jams.
• Stones, glass, metal and grit can accelerate flight, liner and screen wear. Include replaceable wear parts and a practical inspection method.
• Confirm how the discharge restriction is adjusted and guarded. More restriction may improve dewatering but can increase torque, wear and blockage.
• Record baseline motor current, torque, cycle time, noise, vibration, screw clearance and discharge condition at acceptance for later comparison.

Compare screenings-handling arrangements

Integrate the discharge, bagging and collection bin

• State discharge height, press-tube length and direction, chute, bagging sleeve, bag sealer or continuous liner, bin dimensions and vehicle access.
• Check compacted bulk density and centre of gravity against the bin and floor rating. A small-looking pile can still create a heavy handling duty.
• Provide a full-bin switch where overflow can block the press, damage the screen train or expose operators. Define the stop sequence and alarm destination.
• Keep the discharge enclosed enough to control splash, flies and odour while allowing safe observation, cleaning and replacement of bags or liners.
• Agree the authorized disposal route and evidence required by the receiving facility before fixing the washing or dry-solids acceptance criterion.

Control odour, hygiene and the work area

• Minimize retained material and stagnant drains. Define washdown, floor falls, trapped drainage, cleaning frequency and covered collection.
• Where enclosure is required, coordinate it with extraction ventilation, access doors, negative pressure and the selected odour-treatment duty.
• Contain aerosols and splash, provide suitable lighting and establish site-specific hygiene, protective equipment and handwashing arrangements.
• Treat an enclosed washer, chute or bin as a potential hazardous maintenance area. Assess gas, isolation and confined-space risks for the actual installation.

Controls, interlocks and safe failure response

• Start downstream handling before the feeding screen or conveyor, then stop in the reverse sequence with enough run-on time to clear material.
• Interlock high torque, motor overload, low wash-water pressure, drain blockage, open guard, full bin and downstream conveyor fault with the correct upstream response.
• Use a maintained safe condition after power failure. Define automatic or manual restart, retained material, wash sequence and alarm acknowledgement.
• Specify local manual controls for commissioning and maintenance without defeating guards, emergency stops or the plant sequence.
• Coordinate the screen, washer, conveyor, wash water, drain alarms and bin through the MCC and control panel.

Provide safe access and maintainability

• Guard screws, shafts, press outlets, conveyors and pinch points. Provide lockable isolation for electrical, hydraulic, pneumatic, water and upstream feed energy.
• Show access to spray nozzles, drain screen, screw, press restriction, gearbox, seals and every wear part without reaching through a chute.
• Use platforms, handrails and lifting equipment rated for the heaviest removable part and a clear route to the service floor.
• Provide drain-down, flushing and containment before opening equipment. State how jammed screenings are removed without uncontrolled release.
• Include initial wear parts, special tools, lifting points and the supplier's inspection and replacement limits in the handover package.

Commissioning and acceptance checks

• Verify alignment, supports, chute and launder fall, drain, wash-water pressure, guards, access, bin position, instruments and interlocks before feeding screenings.
• Test clean-water sprays and drainage, then use representative screenings from each feeding screen at minimum, normal and short-peak conditions.
• Measure inlet wet mass and volume, inlet and outlet dry solids, outlet wet mass and volume, wash-water use, liquid return, throughput, torque and energy over agreed periods.
• Demonstrate transfer into the final bag or bin, full-bin response, restart after a jam or power interruption and operation with one upstream or downstream item unavailable.
• State sampling, laboratory, weighing and volume methods in advance. A dry-solids percentage alone does not prove throughput, washing, volume reduction or acceptable drain return.

Operating and maintenance requirements

• Each shift, check feed, wash pressure, drainage, discharge plug, bin level, odour, leaks, unusual current, torque, noise and vibration.
• At the planned interval, clean nozzles and drain screens and inspect flights, liner, perforations or wedge wire, press tube, seals, bearings and gearbox.
• Trend wet mass, dry-solids percentage, wash-water use, return flow, compactor current or torque, jams and bin collections against the screen and wastewater record.
• Do not repeatedly increase reverse cycles or press restriction until feed changes, hard objects, wear, drain blockage and discharge obstruction have been checked.

Information needed for a useful quotation

• Plant and screen type, openings, number of screens, operating hours, normal and short-peak feed, wet mass, loose volume, free water and dry-solids content.
• Representative description and samples of rags, wipes, plastics, fibres, grease, organics, stones, glass, metal and grit.
• Required washing, dewatering and compaction acceptance, allowed drain-return point, disposal route and receiving-facility conditions.
• Feed method, chute or launder survey, wash-water supply, drainage levels, discharge height, bag or bin, collection vehicle, odour enclosure and available footprint.
• Power, controls, interlocks, materials, access, lifting, installation, commissioning, training, documentation, spares and performance-test scope.

For a new inlet works, place the washer within the complete sewage-treatment process. For recurring jams, wet discharge or odour, use the upgrade and maintenance service to review the screen, feed, washer, drain, controls and collection route together.

Common screenings washer and compactor questions

Can we size the washer from wastewater flow?

No. Wastewater flow helps define the screen, but washer duty comes from measured screenings mass, volume, moisture, composition, discharge pattern and peak rate.

Does compaction alone wash the screenings?

Not necessarily. Compaction can remove free water and reduce volume. Organic washing needs a defined water and mixing sequence with measured inlet, outlet and return results.

Where should the drain return?

Return it to an agreed treatment point with enough hydraulic and organic capacity, without bypassing measurement or creating a repeated solids loop. The correct point is project-specific.

Will higher outlet dry solids always be better?

No. Higher press restriction can increase torque, wear, blockage and maintenance. Set the acceptance around disposal, handling and whole-life operation, then verify it on representative material.

Receive the measured mechanical-screen duty

Use the mechanical bar-screen screenings-volume example to define loose and compacted volume, short peak rate, free water, discharge height, drainage, bin capacity, interlocks and the authorized disposal route.

Receive the measured fine-screen duty

Use the fine-screen wash-water and screenings guide to define loose volume, wet mass, free water, short peak rate, chute or launder, drainage return, compaction, bin capacity, alarms and disposal.

Receive the measured rotary-drum reject duty

Use the rotary drum mass-balance and package guide to define retained dry solids, wet screenings mass, short peak rate, integrated or separate washing, chute or launder, drainage return, compaction, bin capacity and disposal.

Receive the measured step-screen duty

Use the step-screen solids and handling example to define dry solids, wet mass, loose volume, short peak discharge, fall-back prevention, drainage, washing, compaction, bin capacity and disposal.

Receive the measured screw-screen duty

Use the screw-screen mass-balance and package guide to define retained dry solids, wet mass, short peak discharge, integrated or separate washing, compaction, drainage return, bin capacity and disposal.

Receive static-screen solids on a measured basis

Use the static wedge-wire solids and water-balance example to define dry and wet mass, short peak discharge, free drainage, chute, bin, washing or compaction and the return-water route.