Mechanical equipment for water and wastewater plants

The screens, clarifiers, filters, vessels, mixers and sludge machines that make up a treatment plant: what each is, how it works, and how to choose.

How we supply mechanical equipment

We supply mechanical equipment as part of a plant, as a package for a plant you are building, or as replacements for an existing plant. Each item is selected from your flow, water analysis and duty, and supplied against your project specification, datasheet and approved make list. Where you have none, we propose suitable options in the quotation and agree the make with you before ordering. Pumps and blowers have their own pages: pumps and blowers and aeration.

Screening and grit removal

Manual bar screens: Fixed bars set in the channel, raked by hand. For small plants and as a bypass screen beside a mechanical one.
Mechanical bar screens: A rake or step mechanism clears the bars automatically on a timer or on level difference. Used where the flow or the screenings load is too high for manual raking.
Fine screens: rotary drum, band and static screens: Remove smaller solids and fibres with slotted or perforated screens. Protect pumps, membranes and downstream equipment. Common in industrial effluent, food and slaughterhouse plants.
Screenings handling: Screw conveyors and compactors reduce the volume and wetness of screenings before disposal.
Grit chambers and grit classifiers: Remove sand and heavy particles that wear pumps and fill tanks. Types include aerated grit chambers and vortex units, with a classifier to wash and dewater the grit.

Oil and grease removal

Oil skimmers: Belt, tube and rope skimmers lift floating oil from the surface of tanks.
Oil-water separators: Gravity separators, including plate or lamella types, for free oil from workshops, refineries and fuel areas. See DAF and oil-water separators.
Grease traps: Hold back fat, oil and grease from kitchens and food units before the biological stage.

Settling and clarification

Circular clarifiers: A rotating scraper or suction mechanism moves settled sludge to a central hopper. Centre-drive and peripheral-drive types are used, depending on the diameter.
Rectangular clarifiers: Chain-and-flight or travelling bridge scrapers on a rectangular tank. Suited to site layouts with limited width.
Lamella and tube settlers: Inclined plates or tubes add settling area in a small footprint, so a compact tank can clarify the same flow. Used in raw-water plants, ETPs and as upgrades to existing clarifiers.
Sludge scrapers and sludge withdrawal: Scraper arms, suction headers and sludge valves move and remove sludge at a controlled rate.

Flotation (DAF)

Dissolved air flotation: Air dissolved in water under pressure is released in the flotation tank as fine bubbles that lift oil, grease, fibres and flocculated solids to the surface, where a skimmer removes them.
Main parts: A saturation (pressure) vessel, air compressor, recycle pump, flotation tank, skimmer and float sludge hopper.
Where used: Oily and fatty food effluent, dairy, textile, pulp and paper, and slaughterhouse effluents, and for light algae-laden water.

Filtration units

Pressure sand filters: Remove suspended solids and turbidity. Pressure vessels filled with graded sand and gravel, backwashed on pressure drop or time.
Activated carbon filters: Remove organics, chlorine, colour and odour. Often follow the sand filter and protect RO membranes from chlorine.
Multigrade and dual-media filters: Layers of different media, such as anthracite over sand, hold solids deeper in the bed for longer runs between backwashes.
Iron removal filters: Remove iron and manganese from borewell water after oxidation.
Cartridge and bag filters: Safety filters ahead of RO and fine polishing.
Self-cleaning and disc filters: Automatic screen or disc filters for water with moderate solids, used on irrigation reuse and cooling tower side-streams.
Gravity filters: Open or concrete filters for larger flows, with controls and backwash.
Valves and controls: Manual or automatic valve sets, with timer or differential-pressure backwash.

Vessels, tanks and mixers

Pressure vessels: Mild steel, rubber-lined mild steel, stainless steel and FRP vessels for filters and other duties, designed to the pressure code that applies. See design standards.
Storage tanks: Tanks for treated water, process water and effluent in MS, FRP, HDPE or concrete.
Chemical storage tanks: HDPE, PP, FRP and rubber-lined MS tanks, chosen for the chemical, with bunds, level indicators and vents.
Agitators and mixers: Top-entry and side-entry agitators for chemical and neutralisation tanks, slow-speed submersible mixers for equalisation and anoxic tanks, and paddle mixers for flash mixing and flocculation.

Sludge handling

Thickeners: Gravity thickeners and drum thickeners raise the sludge solids before dewatering.
Filter presses: Plate and frame or recessed plate presses give a dry cake for hard-to-dewater sludge, in batch operation.
Belt presses: Continuous dewatering with polymer on moving belts. Common for biological sludge.
Screw presses and decanter centrifuges: Compact, enclosed continuous dewatering. Centrifuges give high throughput in a small footprint at higher power use.
Sludge drying beds: Low-cost drying for small plants and for faecal sludge where land is available. See FSTP.
Polymer preparation units: Automatic make-up and ageing of polymer for dewatering. See sludge dewatering.

Evaporation and drying (ZLD)

Multiple effect evaporators (MEE): Steam-heated stages reuse the vapour of one stage to heat the next, to concentrate reject water.
Mechanical vapour recompression (MVR): Compresses the vapour to reuse its heat, cutting steam use at the cost of electrical power.
Agitated thin film dryers (ATFD): Dry the concentrated reject to a solid.
Crystallisers: Recover salts from concentrated reject in a controlled way. See ZLD and ZLD operating cost.

Disinfection

Chlorination and hypochlorite dosing: Dosing systems for sodium hypochlorite or calcium hypochlorite, with contact tank sizing for the required contact time.
UV disinfection: UV lamps in a channel or closed reactor inactivate microorganisms without adding chemicals, provided the water is clear enough. Needs lamp replacement and sleeve cleaning.

Valves and piping

Valves: Gate, butterfly, ball, check and plug valves, with manual, electric or pneumatic actuation where needed, plus air release valves and flow control valves.
Piping: Mild steel, stainless steel, UPVC, CPVC, HDPE and FRP, selected to the piping material specification for the fluid, pressure and temperature.
Support and accessories: Pipe supports, expansion joints, strainers, flow meters and sampling points.

Packages and skids

Chemical dosing skids: Tank, pumps, mixer, level switch and piping on one frame, ready to connect. See dosing systems.
Polymer and lime preparation skids: Make-up and feed packages for polymer and lime slurry.
Containerised plants: Process and mechanical equipment assembled in a container. See containerised plants.

Which equipment for which duty

Duty	Usual equipment
Remove rags and solids at the inlet	Bar screen (manual or mechanical), fine screen for industrial effluent
Remove sand and grit	Grit chamber with classifier
Remove floating oil	Oil skimmer, oil-water separator or DAF
Settle solids after chemicals or biology	Clarifier, with lamella or tube settlers for a smaller footprint
Remove fine oil, fat and fibres	Dissolved air flotation
Polish for turbidity	Pressure sand or multigrade filter
Remove chlorine, organics, colour	Activated carbon filter
Dewater sludge	Belt press, filter press, screw press or decanter
Concentrate reject water	MEE, MVR or ATFD, crystalliser
Disinfect treated water	Hypochlorite dosing or UV

What to check when selecting equipment

Design basis: Flow range, water or effluent analysis, solids and oil content, and the treated quality needed.
Materials of construction: Select to the chemistry: mild steel with coating or lining, stainless steel for corrosive or hygienic duty, FRP or plastic for acid and salt.
Codes: Pressure vessels, piping, electrical and instrument items to the codes in your specification.
Operation and access: Space for maintenance, lifting points, safe access and manual bypasses.
Running cost: Power, chemicals and consumables over the life of the equipment, not only purchase price.
Spares and support: Availability of spares and local service, particularly for remote sites.

Common questions

Do you supply equipment without a full plant?

Yes. We supply individual items or packages for a plant you are building, or replacements for an existing plant.

Can I specify the make?

Yes. Send your approved make list. If you have none, we propose options and agree the make with you before ordering.

Do you also install and commission?

Yes, as supply with supervision or as a turnkey project. Tell us the scope you want.

What is the difference between a clarifier and a DAF?

A clarifier lets heavy solids settle to the bottom. A DAF floats light solids, oil and fat to the surface using fine air bubbles. The choice depends on the material you need to remove.