An effluent treatment plant (ETP) treats industrial wastewater so it can be discharged to sewer or surface water, or reused. Unlike sewage, industrial effluent varies enormously between industries and even between shifts at the same factory, so no two ETPs are quite the same.
Good ETP procurement starts with understanding your effluent: how much of it there is, how strong it is, how much it varies, and what standard the treated water must meet.
Typical treatment stages and equipment
- Preliminary treatment
- Bar screens, fine screens, grit removal and oil and grease separation (oil skimmers, API or plate separators).
- Equalisation
- A mixed holding tank that evens out swings in flow, pH and strength before treatment. It protects every downstream step, especially biological treatment.
- Chemical treatment
- pH neutralisation, coagulation and flocculation, followed by separation in clarifiers, lamella or tube settlers, or dissolved air flotation (DAF).
- Biological treatment
- Activated sludge, sequencing batch reactors (SBR), moving bed biofilm reactors (MBBR) or membrane bioreactors (MBR) break down dissolved organic load.
- Tertiary treatment
- Sand and carbon filtration, ultrafiltration and disinfection where discharge limits are strict or water is reused.
- Sludge handling
- Thickeners and dewatering equipment such as filter presses, screw presses, belt presses or decanter centrifuges.
- Zero liquid discharge (ZLD)
- In some regions and industries, RO followed by evaporators and crystallisers so no liquid effluent leaves the site.
Specifications to compare before you request quotes
- Design flow and pollutant load
- Average and peak flow in m³/day, and load in kg COD, BOD and TSS per day. Biological systems are sized on load, so a plant quoted on flow alone may be undersized.
- Inlet design basis
- The pH, COD, BOD, TSS, TDS, oil and grease, temperature, colour and any specific pollutants (such as heavy metals or ammonia) that the supplier has assumed.
- Outlet guarantee
- Treated-water quality the supplier will guarantee, set against your discharge permit or reuse requirement.
- Sizing basis for each unit
- Retention times, tank volumes, surface loading rates and aeration capacity (kg O₂ per hour). These let you check that two designs are genuinely comparable.
- Sludge production and cake dryness
- Expected kg of dry solids per day and the percentage dry solids after dewatering. Sludge disposal is often a major running cost.
- Running costs
- Chemical consumption and power use per m³ treated, stated by the supplier rather than estimated by you.
- Materials and civil scope
- Concrete, coated mild steel or FRP tanks, and which civil works are included in the price.
Information to send suppliers with your enquiry
- Effluent test results from several days or batches, ideally composite samples rather than single grab samples.
- Your production schedule, including cleaning cycles and shutdowns that create peaks.
- The applicable discharge standard or permit, and where the treated water goes.
- Existing tanks or equipment you want to reuse.
- Whether you want civil works, operation and maintenance, and performance testing included.
Common sourcing mistakes
- Designing from one grab sample taken on a quiet day.
- Leaving out equalisation to save space, then suffering biological upsets.
- Mixing a small, difficult stream (for example high-TDS or toxic) into the main flow when it could be segregated and treated separately.
- Choosing on capital cost alone and ignoring power, chemicals and sludge disposal over the life of the plant.