A public sewer is designed to receive used water. It is not permission to pour every industrial liquid into one underground pipe.
Factories can generate acids, alkalis, solvents, dyes, oils, heavy metals, high organic loads and other substances very different from ordinary domestic wastewater.
If unsuitable trade effluent enters the sewer, the damage can travel. Corrosive or dangerous substances can threaten workers and infrastructure. Toxic compounds can inhibit the microorganisms used at water reclamation plants. High solids or grease can disrupt conveyance. Contamination can interfere with NEWater production long after the discharge has left the factory gate.
Singapore therefore controls industrial wastewater at source.
Trade premises must obtain PUB’s Written Approval before discharging trade effluent into the public sewerage system, comply continuously with the Sewerage, Drainage and Coastal Protection Act and the Sewerage and Drainage (Trade Effluent) Regulations, operate suitable pre-treatment where required and test the parameters relevant to their processes.
The operating loop is: understand the industrial process → identify pollutants → separate incompatible waste streams → design pre-treatment → obtain Written Approval → sample representative effluent → verify compliance → discharge only within limits → monitor operations → correct deviations before they reach the public sewer.
Quick answer: what do the rules protect?
- Sewer conveyance: preventing blockage, corrosion, gas and other operational disruption.
- Workers: reducing exposure to toxic, flammable, reactive or otherwise hazardous discharges.
- Biological treatment: protecting the microorganisms that remove organic pollution at WRPs.
- NEWater production: preventing industrial contaminants from destabilising advanced water-recycling processes.
- Receiving waters: ensuring the WRP can produce compliant treated effluent before discharge.
- Fair cost allocation: requiring higher organic or solids loading to be pre-treated, separately managed or paid for through the approved fee route where applicable.
1. Trade effluent is used water produced by economic activity
Domestic used water has broadly predictable characteristics.
Industrial and commercial processes can produce wastewater whose composition varies with raw materials, production batches, cleaning cycles and accidental releases.
The regulation therefore follows the activity that created the water rather than assuming every drain from every premises carries the same pollution load.
2. Written Approval is the legal entry gate
PUB’s current trade-effluent guidance requires trade premises to obtain Written Approval, or WA, before discharging trade effluent into the public sewerage system.
The WA sets conditions for the discharge and creates an identifiable regulatory relationship between PUB and the premises.
The sewer connection may exist physically, but the industrial discharge is not lawful merely because a pipe can carry it away.
3. Approval does not replace continuous compliance
A WA is not a one-time certificate saying every future discharge is acceptable.
PUB states that trade effluent must comply with the applicable requirements and discharge limits at all times.
If the factory changes chemicals, production scale or cleaning methods, the wastewater can change even though the approval document remains the same. Operational control therefore has to continue after approval.
4. The Act and Regulations perform different jobs
PUB administers the Sewerage, Drainage and Coastal Protection Act, which provides the broader framework for Singapore’s public sewerage system.
The Sewerage and Drainage (Trade Effluent) Regulations set more specific controls on industrial wastewater, including prohibited substances and parameter limits.
The legal structure therefore combines system-level authority with detailed discharge conditions.
5. Pre-treatment keeps the factory’s special pollution problem at the factory
A public WRP is designed to treat the combined used-water stream within known operating limits.
Where a trade process produces wastewater outside those limits, the premises may need its own pre-treatment plant to neutralise, separate, precipitate, filter or otherwise remove the relevant pollutants before sewer discharge.
The principle is responsibility at source: the factory that creates the unusual contaminant should not export the full treatment burden invisibly to the public network.
6. Different industries need different treatment trains
Food manufacturing may produce high biodegradable organic loads and suspended solids.
Electroplating can produce metal-bearing wastewater. Chemical manufacturing can produce specific organic compounds. Workshops can generate oils and cleaning fluids.
There is therefore no single universal pre-treatment machine. The design has to follow the actual pollutant profile of the premises.
7. BOD measures biodegradable organic loading
Biochemical Oxygen Demand, or BOD, indicates how much oxygen microorganisms may consume while breaking down biodegradable organic matter.
Very high BOD can overload the biological treatment system and increase aeration demand.
BOD is therefore not simply a laboratory number. It estimates how much biological work the downstream WRP will be asked to perform.
8. COD provides a broader measure of oxidisable material
Chemical Oxygen Demand, or COD, measures a wider range of material that can be chemically oxidised.
Comparing COD and BOD can help a premises understand whether the wastewater contains material that is readily biodegradable or more resistant to biological treatment.
PUB identifies BOD, COD and Total Suspended Solids as general parameters trade premises should consider testing, alongside industry-specific pollutants.
9. Total Suspended Solids affect both pipes and plants
High TSS can settle in sewers, obstruct conveyance and increase the solids load entering treatment.
Source control can include settlement, filtration or process changes that keep solids out of the wastewater stream before it reaches the sewer.
The sewer is designed to move used water, not to serve as a hidden conveyor for unmanaged industrial sludge.
10. Industry-specific testing closes the blind spot
General parameters cannot reveal every hazardous contaminant.
PUB gives the example of an electroplating facility using copper processes: the premises should test for relevant heavy metals such as copper, not only BOD, COD and TSS.
The correct monitoring list therefore begins with the chemicals and raw materials actually used by the business.
11. Prohibited compounds are not converted into acceptable effluent by dilution
The Trade Effluent Regulations identify prohibited substances and impose limits for specified parameters.
A premises cannot treat dilution as disposal by mixing a concentrated waste stream with large amounts of clean water merely to lower the measured concentration.
Proper management removes or separately disposes of the pollutant rather than hiding it inside additional volume.
12. Representative sampling must occur after pre-treatment
PUB states that trade-effluent samples should be representative of the treatment quality produced by the pre-treatment plant.
Samples are taken from the designated sampling tank or sump downstream of pre-treatment under the applicable arrangement.
Sampling clean water from one convenient point while the actual industrial discharge bypasses it would not prove compliance. The sample has to represent what is truly entering the public sewer.
13. Batch processes require time-aware sampling
A factory’s wastewater can vary through the production cycle.
Cleaning at the end of a batch may create a different pollutant load from steady production. An equalisation tank can smooth some variation, but monitoring still has to capture the operating states most likely to determine compliance.
A single convenient sample during the cleanest hour cannot represent an entire unstable process reliably.
14. Accredited laboratories support credible evidence
PUB recommends that trade premises use third-party accredited laboratories when testing for relevant hazardous organic compounds and other parameters.
Accredited testing improves confidence in sampling methods, analytical procedures and result traceability.
The premises needs evidence strong enough to guide treatment decisions, not merely a number printed by an unknown method.
15. Heavy metals can disrupt the biological plant far downstream
PUB documents examples in which illegal discharges have affected WRP operations.
Certain heavy metals can inhibit biological treatment and interfere with the microorganisms needed to break down detergents and other pollutants, creating abnormal foaming and process disturbance.
The discharge may be invisible after entering the sewer. Its effect becomes visible later in the biology of the treatment tank.
16. Dyes and persistent chemicals can travel through more of the treatment chain
Some industrial compounds are not readily removed by ordinary biological treatment.
They can colour the incoming flow, pass partly through treatment or impose additional load on later membrane and water-reclamation processes.
Source substitution, stream separation and specialised pre-treatment can therefore be more effective than asking a general municipal plant to solve the problem after mixing has occurred.
17. Worker safety extends beyond what the final effluent looks like
Sewer workers may enter or work near enclosed infrastructure where toxic gases, flammable substances or corrosive liquids create serious hazards.
A discharge can therefore be dangerous even if the WRP might eventually remove part of it.
Trade-effluent rules protect the human beings maintaining the conveyance system before the water ever reaches treatment.
18. The Trade Effluent Fee scheme is a controlled exception for biodegradable load
PUB operates an opt-in Trade Effluent Fee, or TEF, scheme for qualifying businesses that cannot economically install their own treatment plant or engage licensed waste collectors to meet ordinary limits for specified biodegradable pollution.
Approved participants can discharge higher loadings of BOD and TSS and pay fees according to the applicable schedule.
The scheme recognises that a WRP can treat additional biodegradable load if the discharge is known, controlled and priced appropriately.
19. TEF is not a licence for toxic or prohibited discharges
The fee scheme is specific.
It does not convert prohibited substances, heavy metals, solvents or every excess parameter into lawful discharge simply because a business is willing to pay.
The public sewer can accept selected additional treatable load through the approved route; it does not become a market for unrestricted pollution.
20. On-site reuse can remove both water demand and effluent load
PUB encourages industries to treat and reuse suitable process water for purposes such as cooling, washing or other fit-for-purpose applications.
Each reused litre can reduce potable or NEWater demand and reduce the volume discharged to the public sewer.
Water efficiency therefore acts upstream of regulation: the cleanest discharge is sometimes the water the factory never needed to discharge.
21. Off-site licensed disposal is necessary for some concentrated wastes
Not every industrial residual belongs in a sewer, even after reasonable pre-treatment.
PUB advises businesses to consider separating hazardous or unsuitable waste streams for off-site disposal by licensed waste collectors.
The sewer is one waste-management route, not the universal destination for every liquid generated on industrial land.
22. Enforcement protects the shared network
Discharging without approval, exceeding regulated limits or releasing prohibited substances can lead to enforcement under the Act and Regulations.
PUB’s current guidance states that Written Approval may be revoked for specified non-compliance offences.
The enforcement power exists because one factory’s hidden discharge can impose treatment cost and risk on the entire public water-reclamation system.
23. A separate industrial tunnel at Tuas does not remove source control
DTSS Phase 2 will convey high-strength industrial used water separately to the future Tuas WRP.
This separation allows a treatment module designed for that stream. It does not mean factories may send any untreated chemical mixture into the tunnel.
Written Approval and discharge controls remain important because conveyance, worker safety and treatment biology still depend on knowing and limiting what enters the network.
24. A worked example: metal-finishing factory
Imagine a factory uses copper-bearing solutions.
The premises maps the process streams and keeps concentrated chemicals out of the sewer. Its pre-treatment plant adjusts and removes the relevant metal load. A representative sample is taken from the designated post-treatment point and tested for general parameters and copper. Only compliant effluent is discharged under the WA conditions. Concentrated residual sludge follows a licensed disposal route.
The treatment plant downstream receives ordinary controlled trade effluent rather than inheriting the factory’s raw chemical bath.
25. A worked example: food-manufacturing wastewater
Suppose a food factory produces high BOD and suspended solids from washing and product residue.
Screening and solids separation reduce the load. Process-water reuse lowers total discharge. The remaining effluent is tested. The business meets ordinary limits or enters the approved TEF route for eligible additional BOD and TSS loading.
The system distinguishes biodegradable pollution that the WRP can treat from hazardous pollution that must not be accepted merely for a fee.
26. Common misconceptions
Misconception: Anything liquid can go into the sewer.
No. trade premises need approval and effluent must meet statutory conditions and limits.
Misconception: The WRP can remove every industrial chemical.
No. toxic or persistent compounds can disrupt biological treatment, NEWater production and worker safety.
Misconception: A compliant sample proves the process is always compliant.
No. sampling must be representative and operational control must remain effective across production states.
Misconception: Paying TEF permits any excess pollutant.
No. the scheme applies to approved higher BOD and TSS loads and does not authorise prohibited or toxic substances.
Misconception: Dilution is equivalent to treatment.
No. proper pollution control removes, transforms, reuses or separately disposes of contaminants rather than concealing them in more water.
27. The deeper idea: a shared sewer requires private restraint
Every factory sees one pipe leaving its premises.
The city sees one shared biological and hydraulic system receiving thousands of those pipes.
Trade-effluent regulation connects the two views. Written Approval identifies the source. Limits define what the shared system can accept. Pre-treatment keeps special pollutants under the control of the premises that created them. Sampling returns evidence. Enforcement protects everybody downstream.
The public sewer works because no individual user is allowed to behave as though the pipe ends at the property boundary.