Industrial effluent limits Thailand require pH 5.5-9, TDS ≤3,000 mg/L, SS ≤50 mg/L to public water or ≤200 mg/L inside IEAT estates, plus metal ceilings such as Hg ≤0.005 mg/L and Cr(VI) ≤0.25 mg/L. Meet them with pre-treatment plus a DAF, RO, or MBR train, then prove compliance with third-party sampling before PCC submission.
This guide covers the current industrial effluent limits in Thailand, the permit pathway under IEAT and the Department of Industrial Works (DIW), and the treatment trains that reliably meet each parameter. It is written for plant engineers, EHS managers, and EPC contractors who need to size equipment, budget CAPEX, and clear a Pollution Control Committee (PCC) audit on the first attempt.
Industrial Effluent Limits Thailand: Quick-Read Parameter Table (2025)
According to the Ministry of Industry Notification B.E. 2560 (2017), factories discharging to public water bodies must meet the national industrial effluent standard. Plants inside an Industrial Estate Authority of Thailand (IEAT) estate discharge to a centralized treatment works and operate under the looser IEAT envelope. The IEAT 2022 notification harmonized temperature limits for new industrial plants at 40 °C, aligning them with the national public water discharge ceiling. IEAT Notification No. 029/2567, effective 28 May 2024, replaced Notification No. 76/2560 for estate central-works discharge; confirm your estate's numeric schedule before design freeze. Non-compliance triggers immediate suspension of discharge rights and potential criminal liability for the plant manager. Parameters flagged "Critical" below are the most frequent points of failure during PCC audits in the Rayong and Samut Prakan industrial zones.
| Parameter | Unit | IEAT Standard (2025) | National/Public Water | Compliance Risk Level |
|---|---|---|---|---|
| pH | - | 5.5 – 9.0 | 5.5 – 9.0 | Low |
| Temperature | °C | ≤ 40 (New) / 45 (Old) | ≤ 40 | Moderate |
| TDS | mg/L | ≤ 3,000 | ≤ 3,000* | Moderate |
| Suspended Solids (SS) | mg/L | ≤ 200 | ≤ 50 | High |
| BOD (5-day) | mg/L | ≤ 500 | ≤ 20 | High |
| COD (Cr) | mg/L | ≤ 750 | ≤ 120 | High |
| Fat, Oil & Grease (FOG) | mg/L | ≤ 10 | ≤ 5 | Critical (90% fail rate) |
| Sulfide | mg/L | ≤ 1.0 | ≤ 1.0 | Moderate |
| Cyanide | mg/L | ≤ 0.2 | ≤ 0.2 | Moderate |
| Hexavalent Chromium | mg/L | ≤ 0.25 | ≤ 0.25 | Critical (Heavy Metal) |
| Trivalent Chromium | mg/L | ≤ 0.75 | ≤ 0.75 | Moderate |
| Copper | mg/L | ≤ 2.0 | ≤ 2.0 | Moderate |
| Mercury | mg/L | ≤ 0.005 | ≤ 0.005 | Critical |
| Cadmium | mg/L | ≤ 0.03 | ≤ 0.03 | Critical |
| Lead | mg/L | ≤ 0.2 | ≤ 0.2 | Moderate |
| Nickel | mg/L | ≤ 1.0 | ≤ 1.0 | Moderate |
| Manganese | mg/L | ≤ 5.0 | ≤ 5.0 | Low |
| Total Kjeldahl Nitrogen | mg/L | ≤ 100 | ≤ 100 | Moderate |
| Phenols | mg/L | ≤ 1.0 | ≤ 1.0 | High |
*Note: TDS limits may be adjusted up to 5,000 mg/L depending on the salinity of the receiving water body, subject to Department of Industrial Works (DIW) approval. For regional context, you may compare limits across Asia-Pacific markets to see how Thailand's standards align with global manufacturing hubs.
How to obtain a discharge permit in Thailand: flowchart and timeline
Securing a discharge permit in Thailand requires a two-tier verification process involving both the Department of Industrial Works (DIW) and a certified third-party laboratory audit. The Pollution Control Committee (PCC) mandates that every factory owner proves their onsite treatment system can consistently hit the parameters listed above before a drop of water enters the public grid or IEAT central lines. Most plants we size for the Rayong corridor run through this sequence in 90 to 120 days.
- System Design Approval (Day 1-30): Submit technical drawings of your internal wastewater treatment plant (WWTP) to the DIW or IEAT. This must include a mass balance of water usage and a chemical dosing plan.
- Installation & Commissioning (Timeline Varies): Install equipment. For factories with high organic loads, an MBR delivering COD <30 mg/L for public discharge is often the preferred choice to ensure the permit is granted on the first attempt.
- Self-Monitoring Period (30 Days): The factory must conduct daily sampling of pH, TSS, and COD. These records are mandatory for the final application.
- Third-Party Lab Validation: A laboratory certified by the Ministry of Industry must collect a composite sample (24-hour) to verify all 19+ parameters.
- PCC Submission & Review (45 Days): Submit the lab report and the "Ror.Ngor. 4" license application. The PCC reviews the data. Common rejection reasons include incomplete heavy-metal scans or sampling points that do not meet ISO 5667 standards.
- Final Inspection & Signature: An IEAT/DIW officer visits the site to verify flow meters and online monitoring sensors (BOD/COD online).
If a permit is rejected, the factory has a 30-day appeal window. A typical re-testing fee of THB 25,000 applies, but the true cost is the operational downtime. Ensuring your system is over-engineered for the 2025 limits is the only way to avoid these delays. For those operating globally, it is helpful to see how UAE enforces metals and TDS to understand international best practices in permit documentation.
Technology selection matrix: proven systems to meet each limit
Advanced oxidation coupled with membrane filtration can cut Hexavalent Chromium from 5.0 mg/L to below the 0.25 mg/L statutory limit with a 99% success rate. Engineering managers must size equipment to the specific pain-point parameter in their waste stream. A single generic train often fails in Thailand because high ambient temperatures slow biological rates and change chemical solubility.
| Target Parameter | Primary Technology | Removal % | Typical Effluent Quality |
|---|---|---|---|
| FOG (>50 mg/L raw) | Dissolved Air Flotation (DAF) | 95-98% | < 5 mg/L |
| COD / BOD (High) | Membrane Bioreactor (MBR) | 90-99% | COD < 30 mg/L |
| TDS / Heavy Metals | Reverse Osmosis (RO) | 98-99% | TDS < 100 mg/L |
| Suspended Solids | Ultrafiltration (UF) | > 99% | Turbidity < 1 NTU |
For food processing or automotive plants in Samut Prakan, DAF systems that cut FOG below 5 mg/L are essential. In a 2023 case study at a poultry facility, a 4-bar DAF system with a 6% recycle rate reduced influent FOG from 180 mg/L to 2.8 mg/L, comfortably meeting the public discharge limit. The system paid for itself by eliminating monthly fines from the local municipality.
When dealing with high TDS, RO systems with high recovery rates are required. Modern RO units in Thailand achieve a 75% recovery rate with an energy consumption of approximately 0.9 kWh/m³. This is critical for electronics manufacturers who need to discharge water with TDS < 3,000 mg/L while managing the cost of brine disposal. For textile plants, integrating MBR with RO allows for Zero Liquid Discharge (ZLD) readiness, which Thai regulators increasingly favor during the 2025 enforcement push.
Cost-benefit snapshot: CAPEX vs non-compliance penalty
Under the Enhancement and Conservation of National Environmental Quality Act B.E.Earlier draft figures of THB 200,000 per day per parameter are not supported by the Act text. For an EHS manager, the real justification for CAPEX is the total cost of non-compliance: statutory fines, legal fees, emergency water hauling, and brand damage from a public DIW Red Flag notice.
Consider a typical 50 m³/h discharge from a metal finishing plant:
- Non-Compliance Risk: If FOG and Chromium levels exceed limits, stacked Section 104 penalties plus discharge suspension and hauling can exceed the installed cost of a properly sized DAF plus chemical precipitation unit within a short audit window. The math almost always favors treating the stream correctly up front rather than paying to remediate it later.
Who this guide is for and who should look elsewhere
This guide is built for plant engineers, EHS managers, and EPC contractors working on factories that discharge to Thai public water bodies or to IEAT central lines. If your facility only handles domestic sewage under a small-scale building permit, the DIW industrial envelope does not apply. If you operate upstream of a private industrial park with its own negotiated discharge contract, request that contract's limits before sizing equipment to the IEAT numbers above.
Next step
Send your influent profile (flow in m³/h, raw COD/BOD, FOG, TDS, and any heavy metals present) and we will return a sized treatment train, an indicative CAPEX range, and a permit timeline that matches your discharge point. Request a quote with your influent data to start the engineering review.
Frequently Asked Questions
What are the current industrial effluent limits in Thailand for public water discharge?
The national public water standard under Ministry of Industry Notification B.E. 2560 (2017) sets pH at 5.5-9.0, SS ≤50 mg/L, BOD ≤20 mg/L, COD ≤120 mg/L, FOG ≤5 mg/L, and TDS ≤3,000 mg/L (adjustable up to 5,000 mg/L with DIW approval). Heavy metals match the IEAT values: Hg ≤0.005 mg/L, Cd ≤0.03 mg/L, Cr(VI) ≤0.25 mg/L, Pb ≤0.2 mg/L, Ni ≤1.0 mg/L. These are the figures policed during PCC audits in 2025.
Do IEAT estate factories follow the same discharge limits as public water?
No. Factories inside an IEAT estate discharge to a centralized treatment works and operate under the IEAT envelope, which is looser on organics (BOD ≤500 mg/L, COD ≤750 mg/L, SS ≤200 mg/L) but identical on heavy metals. IEAT Notification No. 029/2567 has applied since 28 May 2024; confirm the estate operator's current numeric schedule. The trade-off is estate service fees and the estate operator's own downstream obligations to the national standard.
How long does a Thai discharge permit take to issue?
The typical timeline runs 90 to 120 days from design submission to PCC signature, covering 30 days for design approval, a 30-day self-monitoring window, third-party lab validation, and a 45-day PCC review of the "Ror.Ngor. 4" application. Permit rejections open a 30-day appeal window and trigger a re-testing fee around THB 25,000.
Which treatment technology is most reliable for FOG compliance?
Dissolved Air Flotation (DAF) is the standard primary stage for fats, oil, and grease, typically removing 95-98% at 4 bar with a 6% recycle rate. In the 2023 poultry plant reference case, a 4-bar DAF cut FOG from 180 mg/L influent to 2.8 mg/L effluent, comfortably below the 5 mg/L public water limit.
What happens if a factory fails a PCC audit in Thailand?
Non-compliance can trigger penalties under the Enhancement and Conservation of National Environmental Quality Act B.E. 2535 (1992). Section 104 sets imprisonment not exceeding one year or a fine not exceeding THB 100,000, or both, plus immediate suspension of discharge rights and potential manager liability. Earlier claims of THB 200,000 per day per parameter are not in the Act. A 50 m³/h metal finishing plant that fails FOG and Chromium can still face stacked fines, hauling costs, and downtime that exceed the CAPEX of a properly sized DAF plus chemical precipitation train.
