[Thailand] 2026 COD Discharge Limit Compliance Guide: A Dual-Track Regulatory Framework of Factory Classification + IEAT Estate Influent Standards

Overview

Thailand's industrial wastewater COD discharge limits follow a refined management system anchored on three dimensions — receiving water classification, factory category and the estate regime. The key compliance points for 2026 are: direct discharge into natural water bodies and discharge into municipal sewers are subject to different limits; only 10 specific factory types may apply the 400 mg/L COD cap (and even then on a case-by-case basis); and IEAT industrial estates operate a two-tier standard that is "lenient on influent, strict on effluent". Understanding this dual-track framework is the first step in equipment selection and compliance-driven engineering design.

Background: Where the Dual-Track System Comes From

Thailand's industrial wastewater regulation is composed of two parallel systems. The first is the factory system: under the 1992 Factory Act B.E. 2535 and Ministry of Industry notifications, factories discharging into municipal centralized treatment systems are subject to BOD≤20, COD≤120 and TSS≤50 mg/L (pH 5.5–9.0), while direct discharge into natural water bodies is subject to the stricter limits of BOD≤15 and COD≤100 mg/L, requiring tertiary treatment. The second is the estate system: under IEAT Announcement No. 45/2541, wastewater from factories within an estate must meet the "influent limits" — BOD 500 / COD 750 / SS 200 / TDS 3000 / TKN 100 mg/L (pH 5.5–9.0) — before entering the centralized wastewater treatment plant, which then treats the combined flow to the 120 mg/L national standard before discharge. In addition, factories in large cities such as Bangkok discharging into municipal sewers must also comply with Bangkok Metropolitan Administration (BMA) treatment plant connection and transfer pricing rules.

It is worth emphasizing that influent limits are "interface specifications" rather than "discharge standards": the estate's centralized plant is responsible for treating the combined influent to the 120 mg/L compliant discharge, and factories only need to meet the interface influent requirements. However, estates such as Bangchan, Padaeng and Mabtapud that allow direct discharge into public water bodies are directly subject to Ministry of Industry Notification No. 2 (B.E. 2539) or the Ministry of Environment Notification No. 3 (MoSTE Notification No. 3), with a COD cap of 400 mg/L depending on estate load and the receiving water body; the Pinthong estate is the only known estate that enforces a stricter 500 mg/L COD limit at the estate boundary.

Core: The 400 mg/L Cap Is Not a Default Entitlement

The most commonly misread element of Thailand's discharge standards is the 400 mg/L COD cap. It is a conditional cap rather than a default entitlement: it applies only to 10 factory types — food processing (Type 13(2)), animal feed (Type 15(1)), textiles (Type 22), tanning (Type 29), pulp and paper (Type 38), chemicals (Type 42), pharmaceuticals (Type 46), frozen food (Type 92), starch (Type 9(2)) and animal slaughtering (Type 4(1)). The actual allowable value is determined by the Pollution Control Department (PCD) on a case-by-case basis, taking into account factory scale, the category of the receiving water body and the pollution treatment facilities already installed. Moreover, this cap does not exempt compliance with other parameters: while the 400 mg/L cap applies, BOD must still be ≤60 mg/L, and TSS, TDS, pH (5.5–9.0) and heavy metal indicators must simultaneously comply — exceeding any single parameter constitutes a violation.

Taking pulp and papermaking as an example, typical influent COD is 1500–6000 mg/L; even with the 400 mg/L cap, the biological treatment stage must still achieve a removal rate of 75%–93%, almost the same as the removal required to bring a 1000 mg/L influent down to the 120 mg/L standard. A "relaxed cap" does not mean "simplified treatment", and compliance cost and process difficulty have not materially declined.

Estate-side enforcement is equally strict: the IEAT's own laboratory conducts unannounced sampling, and violations trigger suspension of discharge rights under the estate operating contract — a commercial penalty that is often faster and heavier than PCD's administrative fines. Factories within estates must therefore not only meet influent interface requirements but also possess end-to-end traceable monitoring and reporting capabilities.

Significance: What It Means for Us

For TIANYI TECH, Thailand's dual COD standards are both a technical threshold and a differentiation opportunity. First, selection logic: for factories within estates, pretreatment (air flotation, coagulation and sedimentation, oil separation) plus biological treatment must be designed to the influent limits; for direct-discharge factories, advanced treatment (MBR or ozone/activated carbon) must be configured to target the stricter 100 mg/L limit. Our complete capabilities in MBR, reverse osmosis and advanced treatment cover both tiers. Second, service value: Thailand's PCD accepts imported equipment but requires English manuals, ISO 9001, factory acceptance test (FAT) certificates and performance guarantees — complete document compliance delivery is precisely the key for Chinese equipment to enter, and forms our service barrier relative to small local manufacturers. Third, cost leverage: BOI Category 3.2 environmental machinery enjoys an 8-year corporate income tax exemption, and projects within the EEC can additionally reduce effective CAPEX by 30–60%; equipment solutions should therefore be incorporated into the customer's investment calculations at the design stage.

Industry Perspective: Our Assessment

Thailand's discharge standards (BOD≤20 mg/L) are significantly stricter than Indonesia's (BOD≤50 mg/L), yet slightly more lenient than Singapore's NEWater system, placing them in the upper-middle tier of ASEAN. Their "factory classification + dual estate tiers" design provides a referable regulatory template for many Southeast Asian countries. As Thailand's Eastern Economic Corridor (EEC) upgrades estate wastewater standards and ASEAN overall discharge regulation tightens, enterprises with membrane-based advanced treatment and water reuse capabilities will continue to benefit from the regional wave of water quality upgrades. For us, mastering Thailand's standards system and building an engineering methodology for compliance design is the key step in elevating the Southeast Asian market from "order-based business" to "standards influence".