COD Discharge Limit in Thailand: 2026 Compliance & Engineering Guide

Thailand COD Discharge Limits at a Glance: The 2026 Numbers

Thailand's general Chemical Oxygen Demand (COD) discharge limit is 120 mg/L under Notification of the Ministry of Science, Technology and Environment (MoSTE) No. 3 (B.E. 2539 / 1996), which remains the binding baseline in 2026. The same notification permits 10 specific heavy-industry categories — food furnishing, animal food, textile, tanning, pulp and paper, chemical, pharmaceutical, frozen food, starch, and animal finishing — to discharge up to 400 mg/L where receiving-water quality allows, while Total Kjeldahl Nitrogen (TKN) sits at 100 mg/L standard or 200 mg/L maximum (Industrial Effluent Standard, Thailand). Factories inside Industrial Estate Authority of Thailand (IEAT) estates that pipe to a central wastewater treatment plant (WWTP) face a separate instrument: Announcement No. 45/2541, which caps chemical oxygen demand at 750 mg/L and biochemical oxygen demand (BOD₅) at 500 mg/L at the estate boundary (IEAT Announcement No. 45/2541, Table annexed). Pinthong Industrial Estate operates under a tighter 500 mg/L ceiling. The umbrella enforcement law is the Enhancement and Conservation of National Environmental Quality Act B.E. 2560 (2017), which raised maximum fines and allows the Pollution Control Committee (PCC) to tighten the 120/400 mg/L values case-by-case when receiving-water sensitivity demands it.

Which Thai Authority Governs Your Discharge: PCD, IEAT, or BOI?

Three regulators can simultaneously touch a factory's discharge permit, and the right answer depends on where the pipe terminates, not where the factory sits. The PCD under the Ministry of Natural Resources and Environment (MoNRE) enforces MoSTE Notification No. 3 for any factory discharging directly to a public waterway. The IEAT governs the 65+ industrial estates that operate a central WWTP, applying Announcement No. 45/2541 at the estate boundary; the central plant is then engineered to bring the combined effluent to 120 mg/L before final release. Board of Investment (BOI)-promoted factories must hit the same technical limits but carry additional environmental reporting and audit obligations tied to their promotion certificate. Receiving-water classification matters more than factory size: surface-water standards in Thailand are tiered into Class 1 (drinking source, effectively no discharge), Class 2 (recreational/conservation), Class 3 (industrial supply), and Class 4 (irrigation), and the PCC tightens the COD cap as classification rises. Factories discharging to a municipal sewer — common in greater Bangkok — face Bangkok Metropolitan Administration (BMA) treatment-plant transfer-pricing rules on top of the national limits, and Industrial Estate Act transfer pricing applies inside estate zones.

Factory Categories That Trigger the 400 mg/L Cap

The 400 mg/L ceiling is a conditional cap, not a default right, and only 10 factory categories under MoSTE Notification No. 3 qualify: food furnishing (category 13(2)), animal food (category 15(1)), textile (category 22), tanning (category 29), pulp and paper (category 38), chemical (category 42), pharmaceutical (category 46), frozen food (category 92), starch (category 9(2)), and animal finishing (category 4(1)) (Industrial Effluent Standard, Thailand). The actual permitted value is set by the PCD case-by-case, weighing factory size, receiving-water classification, and the operator's documented pollution-control investment. The cap also does not exempt operators from parallel limits on BOD (≤60 mg/L where the cap applies), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), pH (5.5–9.0), and heavy metals — every parameter must be hit simultaneously, and one excursion on any one of them is a violation. The pulp and paper case illustrates why the headline number alone is misleading: typical influent COD runs 1,500–6,000 mg/L, so even at the 400 mg/L ceiling the biological stage must still deliver 75–93% removal, which is the same removal envelope demanded of a 120 mg/L site with a 1,000 mg/L influent.

How to Read the IEAT Announcement No. 45/2541

Announcement No. 45/2541 sets the maximum permissible values for factories discharging into an estate's central WWTP at BOD 500 / COD 750 / SS 200 / TDS 3,000 / TKN 100 mg/L (all in mg/L, pH 5.5–9.0), measured at the point of connection to the estate collection system (IEAT Announcement No. 45/2541, Article 2 and annex). The central plant is designed and permitted to polish the combined flow down to the 120 mg/L national standard before final release, so the estate figure is an inlet spec, not a discharge spec. Special cases apply: Bangchan, Padaeng, and Mabtapud industrial estates — which are permitted to release to public channels rather than only to a central WWTP — follow MoI Notification No. 2 (B.E. 2539) or MoSTE Notification No. 3 directly, capped at 400 mg/L depending on estate load and receiving water. Pinthong Industrial Estate is the only known estate with a tighter 500 mg/L COD limit at the estate boundary. IEAT's own laboratory conducts unannounced sampling, and non-compliance triggers discharge suspension under the estate operating contract — a commercial penalty that often bites faster than the PCD's regulatory fine.

Treatment Process Selection: What Equipment Actually Hits 120 mg/L or 400 mg/L

Selecting a treatment train starts with the actual influent COD, not the regulatory target, and the influent range dictates whether a single biological stage will do or whether a membrane bioreactor (MBR) is mandatory. The table below maps the four common influent bands in Thai industry to the trains that have proven they can hold the line at 120 or 400 mg/L.

The cost logic is straightforward: holding 120 mg/L from a 5,000 mg/L influent typically demands 40–60% more capital expenditure (CAPEX) than holding 400 mg/L, mostly because the MBR stage and tighter disinfection add membrane modules, blower capacity, and a larger footprint. That delta buys elimination of enforcement risk, eligibility for water-reuse certification, and headroom against any future PCC tightening — which, as the next section shows, is no longer hypothetical in 2026. For anaerobic sizing on the high-COD bands, the UASB reactor design for high-COD industrial wastewater is worth reviewing alongside the train selection.

Equipment That Helps Thai Factories Hit Their COD Target

Five equipment categories cover the majority of 2026 Thai bids. DAF pre-treatment for high-COD streams (ZSQ series, 4–300 m³/h) is the standard first step for fats, oils, and grease (FOG) and colloidal COD across food, textile, and pulp/paper lines, typically cutting influent loading 25–40% before the biological stage. MBR systems for sub-120 mg/L COD compliance using polyvinylidene fluoride (PVDF) flat-sheet or hollow-fiber modules (0.1 µm nominal pore size) deliver effluent consistently below 120 mg/L across a 10–2,000 m³/day capacity band, and are the single most common upgrade path for 400 mg/L factories facing tightening site rules. A high-rate lamella clarifier for space-constrained IEAT sites is the right pick where an existing estate footprint cannot accept a conventional clarifier. PLC-controlled chemical dosing skids stabilize coagulant, flocculant, and pH control, which is what keeps the biological stage from drifting under variable load. An RO polishing stage is optional but increasingly specified for factories in Class 2 receiving-water catchments or those pursuing water-reuse certification. The Bangkok industrial wastewater treatment cost models piece is the right reference for OPEX benchmarking against these line items.

Compliance Risk and 2026 Enforcement Trends in Thailand

Three enforcement trends in 2026 have shifted the cost-benefit math in favor of designing to 120 mg/L even when a factory is nominally allowed 400 mg/L. First, the PCD has expanded unannounced sampling and now mandates online effluent monitoring for factories discharging above 500 m³/day, with real-time data feeds to the regulator. Second, the B.E. 2560 (2017) amendment raised maximum fines and added criminal liability for repeat offenders, replacing what had been a routine administrative penalty. Third, IEAT renewal audits now score COD compliance as a primary criterion, and BOI-promoted factories face additional reputational risk because PCD publishes compliance records that flow into investor and customer ESG reviews. An MBR upgrade, in this environment, is best framed as compliance insurance with a water-reuse upside — not a discretionary capex. For a cross-jurisdictional view of the pH and COD interaction, the global industrial pH discharge limit comparison provides useful context.

Frequently Asked Questions

Does the 120 mg/L COD limit apply to my textile factory?
Not by default. Under MoSTE Notification No. 3 (B.E. 2539), textile factories (category 22) qualify for the 400 mg/L ceiling, but the Pollution Control Department sets the actual limit based on receiving-water classification, so a site discharging to a Class 2 stream will likely be required to hold 120 mg/L. Confirm with the PCD's regional office before sizing equipment.

What is the IEAT discharge limit at the estate boundary?
IEAT Announcement No. 45/2541 caps COD at 750 mg/L and BOD at 500 mg/L at the connection to the central WWTP. Pinthong Industrial Estate is tighter at 500 mg/L COD. The 120 mg/L national standard is the central plant's discharge spec, not the individual factory's inlet spec.

Can a factory upgrade from 400 mg/L to 120 mg/L capability without replacing the biological stage?
Usually no. Hitting 120 mg/L reliably from a 2,000–10,000 mg/L influent almost always requires adding an MBR stage (PVDF 0.1 µm) downstream of the existing UASB or activated-sludge basin, plus upgraded blowers and finer screening. Treat it as a new polishing train, not a control-loop tweak.

Which authority do I contact first to confirm my COD limit?
Start with the PCD regional office if you discharge to a public waterway, or the IEAT estate operator if you are inside one of the 65+ industrial estates. BOI-promoted factories should also notify the BOI office, because promotion certificate conditions can layer additional reporting on top of the PCD or IEAT limit.