[Mainland China] Amendment to Discharge Standards for Urban Sewage Treatment Plants Takes Effect, Instantaneous Limits Added for 4 Parameters Including COD

Amendment to the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) was jointly issued by the Ministry of Ecology and Environment together with the State Administration for Market Regulation, and has been officially implemented since 2026年3月1日. The amendment introduces instantaneous values for 4 major water pollutants, namely Chemical Oxygen Demand, ammonia nitrogen, Total Nitrogen, and Total Phosphorus; adjusts pH, color, and fecal coliform count — 3 indicators — from daily average values to instantaneous values; and revises the Grade A fecal coliform limit for effluent not intended for reuse to 10000 MPN/L. The Ministry of Ecology and Environment has made it clear that after the amendment takes effect, municipal wastewater treatment plants do not need to change their treatment processes and will not face increased economic pressure.

I. Why the Change: Daily Average Values "Cannot Control" Instantaneous Shocks

Municipal wastewater treatment plants are both important pollution control facilities and key dischargers of water pollutants. Since the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) was issued and implemented, it has played an important role in controlling pollutant discharges from municipal wastewater treatment plants and in protecting and improving ecological and environmental quality. However, during long-term implementation, some technical provisions of the standard have gradually revealed problems of mismatching with the realities of supervision.

In response to questions from journalists, officials from the Department of Water Ecology and Environment of the Ministry of Ecology and Environment and the Department of Urban Construction of the Ministry of Housing and Urban-Rural Development pointed out that this is mainly reflected in three aspects:

• Daily average value provisions cannot scientifically support the determination of instantaneous value exceedances — on-site enforcement often faces the result of a single sampling, lacking corresponding limit basis, leading to the awkward situation where "the measured value is clearly high, yet it is difficult to determine an exceedance."
• The fecal coliform limit in the Grade A standard is not precise enough for non-reuse water — this limit was mainly set for reuse water requirements and is clearly too strict for effluent discharged to environmental water bodies.
• The 3 indicators of pH, color, and fecal coliform count adopt daily average values and cannot effectively prevent instantaneous shocks — the impact of instantaneous high values on environmental water bodies cannot be constrained, creating a regulatory blind spot.

In order to further strengthen the precision and scientific rigor of the standard's technical content and enhance the coordination and compatibility between the standard and the regulatory enforcement system, the Ministry of Ecology and Environment organized the drafting of the amendment and jointly issued it with the State Administration for Market Regulation.

II. Four Major Amendments: From "Average Value Control" to "Precise Control"

1. Adding Instantaneous Values for 4 Major Water Pollutants

Focusing on solving the prominent problems currently faced in the supervision and enforcement of municipal wastewater treatment plants, the amendment, based on scientific statistical analysis, adds instantaneous value requirements for Chemical Oxygen Demand, ammonia nitrogen, Total Nitrogen, and Total Phosphorus — 4 pollutants — that are slightly higher than the daily average values, making them more realistic.

Taking the Grade A standard as an example, the daily average value for Chemical Oxygen Demand is 50 mg/L, and the instantaneous value added by the amendment is 75 mg/L. This setting both leaves reasonable room for operational fluctuations and provides a clear yardstick for enforcement determination.

2. Adjusting pH, Color, and Fecal Coliform Count from Daily Average Values to Instantaneous Values

Enforcement based on daily average values for these three indicators cannot effectively prevent the impact of instantaneous high values on environmental water bodies. Based on the analytical testing characteristics of the 3 indicators, combined with international common practices and China's regulatory realities, the amendment adjusts their limit type from daily average values to instantaneous values.

3. Refining the Grade A Fecal Coliform Limit by Distinguishing Effluent Discharge Destinations

The Grade A limit for fecal coliform count in the current standard was mainly set for reuse water requirements. For effluent discharged to environmental water bodies, this limit is too strict and may also lead to excessive dosing of disinfectants, which in turn harms the aquatic ecological environment.

The amendment adjusts the fecal coliform limit for effluent not intended for reuse to 10000 MPN/L, the same as the limit for Class III surface water quality. This adjustment not only safeguards water environmental quality but also avoids secondary impacts on the aquatic ecological environment caused by excessive disinfection, while also reducing the disinfection costs of wastewater treatment plants.

4. Improving Implementation and Supervision Provisions

• Clearer determination rules — it is clarified that either instantaneous values or daily average values can serve as the basis for exceedance determination and enforcement supervision, and exceeding either limit constitutes an exceedance.
• Basis for sampling and monitoring — in accordance with the Technical Specifications for Wastewater Monitoring (HJ 91.1—2019), the sampling and monitoring requirements for daily average values and instantaneous values are clarified.
• More realistic for designated towns — the applicable requirements for wastewater treatment plants in designated towns are adjusted, making the requirements for smaller-scale designated town wastewater treatment plants more realistic.

III. What It Means for the Industry: No Process Changes, No Added Burden, but More Refined Management

For wastewater treatment operating entities, the most concerning question is "will there be another upgrade and retrofit requirement." The official response is clear: after the implementation of the amendment, urban wastewater treatment plants do not need to change their treatment processes and will not face increased economic pressure.

However, from the perspective of operation and management, the signal conveyed by the amendment is not reassuring. The inclusion of instantaneous values in the regulation means that any single sampling exceedance may be directly judged as non-compliant, and operational fluctuations that were previously "smoothed out" by daily averages will no longer be tolerated. This imposes new requirements on wastewater plants in three aspects:

• Process operation stability — Impacts from influent water quality and quantity, fluctuations in the aeration system, and lag in the chemical dosing system will all be directly reflected in instantaneous values, requiring more refined process control and more reliable redundancy design.
• Online monitoring and data quality — Enforcement based on instantaneous values relies heavily on the authenticity and representativeness of automatic monitoring data. The standardization of sampling points, frequency, and instrument calibration will directly affect compliance determination.
• Precise dosing in the disinfection stage — After the limit for fecal coliforms in non-reuse effluent is relaxed to 10000 MPN/L, wastewater plants can optimize disinfectant dosage while ensuring compliance, balancing cost and ecological risk, which imposes new technical requirements for precise dosing control.

IV. Industry Observation: Standard Refinement Is the Common Direction of the Entire Industry

It is worth noting that this amendment is not an isolated single adjustment. In recent years, the standard system in the wastewater treatment field has been accelerating toward refined management featuring "classification, zoning, and destination-based control": at the watershed level, the Water Pollutant Discharge Standard for the Chishui River Basin (GB 47945—2026) was issued on 2026年6月11日 and came into effect on 2026年9月1日; at the local level, multiple provinces have successively introduced local discharge standards stricter than national standards; at the accounting level, Jiangsu and other regions have drafted for public comment the group standard Greenhouse Gases — Quantification Methods and Requirements for Corporate Carbon Footprint — Wastewater Treatment Plants, establishing for the first time a carbon accounting methodology covering the entire process of "sewer network — wastewater treatment plant — sludge treatment and disposal."

At the same time, the Regulations on Urban Drainage and Wastewater Treatment were revised in accordance with the Decision of the State Council on Amending and Repealing Certain Administrative Regulations under 2026年8月8日, explicitly encouraging at the administrative regulation level the promotion of advanced and applicable technologies, processes, equipment, and materials, and facilitating the reuse of reclaimed water and the resource utilization of sludge and rainwater.

For the wastewater treatment and reclaimed water reuse industry, the coordinated efforts of standards and regulations are pushing the industry's competitive focus from "can it meet standards" to "can it meet standards stably, with low carbon emissions, and at low cost." Whether it is process optimization, intelligent dosing, online monitoring, or reclaimed water and resource utilization, all will gain broader application space in this refined transformation.

TIANYI TECH (TIANYI LIMITED) has long been deeply engaged in the fields of wastewater treatment and reclaimed water reuse, committed to providing full-chain solutions from process design, equipment manufacturing, engineering construction to intelligent operation management for municipal wastewater plants, industrial parks, and various water-using entities. Centering on core scenarios such as upgrade and retrofit, energy saving and carbon reduction, reclaimed water reuse, and resource utilization, the company continues to provide customers with stable compliance and cost-effective system services, helping the industry achieve high-quality development in the era of standard refinement.

Source: Compiled from public information from the Ministry of Ecology and Environment and the State Administration for Market Regulation, answers by relevant officials of the Department of Water Ecology and Environment of the Ministry of Ecology and Environment and the Department of Urban Construction of the Ministry of Housing and Urban-Rural Development to reporters' questions, and publicly released content on the Chinese government website and the official website of the Ministry of Ecology and Environment.