[Chinese Mainland] First revision after 24 years of implementation: The amendment to GB 18918—2002 adds 4 instantaneous values, and the limit for fecal coliforms in non-reuse scenarios is relaxed to 10,000 MPN/L.

Key Facts: The Ministry of Ecology and Environment and the State Administration for Market Regulation jointly issued an amendment sheet to the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002), marking the first substantive amendment since the standard was issued and implemented in 2002年. Four key changes: instantaneous values for 4 parameters—Chemical Oxygen Demand, ammonia nitrogen, Total Nitrogen, and Total Phosphorus—are newly added; pH, color, and fecal coliform count, 3 indicators, are adjusted from daily average values to instantaneous values; the Grade A limit for fecal coliform count in effluent for non-reuse destinations is adjusted to 10000 MPN/L, consistent with the Class III surface water quality limit; it is clarified that both instantaneous values and daily average values can serve as the basis for exceedance determination and enforcement, and exceeding either constitutes an exceedance.

I. Why the Amendment: Daily Average Values Cannot Support Instantaneous Exceedance Determination

For more than two decades since the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) was issued and implemented, it has played a fundamental role in controlling pollutant discharges from municipal wastewater treatment plants and in protecting and improving ecological and environmental quality. However, during long-term implementation, three misalignments between the standard's technical content and regulatory enforcement practice gradually emerged.

• Daily average values cannot support instantaneous determination—The current standard uses daily average values as the primary limit form. In regulation, it was found that daily average value provisions cannot scientifically support instantaneous exceedance determination: when an instantaneous high-concentration data point is produced, the enforcement side lacks a corresponding basis for determination.
• The Grade A fecal coliform limit is a "one-size-fits-all" approach—The fecal coliform count limit in the current Grade A standard is essentially set for reuse water requirements, and is too stringent for effluent discharged to environmental water bodies.
• Daily average values for three indicators cannot block shock loads—The 3 indicators of pH, color, and fecal coliform count are enforced using daily average values, which cannot effectively prevent instantaneous high values from impacting environmental water bodies. A plant can meet the standard on a full-day average basis while discharging strongly acidic or alkaline or high-color wastewater within a few minutes.

It is against this background that the Ministry of Ecology and Environment organized the drafting of the amendment sheet and jointly issued it with the State Administration for Market Regulation, with the goal of strengthening the precision and scientific rigor of the standard's technical content and improving the coordination and compatibility between the standard and the regulatory enforcement system.

II. Item-by-Item Breakdown of the Four Main Amendments

Amendment 1: Add Instantaneous Values for 4 Major Water Pollutants

Focusing on the prominent problems currently faced in the regulation and enforcement of municipal wastewater treatment plants, and based on scientific statistical analysis, the amendment sheet adds instantaneous value requirements for the 4 pollutants Chemical Oxygen Demand, ammonia nitrogen, Total Nitrogen, and Total Phosphorus that are slightly higher than the daily average values. Using "slightly higher" rather than directly applying the daily average values reflects recognition of the objective fluctuation patterns of wastewater treatment processes—biological systems inherently experience short-term fluctuations under hydraulic and water quality shocks, and setting instantaneous values too strictly would create a large number of "technical exceedances."

Amendment 2: pH, Color, and Fecal Coliform Count Changed from Daily Average Values to Instantaneous Values

Based on the analytical testing characteristics of these 3 indicators, combined with internationally accepted practices and China's regulatory reality, the amendment sheet adjusts their limit type from daily average values to instantaneous values. This change may appear to be merely a switch in limit type, but the actual enforcement effect differs greatly: instantaneous values mean that any single sampling exceedance constitutes an illegal fact, forcing operating units to shift their control focus from "full-day average" to "whole-process stability."

Amendment 3: Differentiate Discharge Destinations to Refine the Grade A Fecal Coliform Count Limit

This is the item with the most direct impact on operating costs in this amendment. The Grade A limit for fecal coliform count in the current standard is mainly set for reuse water, and the limit is too stringent for effluent discharged to environmental water bodies, which may also lead to excessive dosing of disinfectants, thereby harming the aquatic ecological environment. The amendment sheet adjusts the fecal coliform count limit for effluent for non-reuse destinations to 10000 MPN/L, the same as the Class III surface water quality limit. Three effects hold simultaneously:

• Ensuring Water Environment Quality — The limits remain consistent with Class III surface water standards, and environmental risks are controllable.
• Avoiding the Secondary Impacts of Over-Disinfection — Excessive disinfectant residuals are themselves harmful to the biological communities of receiving water bodies; relaxing the limits reduces this risk.
• Reducing Disinfection Costs at Wastewater Treatment Plants — Disinfectant dosing can be directly reduced, with substantial cost implications for different disinfection routes such as sodium hypochlorite, UV, and chlorine dioxide.

Amendment Four: Improving Implementation and Supervision Provisions

The amendment order clarifies that either instantaneous values or daily average values can serve as the basis for exceedance determination and enforcement supervision, and that exceeding any limit constitutes an exceedance; at the same time, in accordance with the provisions of the Technical Specifications for Wastewater Monitoring (HJ 91.1—2019), it clarifies the sampling and monitoring requirements for daily average values and instantaneous values; and it adjusts the applicable requirements for wastewater treatment plants in designated towns, making the requirements for smaller-scale designated town wastewater plants more realistic.

III. What It Means for Wastewater Treatment Plants

For operating entities, this amendment is not simply a "tightening" or "relaxation," but a reconstruction of compliance determination logic, requiring synchronized adjustments at three levels.

• Process Control Level — With instantaneous values incorporated into the enforcement basis, shock load resistance capacity shifts from a "bonus item" to a "mandatory requirement." The buffer capacity of biological tanks, the volume of emergency tanks, and the linkage between online influent warning and emergency chemical dosing all need to be re-evaluated. The response speed and dosing curves of carbon source dosing and phosphorus removal chemicals will become more important than the total daily average dosage.
• Monitoring and Data Level — The dual-track parallel of daily average values and instantaneous values means that data collection frequency, validity, and evidence preservation requirements are elevated. The calibration cycles, comparison frequencies, and fault response of online instruments (COD, ammonia nitrogen, Total Nitrogen, Total Phosphorus, pH) require traceable records; otherwise, a single instrument drift could be judged as an exceedance.
• Disinfection Unit Level — After the limit for non-reuse destinations is relaxed to 10000 MPN/L, plants whose effluent is not for reuse can recalculate disinfection dosages, resulting in direct cost savings; however, plants with reuse obligations must still comply with the original limits and need to implement quality-based and line-based management according to discharge destinations to avoid misapplication of the relaxed provisions.

IV. Industry Impact: From "Compliance" to "Precision Compliance"

Viewed against the broader policy background, the direction of this amendment order is very clear. 2026年, China's wastewater treatment industry simultaneously faces three major changes: the Ecological Environment Code has clarified that wastewater treatment fees should be used for facility construction, operation, and harmless sludge treatment and disposal; the Regulations on Urban Drainage and Wastewater Treatment (State Council Decree No. 843) requires that wastewater treatment fee standards should not be lower than normal operating costs; and this amendment order addresses the technical foundation of "what constitutes compliance and what is used to determine compliance."

The logic formed by these three together is: first make compliance determination accurate, then make cost coverage solid. Two long-standing distortions in the industry — one being the use of daily averages to "smooth over" instantaneous exceedances, and the other being the sacrifice of process redundancy to suppress costs — will both lose their institutional space. Conversely, this also means that operators with genuine stable operational capabilities will gain a fairer competitive environment: no longer needing to compete at the same price with low-quality operators who "make their data look good."

There is also an easily overlooked associated impact: the fecal coliform limit is directly linked to reuse destinations, which amounts to the first time at the national standard level that the hygienic requirements of the two pathways — "discharge" and "reuse" — are explicitly differentiated. This is favorable for the ongoing reclaimed water utilization allocation pilot program — the standard pathway for reuse water is clearer, the cost burden for non-reuse water is more reasonable, and neither end remains ambiguous.

V. TIANYI TECH's Perspective

TIANYI TECH believes that the most noteworthy aspect of this amendment order is not the rise or fall of any particular limit, but rather that "instantaneous values" have been formally established as an enforcement basis on par with daily average values. It compresses the management granularity of wastewater treatment plants from "one day" to "one sampling," imposing system-level requirements on process stability, online monitoring reliability, and emergency response mechanisms. For operators, the response is not to continue focusing on end-of-pipe chemical dosing, but to solidly execute three things: influent quality warning, process redundancy design, and full lifecycle management of key instruments. In the short term, this is a compliance cost; in the long term, it is another increase in industry concentration.

About TIANYI LIMITED

TIANYI TECH focuses on the fields of wastewater treatment, reclaimed water reuse, and water resource recycling, providing one-stop services from process consulting, solution design, equipment integration, and engineering implementation to smart operation and maintenance. The company is committed to promoting wastewater resource recovery through technological innovation, helping industrial enterprises and municipal clients achieve multiple goals including water conservation and carbon reduction, compliant discharge, and sustainable development.

Source: Q&A with relevant heads 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 on the Amendment Sheet to the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) (publicly reposted by local ecology and environment departments); Technical Specification for Wastewater Monitoring HJ 91.1—2019