Compliance Determination for Centralized Wastewater Treatment in Industrial Parks: Classification, Control Items and Responsibility Boundaries under HJ 945.4-2026

1. Before 1 September 2026: park plants had no standard of their own

The Technical Guideline for the Development of Water Pollutant Discharge Standards for Centralized Wastewater Treatment Facilities for Industrial Parks, HJ 945.4-2026, was approved by the Ministry of Ecology and Environment on 2026-04-07, issued on 2026-04-09, effective from 2026-09-01, and is a first release. The responsible official of the Department of Aquatic Ecological Environment stated the background plainly in a press interview: with industrial transformation and upgrading, more industrial enterprises are relocating into parks, yet centralized wastewater treatment facilities in industrial parks lacked a dedicated discharge standard and mainly applied the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002) by reference, resulting in incomplete control of characteristic pollutants, imprecise limit values and insufficient risk prevention and control.

The nature of this standard must be understood clearly: it does not itself set discharge limits. Its content summary states that it specifies the basic principles and technical route for developing such standards, the needs analysis and classification, determination of the main technical content, analysis of benefits and feasibility of implementation, and the required content of the standard text structure and the explanatory report. It applies to guiding and regulating the development and revision of park discharge standards by local authorities; the determination of discharge control requirements for a single industrial park's centralized wastewater treatment facility may also refer to it. In other words, to judge whether a park plant is compliant one must still look to the park discharge standard published by the province, autonomous region or municipality, or to the limits entered in the pollutant permit. HJ 945.4-2026 is a methodological document for judging how those limits should be set and whether they are reasonable.

2. Park classification: uniform standard or one-park-one-policy

The needs analysis and classification part of the standard requires the types of industrial parks in the jurisdiction to be sorted first, dividing them into single-industry and comprehensive categories, with comprehensive parks further split into three sub-types:

• Similar-industry type: all enterprises in the park belong to the same industry class in the National Economy Industry Classification, such as pharmaceuticals, but apply different discharge standards;
• Dominant-industry type: enterprises are not all in the same industry class, but those applying the same discharge standard account for a relatively high share - 70% or more - of the park's total wastewater discharge, such as chemical industry parks;
• Differentiated-industry type: enterprises from different industry classes with no single absolutely dominant sector, for example a park covering dyeing and printing, non-ferrous metals and chemicals at the same time.

The screening principle is that local authorities should select parks with large discharge volumes, many types of toxic and hazardous water pollutants, high risk to the aquatic ecological environment of the receiving water body, and existing discharge standards that do not fit, and among these differentiated-industry parks should give priority to formulating one-park-one-policy control requirements. The 70% threshold is the key quantitative test for deciding whether a comprehensive park can be managed under uniform limits based on its dominant industry.

3. Four principles and the bottom line of "no less strict than national standards"

The standard sets out four principles for developing park discharge standards:

1. Classified management: classify and control by park type, and after assessment decide whether to develop a uniform discharge standard or to set differentiated control requirements under a one-park-one-policy approach;
2. Comprehensive prevention and control: determine the controlled pollutant items by considering both the discharge standards applied by enterprises in the park and the characteristic pollutants actually detected in the effluent;
3. Scientific and feasible: determine limit values using the technical methods specified in the relevant current guidelines, balancing water quality improvement needs against technical and economic feasibility;
4. Lawful and compliant: the development must comply with national and local requirements for industrial park management and must hold the bottom line of being no less strict than national standards.

The fourth principle is a hard constraint, and it is the one that park operators most need to hold to when arguing for particular limit values: local park standards may be stricter than national standards but never more lenient.

4. Control items: basic items plus other items

The standard divides the pollutant control items of a park discharge standard into basic items and other items:

• Basic items: determined mainly from the discharge standards applied by the enterprises in the park;
• Other items: pollutants specified in environmental impact assessment approval documents and pollutant permits, pollutants with a significant impact on the receiving water body or causing exceedances, and - where the conditions specified in the standard apply - the three indicators of comprehensive toxicity, salinity and perfluorooctanoic acid (PFOA), all of which must be brought into the control scope. On that basis, local authorities may add further items such as priority-controlled new pollutants and typical PFOA substitutes.

Three practical implications follow. First, comprehensive toxicity appears as an indicator in a national-level standard document, providing a backstop where the list of characteristic pollutants cannot be exhaustive. Second, salinity is listed separately, which directly affects parks concentrating high-salinity wastewater. Third, PFOA and its substitutes are named explicitly, so parks involving fluorochemicals, electroplating or textiles should prepare in advance.

On limit determination, the standard sets out the basic method for single-industry parks and for similar-industry and dominant-industry comprehensive parks. For differentiated-industry comprehensive parks, it proposes giving priority to determining control requirements for individual parks where conditions permit, while also allowing uniform limits, and gives specific guidance for both cases. In addition, recognizing that industrial parks are major water users and dischargers and in order to encourage recycled water reuse, the standard sets out provisions on standards interface for scenarios where effluent is used for greening, urban miscellaneous use and other resource recovery purposes.

5. Allocation of responsibility: who is accountable for compliance

The Notice on Further Regulating the Environmental Management of Urban (Industrial Park) Wastewater Treatment, issued by the Ministry of Ecology and Environment on 2020-12-13, is the most direct document allocating responsibility between discharging enterprises and operators:

• Discharging enterprises must apply for a pollutant permit as required and discharge only in accordance with it. They must pre-treat industrial wastewater as required; category I pollutants and other toxic and hazardous pollutants specified in the applicable standards must be treated to compliance at the workshop or workshop treatment facility outlet; other pollutants may be discharged only after meeting the process requirements of the centralized facility. They must carry out self-monitoring according to the relevant technical specifications and proactively disclose pollutant discharge information, and those classified as key water environment dischargers must install and use automatic monitoring equipment and share data with the local ecological environment authority and the operator. Where an accident may cause discharged wastewater to endanger safe operation, they must immediately activate emergency measures such as accident storage tanks, notify the operator and report to the authorities.
• Operators are responsible for the effluent quality of the centralized facility and must not discharge non-compliant wastewater. Before taking on a project they must thoroughly investigate the sources, quality, quantity and discharge characteristics of wastewater in the service area, determine design water quality and treatment process appropriately, and state in the contract any types of industrial wastewater they cannot accept. Where industrial wastewater is found that the existing process cannot treat and that cannot be resolved with the source, they must request in writing that the local government take corresponding measures according to law. They must provide accident storage facilities and emergency measures matched to their risk-bearing capacity, and on detecting abnormal influent must immediately activate the emergency plan, trace the pollutants, retain water and sludge samples, preserve monitoring records and on-site video evidence, and report at the first opportunity.
• Negotiated influent concentrations: where responsibilities are clearly defined, operators and discharging enterprises may negotiate the influent concentration for industrial wastewater, report it to the ecological environment authority, and have it entered into the pollutant permit as a basis for supervision and management.

6. Determining responsibility when abnormal influent causes an exceedance

This is the set of provisions that park operators care about most and that is most often misread. The section on reasonable determination of responsibility for exceedances states:

• Where an operator has reported to the ecological environment authority and, for the purpose of process optimization or efficiency improvement, suspends part of the process units according to actual conditions while the effluent still meets standards, this is not deemed abnormal use of water pollution control facilities;
• Where a plant's effluent exceeds the limits, if the violation is minor and corrected promptly with no harmful consequences, an administrative penalty may be waived;
• Where the competent industry authority, the ecological environment authority, or both jointly determine that the exceedance was caused by influent beyond the design specification or actual treatment capacity, and the operator reported proactively and proactively eliminated or mitigated the harmful consequences, the penalty may be reduced or mitigated according to law.

All three share the same precondition: the incident was reported and evidence was preserved. The operator must activate the emergency plan immediately on detecting abnormal influent, trace the source, and retain water and sludge samples and monitoring records; otherwise the mitigation provisions cannot be invoked.

7. Park wastewater must be collected separately: the mandatory requirement in GB 55027

A 2025 reply by the Ministry of Ecology and Environment to a proposal from a national legislator sets out the collection and treatment principles for park wastewater: industrial agglomerations must provide matching centralized wastewater treatment facilities, install automatic monitoring equipment, connect it to the monitoring equipment of the ecological environment authority, and ensure the equipment operates properly; and the Project Code for Urban and Rural Drainage Engineering (GB 55027) explicitly requires industrial enterprises to concentrate in parks, that wastewater from industrial parks be collected and treated separately, and that its tailwater not be discharged into municipal sewage pipes or stormwater channels; tailwater from decentralized industrial wastewater treatment that meets environmental discharge standards must not be discharged into municipal sewage pipes either.

The reply also reaffirms source control requirements: newly built metallurgical, electroplating, non-ferrous metal, chemical, dyeing and printing, tanning and active pharmaceutical ingredient manufacturing enterprises should in principle be located in parks matching their industry positioning, with their wastewater treated centrally by the park treatment plant; and wastewater containing heavy metals or refractory organic compounds, and high-salinity wastewater from relevant newly built industrial enterprises must not be discharged into municipal wastewater collection and treatment facilities.

8. Operational checklist for compliance determination

1. Find the instrument carrying your applicable limit values first: a published provincial park discharge standard outranks the limits entered in the pollutant permit, which in turn outrank environmental impact assessment approval requirements. HJ 945.4-2026 itself sets no limits.
2. Confirm the park type: single-industry or comprehensive; for comprehensive parks determine whether it is dominant-industry type (whether the dominant industry's discharge share reaches 70% or more); differentiated-industry parks should pursue one-park-one-policy.
3. Check that the three categories of other items are covered: items specified in the environmental impact assessment approval and pollutant permit, items with significant impact on or causing exceedances in the receiving water, and comprehensive toxicity, salinity and PFOA where the specified conditions apply.
4. Hold the bottom line: no local park standard may be more lenient than the national standard.
5. Allocate responsibility for category I pollutants correctly: they must be treated to compliance at the workshop or workshop treatment facility outlet and cannot rely on dilution at the end of the centralized plant.
6. Have the negotiated influent concentration entered into the pollutant permit so that it serves as a basis for subsequent supervision.
7. Establish an evidence procedure for abnormal influent: emergency plan, source tracing, water and sludge samples, monitoring records, on-site video and immediate reporting. Missing any one element makes the mitigation provisions hard to invoke.
8. Check the interface requirements for reuse scenarios: where effluent is used for greening or urban miscellaneous purposes, the corresponding reclaimed water quality standard must also be met.

Note: HJ 945.4-2026 has been effective since 2026-09-01 and is a methodological document for standard development and revision; it does not set discharge limits directly. The responsibility provisions are taken from the notice issued by the Ministry of Ecology and Environment on 2020-12-13.