Three types of monitoring indicators for wastewater discharged by packaging and printing plants: COD / ammonia nitrogen / total phosphorus—common reasons for failing environmental impact assessment in one go

A medium-sized food packaging printing plant in Wuxi had its environmental impact assessment rejected by the environmental protection bureau last year after expanding and constructing a new factory. The reason was that its wastewater testing showed a COD concentration of 580 mg/L, exceeding the 100 mg/L limit under the Class I standard of the Comprehensive Sewage Discharge Standard GB 8978-1996. The complication was that subsequent retesting also found ammonia nitrogen levels to exceed the limit (limit: 15 mg/L; measured: 22 mg/L). Exceeding the limits for both parameters resulted in the environmental impact assessment having to be redone. As the plant put it: “I thought treating COD would be enough. I didn’t know there were also limits for ammonia nitrogen and total phosphorus.” This plant is not an isolated case. Wastewater compliance for packaging and printing plants is governed not by a single parameter, but by combined limits for three types of indicators: chemical oxygen demand, ammonia nitrogen, and total phosphorus.

Where Does Wastewater from Packaging Printing Plants Come From? 3 Types of Sources

Many people assume that printing plants perform “dry operations” and generate no wastewater, but this is incorrect. Wastewater generated by packaging printing plants falls into 3 categories: ① plate-washing wastewater (wastewater containing developer generated from washing offset printing plates and CTP plates); ② waste ink (wastewater containing solvents/pigments generated from cleaning ink drums and ink rollers); and ③ domestic sewage (from canteens, restrooms, and washing facilities). The first two categories are industrial pollution sources and must be tested in accordance with industrial discharge standards; the third category may be discharged into the domestic sewage network.

The primary wastewater challenges at offset printing plants are developer solutions (containing hydroquinone and sodium sulfite) and ink cleaning solutions (containing solvents); at flexographic and gravure plants, the primary challenges are solvent residues and water-based ink wastewater; digital printing plants generate the smallest volume of wastewater, but wastewater from water-based ink must still be treated. The wastewater characteristics and treatment approaches vary by printing process.

Three Types of Monitoring Indicators—A Combination of Three Metrics Rather Than a Single Metric

The Grade I standard of the Integrated Wastewater Discharge Standard GB 8978-1996 (also the standard most commonly cited by packaging and printing plants) specifies 3 categories of core indicators:

Chemical Oxygen Demand (COD): Class I standard ≤ 100 mg/L, Class II standard ≤ 150 mg/L, and Class III standard ≤ 500 mg/L. COD is an aggregate indicator of oxidizable reducing substances (primarily organic matter) in water and reflects the degree of water pollution. In packaging printing plants, COD mainly originates from organic substances in inks and developer solutions. Exceeding the standard is commonly caused by inadequate pretreatment (failure to perform sedimentation or air flotation).

Ammonia nitrogen (NH3-N): Class I standard ≤ 15 mg/L; Class II standard ≤ 25 mg/L. Ammonia nitrogen is the total of ammonia and ammonium salts in water and reflects the risk of eutrophication. In packaging and printing plants, ammonia nitrogen mainly comes from developer solutions (containing sodium sulfite and ammonia water) and ink wastewater (some inks contain amine-based additives). Not every plant exceeds the standard, but once it does, the level is difficult to reduce in the short term. Ammonia nitrogen treatment requires nitrification/denitrification processes, and the equipment investment is twice that of COD treatment.

Total phosphorus (TP): Grade I standard ≤ 0.5 mg/L (in areas with stringent environmental requirements) or ≤ 1.0 mg/L (in general areas). Total phosphorus is the sum of all phosphates in the water and reflects the eutrophication of the water body. At packaging printing plants, total phosphorus mainly comes from surfactants (such as fountain solution and ink dispersants). Many printing plants are simply unaware that this is a regulated parameter—until their environmental impact assessment is rejected.

3 Common Reasons for Failing to Pass the Environmental Impact Assessment in One Go

Reason 1: Only COD is tested, while ammonia nitrogen and total phosphorus are not tested.Many printing plants believe that “meeting the COD standard is enough,” but the environmental impact assessment requires testing of 3 items, and failure to test even one item is deemed noncompliant. Last year, a printing plant in Zhejiang that produces color boxes conducted a self-test showing COD of 95 mg/L (compliant), but a spot check by the environmental protection bureau found ammonia nitrogen at 28 mg/L (87% above the limit). The plant was ultimately fined 80,000 yuan and ordered to suspend production for rectification.

Reason 2: Wastewater was tested, but the sampling method was incorrect.Wastewater from a printing plant is not discharged continuously but intermittently—the concentration is high during peak production and low during shutdowns. Sampling must be conducted during the peak discharge period (for example, 4-6 hours after startup), rather than collecting a low-concentration sample immediately after operations begin in the early morning; otherwise, the monitoring data will not be representative.

Reason three: Treatment facilities are not operating as designed.Many printing plants have spent money installing wastewater treatment equipment, but during actual operation, to save on chemical costs, they leave it off or run it only at half capacity—the dissolved air flotation unit is not started, the aeration tank is not aerated, and nutrients are not added to the biological treatment tank. This “pretend treatment” may meet COD standards in the short term, but will inevitably reveal problems with ammonia nitrogen/total phosphorus over the long term.

3 Types of Costs Associated with Printing Plant Wastewater Compliance

① Testing fees: A single COD test costs 200-300 yuan, ammonia nitrogen testing costs 200 yuan, and total phosphorus testing costs 200 yuan, making the total cost for all three tests approximately 600-700 yuan. The printing plant must conduct its own tests once a month and engage a third-party testing agency twice a year for comparative testing, in accordance with the requirements of the local Environmental Protection Bureau.

② Treatment Facility Investment: A small-scale treatment facility using air flotation and biological treatment (activated sludge process) requires an investment of RMB 300,000-800,000, with monthly operating costs (chemicals, electricity, and labor) of RMB 15,000-30,000. For a medium-sized printing plant (annual output value exceeding RMB 20 million), wastewater compliance costs represent approximately 1.5-2.5% of output value.

③ Costs of Noncompliance: Under Article 83 of the Water Pollution Prevention and Control Law, discharge exceeding the applicable standards is subject to a fine of 10-100 ten-thousand yuan; in serious cases, the facility may be ordered to suspend production for rectification or even shut down. Repeated violations or cases subject to public listing for supervision will be entered into the enterprise’s credit records, affecting subsequent bidding activities.

Differentiated Handling of Three Printing Processes

For offset printing plants, wastewater treatment focuses on developer solution (containing hydroquinone) and ink cleaning wastewater. The treatment approach is: separate collection and pretreatment of developer solution (chemical oxidation), followed by air flotation separation for ink wastewater and combined biological treatment. Flexographic and gravure plants (including those using solvent-based inks) produce wastewater characterized by a high organic solvent content, requiring air flotation or adsorption pretreatment before biological treatment. Digital printing plants generate relatively small wastewater volumes, with the primary concern being water-based ink wastewater containing pigments and surfactants, for which treatment is comparatively straightforward.

Regardless of the process, the core principle of wastewater treatment is “separate collection and treatment according to waste type”—collecting developer solution, waste ink, and domestic sewage through separate pipelines, pretreating them individually, and then combining them for entry into the integrated treatment facility. This is the foundation for ensuring that the printing plant’s environmental impact assessment can pass on the first attempt without being repeatedly returned for revision.

Further Reading

Three Key Performance Indicators for Packaging Printing VOC Management: Employee Health First, Then Environmental Compliance

Carbon Emission Accounting for Packaging Companies: 3 Methods — ISO 14064 / GHG Protocol / National Standard GB/T 51316

Five Years into the New Solid Waste Law, Packaging and Printing Plants Are Still Operating in the Wild: Three Types of Business Owners Most Likely to Step on the Fines Minefield

Three Major Categories of Cosmetics Packaging Regulations Take Effect: Cosmetics Supervision and Administration Regulations + Children's Cosmetics + Labeling Measures—The 4 Key Items Printers Should Focus On