Water Treatment for Packaging Printing Plants: 3 Key Indicators - COD, Ammonia Nitrogen, and Chromaticity, The Real Story of Environmental Assessment, Acceptance, and Discharge Permits

Wuxi Lexiang has been incurring an annual operating cost of 180,000-250,000 CNY for water treatment equipment since its environmental assessment approval in 2018 (electricity + chemicals + labor + testing). Many printing factory owners believe that water treatment simply involves installing a device + connecting a pipe to the sewage network, but starting from 2024, the Ministry of Ecology and Environment's supervision of the packaging and printing industry's emissions has been upgraded to four stages: "installation, transportation, monitoring, and reporting". Below are the real accounts of three types of hard indicators.

Why Printing Factories Cannot Avoid Water Treatment

The wastewater from packaging and printing factories mainly comes from three processes: pre-press plate making (developer, fixer rinse water), printing workshop (cleaning water for rubber blankets, ink roller cleaning water), and post-press varnishing (UV varnishing equipment rinse water). The main pollution indicators in the wastewater are five items: COD (Chemical Oxygen Demand), ammonia nitrogen, color, pH, and suspended solids. However, the three hard indicators that printing factory owners are most likely to stumble over are COD, ammonia nitrogen, and color.

Real Data: In 2025, the Wuxi Municipal Bureau of Ecology and Environment inspected 67 packaging and printing factories, and 35 of them (52%) were penalized for exceeding COD limits, 12 for exceeding ammonia nitrogen limits, and 8 for exceeding color limits. The penalty amounts ranged from 50,000 to 500,000 CNY, with the most serious case being shut down for rectification due to consecutive years of exceeding limits.

First Hard Indicator: COD (Chemical Oxygen Demand) – The Most Common Pitfall for Printing Factories

COD is a core indicator of water treatment, measured in mg/L. The emission standards for the packaging and printing industry (GB 4281-84 revised version + local emission standards) set different limits for COD depending on the region and the receiving water body:

- Indirect discharge (connected to municipal sewage network): COD ≤ 500 mg/L (most regions), strict regions like Shanghai and Beijing ≤ 300 mg/L.
- Direct discharge (into rivers, lakes): COD ≤ 100 mg/L (surface water class III), COD ≤ 60 mg/L (surface water class II).

The three most common pitfalls for printing factories are:

1. Mixing ink wastewater with domestic sewage – Many small printing workshops discharge cleaning wastewater directly into domestic sewage pipes, which violates Article 39 of the Water Pollution Prevention and Control Law and can result in a fine of 100,000-500,000 CNY.
2. Insufficient treatment capacity of water treatment equipment – The peak COD concentration (e.g., COD of UV varnishing equipment rinse water can reach 8,000-15,000 mg/L) far exceeds the equipment's processing capacity, leading to COD exceeding the discharge standard. The solution is to collect wastewater in a regulating tank first, homogenize it, and then enter the treatment equipment.
3. Collapse of the biochemical treatment section – The activated sludge in the aerobic tank is poisoned (benzene compounds in ink, acrylates in UV varnish are toxic to microorganisms), causing the COD removal rate to plummet from 90% to 30%. Printing factories should control the influent water quality to avoid highly toxic wastewater directly entering the biochemical section.

Real Crash Case: In June 2024, a cooperative printing factory of ours experienced poisoning of the aerobic tank activated sludge, causing the effluent COD to soar from 280 mg/L to 1,200 mg/L. The local ecological environment bureau's online monitoring system issued an alarm, resulting in a fine of 180,000 CNY + 30 days of production suspension for rectification. The rectification cost (replacing sludge + commissioning) was another 120,000 CNY.

Second Hard Indicator: Ammonia Nitrogen – Most Likely to Exceed Limits Due to Seasonal Changes

Ammonia nitrogen refers to ammonia (NH3-N) and ammonium salts (NH4+-N) in water, measured in mg/L. The emission standards for the packaging and printing industry set the following limits for ammonia nitrogen:

- Indirect discharge: Ammonia nitrogen ≤ 45 mg/L (most regions), strict regions ≤ 30 mg/L.
- Direct discharge: Ammonia nitrogen ≤ 15 mg/L (surface water class III), ammonia nitrogen ≤ 10 mg/L (surface water class II).

The three real sources of ammonia nitrogen in printing factories are:

1. Developer – Traditional phenidone-hydroquinone developer contains amine compounds, with the waste developer having an ammonia nitrogen concentration as high as 200-500 mg/L.
2. UV varnish dilution wastewater – Some UV varnishes contain amine photoinitiators.
3. Domestic sewage – The ammonia nitrogen concentration of septic tank effluent is 30-80 mg/L. If the domestic sewage of a printing factory is mixed with production wastewater for discharge, it will significantly increase the total ammonia nitrogen concentration.

Seasonal exceeding of limits is the most insidious pitfall for ammonia nitrogen: In winter, the low water temperature reduces the efficiency of biochemical treatment by 30-50%, causing the ammonia nitrogen removal rate to drop from 95% to 60-70%, making it easy to exceed limits in winter months from December to February. The solution is to increase sludge concentration and aeration volume in winter.

Third Hard Indicator: Color – The Fastest Upgraded Regulatory Item

Color refers to the depth of the water sample's color, measured in dilution multiples (e.g., 50 times, 100 times). The emission standards for the packaging and printing industry set the following limits for color:

- Indirect discharge: Color ≤ 64 times (most regions).
- Direct discharge: Color ≤ 40 times (surface water class III).

The three real reasons for color exceeding limits in printing factories are:

1. Mixed colored ink wastewater – The wastewater from special color inks (such as brand color customized Pantone 1655) has an extremely high color value, and a single treatment device (coagulation sedimentation + biochemical) cannot remove water-soluble dyes.
2. UV varnish containing dyes – Colored UV varnishes require separate pre-treatment after dilution due to their high color value.
3. Equipment aging – After the activated carbon adsorption reaches saturation, the color removal efficiency drops sharply, requiring regular replacement of activated carbon (every 3-6 months).

2024 Regulatory Upgrade: Provinces like Jiangsu, Zhejiang, and Guangdong have tightened the color emission limits for printing factories from 64 times to 40 times. The water that was originally qualified for printing factories is now unqualified, requiring the upgrading of treatment processes (such as adding ozone oxidation, UV advanced oxidation stages), with an upgrade cost of 300,000-800,000 CNY.

The Four Stages of Water Treatment in Printing Factories: "Installation, Transportation, Monitoring, and Reporting"

1. Installation (equipment installation) – According to the process selection approved in the environmental assessment, do not install equipment with insufficient processing capacity just to save money. The COD processing capacity should be ≥ 1.5 times the actual peak concentration.
2. Transportation (daily operation) – Establish an operation log to record daily water intake, chemical dosage, effluent COD, and sludge concentration. Data should be retained for ≥ 5 years for inspection.
3. Monitoring (online monitoring + third-party monitoring) – According to Article 21 of the "Pollutant Discharge Permit Management Regulations", COD, ammonia nitrogen, flow, and pH must be equipped with online monitoring equipment and connected to the network. Color, total nitrogen, total phosphorus, etc., should be monitored by third parties at least quarterly.
4. Reporting (implementation report + annual report) – According to Article 22 of the "Pollutant Discharge Permit Management Regulations", an annual pollutant discharge permit implementation report must be submitted, truthfully recording the actual emission data.

Conclusion: Water Treatment Is the Compliance Baseline, Not an Option

The water treatment cost for packaging and printing factories (annual 180,000-250,000 CNY) is a highly cost-effective compliance investment compared to environmental penalties (50,000-500,000 CNY per incident + production loss). The most common mistake owners make is treating water treatment as a "set it and forget it" matter, but the Ministry of Ecology and Environment's "installation, transportation, monitoring, and reporting" four stages are continuous actions. From 2018 until now, we have invested more than 2 million CNY in water treatment, with each upgrade coming from tightened supervision + actual emission data. If your factory has not yet built water treatment or is currently upgrading, it is recommended to first clarify the limits of the three hard indicators of COD, ammonia nitrogen, and color, do not copy the processes of peers, because emission standards vary from region to region.

Extended Reading

- Three Monitoring Indicators for Wastewater Discharge in Packaging and Printing Factories
- Three Real Disposal Price Differences for Printing Waste Liquids – "Market Price vs. Actual Price" between Printing Factories and Hazardous Waste Disposal Companies
- Three Hard Indicators for Occupational Health in Packaging and Printing Factories: VOC / Noise / Dust
- Three Hard Indicators for VOC Treatment in Packaging and Printing: First Protect Employee Health, Then Talk About Environmental Compliance