3 Monitoring Indicators for Wastewater Discharge from Packaging Printing Plants: COD / Ammonia Nitrogen / Total Phosphorus — Common Reasons for Failing Environmental Assessment

Last year, a mid-sized food packaging printing plant in Wuxi had its environmental assessment rejected when expanding a new workshop, because the drainage test showed COD concentration of 580 mg/L, exceeding the 100 mg/L limit of Class 1 of the «Integrated Wastewater Discharge Standard» GB 8978-1996. But more troubling was the follow-up retest revealing ammonia nitrogen also over the limit (15 mg/L limit, 22 mg/L measured), with two items exceeding simultaneously leading to environmental re-assessment. The plant’s words: «I thought treating COD was enough, didn’t know there were also ammonia nitrogen and total phosphorus.» This plant is not an isolated case. Wastewater compliance for packaging printing plants is not a single indicator but a combined limitation of 3 indicators: chemical oxygen demand, ammonia nitrogen, and total phosphorus.

Where Does Wastewater from Packaging Printing Plants Come From — 3 Sources

Many people think printing plants are «dry operations» that don’t generate wastewater. They are wrong. Wastewater sources at packaging printing plants are 3 types: ① Printing plate washing water (developer-containing wastewater from offset plate, CTP plate washing); ② Ink waste liquid (solvent/pigment-containing wastewater from cleaning ink buckets, ink rollers); ③ Domestic wastewater (canteens, toilets, washing). The first two are industrial pollution sources that must be tested according to industrial discharge standards; the third can be merged into the domestic sewage network.

Offset printing plant wastewater’s main issue is developer (containing hydroquinone, sodium sulfite) and ink cleaning fluid (containing solvents); flexo/gravure printing plant wastewater’s main issue is solvent residue and water-based ink wastewater; digital printing plants have the smallest wastewater volume, but water-based ink waste liquid still needs treatment. Different printing processes have different wastewater characteristics and treatment plans.

3 Monitoring Indicators — Not a Single Indicator but 3 Combined

The Class 1 standard (most commonly cited by packaging printing plants) of the «Integrated Wastewater Discharge Standard» GB 8978-1996 specifies 3 core indicators:

Chemical Oxygen Demand (COD): Class 1 standard ≤ 100 mg/L, Class 2 standard ≤ 150 mg/L, Class 3 standard ≤ 500 mg/L. COD is a comprehensive indicator of reductants (mainly organic matter) in water that can be chemically oxidized, reflecting the degree of water pollution. Packaging printing plant COD mainly comes from organic matter in ink and developer, and common reasons for exceeding the limit are insufficient pretreatment (sedimentation/air flotation not performed).

Ammonia Nitrogen (NH3-N): Class 1 standard ≤ 15 mg/L, Class 2 standard ≤ 25 mg/L. Ammonia nitrogen is the sum of ammonia and ammonium salts in water, reflecting the risk of water eutrophication. Packaging printing plant ammonia nitrogen mainly comes from developer (containing sodium sulfite, ammonia) and ink wastewater (some inks contain amine additives), not every plant exceeds the limit, but once exceeded it is difficult to reduce in the short term — ammonia nitrogen treatment requires nitrification/denitrification processes, with equipment investment double that of COD treatment.

Total Phosphorus (TP): Class 1 standard ≤ 0.5 mg/L (in areas with high environmental requirements) or ≤ 1.0 mg/L (general areas). Total phosphorus is the sum of phosphates in water, reflecting water eutrophication. Packaging printing plant total phosphorus mainly comes from surfactants (such as fountain solution, ink dispersants), and many printing plants don’t even realize this is an indicator — until environmental assessment is rejected.

3 Common Reasons for Failing Environmental Assessment on the First Try

Reason 1: Testing only COD but not ammonia nitrogen and total phosphorus. Many printing plants believe «meeting COD standards is enough», but environmental assessment reports require 3 items, missing one will be judged as non-compliant. Last year, a Zhejiang carton printing plant self-tested COD at 95 mg/L (meeting the standard), but environmental protection bureau sampling found ammonia nitrogen at 28 mg/L (exceeding by 87%), ultimately fined 80,000 yuan and ordered production suspension for rectification.

Reason 2: Testing but with incorrect sampling methods. Wastewater from packaging printing plants is not continuously discharged but intermittent — concentration is high during printing peaks and low when stopped. Sampling must be during drainage peaks (such as 4-6 hours after start-up), not during low concentration samples in the early morning when just starting work, otherwise monitoring data is not representative.

Reason 3: Treatment facilities not operating as designed. Many printing plants spend money on wastewater treatment equipment, but actually operate half-open or unopen to save chemical costs — air flotation machine not turned on, aeration tank not aerated, biochemical tank not adding nutrients. This «fake treatment» may meet COD standards in the short term, but will inevitably expose problems in ammonia nitrogen/total phosphorus in the long term.

3 Categories of Costs for Printing Plant Wastewater Compliance

① Testing fees: Single COD test 200-300 yuan, ammonia nitrogen 200 yuan, total phosphorus 200 yuan, total for 3 tests approximately 600-700 yuan. Printing plants must self-test at least once a month, and commission third-party testing institutions to do 2 comparisons per year (according to local environmental protection bureau requirements).

② Treatment facility investment: Small-scale treatment facility for air flotation + biochemistry (activated sludge method) investment 300,000-800,000 yuan, operating costs (chemicals + electricity + labor) 15,000-30,000 yuan per month. Mid-sized printing plants (annual output value over 20 million yuan) wastewater compliance costs are roughly 1.5-2.5% of output value.

③ Violation costs: According to Article 83 of the «Water Pollution Prevention Law», fines for exceeding discharge standards are 100,000-1,000,000 yuan; in serious cases, ordered production suspension for rectification or even closure. Multiple violations or being listed for supervision will be included in corporate credit records, affecting subsequent bidding.

Differentiated Treatment for 3 Types of Processes

Offset printing plant wastewater treatment focus is on developer (containing hydroquinone) and ink cleaning fluid. Treatment idea: developer separately collected pretreatment (chemical oxidation) + ink wastewater air flotation separation + comprehensive biochemistry. Flexo/gravure printing plants (with solvent-based inks) wastewater is characterized by high organic solvent content, requiring first air flotation/adsorption pretreatment before entering biochemistry. Digital printing plants have small wastewater volume, focus is on water-based ink waste liquid (containing pigments and surfactants), treatment is relatively simple.

Regardless of the process, the core principle of wastewater treatment is «classified collection, quality-based treatment» — collecting developer, ink waste liquid, and domestic wastewater through separate pipelines, with separate pretreatment, then merged into the comprehensive treatment facility. This is the foundation for the printing plant’s environmental assessment to pass on the first try and not be repeatedly rejected.

Further Reading

3 Hard Indicators for Packaging Printing VOC Treatment

3 Methods for Packaging Enterprise Carbon Emission Accounting

5 Years of New Solid Waste Law, Packaging Printing Plants Still Running Naked

3 Categories of Cosmetic Packaging Regulations Landing Densely