Wastewater Discharge Standards for Printing Plants

Printing production generates wastewater from plate washing, ink mixing equipment cleaning, dampening solution replacement, and floor rinsing. This effluent is typically characterized by high chemical oxygen demand, intense color, high suspended solids, trace heavy metals, moderate biodegradability, and wide pH fluctuations. Understanding and complying with discharge standards is not just a regulatory obligation—it is the foundation of responsible environmental management for any printing facility.

The Regulatory Framework

At the national level, China has not yet issued a water pollutant discharge standard specifically for the printing industry. (An atmospheric standard, GB 41616-2022, does exist for printing.) Instead, printing wastewater is governed by a combination of general and sector-specific standards.

The foundational document is the Integrated Wastewater Discharge Standard (GB 8978-1996) . This standard establishes maximum allowable discharge concentrations for 69 pollutants, differentiated by discharge destination and by the age of the facility. For facilities that discharge into municipal sewers, the Wastewater Quality Standard for Discharge into Municipal Sewers (GB/T 31962-2015) also applies.

For printing operations that manufacture ink, the Discharge Standard of Water Pollutants for Printing Ink Industry (GB 25463-2010) provides additional, more specific limits. This standard applies to both direct and indirect discharge.

It is also important to note that many provinces and municipalities have issued local standards that are stricter than the national requirements. Operators must always check the specific rules applicable to their region.

Key Pollutants Under Control

While exact limits vary by discharge route and local rules, the core parameters routinely monitored include:

pH: typically required to stay within the range of 6 to 9.

Chemical Oxygen Demand (CODcr) : the primary control indicator. Direct discharge limits are generally around 100 mg/L, while indirect discharge (to a municipal treatment plant) typically allows up to 500 mg/L.

Biochemical Oxygen Demand (BOD₅) and Suspended Solids (SS) : indirect discharge limits are often set at 300 mg/L and 400 mg/L, respectively.

Heavy metals: inks, pigments, and cleaners may introduce pollutants such as total cadmium, hexavalent chromium, total chromium, total lead, and total mercury, each with specific concentration caps.

Color, total phosphorus, and ammonia nitrogen are also standard monitoring items.

Direct vs. Indirect Discharge

The applicable standards depend first and foremost on where the treated wastewater goes.

Direct discharge—releasing treated effluent directly into rivers, lakes, or other natural water bodies—requires compliance with the most stringent Grade I standards of GB 8978-1996.