Nitrate–Nitrogen Discharge Standards for Industrial Wastewater

Nitrate–nitrogen (NO₃⁻–N) is the final oxidation product of nitrogenous compounds under aerobic conditions. In industrial effluents, excessive nitrate–nitrogen can accelerate eutrophication of receiving waters and, when accumulated in groundwater, threaten drinking water sources. Therefore, establishing clear discharge limits for nitrate–nitrogen is essential for both industrial compliance and environmental supervision.

It should be noted that, with a few exceptions for nitric acid production, China's current national and sectoral water pollutant discharge standards do not directly set individual limits for nitrate–nitrogen. Instead, nitrate–nitrogen is regulated under the broader total nitrogen (TN) indicator. Total nitrogen encompasses ammonia nitrogen, nitrate–nitrogen, nitrite–nitrogen, and organic nitrogen, and setting a TN limit effectively imposes a comprehensive restriction on all nitrogenous pollutants.

China’s industrial wastewater discharge standards follow a three‑tier framework: comprehensive standards as the base, industry‑specific standards as the primary, and local standards as the supplement. Industry‑specific standards take precedence; once an industry has its own discharge standard, the Integrated Wastewater Discharge Standard (GB 8978‑1996) no longer applies to that industry.

Sectoral TN Limits. Taking the textile dyeing and finishing industry as an example, GB 4287‑2012 sets the TN limit for new facilities at 15 mg/L for direct discharge and 25 mg/L for indirect discharge. For the fermentation‑based pharmaceutical industry, GB 21903‑2008 sets a TN limit of 30 mg/L for direct discharge and 50 mg/L for indirect discharge. For industrial categories without specific sectoral standards, wastewater discharges are still regulated under GB 8978‑1996, which classifies discharge destinations into three tiers with different limit values.

Local and Stricter Standards. Local governments may impose tighter limits than national standards. For instance, in Jiangsu Province, the indirect discharge TN limit for the textile printing and dyeing industry when discharging to a centralized wastewater treatment plant within a chemical industrial park is 70 mg/L. In some regions, TN limits have been further tightened; for key sectors such as electroplating, chemicals, and pharmaceuticals, TN discharges are now required to be ≤15 mg/L.