In industrial wastewater discharged from various sectors, including fertilizer manufacturing, steel production, gunpowder manufacturing, feed production, meat processing, electronic component manufacturing, and nuclear fuel production, high concentrations of nitrate and nitrite are often present. Initially, certain industrial wastewater containing organic nitrogen or ammonia nitrogen may not contain these substances. However, during the aerobic biological treatment of such wastewater, they can potentially be converted into nitrate or nitrite.
Nitrite, as an intermediate product in the nitrogen cycle, exhibits poor stability in water. Under the influence of oxygen and microorganisms, it can be oxidized to nitrate, while under anaerobic or anoxic conditions, it can be reduced to ammonia. Consequently, in clean water bodies, the nitrite content remains relatively low. Nitrate represents the end product of the inorganic decomposition of nitrogen – containing organic matter. Thus, when nitrogen in water exists predominantly in the form of nitrate, it indicates that the content of nitrogen – containing organic matter in the water is minimal, signifying that the water body has achieved self – purification.
When water contains a significant amount of nitrate along with other nitrogen compounds, it suggests that either the self – purification process of the water body is in progress or the water body is being contaminated by nitrate – containing wastewater. By simultaneously monitoring three forms of inorganic nitrogen in the water body, namely ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, and integrating the analytical results of organic nitrogen and total nitrogen, it is possible to comprehensively assess the degree of pollution by nitrogen – containing compounds and the self – purification status of the water body.
Likewise, these nitrogen compound analysis results can be effectively utilized to evaluate the efficiency of sewage treatment and provide guidance for optimizing the operation of the denitrification process. Nitrite can react with secondary amines in the stomach to form potent carcinogens. Moreover, nitrate can be reduced to nitrite within the human body. Therefore, consuming water with a high nitrate concentration poses potential risks to human health. In particular, when children drink water with elevated nitrate levels, it can lead to an increase in methemoglobin in the blood, resulting in poisoning.
To address these concerns, relevant national standards have been established to regulate the nitrate concentration in water bodies. Specifically, the drinking water hygiene standard stipulates that the maximum allowable concentration is 20 mg/L (expressed as N). The surface water quality standard (GB 3838 – 2002) specifies that the maximum allowable concentration of nitrate in centralized surface water sources for domestic use is 10 mg/L (expressed as N).
The conventional approach for treating industrial wastewater containing nitrate or nitrite involves biological denitrification using micro – electrolytic fillers. For small – scale industrial wastewater containing nitrate or nitrite, alternative methods such as electrodialysis, reverse osmosis, and ion exchange can also be considered.
