Factors Affecting the Detection of Dissolved Organic Nitrogen Via Electrodialysis Pretreatment

Abstract

Dissolved organic nitrogen (DON) is ubiquitously present in the environment and its presence in drinking water has been related to the formation of nitrogenous disinfection byproducts recently. Therefore, a better understanding of the occurrence and control of DON is important. However, conventional DON method calculates DON as the difference between total dissolved nitrogen (TDN) and dissolved organic nitrogen (DIN), in which the subtraction process is likely to be subject to accumulated analytical errors and therefore sometimes results in unreliable DON data. Electrodialysis (ED) as a pretreatment tool may separate completely DON from DIN and enable direct and improved DON analysis. However, the important factors affecting the efficiency of ED process are unknown now. So, this study investigates a series of operational and instrumental options on the removal efficiency of ED for DON measurement. These factors include the type and concentration of electrolyte(s) in the sample and electrolyte media, flowrate, power input, specific area of ion exchange membrane (IEM), and electrode materials, etc. Ultimately, we have developed an ED unit capable of separating DON from DIN by 99% within 90 minutes with a consumption of sample of only 50 ml. The main purpose is to optimize the ED process while avoiding potential problems. The information may help optimize the ED process to provide automatic tools for DON analysis in the future.