Measurements of Dissolved Organic Nitrogen in Wastewater Samples with Nanofiltration Pretreatment

Abstract

Conventional dissolved organic nitrogen (DON) measurements for water samples with high dissolved inorganic nitrogen (DIN) to total dissolved nitrogen (TDN) ratio are incorrect due to the cumulative analytical errors of independently measured nitrogen species (DIN and TDN). In this study, we present a nanofiltration (NF) pretreatment to increase the accuracy and precision of DON measurements by selectively concentrating DON while passing through DIN species in water samples to reduce the DIN/TDN ratio. Compared to the available dialysis pretreatment method, the NF pretreatment method shows a similar improved performance for DON measurement for aqueous samples and can save at least 20 h of operating time and a large volume of deionized water, which is beneficial for laboratories involved in DON analysis. To prove the feasibility of the pretreatment, we collected and compared effluent samples from two sewage water treatment plants. The result shows that with the pretreatment, the DIN to TDN ratio has significantly decreased while the dissolved organic carbon (DOC) recovery has been increased. So this NF pretreatment is available.