Dialysis Pretreatment for Dissolved Organic Nitrogen Analysis in Freshwaters

Qiang Wang,Bin Hua,John Yang,Guocheng Zhu,Baolin Deng,Fengjing Liu

doi:10.1155/2015/629794

Abstract

Total dissolved nitrogen (TDN), including dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON), plays an important role in numerous environmental processes, such as nutrient cycling and lake and estuary eutrophication. The impact of DIN on environmental processes has been extensively studied. However, the understanding on DON in the environment is largely unknown, as there is no direct method for DON measurement. In practice, DON was determined by subtracting DIN from TDN. Large measurement errors could be induced when DIN becomes dominant in sample. This study was to investigate the impact of two pretreatments of dialysis, dialysis against Millipore water and dialysis against phosphate buffer (4.7 mM H3PO4-5.3 mM KH2PO4, pH 2.2) using a cellulose ester (CE) membrane (100–500 Da molecular weight cutoff), on DON measurement in a broad DIN range from various aquatic ecosystems. Results showed that the removal of NH4-N and NO3-N by both dialysis approaches was highly effective (>80%), but the DON loss by the former was significantly lower than by the latter. This study demonstrated that dialysis against Millipore water with the membrane would be more effective as a sample pretreatment for DIN removal, leading to a reliable and accurate DON measurement.

Highlights

Total dissolved nitrogen (TDN) in surface water has been increasing globally, primarily due to agriculture-related activities and inappropriate discharge of wastewater [1]
Many components in dissolved organic nitrogen (DON) pool play an active role in providing N nutrition to phytoplankton and bacteria, affecting the DON components have been linked to the formation of toxic disinfection byproducts [DBPs, e.g., N-nitrosodimethylamine (NDMA)] during drinking water disinfection process [13,14,15,16]
The raw water samples displayed a broad range of TDN (1.27–633 mg L−1), with 6 surface waters having low TDN (5 might not Original DOC (mg/L) and 100 mg L−1)

Summary

Introduction

Total dissolved nitrogen (TDN) in surface water has been increasing globally, primarily due to agriculture-related activities and inappropriate discharge of wastewater [1]. Nitrogen (N) in aquatic system exists in different forms, reflecting complex environmental and geochemical processes. TDN includes dissolved organic nitrogen (DON, e.g., protein and amino sugar) and dissolved inorganic nitrogen (DIN, e.g., nitrate, nitrite, and ammonia). The N-forms are interconvertible by microorganisms, DON is often a dominant N-form in aquatic systems, accounting for >50% of TDN [2,3,4]. Organic nitrogen is composed of >90% of total nitrogen in most soils [5], which could have a significant impact on DON composition in aquatic system due to surface runoff. Many components in DON pool play an active role in providing N nutrition to phytoplankton and bacteria, affecting the DON components have been linked to the formation of toxic disinfection byproducts [DBPs, e.g., N-nitrosodimethylamine (NDMA)] during drinking water disinfection process [13,14,15,16]

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Methods

Results

Conclusion