Quantitative Study on the Structure-bioavailability Relationship of Dissolved Organic Nitrogen in Wastewater Treatment Plant Effluent

Abstract

This study systematically investigated the relationship between the structure properties and biological characteristics of DON in the effluents from municipal wastewater treatment plants. Ultrafiltration, FTIR spectroscopy, UV spectroscopy and EEM fluorescence spectroscopy were used to characterize the structure of organic matters in the effluent samples, and the bioavailability of DON was determined by algal/bacterial based bioassay. The quantitatively analysis of EEM spectra conducted by fluorescence regional integration method showed that the organic portion of all samples were mainly consistent with fulvic acid and protein. Combined with the bioassay results, a positive correlation between the DON bioavailability and the protein content (sum of region I and region II) (r=0.80, P＜0.02) and soluble microbial byproduct-like materials (region IV) (r=0.76, P＜0.03) were observed. Nevertheless, the humic substances content represented by the region III and V would negatively affect the DON bioavailability. High humification degree (high HIX value) (r=-0.77, P＜0.03) was related to low bioavailability. Furthermore, according to UV spectroscopy results, strong aromaticity (high UV254 values) (r=-0.78, P＜0.03) suggested low DON bioavailability. The ultrafiltration experiment showed that the low molecular weight DON (＜3kDa) accounted for 30-73% of the total DON, and no notable relationship was observed for DON molecular weight and its bioavailability.