An evaluation of measurement techniques for algal-derived organic nitrogen

X Li; N R H Rao; K L Linge; C A Joll; S Khan; R K Henderson

doi:10.1016/j.watres.2019.114998

An evaluation of measurement techniques for algal-derived organic nitrogen

Water Res. 2019 Nov 15:165:114998. doi: 10.1016/j.watres.2019.114998. Epub 2019 Aug 19.

Authors

X Li¹, N R H Rao¹, K L Linge², C A Joll³, S Khan⁴, R K Henderson⁵

Affiliations

¹ AOM Lab, School of Chemical Engineering, The University of New South Wales, Sydney, Australia.
² Curtin Water Quality Research Centre, Chemistry, School of Molecular and Life Sciences, Curtin University, Perth, Australia; ChemCentre, Perth, Australia.
³ Curtin Water Quality Research Centre, Chemistry, School of Molecular and Life Sciences, Curtin University, Perth, Australia.
⁴ UNSW Water Research Centre, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, Australia.
⁵ AOM Lab, School of Chemical Engineering, The University of New South Wales, Sydney, Australia. Electronic address: r.henderson@unsw.edu.au.

PMID: 31470284
DOI: 10.1016/j.watres.2019.114998

Abstract

Algal-derived organic matter (AOM) from algal blooms in water supply systems contains dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) among other constituents. The DON and DOC are disinfection by-product (DBP) precursor compounds, and must be well characterised to facilitate effective removal, thus minimising DBP formation during disinfection. While DOC character has been studied extensively, DON analysis suffers from inaccuracies due to sample pre-treatment and instrument sensitivities. A liquid chromatography method that combines size exclusion chromatography with highly sensitive organic carbon and nitrogen detectors (LC-OCND) has been widely adopted for DOC analysis; however, its potential for application for DON charactersation has been suggested as a viable alternative to existing DON characterisation techniquesnot been assessed despite its potential. Hence, the aim was to compare the effectiveness of conventional total dissolved N-dissolved inorganic N (TN-DIN), and LC-OCND methods for analysing DON in AOM. A suite of N-containing model compounds representative of DON and AOM extracted from Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-555/1 were used to evaluate the techniques. The DON of both model compounds and AOM was first analysed using the conventional method and, then, via LC-OCND. It was observed that LC-OCND had a better precision for DON when TN contained more DIN. LC-OCND provided direct quantitative measurements for bulk and fractionated DON and DIN, with little interference caused by DIN. Additionally, LC-OCND provided information on MW distribution and protein content of the AOM. For example, LC-OCND results showed that M. aeruginosa AOM contained more HMW material than C. vulgaris AOM. However, as LC-OCND uses UV oxidation, it could not completely oxidise complex aromatic structures, and thus had a lower recovery for HMW model compounds and algal DON in comparison to the conventional method that used high temperature catalytic oxidation. Overall, it is advised that a combination of LC-OCND and TN analysis be used to provide a more detailed characterisation of N-containing AOM and other similar HMW aquatic NOM samples.

Keywords: Algae; Cyanobacteria; Flow injection analysis; LC-OCD; Limit of detection.

MeSH terms

Carbon
Chlorella vulgaris*
Microcystis*
Nitrogen
Water Purification*

Substances

Carbon
Nitrogen