Characterisation of Organic Nitrogen in Algal Organic Matter and Formation of N-DBPs After Chlorination

Abstract

Drinking water quality can be impacted by the presence of algogenic organic matter (AOM), rich in dissolved organic nitrogen (DON) that can act as precursors of nitrogenous disinfection by-products (N-DBPs). Better characterisation of algogenic DON is therefore important in order to optimise treatment processes so that N-DBP concentrations in treated water are minimised. This paper characterises the DON exuded by the green algae Chlorella vulgaris and the cyanobacteria Microcystis aeruginosa and Anabaena circinalis using ultrafiltration, measurements of total organic carbon and total nitrogen (TOC/TN), dissolved inorganic nitrogen (DIN), and size exclusion liquid chromatography detection with organic carbon and nitrogen detection (SEC-LC-OCD-OND). Potential N-DBP formation of three haloacetonitriles (HANs), two halonitromethanes (HNMs) and two haloacetamides (HAAms) was evaluated by chlorination of fractional AOM with a mass ratio of free Cl2: TOC of 8:2, and subsequently measuring target N-DBPs using GC-MS. Results showed that AOM primarily contained org-N contents at >50 kDa and around 1 kDa. Among the chlorinated AOM, only HANs were detected in N-DBP formation experiments. The algal species and fractions containing higher org-N content produced greater HAN. The fractional high molecular weight (HMW) AOM (1–50 kDa) of Anabaena circinalis had the highest yield of dichloroacetonitrile (DCAN) at 2.4 µgL−1 or 1.2 µgmg−1C−1. Overall, there was more N-DBP formation from HMW AOM fractions than low molecular weight (LMW) AOM fractions.