Release of nitrogenous disinfection by-product precursors in algae-laden water under UV radiation

Nitrogen-containing organic compounds and nitrogenous disinfection by-products (N-DBPs) in drinking water have attracted attention in the field of water treatment. Metabolites released during algae growth contain a variety of organic nitrogen species, which are called N-DBP precursors. The aim of this paper is to elucidate how N-DBP precursors are released, as well as the variations of their chemical properties, under UV radiation. The results show that through UV radiation, the physiological metabolism of algal cells was disordered and the properties of their metabolites were changed. The dissolved organic nitrogenous compound (DON) concentration increased rapidly from 5.38 at the beginning to 11.11 mg/L after 30 min of radiation, and then increased steadily from 11.11 to 23.71 mg/L during further 210 min of radiation. Derivation results of the curves for algae and DON concentration variations shows that when 1 × 1010 algal cells were destroyed, 8.31 mg DON was released into the solution during the first 30 min of radiation. Low dose UV radiation brought a slight decline of the specific N-DBP formation potential due to change of the EOM (Extracellular Organic Matter) structure without destructing the algae cell, which was conducive in controlling the formation potential of N-DBPs. Long-time UV radiation can bring a significant increase in N-DBP formation potential. After 4 hours of ultraviolet radiation, the total formation potential of N-DBPS in the solution increased from about 84.9 μg/L to about 213.5 μg/L, 2.5 times higher than the initial solution. The N-DBPs formation potential increase obviously during the first 10–30 min UV radiation, and then they decrease slightly in subsequent 30–240 min radiation.