Formation and toxicity alteration of brominated halonitromethanes from the intracellular organic matter of Chlorella vulgaris during UV/chlorine disinfection

Abstract

Eutrophication leads to massive algal proliferation. During algal blooms, cyanobacteria often serve as the dominant species, while green algae are frequently the subdominant species. Algal organic matter can become a potential source for the formation of halonitromethanes (HNMs). During ultraviolet/chlorine treatment, bromide ions (Br⁻) promote the formation of brominated halonitromethanes (Br-HNMs), which exhibit greater toxicity compared to chlorinated halonitromethanes (Cl-HNMs). While the formation of Br-HNMs from cyanobacteria has been documented, research on how green algae contribute during UV/chlorine disinfection in the presence of Br^- remains limited. Therefore, Chlorella vulgaris, a widely distributed green alga, was selected as a model precursor to investigate the formation patterns and toxicity of Br-HNMs derived from its intracellular organic matter (IOM) during UV/chlorine disinfection. Bromonitromethane (BNM) and bromodichloronitromethane (BDCNM) were observed to form from the IOM of Chlorella vulgaris, with their concentrations rising initially and then falling as Br⁻ concentration and reaction time increased. Additionally, higher free chlorine concentration, UV intensity, and IOM concentration promoted Br-HNMs formation (i.e., BNM and BDCNM), whereas an increase in pH inhibited their formation. Potential pathways for the formation of Br-HNMs were deduced based on the experimental results. Moreover, Br-HNMs formation patterns from the IOM of Chlorella vulgaris in actual water samples closely resemble the results in simulated waters. This study elucidates the risks associated with Br-HNMs formation from the IOM of Chlorella vulgaris during UV/chlorine disinfection. These findings provide theoretical and technical support for optimizing water treatment processes and controlling Br-HNMs formation at water treatment facilities.

Graphical abstract

Keywords

UV/chlorine / Brominated halonitromethanes / Chlorella vulgaris / Intracellular organic matter / Disinfection byproducts / Bromide ion

Highlight

	● Chlorella vulgaris IOM can form Br-HNMs during UV/chlorine disinfection with Br−.
	● Concentration and toxicity of Br-HNMs raised and then declined with increasing Br−.
	● Chlorine and Chlorella vulgaris concentration, UV, and pH affect Br-HNMs formation.
	● Possible formation pathways of Br-HNMs from Chlorella vulgaris IOM were deduced.
	● Formation law of Br-HNMs in actual and simulated water were similar.

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