Mechanism and degradation pathways of photo-Fenton system using Fe(III)-EDDS for Microcystis aeruginosa and microcystin-LR removal

Abstract

Harmful algal blooms is a global problem of water pollution causing great economic losses to countries. Microcystis aeruginosa, as a dominant algal species in cyanobacterial blooms, has attracted extensive attention. However, most of the current studies on the treatment of alga-containing waters focus on the removal of algal cells or microcystins, lacking the exploration of the degradation pathways and analyses of the toxicity of the products. In this paper, we constructed a photo-Fenton system using Fe(III)-EDDS (EDDS: Ethylenediamine-N,N’-disuccinic acid) complex as an iron source for the simultaneous removal of Microcystis aeruginosa as well as microcystin-LR (MC-LR). The results showed that adding 0.1 mM of Fe(III)-EDDS complex and 1.0 mM of H2O2 achieved 83.3% algal cell removal in 240 min under neutral pH conditions and also degraded 72.5% of MC-LR. Moreover, the degradation products of MC-LR and EDDS were analyzed by LC-MS, which showed that the toxicity of the MC-LR molecule was greatly reduced by benzene ring removal and decarboxylation of partial amino acids, while its degradation resulted from the destruction of amino acids in the MC-LR molecule. The toxicity analyses provide a basis for the practical application of the system, hence consideration can be given to combining or improving it with the existing UV disinfection technologies in water supply plants for potential algal bloom outbreaks. This study was the first time to apply the Fe(III)-EDDS system to the field of microalgae removal and MC-LR detoxication, aiming to provide new development ideas for water purification and photochemical algae removal technology.