Photo-electrochemical oxidation herbicides removal in stormwater: Degradation mechanism and pathway investigation

Although advanced oxidation processes (AOPs) such as photoelectrochemical oxidation (PECO), electrochemical oxidation (ECO) and photocatalytic oxidation (PCO), have shown potential for wastewater treatment, their application in urban stormwater has rarely been studied. This paper explored their major degradation mechanisms and possible degradation pathways of herbicides for stormwater applications (with treatment difficulty compared with wastewater). PECO and ECO showed excellent removal performance for diuron (100 %) and moderate for atrazine (around 35 %) under a relatively low potential (2 V). Superoxide radical (center dot O-2(-)) has been found to be the dominant reactive species. Besides, there is evidence to indicate that hydroxyl radical (center dot OH) and free chlorine (center dot Cl) also support the degradation reactions. Up to 11 possible intermediate products have been identified during both diuron and atrazine degradation processes under PECO operation. Based on the proposed possible degradation pathways, the intermediates presented during PECO are species with further oxidation. As evidenced by the undetected species of more oxidized intermediates for ECO and PCO, some further degradation steps are missing, which demonstrate their lower oxidation capacity leading to incomplete decomposition of stormwater herbicides. Thus, PECO has a great potential to be developed into a passive stormwater degradation system due to its strong oxidation potential.

Automated summary

This study explored the potential and application of advanced oxidation processes (AOPs) in urban stormwater treatment. It was found that photoelectrochemical oxidation (PECO) and electrochemical oxidation (ECO) showed good removal performance for diuron, with superoxide radical being the dominant reactive species. Additionally, hydroxyl radical and free chlorine also supported the degradation reactions. The proposed degradation pathways identified several intermediate products. PECO demonstrated higher oxidation capacity compared to ECO and photocatalytic oxidation (PCO), which resulted in more complete decomposition of stormwater herbicides.