Removal of organic compounds from aquatic environments by advanced oxidation processes.

Menezes, Indira

Abstract

Agricultural practices and eutrophication contribute to cyanobacteria proliferation, cyanotoxin contamination and pesticide pollution in aquatic environments. Conventional treatments can be ineffective for the removal of high cell densities of cyanobacteria, dissolved toxins and pesticides. Therefore, complementary technologies are required to effectively remove these contaminants at source. The current study aims to apply photolysis and photocatalysis (advanced oxidation processes) as novel technologies for in-situ removal of harmful contaminants. Photoinduced photolysis by UV-A 365 nm LED irradiation was explored during bench-scale experiments for the removal of Microcystis aeruginosa cells and microcystins. A common way of verifying the effects of light-driven treatments on cyanobacteria is by performing lab-scale experiments, where cyanobacteria are cultured in growth media. In the current study, six Microcystis aeruginosa strains (SCIENTO, NIES 1099, B2666, PCC 7820, 7813 and 7806) in BG-11 medium were exposed for seven days to UV-A (365 nm) irradiation. Photosynthetic activity significantly decreased after 24 hours of irradiation with samples showing no photosynthetic activity by the end of the experiment. Intra- and extracellular microcystin (MC) concentrations were markedly decreased in UV-A treated samples with a combined microcystin removal of 86%. It was observed, however, that nutrients present in the BG-11 growth medium (e.g., nitrate and iron) enhanced the UV-A photolytic effects on microcystins concentration. Therefore, it is important to consider the media composition for lab-scale experiments focused on cyanobacterial removal to effectively evaluate light-driven strategies for cyanobacteria and toxin removal. Photocatalysis was explored for the removal of pesticides at source. Bench-scale experiments were performed to demonstrate the effectiveness of graphitic carbon nitride (g-C3N4) coated glass beads and UV-A LED irradiation for the removal of a mixture containing nine pesticides (1 mg L-1 each in artificial freshwater; acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam, diuron, atrazine, dimethoate and 2,4-dichlorophenoxyacetic acid). The photocatalytic system was able to successfully remove a range of pesticides at the same time. Finally, a photocatalytic reactor prototype based on g-C3N4 coated beads and UV-A LED irradiation was developed to be applied at source for pesticide removal from aquatic environments. The reactor could be deployed in different locations, which include storage tanks with residual pesticides, ponds, drainage systems, farmyards and other aquatic environments around farms to treat water contaminated with pesticides. Both treatments based on photolysis and photocatalysis have the potential to be novel, long-lasting, environmentally safe, economical, modular and flexible approaches for the removal of contaminants at source from aquatic environments.

Citation

MENEZES, I. 2024. Removal of organic compounds from aquatic environments by advanced oxidation processes. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2795681

• Thesis Type: Thesis
• Deposit Date: Apr 18, 2025
• Publicly Available Date: Apr 18, 2025
• DOI: https://doi.org/10.48526/rgu-wt-2795681
• Keywords: Cyanobacteria; Cyanotoxins; Pesticides; Water pollution; Water treatment; Water purification; Photolysis; Photocatalysis; Oxidation
• Public URL: https://rgu-repository.worktribe.com/output/2795681
• Award Date: Aug 31, 2024