Kinetics of Microcystin-LR Removal in a Real Lake Water by UV/H ₂O ₂ Treatment and Analysis of Specific Energy Consumption

Abstract

The hepatotoxin microcystin-LR (MC-LR) represents one of the most toxic cyanotoxins for human health. Considering its harmful effect, the World Health Organization recommended a limit in drinking water (DW) of 1 µg L ⁻¹. Due to the ineffectiveness of conventional treatments present in DW treatment plants against MC-LR, advanced oxidation processes (AOPs) are gaining interest due to the high redox potential of the OH ^• radicals. In this work UV/H ₂O ₂ was applied to a real lake water to remove MC-LR. The kinetics of the UV/H ₂O ₂ were compared with those of UV and H ₂O ₂ showing the following result: UV/H ₂O ₂ > UV > H ₂O ₂. Within the range of H ₂O ₂ tested (0–0.9 mM), the results showed that H ₂O ₂ concentration and the removal kinetics followed an increasing quadratic relation. By increasing the initial concentration of H ₂O ₂, the consumption of oxidant also increased but, in terms of MC-LR degraded for H ₂O ₂ dosed, the removal efficiency decreased. As the initial MC-LR initial concentration increased, the removal kinetics increased up to a limit concentration (80 µg L ⁻¹) in which the presence of high amounts of the toxin slowed down the process. Operating with UV fluence lower than 950 mJ cm ⁻², UV alone minimized the specific energy consumption required. UV/H ₂O ₂ (0.3 mM) and UV/H ₂O ₂ (0.9 mM) were the most advantageous combination when operating with UV fluence of 950–1400 mJ cm ⁻² and higher than 1400 mJ cm ⁻², respectively.