Action of chlorine, peracetic acid, UV-LED radiation, and advanced oxidation process on Giardia lamblia cysts for reclaimed water production

Resistant pathogens such as the protozoa Giardia lamblia are frequently identified in effluents from wastewater treatment plants, even after the disinfection process, threatening the safe practice of agricultural effluent reuse. The high resistance of Giardia cysts is conferred by their wall, a rigid extracellular component formed by carbohydrate and protein molecules arranged in two layers. Thus, this study aimed to evaluate the action of chlorine, peracetic acid, ultraviolet (UV) radiation, and an advanced oxidation process (AOP), which consist in the association between UV radiation and hydrogen peroxide, on Giardia lamblia cysts, artificially inoculated in samples of treated domestic wastewater, to produce reclaimed water safe for agricultural irrigation. The 4 disinfectants evaluated showed effective action against Giardia cysts, demonstrated by the formation of morphological damage on the cyst wall, and the best performance was achieved by the AOP, using 15 mg L⁻¹ of H₂O₂ associated with 103 mJ cm⁻² of UV radiation, emitted by light-emitting diodes (LEDs), at wavelengths of 255/280/400 nm. Understanding how different disinfecting agents act on pathogenic organisms in complex matrices such as domestic wastewater is fundamental for the process of choosing the treatment to be used to produce reclaimed water.