Deactivation of algae from water treatment by using ultraviolet-C with chlorine as pre-treatment

Abstract

The overgrowth of algae in freshwater has become a challenge and concern for the treatment facilities, which can lead to reduced water quality and water scarcity. There are many algae species, among those Scenedesmus sp. is one of the commonly found green microalgae that belongs to the Chlorophyceae class, which is under the phylum of Chlorophyta. This study investigated the effectiveness of UVC/chlorine pre-treatment for the inactivation of Scenedesmus sp. under different treatment conditions. The experiments were conducted using UVC exposure times of 1, 5, 10, and 15 minutes, followed by chlorine doses of 1, 3, 5, and 10 mg/L. The influence of turbidity was also examined using bentonite at 50 NTU and 100 NTU. Treatment performance was evaluated using optical density (OD680), residual chlorine, chlorophyll-a (Chl-a), UV254, and dissolved organic carbon (DOC). The OD680 results showed that algae growth decreased with increasing UVC exposure time and chlorine dose, indicating stronger algae inactivation under higher treatment intensity. Residual chlorine increased with higher chlorine doses, but decreased after longer UVC exposure. The Chl-a results showed that the combined UVC/chlorine treatment performed effectively without turbidity conditions, especially at 5 minutes of UVC exposure and 5 mg/L chlorine, the Chl-a concentration reached 59.12 μg/L. However, under the same treatment condition, the Chl-a concentration increased to 77.65 μg/L at 50 NTU and 82.95 μg/L at 100 NTU, showing that turbidity reduced treatment efficiency. UV254 and DOC increased after treatment, especially at higher chlorine doses and longer UVC exposure times, indicating the release of dissolved organic matter from damaged algae cells. Without turbidity, the UVC/Cl2 can be 5 min and 3 mg/L, while with high turbidity, it can vary between 5-10 min and 5 mg/L of Cl2. Overall, UVC/chlorine pre-treatment was effective for Scenedesmus sp. inactivation, but turbidity reduced its performance by limiting UVC penetration and increasing chlorine demand.