Background and purpose: Access to safe drinking water is of the utmost importance in public health around the world. Presence of contaminants, such as secondary bacterial growth and endotoxins could reduce the quality of water resources. This study aimed at investigating the occurrence, seasonal variation, and removal of endotoxins in a conventional water treatment plant (WTP) in Tehran, Iran.

Materials and methods: A total of 36 samples was collected on a monthly basis from raw water and treated water in each uint of Tehran-pars drinking WTP during summer and fall (2015). Endotoxin concentrations were assessed using the Endpoint Chromogenic Limulus Amebocyte Lysate (LAL) detection method. Furthermore, turbidity, heterotrophic plate count (HPC) and  pH measurements were done to assist in the analysis of data.

Results: The mean values for the total endotoxin activities in summer and fall in the raw water were 44-54.5 and 17.62-54.5 Eu/ml, respectively. The results demonstrated a 34% decrease in endotoxin activity following the full-scale treatment process at the WTP. The highest concentration of endotoxin was detected in summer. Coagulation, clarification and sand filtration resulted in the highest endotoxin removal (38.16 %), while chlorination contributed to the concentration of total endotoxins by 5.6-6.7%.  

Conclusion: Water treatment processes aiming at the removal of particulate matter in the WTP revealed the most effective removal rates of total endotoxins. However, endotoxin contamination exists in the drinking water treated.