Direct centrifugation for detecting Giardia spp. cysts in filter backwash water

Abstract

Pathogenic protozoa endanger human health and challenge water treatment, especially during outbreaks in developing countries. For instance, Giardia spp. cysts can recirculate in the filter backwash water (FBW), reinforcing the relevance of their detection protocol in negligible matrices. This study aimed to detect Giardia spp. cysts in the FBW by direct centrifugation (DC) and immunomagnetic separation (IMS) with the addition of the detergent dispersion solution ICN 7X at 1.0%. To do this, cyst suspensions were inoculated into FBW samples (14 NTU), which was generated in bench-scale drinking-water treatment with high-turbidity study water (112 NTU). Furthermore, the DC+ICN 7X method was compared with the calcium carbonate flocculation. For instance, the DC+ICN 7X method provided cleaner microscope slides and minor damage to the cyst walls. The commercial suspension of Giardia lamblia had an adequate recovery rate (19.5%). However, the recovery rate of the EasySeed® suspension was 7.8%, which was below the required range by Method 1623.1 (above 8%). High costs and low efficiencies challenge several methods for detecting Giardia spp. cysts. Therefore, future studies should develop and improve detection protocols, especially for complex matrices. Detecting cysts in water treatment residues is crucial for addressing current sanitation issues in developing countries.