Factors Contributing to Cryptosporidium and Giardia Variability for Future Direct Potable Reuse Applications

Investigating the fate of pathogenic protozoa and their reduction in wastewater treatment units is of a great interest in helping to define treatment goals for direct and indirect potable water use. This study explores the Cryptosporidium and Giardia log removal variations in wastewater treatment plants (WWTPs) with different conditions (i.e., seasonal, wastewater characteristic and process operational parameters). To investigate the impact of these variables, a year-long field study was conducted in 5 local WWTPs. Protozoa log reduction in these facilities ranged from 1.5 to 3. Higher protozoa log removal was observed with higher SRT (>15days) and higher HRT (>10 days). The log removal between influents and secondary effluents in the field study was in the higher end of the reported values in the literature for both Cryptosporidium and Giardia. However, both literature surveys and field study for comparison between trickling filter and activated sludge units indicated a higher log reduction of Cryptosporidium in the filtration units.