Potential Biorisks of Cryptosporidium spp. and Giardia spp. from Reclaimed Water and Countermeasures

Purpose of Review

This review aims to summarize the occurrence of Cryptosporidium spp. and Giardia spp. in the reclaimed water and their risks in different reuse scenarios, analyze the drawbacks of protozoa detection methods, compare the removal efficiencies of different water treatment technologies, and propose potential management measures.

Recent Findings

Cryptosporidium spp. and Giardia spp. are widely present in the wastewater in the last decade, and the reclaimed water is usually used in agricultural irrigation, recreational activities, and urban reuse. The risks of protozoa infection are generally higher than the WHO defined 10⁻⁴ threshold in agriculture and recreational reuse and partial urban practices. The direct potable reuse with multiple advanced treatments has relatively low risk, while the indirect potable reuse is more risky due to the low removal efficiency of traditional drinking water treatment process. The newest protozoa detection standard applies a cheap way to measure (oo)cysts in high-turbidity water. But it still cannot distinguish live and dead (oo)cysts, and cannot identify pathogenic species. These defects result in the overestimation of the health risks. Potential solutions with fluorescence dye and molecular tools are proposed. About 4-log reduction is needed for agriculture and recreational scenarios with advanced treatments. While for urban reuse, lower log reduction might be achieved by secondary treatment with disinfection.

Summary

This review highlights the potential biorisks of Cryptosporidium spp. and Giardia spp. of the reclaimed water in various reuse scenarios and possible countermeasures to improve the safety issue. Suggestions for more accurate risk assessment and management strategies of protozoa control are proposed.