Influence of sewage treatment plant effluent discharge into multipurpose river on its water quality: A quantitative health risk assessment of Cryptosporidium and Giardia.

Sewage treatment plants (STPs) are one of the sources of pathogens discharged into surface water. An investigation was carried out over the duration of 12 months in Henan Province, China, to evaluate the health influence of municipal wastewater effluent discharge on water quality of the receiving water. A discharge-based quantitative microbial risk assessment (QMRA) was employed, taking into account the vegetables consumption habits of the Chinese, population subgroups with different immune statuses and ages, to evaluate the incremental disease burden from agricultural irrigation and swimming exposure scenarios associated with increased concentration of the protozoan Cryptosporidium and/or Giardia in the receiving river. The results shown that all the STP influent samples contained Cryptosporidium and Giardia with average density of 142.31 oocysts/L and 1187.06 cysts/L, respectively. The QMRA results demonstrated that the estimated additional health burdens due to discharged effluent for both parasites were slightly violated the threshold of 10 DALYs per person per year set by WHO. Mitigation measures should be planned and executed by season since more disease burdens were borne during hot season than other seasons. The sensitivity analysis highlighted the great importance of stability of STP treatment process. This study provides useful information to improve the safety of surface water and deduce the disease burden of the protozoa in Henan Province and other region inside and outside China.