Fate of Cryptosporidium during wastewater treatment via constructed wetland systems

Abstract

Constructed wetlands have been recognized as offering a removal treatment option for high concentrations of chemical and biological contaminants in domestic wastewater. The enteric protozoan parasite Cryptosporidium is considered to be one of the most highly resistant and most infectious organisms for humans, animals and birds. Moreover, some species of Cryptosporidium are known to have a zoonotic nature. In this investigation a pilot scale for a domestic wastewater treatment system is used, consisting of the following steps: (1) up‐flow anaerobic sludge blanket (UASB) reactor; (2) free water surface (FWS) unit; and (3) sub‐surface flow (SSF) unit. This treatment system was fed with domestic wastewater to assess its efficiency in removing Cryptosporidium oocysts. The obtained Cryptosporidium oocysts were detected by two different staining techniques (acid fast trichrome ‘AFT’ and modified Ziehl Neelsen ‘MZN’ stains). Results revealed that the AFT stain was more sensitive and reliable for the detection of Cryptosporidium oocysts than MZN stain. Anaerobic treatment (using UASB reactor) could remove about 47.49% of Cryptosporidium oocysts present in raw wastewater. The FWS unit could remove about 94.35% of the oocysts that escaped from UASB treatment unit. No oocysts were detected after SSF treatment. The physicochemical properties of the final effluent were within the limits for wastewater reuse.