Aims: To evaluate the suitability of Clostridium perfringens, Escherichia coli and enterococci as indicator organisms for Cryptosporidium and Giardia in treated sludge.
Methods and results: Occurrence of Cryptosporidium oocysts and Giardia cysts, detected and enumerated by direct immunofluorescence microscopy, were compared with counts of indicator bacteria during six different sewage sludge hygienization processes, including closed reactor and open windrow composting, and sludge sanitation by quicklime or peat addition. No statistical correlation existed between the counts of indicator bacteria, Cl. perfringens, E. coli, and enterococci and occurrence of Cryptosporidium or Giardia. In sludge end-products, Giardia cysts were detected more frequently than Cryptosporidium oocysts.
Significance of the study: Direct analysis is the best method to confirm the presence of (oo)cysts in sludge.