THE EFFECT OF SEWAGE-SLUDGE TREATMENT PROCESSES ON OOCYSTS OF CRYPTOSPORIDIUM-PARVUM

The effect of common sewage sludge treatment processes on oocysts of t he coccidian protozoan Cryptosporidium was evaluated in laboratory sim ulations. The ability of primary sewage sedimentation to remove Crypto sporidium oocysts was found to be poor. Thermophilic (55 degrees C) ae robic digestion and sludge pasteurization at the same temperature were found to be effective treatments to inactivate Cryptosporidium oocyst s. Approximately 10% of the oocyst population were found to be viable after 18 d exposure to mesophilic (35 degrees C) anaerobically digesti ng sludge. The viability of Cryptosporidium oocysts decreased within t he range 20-40% in sludge-treated soil mesocosms over 30 d. The surviv al results obtained, however, indicated that oocysts would survive wel l beyond this period.