Cryptosporidium oocyst removal from diatomaceous earth at a cyclone recovery pilot plant

Recycling of diatomaceous earth (DE) in a drinking water filtration system was investigated. The plant consists of four stages of cyclones plus a scavenger system for the recover of spent DE. Cryptosporidium oocysts were seeded into the raw water from the DE pilot plant, at a concentration of 10(3) oocysts per titer. Samples were taken prior to injection from the seeded stack, down stream from the point of injection in the influent stream and from the overflow post-cyclone separation. In the DE recovery plant the percentage of oocysts detected in the overflow stream (that volume of water and spent DE, which will not be recovered or reused) ranged from 27 to 79% depending on the number of cyclones present. It appears that while 91% of the oocysts were separated from the DE that was slated for recovery. The levers of this organism in the spent DE over time or after a large concentration spike in the influent, could present a problem if the DE is to be reused as body feed without some type of pretreatment to inactivate this organism.