sorry for the confusion; my second and third link suggests the use of DE as a parasite killer when ingested.
however your first instinct to use bleach is probably the most effective
Giardia ENVIRONMENTAL DECONTAMINATION
The most readily available effective disinfectant is probably bleach diluted 1:32 in water which required less than one minute of contact to kill Giardia cysts in one study. Organic matter such as dirt or stool is protective to the cyst so on a concrete surface basic cleaning should be effected prior to disinfection. Animals should be thoroughly bathed before being reintroduced into a “clean” area.