对于小型公用设施，包装形式的双级过滤（DSF）是传统快速过滤的良好替代品。本文所述研究的目的是测试DSF去除低浊度（<1 ntu）、低温（接近32华氏度[0摄氏度]）水中贾第虫囊肿的有效性。还测定了总大肠菌群的去除率和浊度。对两种不同的水源进行了测试，测试时间长达35小时。当采用适当的化学处理且系统以10 gpm/sq ft（6.8 mm/s）或更低的速度运行时，双级过滤可从浊度为<1 ntu、温度为<46华氏度（<8摄氏度）的水中去除>99%的贾第虫囊肿。总大肠菌群去除率超过98%，浊度去除率超过90%。 包括14个参考文献、表格和图表。

Dual-stage filtration (DSF) in packaged form is a good alternative to conventional rapid-rate filtration for small utilities. The purpose of the study described in this article was to test the effectiveness of DSF for removing Giardia cysts from low turbidity (<1 ntu), low temperature (near 32 degrees F [0 degrees C]) water. Removals of total coliform bacteria and turbidity were also determined. Two different water sources were tested, with runs up to 35 h in length. Dual-stage filtration removed >99 percent of Giardia cysts from water with a turbidity of <1 ntu and a temperature of <46 degrees F (<8 degrees C), when proper chemical treatment was applied and the system was operated at 10 gpm/sq ft (6.8 mm/s) or less. Removal of total coliform bacteria exceeded 98 percent, and removal of turbidity exceeded 90 percent. Includes 14 references, tables, figures.