Removal of bacteria in laboratory filters: models and experiments

Five filtration models were used to predict the effect of particle size on removal in several types of laboratory filters (nylon, cellulose and glass fiber). All models predicted similar trends in removal with particle size, although the capillary-pore model predicted substantially lower removals than the other four fibrous filtration models. These models indicated that bacterium-size (∼ 1 μm) particles are removed in filters primarily through the filtration mechanism of particle interception. Based on advertised pore sizes, removal of bacterium-size particles was a function of filter material in the order cellulose > nylon > glass fiber. The percent of bacteria removed in a nylon filter (5 μ pore diameter) was similar to removal in GF/C filters (1.2 μm pore diameter) as a result of a higher sticking coefficient of bacteria with nylon than with glass. The average sticking coefficients of three bacteria, Pseudomonas sp. JS6, Pseudomonas fluorescens P17 and Bacillus pumilus, in glass fiber (GF/C) filters, were 0.01, 0.24 and 0.20, respectively. These results indicate that filtration models can be used to describe particle removal during laboratory filtration of water and wastewater samples, and that bacteria have relatively high sticking coefficients for filter materials.