Penetration control of invertebrates in the granular activated carbon filtration process with sand bed

In view of the aesthetic problem and potential threat to safe drinking water caused by invertebrates, a series different depth of sand beds were located under granular activated carbon (GAC) media in five pilot-GAC filtration (GAC_F) columns to restrict invertebrates' penetration into the distribution system. During the study period of 10 months, 7 groups of invertebrates (rotifers and crustaceans as the predominant species) were detected in the filtrates of the five GAC_F columns. The experimental results indicated that invertebrates could be removed effectively with the added sand beds compared with the sand bed-free GAC_F column. The mean abundances of invertebrates decreased significantly with the increase of the depth of sand beds. The 46.6 % of rotifers and 85.5% of larger invertebrates (size>200 μm) could be removed from the filtrate. Sand sizes had a greater impact on rotifers removal than larger invertebrates. Also increasing removal ratios of particle matter were detected with the sand beds added. Further data analysis showed that there was significant correlation between the mean values of particle counts and abundances of invertebrates in the filtrates.