Biological activity within the sand bed had the strongest influence on removal efficiency of total coliform bacteria by slow sand filtration, as determined by six pilot filters (shown above). Temperature, sand bed depth, and sand size also had strong influence.

To achieve maximum treatment effectiveness, operators need a tool to determine how well their plants are optimized for pathogen removal. This article presents the results of a study designed to evaluate the use of pathogen surrogates as a tool in treatment optimization and to predict pathogen occurrence. A comprehensive matrix was developed to relate water quality and process variables for 24 potable water sources and 12 possible surrogates to the target pathogens of Giardia, Cryptosporidium, and enteric viruses. No “ideal” surrogate for predicting occurrence of protozoan pathogens or treatment performance was identified because of analytical constraints and low pathogen occurrence. However, it was concluded that aerobic spores and particle counts could be used as surrogate measures to evaluate or improve treatment plant performance. Utilities should select not one but a number of surrogates to assess raw water quality and treatment plant performance.

Pilot-plant studies were undertaken to determine the etTiciency of slow-rate sand filters in removing Giavdiu cysts and other substances. The filters removed vitiually 100 percent of the Giardia cysts, 96 percent of standard plate count bacteria, and 98 percent of particles. Because of the efficiency and the passive nature of slow-rate sand filtration, this technology is especially appropriate for small water systems.This research was undertaken to evaluate the effectiveness of slow-rate sand filtration for the removal of Giardiu lumblia cysts. Other variables studied were turbidity, particles, total coliform bacteria, and standard plate count bacteria. These dependent variables were evaluated with respect to the influence of design and operating conditions (i.e., the independent variables) such as the hydraulic loadingrate, the concentration of cysts, the concentration of bacteria, the biological maturity of sand in the filter bed, the age of the schmutzdecke, and temperature.The first application of slow-rate sand filtration for large-scale community use was in England by the Chelsea Water JOURNAL AWWA

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Pilot‐plant tests resulted in virtually 100 percent removals of Giardia lamblia cysts for both coarse and fine grades of diatomaceous earth over a wide range of conditions. Removals of turbidity and total coliform bacteria were functionally dependent on the grade of diatomaceous earth. Alum coating increased removal rates.