include the Vorticella, Opercularia, and Epistylis species. Along with the protozoans, the higher animal forms in the filter—such as snails, worms, and insects—feed on the biological film, keeping the bacterial population in a state of high growth and rapid substrate utilization. Thus, these higher forms are not commonly found in high-rate trickling filter towers.
Changes in organic loading, hydraulic retention time, pH, temperature, air availability, influent wastewater composition, and other factors vary the populations of each type of microbial community throughout the filter depth.
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