At 0.61 m/module, this is depth is equivalent to 7.2 modules. Since whole modules must be used, eight will be required. This corresponds to a total media depth of 4.9 m. This will result in a modest increase in the THL, which is acceptable. The diameter of the trickling filter would be 23 m.

19.3.3 Sizing Trickling Filters with the Modified Velz/Germain Equation

An empirical model that has been referred to in the literature as either the modified Velz or the Germain equation has been used extensively to size trickling filters for removal of organic matter.11 The Velz equation is described in Section 16.4.1. The development of the Velz/Germain equation assumes first order removal of substrate with respect to both the substrate concentration and the biomass concentration. It also assumes that the biomass concentration is constant throughout the trickling filter and that the trickling filter behaves as a plug-flow reactor with a residence time, t. Based on these assumptions, the concentration of soluble substrate in the effluent, SSc, is related to the concentration of soluble substrate actually applied to the top of the trickling filter, SSa, by:

where k is a reaction rate coefficient and Xb Hf is the biomass concentration. However, empirically it was found that the HRT is related to the trickling filter THL and the media depth, L, according to:

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