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This study presents data pertaining to the hydraulic and particle size characteristics of commercial grades of diatomite used as filter aids. To achieve this, the specific study objectives were to: evaluate the reproducibility and relative simplicity of two ASTM methods for determining the grain size of soils when those methods are used to determine the particle size distribution of diatomite filter aids; determine the particle size distribution of different lots of commercial grades of diatomite filter aids; determine K3 values of different grades and of different lots of the same grade of diatomite (K3 is a constant for a given grade of diatomite at 20°C and is inversely proportional to its coefficient of permeability); and, determine whether a relationship exists between the K3 value and particle size distribution. The determination of the permeability of diatomite filter aids in this study was confined to the evaluation of K3 coefficients in the recently developed diatomite filtration equation. The ASTM Method for Grain Size Analysis of Soils‐Designation D422‐39 (Method 1) and ASTM Tentative Method for Grain Size Analysis of Soils ‐Designation D422‐61T (Method 2) were used in this study for determining particle size distribution.

The primary objective of this study was to develop a digital‐computer program for use in designing diatomite filtration plants that would produce filtered water of requisite quality at least cost. To achieve the objective, it was necessary to be able to predict the variation of filter cake resistance for various conditions, because cake resistance is one of the primary factors influencing costs. Diatomite filtration equations that were theoretically developed from the generally accepted filtration rate equation were used to describe the head loss‐time relationships during formation of diatomite filter cakes. A computer program was developed for determining the optimum operating conditions for a specific type of plant that filters a particular water and uses a specified grade of filter aid. This program was named the Program for Optimization of Plant Operation (POPO). The program determines the optimum combination of filtration rate, body feed concentration, and terminal head loss by simply computing costs of filtration for any desired number of combinations and choosing the ten most economical.

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