with media size of 0.3 mm and 95% removal rate of particles as small as 15 µm for media size of 0.5 mm. Filter media There is a variety of filter media that can be employed in depth filter processes the most common being sand. Choice of filter media has effects on filter rate, turbidity and filter surface area. Clean bed head loss (pressure drop) is sensitive to media diameter where increasing media diameter results in a longer time to design head loss. Increasing the media diameter and filter rate however results in degradation of effluent turbidity. To compensate, media depth can be increased to reduce the effects on effluent turbidity. The max value of media depth used in designs so far for high rate filtration is 100 in, whilst the maximum media size used in pilots is 2mm in diameter. Sand, magnetite, coke and anthracite are the most commonly used particle mediums in industry particularly to their wide availability. Table [1] Process/Design Characteristics of Monomedium Filter Beds for Wastewater treatment (Deep Bed): Table [2] Design Parameters for Pressure Depth Filters: Design heuristics Depth filtration may be used in pre-treatment, removing suspended particles from a carrying fluid intended to be used as a feed stream or in the context of clarification where particulates are removed to purify a product stream. Several heuristics are adopted into the design of depth filters in order to ensure consistent operation throughout the life of the filter. Particle retention and filter media The relationship between retention and particles size is not a step function. Larger particles are easily retained by the filter media; however particulates that are within the intermediate range between the nominal particle and waste components are harder to preserve and as a result are often lost as a waste component. To maximize the retention passage for a range of particle sizes, filter media is layered in a manner such that sections with a higher pore size are closer to the inlet stream, capturing particles of a larger size. Pore sizes decrease as it approaches the outlet stream. By adopting this method, the filter media caters for a wider range of particle sizes, resulting in greater control of retention and extending the life of the filter. Filter media selection Filter selection is reliant on a number of variables such load, duration, shape, size and distribution of the substance desired to be filtered. Ideally