if the medium is too large, filtrate will be of a poor quality as it will fail to collect particulates within its matrix. Conversely if the medium is very small, solids will accumulate on the surface of the cartridge causing close to immediate blockages. In regards to the shape using grains that are round in shape have the tendency to erode due to the pressure the inlet stream may possess on the system, whereas grains that are flat (may increase surface area) however may float out of the system during backwash. Particles which are high on Moh's scale of hardness and have a relatively large specific gravity are often recommended to be used as particle media. The softer and lighter the material is, the more susceptible it is to erosion and fluidization. Thus particles such as silica and sand are often used as they are affordable however are resistant to the high flows of the incoming fluid. The uniformity coefficient is a measure of the uniformity of the material used within the filter. It is a ratio of a sieve pore that allows 60% of the material through in comparison to a pore size that allows 10% of material through. The closer the ratio is to one, means the closer the particles are in size. An ideal system would have a coefficient between 1.3 and 1.5 and must not exceed 1.7. Anything less than 1.3 is an indication that it is unnecessary to the system and may result in higher costs without providing any additional form of optimization. Beyond 1.5 indicates that the system may experience a greater pressure drop and as mentioned may result in clogging, seeping of waste flow and reduced filtration rate. As a guideline it is recommended that the smallest particles used within depth filters should be placed at least 150 mm from the outlet stream to prevent fluidization. Dead end operation of depth filters Particulates (black dots) being caught within the filter media (brown spaces). The white spaces which are smaller in terms of size than the filter media provide a narrow passage for the liquid stream to pass through Depth filters are operated in the context of the dead end filters. With this being said, the velocity of the inlet stream is crucial to the performance of the filter. High velocity inlet streams with relatively large particulates will cause possible clogging and wearing down