Filter aids are generally used only where the liquid phase is required as they cause substantial problems in the recovery of solids. They also sometimes cause loss of enzyme activity from the solution due to physical hold-up in the filter cake. The filter aids used as pollution control accessories are classified as perlite, diamote and dicalock, for better usage and to make them available in high quality. A special milling and classification process gives the perlite filter aids the structure and correct particle size range distribution needed for optimum performance. These perlite filter aids are processed at temperatures exceeding 800°c (1500°f), which eliminates organic matter. They have extremely low solubilities in mineral and organic acids at both low and high temperatures. These industrial pollution control apparatus are at times referred to as contraptions i.E. Mechanical devices, as it reflects their nature. The best quality filters aids are light in weight, chemically inert and form high porosity filter cakes to maintain free flow of the liquid.
