TABLE OF CONTENTS Wastewater contaminants can be separated from water by the use of physical separation technologies including membrane and particulate filtration methods. Particulate filtration is employed for the removal of solids greater than 10 microns in diameter. Particulate filtration is primarily used for the removal of organic and inorganic solids, chemical precipitates (including heavy metal residuals) and biomass and other residuals from secondary treatment. Membrane technologies, on the other hand, are used for the removal of materials that are generally smaller than one micron in diameter. Particulate filtration is often used as a pretreatment step for membrane separation technologies.
Filtration in wastewater treatment is often employed as a tertiary treatment step for the removal of suspended solids. The filtration unit may be located at the end of a biological treatment train and use clarifier or settling lagoon effluent as its feed. Wastewater filters may also be used as part of a physical/chemical process and serve as a polishing step to improve suspended solids/heavy metals removal.
Many types of filters are available on the market, but in the environmental field, granular media filters are most extensively used for wastewater treatment. Granular media filters use sand or a combination of sand and other granular media (garnet, anthracite, etc.). Granular media filters may be operated with gravity feed, or the influent may be pumped in under pressure either in the up-flow or down-flow mode.
In a down-flow, granular media filtration system, wastewater enters the top of the unit. Particulates are...
