Often defined scientifically as a biological or engineered system for separating solids from liquids or gases using a filter medium, filtration has distinct meanings within optics (transmission of light through a lens), computing (sorting and processing data), and mathematics (an algebraic formula). The filtering of pollutants from water (see Ball in SDUK09) or dust from air (see McCallum in SDUK05) may provide alternative models for reducing hazardous waste, and repurposing filtered byproducts in beneficial ways.