TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The chemical treatment is conducted at 10-100 degrees C. The physical treatment is conducted at ambient up to 1000 degrees C. The filtration and/or adsorption of the biogenic silica is improved by a change comprising increasing the surface charge by at least 50% or altering type of the surface charge corresponding to species to be removed, increasing the surface area by at least 100%, increasing total pore volume by at least 50%, decreasing less than 10 micron fines content by 80% and/or increasing the permeability of the silica by at least 300%. The method further comprises pretreating the fluid by a process comprising increasing or decreasing the temperature, increasing or decreasing the pH, adding a chemical to affect the solubility of the species and/or increasing the size of the species. Preferred Components: The biogenic silica is rice hull ash, where the rice hull ash has a purity of 70-98 silica wt %. The acid is hydrochloric acid, sulfuric acid, phosphoric acid and/or nitric acid. The metal ions are chromium3+, chromium6+, iron2+, iron3+,cobalt2+, copper2+, nickel2+, zinc2+, lead2+ and/or mercury2+. The non-metallic anions are arsenic5+, phosphorus5+ and/or selenium6+. The organic compounds are dye molecules and/or phenol, and the odor-producing species is ammonia.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The method at least partially occurs in a device comprising batch filter presses, automatic filter presses, rotary drum filters, belt filters, belt presses, leaf filters, diatomaceous earth filters, Nutsche-type filters, membrane filters and separators, cross-flow filters, gravity granular media filters, vacuum granular media filters, pressure granular media filters, automatic continuous backwashable granular media filters, cartridge filters, candle filters, wedgewire filters, geotubes, settlers, continuous or batch thickeners and/or centrifuges. The device is a granular media filter containing particulate media, and the biogenic silica is applied using a method comprising applying the biogenic silica as a mixture with the particulate media (body feed) and/or applying the biogenic silica as a precoat, where the device contains a filter media or a filter element impregnated with the biogenic silica. EXAMPLE - Wastewater stream with chemical oxygen demand (COD) of 485 mg oxygen/g was added with 2% cationic electrolyte (calcium chloride) treated rice hull ash, after the filtration the COD was reduced to 71 mg oxygen/g.