NOVELTY - Removing a species from a fluid to give a purified liquid, comprises: producing biogenic silica; treating biogenic silica by a treatment comprising chemically treating with e.g. alkali, physically treating by contacting with e.g. steam, washing with e.g. water, size reduction by e.g. grinding, blending with a material e.g. lime, or combinations of chemically treating, physically treating and blending, where the treatment improves filtration and/or adsorption by biogenic silica; contacting a fluid containing the species with treated biogenic silica; and removing species and recovering fluid.    USE - The method is useful for removing species from fluid (drilling fluids, cooking oils, fish oils, biodiesels, ethanol, motor oils, coolants, lubricants, juices, beverages, brewery fluids, sugar solutions, pharmaceutical fluids and/or biosludges) to give purified liquid (all claimed).    ADVANTAGE - The method utilizes rice hull ash (RHA), which: minimize solids production and energy requirements; has good porosity, pre size to allow the desired material to pass through and prevent the undesirable material from passing through, does not readily compact, does not form a sticky mass, comprising clay when wet, is dimensionally stable at the temperature and pressure range that the filtration and separation occurs; possesses adsorption properties; has good filtration characteristics, good flow rates; is low cost; and forms a filter cake containing the filtered out material which produces minimal ash when incinerated and/or increases the heating value of the filter cake so that it will qualify as a fuel under federal recyclic regulations.    DETAILED DESCRIPTION - Removing a species from a fluid to give a purified liquid, comprises: producing biogenic silica by combustion of a biogenic source; treating the biogenic silica by a treatment comprising chemically treating the biogenic silica with a chemical comprising an alkali, an oxidation agent, an acid, a dehydration agent, an enzyme, a microbial material and/or a salt solution, physically treating the biogenic silica by a process comprising contacting the biogenic silica with steam, nitrogen and/or carbon dioxide, washing the biogenic silica with a liquid comprising water and/or an acid; size reduction by a method comprising crushing, grinding, classification, screening and/or dry particle agglomeration, blending the biogenic silica with a material comprising a cementitious material, calcium hydroxide, calcium chloride, calcium carbonate, lime, soda ash, an electrolyte, a polyelectrolyte, a coagulant, a flocculant, calcium silicate, aluminum silicate, magnesium silicate, chabazite zeolites, clinoptilolite zeolites, expanded perlite, diatomaceous earth, cellulose kenaf fiber, ion oxides, an enzyme and/or microbial material, or combinations of chemically treating, physically treating and blending, where the treatment improves filtration and/or adsorption by the biogenic silica; contacting a fluid containing the species with the treated biogenic silica, where the species comprising organic, inorganic or microbial particulates, surfactants, non-metallic anions, metallic ions, dissolved total suspended solids (TSS), total dissolved solids (TDS), color bodies, odor-producing species, chlorinated compound, pigment, free fatty acids, phospholipids, peroxides, oil and/or grease different from the non-aqueous fluid, algae and/or bacteria; removing the species from the fluid by both filtration and adsorption; and recovering the fluid to greater purity.