Zero valent metal composite, manufacturing thereof, using thereof, and system including thereof, for (in-situ or ex-situ) catalytically treating contaminated water, such as sub-surface water, surface water, above-surface water, water vapor, or/and gaseous water. Composite includes powdered diatomite matrix incorporated with nanometer (1-1000 nm) sized particles of a zero valent (transition) metal (iron, cobalt, nickel, copper, zinc, palladium, platinum, or/and gold) and at least one electron transfer mediator (catalyst) from porphyrinogenic organometallic complexes (e.g., metalloporphyrins (chlorophylls, hemes, cytochromes) or metallocorrins (e.g., vitamin B12), and optionally, includes vermiculite. System includes composite and in-situ or/and ex-situ unit containing the composite, enabling exposure of contaminated water thereto. Applicable to in-situ sub-surface permeable reactive barriers (PRBs). Treatable water contaminants are organics (halogenated organic compounds), or/and inorganics (metal elements, metal element containing inorganic species, nonmetal elements, and nonmetal element containing inorganic species). Applicable to non-aqueous fluids (liquids, vapors, gases), for removing contaminants therefrom.