NOVELTY - Biocatalyst (I) comprising a solid structure of hydrated hydrophilic polymer defining an interior structure having many interconnected major cavities having a smallest dimension of 5-100 microns and an hydration expansion volume (HEV) of at least 1000, and a population of microorganisms substantially irreversibly retained in the interior structure, is new. The population of microorganisms is in a concentration of at least 60 g per liter based upon the volume defined by the exterior of the solid structure when fully hydrated. The microorganisms maintain their population substantially stable.    USE - (I) is useful in metabolic process to bioconvert the substrate to bioproduct, and for reducing the concentration of nitrate anion and/or perchlorate anion when present in water, where the substrate comprises at least one of nitrates, perchlorates, taste and odor compounds, chlorinated hydrocarbons, 1,4-dioxane, and oxyanions, hydroxyls or soluble salts of sulfur, phosphorus, selenium, tungsten, molybdenum, bismuth, strontium, cadmium, chromium, titanium, nickel, iron, zinc, copper, arsenic, vanadium, uranium, radium, manganese, germanium, indium, antimony mercury, and rare earth metals (all claimed). (I) is useful: in water supply or waste water clean-up operations, where the substrate is one or more contaminants; to generate metabolites including primary or secondary metabolites, to produce any type of anabolic metabolite, where the bioproducts are e.g.: carbon dioxide, carbon monoxide, hydrogen, carbonyl sulfide, hydrogen sulfide, water, and salts such as carbonate, bicarbonate, sulfide, sulfite, sulfate, phosphate, phosphite, chloride, bromide, iodide, and borate salts of ammonium, or group 1 to 16 (IUPAC) metals such as sodium, potassium, manganese, magnesium, calcium, barium, iron, copper, cobalt, tin, selenium, radium, uranium, bismuth, cadmium, mercury, molybdenum and tungsten; aliphatic compounds and aromatic compounds including hydrocarbons of up to 44C or 50C, and hydrocarbons substituted with one or more of hydroxyl, acyl, carboxyl, amine, amide, halo, nitro, sulfonyl, and phosphino moieties, hydrocarbons containing one or more hetero atoms including nitrogen, sulfur, oxygen, and phosphorus atoms; and p-toluate, terephthalate, terephthalic acid, aniline, putrescine, cyclohexanone, adipate, hexamethylenediamine, 6-aminocaproic acid, malate, methacrylic acid, 3-hydroxypropionic acid, succinate, butadiene, propylene, caprolactam, fatty alcohols, fatty acids, glycerates, acrylic acid, acrylate esters, methacrylic acid, methacrylic acids, fucoidan, muconate, iodine, chlorophyll, carotenoid, calcium, magnesium, iron, sodium, potassium, and phosphate. (I) is useful: for biological detection devices, coatings including antifouling paint and coatings such as for ship hulls and other surfaces immersed in surface water, and filters to remove undesirable components from gases and liquids; in biological fuel cells; for producing hydrogen or hydrogen equivalents using mesophilic or thermophilic, anaerobic or facultative anaerobic microorganisms; in methanogenesis of carbonaceous substrates especially to methane; producing alkenes such as ethylene, propylene, butene, butadiene and styrene from, e.g., carbohydrates such as sugars, syngas, and carbon dioxide; for treatment of various ground, surface, municipal wastewater and industrial water streams and for anaerobic digestion; for removal of sulfate and sulfite anions; and as a layered catalyst for conducting aerobic wastewater treatment, where the bioproduct may be a chemical that provides a biological activity with respect to a plant or animal or human, the biological activity comprises antiviral, antibiotic (e.g. aminoglycosides (e.g. amikacin, gentamicin, kanamycin, neomycin, netilmicin, tobramycin and paromomycin)), depressant, stimulant, growth promoters, hormone, insulin, reproductive, attractant, repellant and biocide. No biological data given.    ADVANTAGE - The microorganism-containing biocatalysts: have a large population of the microorganisms irreversibly retained in the interior of the biocatalysts; possess stable population of microorganisms, and hence stable bioactivity, and an essential absence of debris generation from metabolic activity of the microorganisms; and can exhibit these phenomenons over extended periods of time. The microorganisms in the biocatalysts exhibit phenotypic alterations that, in combination with an internal, cavity-containing structure of the biocatalyst provide highly advantageous biocatalysts including a metabolic shift from growth of the microorganisms and their population to bioconversion activity (anabolic or catabolic), enhanced tolerance to toxins, enhanced ability to enter a substantial state of stasis even for extended periods of time and enhanced ability to efficiently bioconvert substrate. (I) provides desirable bioconversion activity over extended periods of time of at least 3, preferably at least 6, and frequently in excess of 12 or 24 months, and sometimes as much as 5 years or more and enhances the stability of the syntrophic system.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) the preparation of (I);    (2) a metabolic process comprising subjecting (I) to metabolic conditions including the presence substrate to bioconvert the substrate to bioproduct; and    (3) a process for reducing the concentration of nitrate anion and/or perchlorate anion when present in water comprising contacting water with (I) containing a strain of microorganism capable of reducing the anions under metabolic conditions and for a time sufficient to bioconvert such anion.