NOVELTY - Apparatus (100) for denitrifying a solution (215) comprises: denitrification tank (200) to receive portion of solution for period of time, in which controlling amount, duration and frequency of introduction of carbon source (410) into solution promotes indigenous heterotrophic bacteria depleting dissolved oxygen in solution, and obtains oxygen from nitrate in the solution; where carbon source is selected from 20 compounds as given in the specification e.g. polyethers of monoglycerides; ethoxylated monoglycerides; carboxylic acid ester of diol; polyether; or a glycoside ester.    USE - As an apparatus for denitrifying a solution (claimed) e.g. for wastewater treatment; improving freshwater quality; controlling alkalinity and oxygen recovery; producing stabilized effluent; and reducing issues stemming from sludge accumulation in the clarifier.    ADVANTAGE - The denitrification apparatus employs an inexpensive, non-toxic, unregulated carbon source that promotes activity of heterotrophic bacteria and reduces all nitrate (NO3-) in solution; as compared to prior art carbon sources having various disadvantages, such as methanol and ethanol have acute toxicity, volatility, flammability, and lead to formation of explosive vapor mixtures with air in confined spaces; ethanol while grain derived in its natural form is highly regulated and expensive; cheaper and unregulated denatured ethanol is required in excess amounts, inhibits decomposition, yields byproducts including benzene, ethylene, toluene, and xylene, which should not be released into the environment, and causes less and less conversion and builds up in treatment tank and stifles decomposition; and acetic acid is solid and corrosive in pure state and becomes bulky on dilution. Utilizing combination of the alcohols and acetate such as glycerin and acetate in the form of a mixture of glycerol acetates i.e. diacetin (glycerol diacetate)) as carbon source eliminates problems prior art with carbon sources. Acetate is superior to ethanol as ethanol must be converted biologically to acetaldehyde, and then to acetate before denitrifying bacteria can utilize it. This speeds up denitrification by eliminating conversion step. Diacetin is rich in acetate substituents, is non-hazardous, non-toxic and non-flammable, does not evaporate or form solids, is rich in available carbon, and do not inhibit denitrification in surplus amounts. Further, in diacetin, when acetate is consumed, bacteria also utilize remaining glycerin, leaving only water and carbon dioxide as residuals. The bacteria tolerate inadvertent excesses of diacetin much better than ethanol and methanol. The intermediate acetaldehyde and formaldehyde produced are known preservatives (antibacterials). For polyethylene glycol (PEG) ethers as carbon source, incorporation of hydrocarbon based alcohol that is more fat soluble and insoluble in water, produces increased miscibility of compound with water as PEG chain length increases. This allows introduction of hydrocarbon groups, which are very effective carbon source for denitrification. The ether derivatives of PEG are miscible in the solution denitrified, are soluble in water at the desired concentration, ethyleneoxy unit of PEG chain is biologically convertible by indigenous bacteria into acetic acid, are not toxic, do not form explosive mixtures in air, have high concentration of carbon, slightly higher than ethanol, and are compatible with broad range of materials of construction that might be used in containers or in the pumping or metering system.    DETAILED DESCRIPTION - Apparatus (100) for denitrifying a solution (215) comprises: a denitrification tank (200) configured to receive portion of solution for period of time, in which controlling an amount, duration and frequency of introduction of a carbon source (410) into solution promotes indigenous heterotrophic bacteria depleting dissolved oxygen in solution, and obtains oxygen from nitrate in the solution; where carbon source is selected from polyethers of monoglycerides and/or polyethers of diglycerides; ethoxylated monoglycerides, propoxylated monoglycerides, ethoxylated diglycerides, and/or propoxylated diglycerides; a carboxylic acid ester of a diol; a polyether; a glycoside ester; an alkylether of a polyol; a carboxylic acid ester of an ether of glycerol; a polysorbate; a mixed ether of a polyol, and/or a mixed ester of a polyol; a polyol; an ether of glycerol; a sorbitan; a polyethyleneglycol ester; or polyglycerol, and/or esters of polyglycerol.    DESCRIPTION OF DRAWING(S) - The figure shows a vertical, cross-sectional detail view of the apparatus for denitrifying a solution.    Denitrification apparatus (100)    Denitrification tank (200)    Anoxic media cell (205)    Media (210)    Nitrified solution (215)    Carbon source in container (410)