abatement procedure applied microbiology 17 297 302 srb mediated sulfate reduction is expressed by the simplified equation 2ch 3 choh coo u2212 3s0 4 2 u2212 2h 6hco 3 u2212 3h 2 s in the presence of h 2 s divalent metals are precipitated as their sulfides production of carbonate gradually raises the ph to preferred levels even though protons are generated in the precipitation reactions in addition to an electron donor such as a fatty acid trace amounts of phosphate and nitrogen are required the sulfate reducers may be considered as indirect reducers because they produce h2s which in turn precipitates a metal or actinide abiotically as the sulfide a second group of bacteria are indirectly acting because by raising ph or increasing the co2 concentration they cause precipitation through changing the solubility of the metal in the less favorable conditions e g precipitate as the hydroxide or carbonate al which is toxic to many bacterial species is removed in this way as are chromates we have found that a stable nutrient electron donor source is a vegetable oil floated upon the layer of contaminated water unlike needles and leaves no solids are introduced which can plug the outlet from the treatment zone unlike emulsified oils and water soluble nutrients the floated oil does not flow out of the zone with the treated water the nutrient oils useful in this invention are not particularly limited any natural organic compound with negligible water solubility.