Microbiological oxidation of a coal tar fraction

Abstract

A process for the production of edible protein by the microbiological oxidation of petroleum hydrocarbons has recently been developed to pilot-plant scale. By fermentation with yeasts, n-alkanes are selectively oxidized in the presence of other types of saturated hydrocarbons in lubricating-oil fractions, and are converted almost quantitatively to high-protein cellular material.1The use of other forms of fossil organic matter as sources of carbon for the production of protein, amino acids, and other supplementary edible materials is of interest, and it has been found in this laboratory that certain types of coal derivatives and humic materials will support the growth of microorganisms. The microbiological treatment of some by-products of coal processing has lately been investigated2 and it has been shown that Cll-C15 paraffins and olefins present in low-temperature coal tar fractions will support the growth of the yeast Candida, giving cell yields similar to those obtained from petroleum fractions boiling in the same range. Also, the biochemical degradation of hydrocarbons and other compounds present in oils, tars, effluents, and industrial wastes is a research topic of growing importance because of the increasing pollution of rivers, lakes, and beaches and the vital necessity, in many industrial areas, of more efficient conservation and purification of water supplies.I n a preliminary investigation of the microbiological oxidation of materials of this type, a continuous-vertical-retort coal tar was extracted with aqueous acid and alkali to remove bases and phenols. A fraction of the neutral tar (20.2 g, b.p. 220-250°/20 mm) was stirred in a nutrient salt medium (1500 ml) containing ammonium sulphate (0.1 %), magnesium sulphate (0.02%), dipotassium phosphate (0.2%), sodium dihydrogen phosphate (0.3%), sodium carbonate (0.01%), calcium chloride (0.001%), and ammonium nitrate (0.1%) a t 25-35". The mixture was inoculated with enriched cultures of paraffin-consuming and 2-methylnaphthaleneconsuming soil microorganisms, consisting mainly of rod-shaped bacteria.Aliquot samples were removed at intervals during a total incubation period of 40 days. Unconverted neutral material was removed from each fraction by extracting with ether a t pH 8 -0 and the cell material was collected by centrifuging and washed with ether. Acidic and phenolic oxidation products were recovered by adjusting the pH to 3.0 and re-extracting with ether. The aqueous liquors were evaporated to dryness in a rotary evaporator under vacuum at 100'. The solid residue was extracted with acetone to recover other water-soluble products.