Chemical conversions of petroleum hydrocarbons during biochemical purification in aerator tanks

Summary

• 1. When water containing naphthenic, aromatic, and paraffin hydrocarbons is purified biologically in an aerator tank, 33% of the total amount of organic substances to be purified remains in the purified water and 33% is removed from the tank by air.

  The remaining organic matter (34%) goes to increase the active sludge and is completely oxidized to form CO₂ and H₂O.

• 2. Considerable changes occurred in the composition of the organic matter present in the purified water and in the air (66%): a) the amount of methanol-soluble substances, the oxidation products of hydrocarbons, was nearly doubled; b) there was a marked reduction (by a factor of 7.5) in the content of neutral compounds and their relative amount decreased from 83.4% to 55%; c) owing to the decrease in the content of neutral compounds, that of the strong organic acids, phenolic compounds, and substances more soluble in water than in ether increased; d) a quarter of the neutral compounds was oxidized to form neutral oxygen-containing compounds such as aledhydes, ketones, etc.

  Only 10% of the initial petroleum hydrocarbons remained in the purified water.

• 3. Study of the composition of the substances more soluble in water than in ether (group 4) showed that they consisted largely of acids (about 70% were back-titrated with alkali, the pH of an aqueous solution was 3).

• 4. The strong organic acids (group 7) consist of low-molecular acids of the paraffin series with mean molecular weight 76.

• 5. The organic compounds of active sludge consist mainly of neutral compounds (95%) and only 5% are methanol-soluble substances (group 1).

• 6. The extraction of the organic compounds of petroleum -containing water with ether was not accompanied by extraction of substances soluble in chloroform (group 2) or of substances soluble in methanol (group 1). During this process the losses amount to 50% or more.