Removal of Aromatic Nitro Compounds from Water by Ozonation

Experimental studies were carried out on the removal of five species of aromatic nitro hydrocarbons by ozonation. Ultraviolet spectrograms with distinct absorption peaks were plotted for each of them. It has been found that the absorbances of aqueous solutions containing the single compounds mentioned above increase to different extents at the wave lengths ranging from 200 to 230 nanometers with increase of ozone dosages. This is ascribed to the nitrite ions splitting out of the benzene rings and being further oxidized to nitrate ions by ozonation.

It has been indicated that the removal of the five species of aromatic nitro compounds by ozonation can well be expressed mathematically by first order reaction equations. Besides, the reaction constants and half-life periods for various species of the tested nitro compounds were calculated at different temperatures and pH.

An ozonation effect index (OI) was developed in the study to express the degree of degradation of substrates by ozonation, by means of which the five aromatic nitro hydrocarbons were compared with each other and finally ranked in the following order from greatest to smallest degrees of degradation:

p-nitroaniline > nitrobenzene > p-dinitrobenzene > p-nitrotoluene > m-dinitrobenzene

It has also found that the CODm/M ratio increases with ozone doses. This means that some easily degradable intermediates are produced, and increase in concentration with increase of ozone dose in the ozonation process.

The mechanisms of removing the five aromatic nitro hydrocarbons are discussed from the viewpoint of orienting effects of substituent groups on the aromatic rings.