FATE OF COMMERCIAL DISPERSE DYES IN SEDIMENTS

Kinetics of disappearance of seven different disperse dyes were determined in compacted sediments at room temperature. The commercial dyes (in dispersed solid form) were representative of nitroazo, anthraquinone, and quinoline structures that are widely used. Reaction rates were found to be first order over at least two half-lives and were different for the three groups of dyes. Half-lives were on the order of hours, days, and months for the nitroazobenzene, aminoanthraquinone, and quinoline dyes, respectively. Stability of the latter is consistent with detection of a quinoline dye in treatment plant sludge and in sediment from a water body receiving treated effluent. The azobenzene dyes are degraded by cleavage of the azo group to give anilines and ring-substituted phenylenediamines from the diazo component of the molecule. Products from the other portion (coupling component) of the molecule are unidentified, as yet, but are expected to be N,N-disubstituted phenylenediamines. Products of the anthraquinone dyes were unidentified, except for the case of a nitrated dye on which the nitro group was reduced.