The reaction of ozone with sodium sulphide and its application to the treatment of tannery waste waters.
Leather production results in large volumes of waste water containing high levels of
sodium sulphide, which has to be treated before disposal. The use of ozone to facilitate
this oxidation was considered by first studying ozone-sodium sulphide reaction. The
sodium sulphide solutions were found to be adequate models for the tannery effluent.
The reaction order was found to be second order overall (first order in both sulphide
and ozone). The true reaction order was found to be 0.33 for sulphide in the initial
stages of the reaction. The use of ozone in conjunction with either UV radiation or a
manganese catalyst was found to have no benefit to the rate of sulphide oxidation. The
reaction products were thiosulphate, sulphite and sulphate. A mathematical model based
on a first order consecutive reaction scheme was developed.
The liquid phase mass transfer coefficient for physical absotption of ozone into water
was estimated to be k'La=4.76 x 10-3 S-I, while the overall transfer coefficient during the
ozone-sulphide reaction was estimated to be Kt.a=().0719 S-I. This gave an enhancement
factor of 15.1 which indicates that ozone decomposition reactions may be negligable.
It was estimated that a full scale ozone system would require the application of 120 kg
of ozone per hour for 12 hours to treat 200 Itt waste water. An economic comparison
of this proposed system indicates that operating costs for ozone would be approximately
6 times greater per m3 waste water than the costs for the current aeration treatment