Photocatalytic degradation of liquid waste containing EDTA

Ethylenediaminetetracetic acid (EDTA) is widely used as a decontaminating agent in nuclear industry. The presence of complexant interferes in treatment of radioactive effluent. It is therefore essential to degrade EDTA prior to chemical treatment for effective management of radioactive waste. Photocatalytic treatment of EDTA can be used as a pretreatment step. The photocatalytic degradation of EDTA has been investigated in liquid waste using Degussa P-25 titanium dioxide (TiO2) as the semiconductor photocatalyst in presence of UV light. A cylindrical photoreactor has been used for the present purpose. The process of degradation of EDTA was monitored by titrimetric method using magnesium sulphate as the titrant and Erichrome black-T as indicator. The effects of various parameters such as pH, quantity of the catalyst loading, effect of H2O2 were studied. The presence of amides was detected in the degraded waste. The radioactive liquid waste containing degraded EDTA was then subjected a chemical treatment (precipitation) step, which is generally used as a waste treatment step. Results have shown that the degradation products of EDTA does not interfere in the chemical precipitation step and gives a good decontamination factor for the treatment process compared to the radioactive liquid waste where EDTA degradation has not been carried out.

The result of this investigation clearly reveals that EDTA can be effectively degraded by photocatalytic route using TiO2 in a radioactive effluent containing it. TiO2-assisted photocatalytic degradation offers green chemistry and is highly cost-effective due to the requirement of a very small quantity of the catalyst. It has been found that 1 mg of the catalyst is sufficient for the photodegradation of 1000 ml of 1000 ppm EDTA present in radioactive liquid waste indicating that it is quite economical and safer route for degradation. It was also observed that the usage of a smaller quantity of the catalyst (0.5 mg) does not change the kinetics of the degradation significantly. The results show that the degradation products of EDTA do not interfere in the chemical treatment (precipitation) process and give good decontamination factor for the chemical step. Hence the photocatalytic method can be effectively used for the degradation of EDTA present in liquid waste.