Effects of Gamma Irradiated and Non-Irradiated Sewage Sludge on Essential Oil Content and Constituents of Ocimum basilicum L.

The increasing amount of sewage sludge (SS) and more legislative regulation of its disposal have stimulated the need for developing new technologies including gamma irradiation to recycle SS efficiently.

To evaluate the effects of gamma irradiated and non-irradiated SS (SSGI and SSNI, respectively) on essential oil (EO) content and composition of Ocimum basilicum L.

A greenhouse experiment was conducted with 15, 30, and 60 g kg-1 of SS irradiated with absorbed doses of 5, 10, and 20 kGy gamma-ray and soil without SS and irradiation as the control treatment. The essential oil was isolated by hydro-distillation and analyzed by Gas chromatography and Gas chromatography-mass spectrometry techniques.

The applications of SSGI and SSNI at all levels except 15 g kg-1 significantly enhanced EO content compared to the control. The using of 60 g kg-1 SS in each absorbed dose significantly reduced EO yield relative to the control, while it was significantly increased under 15 and 30 g kg-1 SSNI and SSGI. Also, in 60 g SS kg-1, the restriction effects on EO yield were mitigated with increasing the absorbed dose of gamma-ray, but it was insignificant with increasing absorbed dose to 10 and 20 relative to 5 kGy. The methyl chavicol as a major constituent of EO was significantly increased in SSGI and SSNI as compared with the control. However, the increment in the methyl chavicol content was not significant between the treatments ≥ 30 g kg-1 SSGI or SSNI and 15 g kg-1 SS at absorbed dose of ≥10 kGy.

To improve essential oil content and composition, application of ≤ 30 g kg-1 sewage sludge with 5 kGy absorbed dose of gamma-ray can be suggested at similar conditions.