Impact of slow release fertilizers on enhancing biodegradation in oil contaminated tropical sandy beach

Selection of effective slow release and low-cost fertilizers for bioremediation purpose was carried out by testing four different fertilizers and control. A slow-release fertilizer imports (Osm, a product of USA) and three others were produced locally in Indonesia (Gr, TMM and MLT). The three of locally produced fertilizers were never tested before for this purpose. Microcosm approach was performed in triplicates for 28 days with 6 different sampling times, using 50 mL Falcon tube as a reactor. The reactor contains a mixture of 10 g contaminated sediment (100 mg crude oil g^-1 sediment), 15 mL sea water and fertilizer, but no fertilizer in control. All fertilizers were applied as a stimulant in the same concentration which was 1500 µg N g^-1 sediment. Parameters measured were oil concentration, bacterial density and environmental condition. The result showed that addition of slow release fertilizer has increased oil reduction rate. The enhancement of oil depletion in treated reactors have significantly different (p <0.05) compared with control. Oil depletion naturally (in control) occurred for 31.21% during 28 days. Whereas, the oil depletion in treatment was increased variedly between 40 – 62.4% which was in the average rate of 13.4 to 20.6 mg days^-1 or 1.3 - 2 times higher than the control. The order of treatment affectivity was Gr, MLT, TMM and Osm. These results suggested that slow-release fertilizers that locally manufactured were better than imported slow-release fertilizer for oil degradation purpose.