**4.7 Gas chromatography-flame ionization detector (GC-FID) analysis**

The gas chromatography-flame ionization detector (GC-FID) was conducted to measure the degradation rate of the bacteria strains. The bacteria strains were grown back using enrichment culture method in different tubes and each tube was harvested on day 0, day 3, day 6, day 9 and day 12. Next, 1 ml of ethyl acetate was added to 1 ml of each sample and the mixture is vortex for around 10 seconds until a double layer could be observed from the mixture. Then the upper layer was pipetted into a vial tube [35]. The samples were then analyzed using gas chromatography-flame ionization detector machine and the data was collected. The degradation percentage were calculated using the formula given below. The percentage of residual substrate are calculated first using the Eq. 1. Once the percentage is obtained, the degradation percentage are calculated using the formula in Eq. 2.

Percentage of residual substrate : ðaverage peak area average controlÞ � 100 ¼ % (1)

Degradation percentage : 100 � Percentage of residual substrate ¼ X% (2)
