Isolation And Characterization Of Degrading Bacteria From Waste Drilling Slurry

In this study, waste drilling slurry sample collected from different drilling places in Sichuan Province was used to isolate waste drilling slurry degrading bacteria by pour plate method, and 15 bacterial strains were obtained, their biological properties, phylogeny, and ability to degrading drilling slurry was performed. The results were as following.Fifteen strains were inoculated to 400 mL of waste drilling slurry at 5% concentration, and incubated at 28℃by aeration process for 48h, and the supernatant OD and CODcr was determined. Based on the supernatant color density and CODcr removal rate, six good strains, i.e. C-2-3, C-3-1, C-5-2, C-7-2, C-7-4 and C-8-2 were screened.Strain C-5-2 was used as representative, its ability of using waste drilling slurry as sole carbon source was determined, and 2.5g/L,5 g/L,10 g/L,15 g/L,30 g/L and 50 g/L of waste drilling slurry was added to the medium instead of original carbon source, then C-5-2 was inoculated, respectively. After 3 day's incubation at 28℃, the quantity of C-5-2 in these mixtures was checked, the results revealed that, when adding 50g/L waste drilling slurry to the medium, the number of C-2-3 in the mixture reached to 73.76 x 108 cfu/mL; Apparently, strain C-5-2 could use the macromolecular organic matter in the waste drilling slurry as sole carbon source.Furthermore, the CODcr degrading ability of these strains was determined, the results suggested that, all the strains had good effect on degrading the CODcr of drilling slurry, and the CODcr of supernatant decreased from 89864.6 mg/L to 20000 mg/L after treating for 48 h, and the CODcr removal rate was 85%-90%. Especially, when inoculating strain C-7-2 and treated for 48h, the CODcr removal rate was the highest among these strains, and reached to 95.2%.The capacity to degrade the color density of waste drilling slurry at natural pH and neutral pH condition was determined. The results showed that strains C-2-3, C-7-2 and C-7-4 had higher color removal rate at natural pH than that adjusting pH to neutral; on the contrary, strains C-3-1, C-5-2 and C-8-2 had higher ability to degrade color density at neutral pH condition. Numerical taxonomy of these strains was done, and the result showed that these fifteen strains were divided into 6 phenotypes at the level of 80% similarity. Then, five representative strains were chosen to do 16S rDNA sequence analysis, and the phylogenic tree was constructed, and strains C-2-3, C-7-2 and C-8-2 had high homology each other, and they were located in the same branch as H. ventosae Al12T; C-2-3 was 98.3% homology with H. ventosae Al12T, and C-3-1 was 95.4% homology with H. campaniensis 5AGT, perhaps these two strains represented two putative new species of genus halomonas.