S.E. Ibekwe^1,, G.C. Okpokwasili¹

The presence of polycyclic aromatic hydrocarbons (PAH) from crude oil and gas condensate, ferrochrome lignosulphate and lead compounds in drill cuttings and drilling mud additives are of environmental concern during exploration and development drilling operations. These environmental toxicants encountered during drilling operations were reason for carrying out this study. This research was tailored toward adopting scientific and technological method that is efficient and cost effective in reducing these chemical toxicants in the environment below the acceptable limit in order to have sustainable environment and achieve millennium goal on environment. This target was achieved by stimulating the hydrocarbon utilizing bacteria associated with drill cuttings for degradation of PAH and TPH. The physiochemical parameters supporting the proliferation of the hydrocarbon utilizing bacteria were determined. Microbial populations, total petroleum hydrocarbon (TPH) and PAH were monitored at intervals throughout the period of the study. Drill cutting (Dc) from oil well in Usan field was sampled for treatment using bioremediation technology. The five treatment options designated Dc, Dc +S, Dc+F, Dc+S+F+D and Dc + D were set in triplicates in different cells using plastic bowls. A total of 15 plastics bowls of 35cm in diameter by 11cm depth were used. The setup was sampled repeatedly at intervals for analysis within the study period. Four treatment options were biostimulated with soil(S), NPK fertilizer (F), or gold crew dispersant (D) while unamended (Dc) and heat-treated (hDc) options served as controls. For each treatment option, 2kg (wet weight) of drill cutting was amended with 40g of treatment material. The bioremediation process was investigated in a 56-day study period. Unamended treatment (Dc) had the highest heterotrophic bacterial count (4.5 x 10⁵cfu/g) on day 0 while Dc+D had the lowest count (3.0 x 10³ cfu/g) on day 56. The hydrocarbon utilizing bacterial count showed that Dc +D had both the highest (6.5x 10³ cfu/g) on day 28 and also the lowest count (2.6 x 10²cfu/g ) on day 56. For all the treatment options on day 0 the total petroleum hydrocarbon (TPH) ranged from 33.22 to 46.00 mg/kg while polycyclic aromatic hydrocarbons (PAH) ranged from 3.51 to 6.4mg/kg. In all the treatment option by day 56, the TPH was <8.0mg/kg and PAH <2.5mg/kg. By day 56, the percentages of biodegradation of TPH as measured with GC-FID were Dc(71.82%), Dc+S(77.09%),Dc+F(83.58%), Dc+S+F+D(79.95%), Dc+D(81.58%) and heat-treated (30.56%). PAH percentage degradation rates were as follows: Dc (49.92%), Dc+S (52.35%), Dc+F (86.09%), Dc+S+F+D (64.74%), Dc+D (74.20%) and heat-treated (2.23%). Dc+F gave the highest percentage degradation for both TPH and PAH. Fifty-two hydrocarbon utilizing bacterial isolates were obtained. The bacterial isolates were Bacillus spp.(26.92%),Proteus Sp.(1.92%), Pseudomonas spp.(7.46%), Alcaligenes spp.(5.77%), Micrococcus spp(7.55%), Acinetobacter sp(1.92%), Aeromonas spp (21.15%) and unidentified (28.85%). Screen test, for degradative potential of the isolates indicated that many of the bacterial isolates had hydrocarbon degradative potential. This result showed that the drill cuttings investigated could be remediated using microbial agents and that environmental factor (abiotic factors) had a role to play in hydrocarbon alternation as shown in the heat –treated control.

drill cuttings, bioremediation, TPH, PAH