Modeling of Bacterial Remediation of Crude Oil-contaminated Soil

Abstract

Mathematical modeling is a method of simulating real-life situations with mathematical equations to forecast their future behaviour. The modeling of the microbiological parameters was done using SPSS 23 for descriptive statistics while E-view 10 software was used for pooled regression model. Crude oil-contaminated soil from Bodo in Ogoniland was sampled for treatment using bioremediation technology and seven treatment options designated as A to G were setup in triplicates in cells. Five were biostimulated with NH4NO3 and KH2PO4 while unamended and heat-treated served as control. The bioremediation lasted for 56 days with 50 % contaminated media amended with 1 % treatment material. The setup was sampled repeatedly at intervals for analysis within the study period. ES had highest THB count on day 28 while FS had the lowest counts on day 56. For hydrocarbon utilizing bacteria (HUB), CS had the highest count on day 42 while FS had the lowest HUB counts on day 56. For all the treatments options on day 0, the total petroleum hydrocarbon (TPH) ranged from 846.25 to 4406 mg/kg while polycyclic aromatic hydrocarbon (PAH) ranged from 2.02 to 202.70 mg/kg. In all the treatments by day 56, the TPH was < 405 mg/kg while PAH was < 6.5 mg/kg. By day 56, the percentage loss of TPH of treatment options as measured with GC-FID were AS (63 %), BS (72 %), CS (76 %), DS (95 %), ES (98 %), FS (59 %) and heat treated GS (47 % ). ES had the highest TPH (4403.91 mg/kg) on day 0 while CS recorded the lowest TPH (93.01 mg/kg) on day 56. By day 56, the percentage loss of PAH of treatments as measured with GC-FID were AS (98 %), BS (97 %), CS (93 %), DS (94 %), ES (96 %), FS (31 %) and heat treated GS (31 %). However, ES had the highest percentage loss (98 %) of TPH followed by DS (95 %) and lastly GS (47 %). FS had the highest PAH (201.67 mg/kg) on day 0 while AS had the lowest PAH (0.04 mg/kg) on day 56. The AS had the highest percentage loss of PAH (98 %) followed by BS (97 %) and lastly FS and GS (31 %). A total of 121 hydrocarbon utilizing bacteria were obtained which include Micrococcus sp 35 (28.93 %), Acinetobacter sp (9.92 %), Pseudomonas sp (28.93 %), Bacillus sp (14.05%), Alcaligenes sp (4.96 %), Proteus sp (1.65 %) and unidentified isolates (11.57 %). Regression model of bacteria showed the effect of time, nitrogen and phosphorous on microbiological and effect of HUB and THB on physicochemical parameters. Time and nitrogen had positive effect on HUB and THB while phosphorous had negative effect. A unit increase in time and nitrogen increased HUB by 0.0545 and 19.8826 while an increase in total phosphorus decreased HUB by 51.83. Time, HUB and THB affected TPH negatively. A unit increase in time, HUB and THB decreased TPH by 30.84, 74.75 and 145.1 unit respectively. These changes and effects by these mathematical models were statistically significant at P¨Cvalue <0.05 and t-values. F-values implied overall models were statistically significant. These models have established that adjusting of limiting nutrients (nitrogen, phosphorous) is key to effective and efficient bioremediation of crude oil-contaminated media.