ABSTRACT

The bioremediation of petrochemical contaminated soil using indigenous Pseudomonas species was studied. The objective of this study is to monitor the degradation potentials of the consortium of indigenous Pseudomonas spp on petroleum hydrocarbons and their metabolic compounds.  This research was carried out for 28 days under designated periods tagged (T0 – T4) at 7 days intermittent sub-sampling. Twelve uniform 3cm X 3cm sterile plastic boxes, each containing100g soil and another plastic box (3cm X 3cm) with 100g soil as control were used. These boxes were in four sets of three boxes each. Three sets were treated with varying concentrations of individual indigenous Pseudomonas spp and the fourth set was treated with their consortium. Each containing plastic box was labeled P1c1, P1c2, P1c3, P2c1, P2c2, P2c3, P3c1, P3c2, P3c3, P1P2P3c1, P1P2P3c2, P1P2P3c3 and control. The indigenous microorganisms were isolated using standard microbiological procedures and molecular identification technique. Optimization of growth conditions for Pseudomonas spp were also carried out under varying conditions of pH, moisture content, temperature  and nutrient (N:P) using standard microbiological procedures. The physiochemical properties of the petrochemical contaminated soil and control soil (uncontaminated soil located eighty-five meters away from the petrochemical contaminated area at Umurolu along East-West Road, Eleme in Port Harcourt, Rivers state, Nigeria) were tested and compared for levels of the pollution using standard laboratory procedure of American Public Health Association (APHA). Mineral salt medium (MSM) was used during the bioremediation. The bacterial counts of the Pseudomonas species during the bioremediation was determined using standard microbiological procedures while remediation of total petroleum hydrocarbons (TPH) and assessment of metabolic compounds during biodegradation were carried out by gravimetric technique. The identified microorganisms were P. aeruginosa, P. putida, and P. mendocina. Optimization results showed highest microbial growth of 1.83 x 107, 1.92 x 107, 1.88 x 107(cfu/g) at temperature (30oC), 1.78 x 107, 1.82 x 107, 1.94 x 107(cfu/g) at pH 7, 1.94 x 107, 1.88 x 107, 1.79 x 107 (cfu/g) at moisture content (20%), and 2.01 x 107, 1.94 x 107,1.73 x 107 (cfu/g) at N:P ratio (10:1) by P. aeruginosa, P. putida, and P. mendocina respectively. The physiochemical properties of the soil sample were affected due to the pollution level compared to the control soil. Highest bacterial counts of P. aeruginosa, P. putida, and P. mendocina and their consortium were recorded as 2.90 x 107 (cfu/g), 2.95 x 107 (cfu/g), 2.83 x 107 (cfu/g), and 4.00 x 107 (cfu/g), respectively which increased with increase in time. The results on highest percentage remediation level and rate of remediation of the TPH showed P. putida (74.59% and 0.20 kgTPH/wk), P. aeruginosa (67.57% and 0.18 kgTPH/wk), P. mendocina (61.62% and 0.16 kgTPH/wk) and consortium (80.81% and 0.21 kgTPH/wk) which indicated a decrease in TPH level with increase in time. Assessment on the metabolic compound during the degradation showed the maximum percentage reductions with increase in time which include: saturated hydrocarbons (62%, 75%, 68%, and 81%),  phenolic compounds (86.25%, 87.50%, 91%) and 92%), asphaltenes and polar compounds (94.06%, 95.05%, 96.53%, and 97.03%), and aromatic compounds (88.89%, 94.44%, 94.42%, and 97.22%) by P. mendocina, P. putida, P. aeruginosa, and the consortium respectively. This study shows that the petroleum hydrocarbon and their metabolic compounds were largely degraded by the consortium of indigenous Pseudomonas spp and therefore recommended for future bioremediation studies.