Statistical investigation of the effects of control factors on the removal of lead from contaminated agricultural soil using Proteus Mirabilis

Abstract

This study focused on statistical investigation of the effects of factors: volume of nutrient, mass of organism, temperature, pH and stirring frequency in their singular and combined states on lead removal from soil by Proteus mirabilis. Design Expert version 7.0, was engaged on the selected controlling factors in a two levels, 2ⁿ factorial design of a total of 32 experiments with the independent variables (factors) coded as -1 (low) and +1 (high). The designed factors combination were conditioned in thirty two 50ml capacity beakers containing 3g each of soil samples inoculated with 24 hours old organism for a period of 35 days. At the end of this period, the organism was centrifuged from the soil, and the lead content determined by using Atomic Absorption Spectrophotometer (GBC SensAA, Model no. A6358). From the analysis of the experimental results using Design Expert version 7.0., ANOVA showed all tested factors to have probability values (P < 0.05); less than 0.0001 each in this case. All of these tested factors had great significant effects on Pb removal by the organism in the uncombined states of the factors. The factors ranking and the respective percentage contributions as reflected by Pareto chart and the effects list were in the order of nutrient volume, mass of organism, stirring frequency, pH and temperature; and 20.20%, 20.07%, 19.89%, 19.44% and 19.42% respectively. Designed runs with respective percentage removals of 40.47%, 40.56%, 40.45%, 40.65%, 40.34% and 35.78% were regarded not fit for practice due to the organism’s failure to reduce lead ions to below the maximum allowable concentration at these designs.