Abstract
The objective of this study was designed to evaluate the effects of nutrients (inorganic NPK fertilizer and organic fertilizer) and adsorptive amendment agents (activated carbon) as well as their interactions on bioremediation of soil contaminated with Weathered Crude Oil (WECO). The organic fertilizer was made up of cattle dungs, pig dungs and poultry droppings mixtures. Box Behnken Design (BBD) of Response Surface Methodology (RSM) with three levels and three factors was used having inorganic NPK fertilizer (3 - 5 g), activated carbon (20 - 40g) and organic fertilizer (30 - 50 g) as independent variables and percentage WECO degradation as dependent variable (response) in a four weeks remediation period. Results of the study showed that WECO removal rate in soil is invariably dependent on the amount of nutrient and adsorptive agents. The optimum amount of nutrient and adsorptive amendment agents obtained to achieve a predicted maximum WECO removal of 66.24% are: inorganic NPK fertilizer, 4.19 g; activated carbon, 35.42 g and organic fertilizer, 48.94 g. At this predicted optimum amount, validation experiment revealed that 65.55% of WECO removal was achieved. Statistical analyses revealed the closeness of the experimental results to model predictions which thus show the reliability of the quadratic regression model. Therefore, organic and inorganic nutrients as well as adsorptive amendment alone and/or in combination enhances soil indigenous microbial density and activity which thereby accentuates petroleum hydrocarbons biodegradation and subsequently reduces the period of bioremediation and remediation cost. Keywords: Activated carbon; Box-Behnken design; Crude oil; Nutrients; Regression model
Highlights
The soil characterization revealed that the nutrient (NPK) requirements for an efficient biodegradation process are not fulfilled in the soil
These elements were added in the form of inorganic and organic fertilizer to provide the proper nutrients required for the bioremediation process
Effect of different amount of organic fertilizer on total petroleum hydrocarbon (TPH) biodegradation were investigated at the same condition of inorganic NPK fertilizer and activated carbon and the results showed that addition of organic fertilizer can enhance the bioremediation process of soil contaminated with crude oil
Summary
Sample Collection: Escravos crude oil was obtained from an oil producing company located in Warri, Nigeria. Commercial activated carbon was obtained from a chemical store in Benin, Nigeria. The physical, chemical and microbial parameters that were characterized for are: total organic carbon, total nitrogen, total phosphorus, pH, moisture content and total hydrocarbon utilizing bacteria (THUB).The method of characterization for each parameter has been presented in the previous study of Agarry (2017). The crude oil-contaminated soil in each plastic bucket was amended with different amounts of inorganic NPK fertilizer (2 - 5 g), activated carbon (10 – 40 g) and organic fertilizer (20 - 50 g), respectively. Experimental Design for Soil Bioremediation: BoxBehnken factorial experimental design was employed in this study and it had three independent variables viz., inorganic NPK (20:10:10) fertilizer, activated carbon and organic fertilizer.
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