Kinetic Modelling of Insitu Treatment of Petroleum Hydrocarbon Contaminated Soil Using Bone Char and NPK Fertilizers

8 This study investigates the effectiveness of bone char (organic) and NPK (inorganic) fertilizers 9 as stimulants in the degradability of petroleum hydrocarbon contaminants on soil. The 10 Physicochemical properties of the hydrocarbon sludge were used to assess the effectiveness of 11 this process over an 8-week period using 0.5 – 3.5kg mass of each fertilizer at different 12 experiments. A first order kinetic model was used to estimate the rate of degradation of the total 13 hydrocarbon content (THC) and total organic carbon (TOC) contaminants and the half-life of the 14 remediation process. The microbial population within the period was also determined. The P15 Value (P<0.05) indicate that these fertilizers were effective in degrading these contaminants on 16 the soil, because of the significant difference between the treated and the control soil samples. A 17 direct relationship was observed between with the mass and performance of the fertilizers. With 18 3.5 kg mass of the fertilizers, rate constants of 0.018 day and 0.019 day were obtained for the 19 removal of the THC and TOC contaminants, respectively using the bone char fertilizer, whereas 20 NPK fertilizer gave rates of 0.03 day and 0.023 day respectively. The performance of the NPK 21 fertilizer is attributable to its Nitrogen and Phosphorous content. The model adequately described 22 the process and showed the effectiveness of both fertilizers in the remediation process. 23


Introduction
Crude oil exploration and exploitation has given rise to the problem of environmental pollution 27 in many parts of the world. The large scale production and oil exploration activities in the Niger 28 Delta region of Nigeria, renowned for its huge deposit of crude oil and natural gas reserve, has 29 given rise to oil spillage which has impacted negatively on the environment leading to air, water, 30 and land pollution. The effects on terrestrial and aquatic lives are equally huge and devastating, 31 and these consequences include surface layer poisoning, distortion of macro and micro ecology, 32 as well as other environmental degradation and health impacts. The land desolation, soil and 33 water body degradation associated with these spills leads to reduced agricultural production [1]. 34 To this end, the need for remediation of these soils has become vital. Bioremediation has been 35 shown to be an efficient and viable approach in the management of oil spilled soils. This 36 technique involves the use of microorganisms such as bacteria, yeast, and fungi to degrade toxic 37 and nontoxic substances. Hence, it involves the breakdown of these substances using living 38 organisms [2,3]. Various techniques of this approach exist and these include: bio-stimulation, 39 bioaugmentation, bioventing, land farming, phytoremediation, intrinsic bioremediation and  Soil Preparation and in-situ bioremediation procedure 79 The land portion, with no known history of crude oil contamination, was segmented into 7 cells 80 of similar dimension demarcated from each other with a 10 cm wooden structure. Each cell, 81 having a dimension of 1.5metres x 1.5metres and a depth of 30cm (contaminated soil depth), was 82 polluted with 20 litres of the crude oil sample to form a sludge which was allowed to stand for 2 83 weeks under continuous monitoring. At the end of this period, the vegetations on the study site 84 were observed to have died. Thereafter, different concentrations of the bone char and NPK 85 fertilizers were administered on these cells (Table 1), and the soil tilled to expose its surface area 86  into a 9ml test tube containing the diluents and serially diluted stepwise to obtain a 10 -3 dilution.

162
A spatula was used to transfer 0.1ml aliquot of the solution into the sterilized nutrient agar plates 163 in such a way that most of the surface area was exposed for reaction. The inoculated plates were 164 incubated at a temperature of 37 o C for 24 hours, before the nutrient agar plates were examined 165 for bacterial growth. The total viable heterotrophic bacteria were evaluated based on the number 166 of the Colony Forming Units (CFU) using the colony counting technique to determine the 167 number of cells capable of splitting [19]. The CFU was evaluated using the correlation:

168
CFU/g = number of colonies x dilution factor / volume of culture plate 169 a. Identification and Isolation of soil bacteria: The bacteria culture was isolated by aseptically 170 streaking colonies of different culture seen on the plate to a freshly prepared nutrient agar plate.

171
The setup was incubated at 28 o C and allowed to stand for 24 hours to allow the bacteria grow.
isolates were selected. Isolate purification was done using dilute nutrient broth and agar media 174 and stocked at -80 o C. Characterization of these isolates was done using gram stain (methyl and 175 violet test) to confirm the bacterial growth while the viable count was conducted manually. The With an assumption of a first order kinetic, the rate equation of the process for reactant of 185 measured concentration (C) is given by: The half-life is given by:  The particle size analysis of the soil texture within the depth of interest (30cm) prior to treatment 237 showed it to comprise of the following: Soil -75%, clay -15% and silt -10%. The soil texture, 238 which is a classification of the soil based on its physical characteristics, was used to assess the 239 soil sample to ascertain the air and water retention capability, rate of water movement in and out The physicochemical and microbial properties of the soil samples (  The physicochemical properties and microbial properties of the sandy loam soil were adversely The physiochemical properties of the bone char and NPK fertilizers (Table 3)       The R 2 , t-stat and P-values were used to study the effectiveness of the bioremediation treatment The first order kinetic model, which proposes that rate of degradation of substrate is directly 356 proportional to its concentration, was used to model the degradation level of total hydrocarbon 357 carbon (THC) and total organic carbon (TOC) content in the contaminated soil. High K value 358 implies high degradation rate (Table 5), while the fractional efficiency was plotted against time 359 for all samples (Figures 9 -14).    First Order Kinetic Pattern of THC reduction for the Control Sample Pictorial views of experimental site at various stages of treatment