STABILISATION OF NIGER DELTA FAT CLAY WITH BLEND OF BINDERS FOR SUBGRADE APPLICATION - PART 1

Construction of roads on fine-grained soils without any form of stabilisation is a major problem all over the world. In this study, a fat clay having poor subgrade rating (A-7-6) was mixed with blends of sand, drill cuttings ash (DCA), lateralite, and Portland Cement (PC) to improve its plasticity, California Bearing Ratio (CBR), and swell. The sand effected better particle grading of the clay and addition of PC increased its strength. Blends of DCA-PC and lateralite-PC effected friability, improved workability, and also increased the strength of the soil. Blends ratio: sand-PC (4:1); DCA-PC (1:1); and lateralite-PC (2:1) gave the best stabilising effect on the fat clay. The improvements noted were: plasticity index < 30, soaked CBRvalues > 20% after 24 hours and >10% after 96 hours, low swell (0.002 – 0.008%). Thus, this study revealed that the fat clay could be optimised for subgrade application using these stabilising additives. http://dx.doi.org/10.4314/njt.v36i3.1

Bioremediation of a Petroleum-Hydrocarbon Polluted Agricultural Soil at Various Levels of Soil Tillage in Portharcourt, Nigeria

A combination of field cells involving a control and five treatment cells were evaluated under field conditions in the bioremediation of a petroleum- hydrocarbon polluted agricultural soil over a six-week period. Previous works have indicated that crude oil contamination of soils depletes oxygen reserves in the soils and slows down its diffusion rate to the deeper layers. Hence, this hypothesis was tested in the study by the treatments employed. The treatment option used was the application of mineral fertilizer, and different rates of oxygen exposure through various levels of soil tillage. In the experiments described in this paper, conditions of a major spill were simulated by sprinkling crude oil on the cells using perforated cans. The treatment applications were then resorted to and relevant soil physicochemical characteristics monitored at intervals. The results of the study showed an enormous increase in total heterotrophic bacterial (THB) counts in all the treatment cells. The percentage reduction in total hydrocarbon content (88% to 99%) experienced in the cells that received treatment were significantly different from the control. These results highlight the view that the availability of large amounts of oxygen in the soil profile induces an accelerated biodegradation of petroleum hydrocarbons in a polluted agricultural soil and implies that regular tillage of contaminated soils in the presence of nutrients could achieve the decontamination of such soils

Comparative Analysis of Some Techniques in the Biological Reclamation of Crude Oil Polluted Agricultural Soils in Nigeria

Replicate field cells involving some techniques aimed at enhancing the bioremediation of crude oil polluted agricultural soils were used in a comparative study to determine the factors and environmental conditions that could optimize the bioremediation process on crude oil polluted soils in Nigeria. The treatment techniques involved the application of different levels of: nutrient, water, oxygen exposure, and the combined effect of different levels of oxygen, water and nutrient. These formed four options, A, B, C and D. Options E and F were Phytoremediation (using corn and elephant grass) and Biopile treatments respectively. The experiments involved the simulation of conditions of a major spill by pouring crude oil on the cells from perforated cans and the in-situ bioremediation of the polluted soils using the techniques that consisted in the manipulation of different variables within the soil environment. The analysis of soil characteristics after a six-week remediation period indicated that the total heterotrophic bacterial counts increased in all treatment options while the organic carbon and total hydrocarbon content (THC) of the soils decreased with time across the various options. Option C (involving different levels of oxygen exposure) produced the highest hydrocarbon loss of 94% while Option E (phytoremediation using corn and grass) recorded the lowest level of hydrocarbon loss (51%). The THC losses recorded in the other options, which involved different levels of: nutrient application, water application; the combined effect of varying oxygen, water and nutrients and the use of biopiles ranged from 67% to 91%. Option A (the application of different levels of nutrients) had a hydrocarbon loss of 78%, Option B (involving different levels of water application) recorded a 67% hydrocarbon loss, the combined effect of different levels of oxygen, water and nutrients (Option D) recorded a hydrocarbon loss of 91% while the use of biopiles (Option E) had a hydrocarbon loss of 51%. These results were quite different from the control site which had an increased THC level (14 316 - 14 580 mg kg-1) during the study period. The results of the study revealed that different levels of oxygen exposure, water and nutrient application induced different biodegradation rates with the implication that an accelerated bioremediation with the best biodegradation rates could be achieved when polluted soils are remedied with techniques that maintain optimum levels of these factors

Rainfall Runoff Model for Calabar Metropolis Using Multiple Regression

Mathematical analyses were used to develop model that predicts the influence of some hydraulic and hydrologic parameters on the perennial flooding of some parts of the Calabar Metropolis. The parameters were obtained from ten sampling locations all within Calabar metropolis. An empirical model was developed to predict discharge based on the independent variables of cross sectional area of drains, degree imperviousness, gradient, sum of channel length, and basin area. The model developed gave a good multiple regression coefficient of 0.982with a standard error of 0.709at a significance level of 0.10. The R2 value of the regression model shows that 96.4% of the total variation in the storm water discharge is accounted for by the five regressors. Incorrect sizing and spread of drains as well as the existing slopes employed in the generation of the drainsb invert during construction have been seen as some of the key factors that foster flooding in the Metropolis. Designers are encouraged to employ the model developed for drains design and analysis for Calabar Metropolis.http://dx.doi.org/10.4314/njt.v33i4.1

Monitoring of microbial hydrocarbon remediation in the soil

Bioremediation of hydrocarbon pollutants is advantageous owing to the cost-effectiveness of the technology and the ubiquity of hydrocarbon-degrading microorganisms in the soil. Soil microbial diversity is affected by hydrocarbon perturbation, thus selective enrichment of hydrocarbon utilizers occurs. Hydrocarbons interact with the soil matrix and soil microorganisms determining the fate of the contaminants relative to their chemical nature and microbial degradative capabilities, respectively. Provided the polluted soil has requisite values for environmental factors that influence microbial activities and there are no inhibitors of microbial metabolism, there is a good chance that there will be a viable and active population of hydrocarbon-utilizing microorganisms in the soil. Microbial methods for monitoring bioremediation of hydrocarbons include chemical, biochemical and microbiological molecular indices that measure rates of microbial activities to show that in the end the target goal of pollutant reduction to a safe and permissible level has been achieved. Enumeration and characterization of hydrocarbon degraders, use of micro titer plate-based most probable number technique, community level physiological profiling, phospholipid fatty acid analysis, 16S rRNA- and other nucleic acid-based molecular fingerprinting techniques, metagenomics, microarray analysis, respirometry and gas chromatography are some of the methods employed in bio-monitoring of hydrocarbon remediation as presented in this review

Bioremediation of a Petroleum-Hydrocarbon Polluted Agricultural Soil at Various Levels of Soil Tillage in Portharcourt, Nigeria

A combination of field cells involving a control and five treatment cells were evaluated under field conditions in the bioremediation of a petroleum- hydrocarbon polluted agricultural soil over a six-week period. Previous works have indicated that crude oil contamination of soils depletes oxygen reserves in the soils and slows down its diffusion rate to the deeper layers. Hence, this hypothesis was tested in the study by the treatments employed. The treatment option used was the application of mineral fertilizer, and different rates of oxygen exposure through various levels of soil tillage. In the experiments described in this paper, conditions of a major spill were simulated by sprinkling crude oil on the cells using perforated cans. The treatment applications were then resorted to and relevant soil physicochemical characteristics monitored at intervals. The results of the study showed an enormous increase in total heterotrophic bacterial (THB) counts in all the treatment cells. The percentage reduction in total hydrocarbon content (88% to 99%) experienced in the cells that received treatment were significantly different from the control. These results highlight the view that the availability of large amounts of oxygen in the soil profile induces an accelerated biodegradation of petroleum hydrocarbons in a polluted agricultural soil and implies that regular tillage of contaminated soils in the presence of nutrients could achieve the decontamination of such soils