Determining the tolerance level of Zea mays (maize) to a crude oil polluted agricultural soil

This research sought to investigate the tolerance level of Zea mays (maize) on a crude oil contaminated soil using indices of plant performance such as plant height, leaf area and fresh cob yield. In theexperiments described, conditions of a major spill were simulated by pouring different amounts of crude oil on experimental pots containing agricultural soil. Maize seeds were then grown amidst adequate fertilizer application and irrigation. The results of the study revealed that maize can survive soil contamination of about 21% (similar to 177 000 mg/kg) and still produce fresh cob yield of about 60% than on normal soil. There was a stimulated increase in fresh cob yield, than that obtained on normal soil at 12.5% soil contamination (similar to 112240 mg/kg). Hence, contaminant concentrations of 112 240 mg/kg and 177 000 mg/kg are identified as the ‘optimum yield limit’ and ‘lethal threshold’ respectively for maize growing on crude oil polluted soils. These results highlight the fact that, while concerted efforts should be made to remedy petroleum-contaminated agricultural soils, certain crops like maize can still produce beneficial yield in the presence of good soil management practices

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

Response of maize and cucumber intercrop to soil moisture control through irrigation and mulching during the dry season in Nigeria

Replicate field plots were used in experiments aimed at evaluating the yield potentials of maize and cucumber intercrop resulting from the control of soil moisture through irrigation and mulching, for aperiod of eleven weeks. Three irrigation depths, 2.5, 3.5 and 4.5 mm; and two mulch levels, zero mulch and 10 ton/ha of oil palm bunch refuse as mulch material were employed, while the third option involved the combination of the different levels of irrigation and mulching. These were used alongside fertilizer application. The pertinent growth and yield parameters were then determined. Results of the analysis indicated that there were no significant differences in growth parameters such as plantheight, vine length and days to 50% flowering across the treatment variants. Yield components such as total grain yield, total fresh cob yield and total fruit yield differed greatly across the treatmentoptions and also indicated significance at the 1% probability level. It was observed that cucumber total fruit yield was greater in the plots that received only mulching than the other plots. The results ofthe study highlight the position that the best crop yields would be obtained for maize and cucumber intercrop during the dry season, if farmers resort to optimum application levels while using thesynergy of irrigation and mulching to achieve a crop favorable soil moisture regime

Ranking agro-technical methods and environmental parameters in the biodegradation of petroleum-contaminated soils in Nigeria

A combination of experimental cells consisting of some agro-technical methods aimed at accelerating the biodegradation of petroleum contaminated soils were evaluated in order to ascertain the relevance of these methods and the relative attention due necessary soil environmental parameters. The methods of treatment involved the variation of tilling, watering and nutrient application, plus biopile and phytoremediation treatments. In the experiments described, petroleum contamination of soils was simulated under field conditions, the remedial treatments were then utilized for clean up. Analysis of soil parameters after a six-week study period showed an increase in total heterotrophic bacteria (THB) counts across all the treatments, with THB counts increasing with increment in soil nutrient level and initial concentration of the contaminant. The total hydrocarbon content (THC) analysis, based on a performance index introduced in this study, indicated that on the average, the variation of nutrient application, tilling and watering facilitated the attenuation of THC at the rate of 429.4 mg/kg day, 653.2 mg/kg day, and 327.5 mg/kg day respectively. While the combined effect of various levels of nutrients, tiling and watering performed at the rate of 558.7 mg/kg day, biopile and phytoremediation treatments recorded 427.9 mg/kg day and 489.3 mg/kg day respectively. These results imply that though nutrient application, watering and other factors affect the biodegradation process, frequent tilling for maximum oxygen exposure is the most important factor that affects the biodegradation of petroleum-hydrocarbons in tropical soils

The cold store for a pumped thermal energy storage system

In recent years several proposals for thermodynamic cycles involving the compression and expansion of gas and thermal storage have been put forward as effective ways of storing energy. These include the work of Desrues [1] who proposed a thermal energy storage process for large scale electric applications, Isentropic Ltd [2] who were working on a pumped thermal energy storage system and Garvey who proposed storing wind energy using a wind driven thermal pumping system known as Wind-TP [3]. All these systems require a hot and a cold store capable of storing thermal energy which can later be used to generate electricity. The efficiency and ultimately the successful adoption of pumped thermal energy storage will depend on the effectiveness of the thermal stores. In this paper we compare the performance of a packed bed and a liquid thermocline as the cold store for an off-shore Wind-TP system. Simulations are used to compare the exergetic performance of the two options leading to the conclusion that a liquid thermocline has potential to be significantly more effective than a packed bed thermocline. An addition to a liquid store involving a sliding divider separating warm and cold fluid is proposed as a way of avoiding exergy losses associated with the smearing of a thermocline front

A state-of-the-art review of polymers used in soil stabilization

This paper provides a review of the research on use of polymers for soil stabilization in pavement and geotechnical engineering. First, the properties impacting the effectiveness of widely used polymer classes, including geopolymers, biopolymers, and synthetic organic polymers are discussed. These include types and ratios of the precursor and activator of geopolymers, molecular weight, particle size, charge, conformation, solubility, viscosity, pH, and moisture behavior of organic polymers. Next, the paper reviews the mechanisms governing stabilization of soils with the various polymer classes. The key mechanisms for organic polymer–clay interactions are electrostatic forces and entropy increase, which contribute differently depending on whether the polymer is cationic, neutral, or anionic. On the other hand, the interactions between polymers and coarse-grained soils composed predominantly of sands are mainly attributed to three types of structural changes: a thin film covering sand particles, the formation of polymer ties connecting noncontacted neighboring particles, and the development of adhesion between particles. The mechanism of geopolymer stabilization is through the formation of a sodium and/or calcium aluminosilicate gel, which bind the surrounding soil particles and harden into a denser, stronger matrix. The engineering properties of the soil types after stabilization using polymers, including strength improvement, permeability reduction, swell and shrinkage inhibition, and durability and stability enhancement are discussed. Finally, the paper highlights the challenges for wider use of polymer stabilization of soils including limited evaluation standards, life-cycle cost considerations, and moisture susceptibility. To this end, some future research direction to promote the widespread use of polymers in soil stabilization are recommended including the need for establishment of standard testing protocols, evaluation of in-situ properties of polymer stabilized soils, resolution of durability issues and further in-depth examination of stabilizing mechanisms

Stabilization of calcareous subgrade soils with polyelectrolytes: mechanisms and mechanical properties

Organic polyelectrolytes, i.e. anionic poly(sodium 4-styrenesulphonate) (PSS), cationic poly(diallyldimethylammonium chloride) (PDADMAC) and their polyelectrolyte complexes (PECs) were evaluated for stabilisation of calcareous sandy subgrade soil. This paper investigated the effects of polymer type, surface charge type of PEC, concentrations of PEC solutions and dosages of polymer solutions added to the soil on improvement of soil mechanical properties. We found that anionic polymers, for both PECs and individual polyelectrolytes, were superior to their cationic counterparts in improving soil strength. Besides, the constituent polyelectrolytes, PSS and PDADMAC, worked better than their PECs for the specific soil investigated. The strength of polymer-treated soils was also found to increase with the increase in dosages of the polymer solutions as well as curing periods. Furthermore, polymer-treated soil specimens exhibited significant toughness improvement, which was higher than cement-treated samples. Scanning electron microscopy images revealed the abundance of long palygorskite fibres covering the surfaces of larger calcite and dolomite particles and linking surrounding aggregates after adding polymers. This observation suggests the interconnection of palygorskite fibres and their linking networks between and among coarse aggregates as the likely mechanism of polymer stabilisation of the soil studied