The Use of Oil Palm Bunch Ash for Amelioration of Crude Oil
Polluted Soils

1            Introduction

One of the greatest challenges of our time is to find ways and means of applying our Science and Technology to the problem of environmental degradation.   Apart from being a major stimulant to world economy, crude oil exploration and exploitation have equally imposed some negative impact due to the adverse ecological effects of oil spillage in oil producing communities This study shows the use of oil palm bunch ash as amendment supplement for the amelioration of crude oil polluted soils. In this study two ex-situ experiments were conducted to

(a) Test the effectiveness of oil palm bunch ash applied at 10g, 20g, 30g, 40g, 50g and 60g per 2kg soil to ameliorate crude oil polluted soils.

(b)Test the residual effect of oil palm bunch ash applied at the above rates on the amelioration of crude oil polluted soils.

(c) Study the cumulative effect of oil palm bunch ash applied at the above rates on the amelioration of crude oil polluted soils.

(d) To monitor the status of total hydrocarbon content in soils amended with oil palm bunch ash at the rates in (a)

above.

Petroleum hydrocarbons (PHCs) that enter the soil may be adsorbed on the surface of mineral and organic soil constituents, fixed within the soil pores and fissures, found in mobile form or may form a continuous cover on the soil   surface (Trofimov and Rozanova, 2003).   In forest soils, studies have shown that heavier fractions of PHC were retained in the eluvia horizons that contained the larger pores, while the higher fractions of PHC were retained in the alluvial horizon that contained the fine water retention pores (Suleimanov et al. 2005).

TPHC polluted soils have been shown to influence water holding capacity and moisture content of soils  due  to  the  hydrophobic  nature  of  PHCs.    Studies  have  shown  that  soils  polluted  with  PHCs  are characterized by low water holding capacity, moisture content and hydraulic conductivity when compared with unpolluted soil (Trofimov and Rozanova, 2003; Suleimanov et al. 2005; Nwaoguikpe, 2011). Robertson et al (2007)  stated  that  soils  polluted  with  PHCs  were  different  from  unpolluted  soils  due  to  changes  in  their biological and physicochemical properties. Soils polluted with PHC was observed to show an initial reduction in soil microorganism, especially soils that have not been previously polluted.  This reduction however is followed by a rapid increase in the number of microorganism that are capable of degrading the contaminants (Gramss et al.1998; Seghers et al. 2003).   Hofman et al. (2004) however, observed that though the number of soil microorganism increased in PHC polluted soils, species richness often decrease overtime. Similarly, Toogood, et al 1977 observed that the addition of oil to soils increased the microbial population several fold and this in turn increased the organic matter content of the soil.

The effect of oil on soil nutrient status is reported to be related to the energy and carbon obtained by soil microbes from decomposition of the oil (McGill, 1976). According to McGill, (1976) and Odu, (1981), most of the nutrients are tied up in the cells and tissues of microbes that use these nutrients for growth and development. Simpson – Lewis et al. (1983) also reported that the inorganic nutrients such as Nitrogen and phosphorus were temporarily converted to microbial biomas.   However, nutrients become available when properly recycled following good oil decomposition (Odu, 1981).

The limitation of Nitrogen in oil polluted soils has been demonstrated by Bossert and Barther 1984; Obire and Nwaubete (2002). Zuofa et al. (1987) reported increase in organic matter content, pH and total Nitrogen concentration following crude oil application.   Akpoveta et al. (2011) recorded a reduction of soil phosphorus on a PHC polluted soil. This reduction was attributed to the activities of soil microbes which made them immobile or unavailable (Atlas and Barther 1972).  Reductions in soil pH  together with increase in soil organic carbon and organic matter in crude oil polluted soils have also been recorded (Marinescu et al. 2011; Isirimah et al. 1989).

Available evidence suggests that hydrocarbon degradation at contaminated sites proceed naturally (Odu, 1981; Zuofa et al. 1985).   The quest for effective amelioration of contaminated soils has led to the development of a wide range of cleanup techniques. The recovery of polluted soils on its own without any artificial aid is said to be remediation through natural attenuation.  Monitored natural attenuation (MNA) is very effective in soils with high native microbial population (Sarkar et al, 2005). Amelioration of polluted soils can be achieved through the process of bio-stimulation (Peressutti et al. 2003; Bento et al, 2004; Sarkar et al. 2005) which works on the principle that microorganism responsible for degrading pollutants already exists in the soil. The process is enhanced when conditions that promote their activities are made available.   This could be achieved through the addition of nutrients in form of organic manure or other organic materials or through the alteration of soil pH, moisture or aeration status.  The study by Amadi and UeBari (1992) indicated that the rehabilitation of polluted soils can be achieved through the help of soil microbes, good tillage technique and some amendment with organic fertilizers such as poultry manure, yeast extract and peptone water.

2. Methodology

Soil sample for the experiment was obtained from an oil spill site of Well 31 (PPMC Asset) in BOMU OIL FIELD of the SHELL PETROLEUM DEVELOPMENT COMPANY, NIGERIA LIMITED in Gokana Local Government Area (OGONI) Rivers State.

Surface soil (0 – 20cm) of the polluted site and that of unpolluted adjoining site were collected and bulked to form composite representative samples respectively.  The samples were transported to the green house of the Biological Science Department of Rivers State University of Science and Technology, Port Harcourt for experimentation.

The experiment was conducted in two phases.  Experiment I and Experiment II. The first experiment (experiment I) was a completely randomized block design (CDR) with six replications treated at 10g, 20g, 30g, 40g, 50g and 60g of oil palm bunch ash per 2kg soil, with a control plot of unpolluted soils without amendments. At the end of experiment I, the original completely randomized block design was transformed into a split block design.  This was achieved by splitting the original treatment into two equal halves, with three replications each. One of the halves representing the residual treatment was not subjected to further treatment, while the other half received additional treatments as in the original (experiment 1), serving as the cumulative treatment.  Oil palm bunch ash was applied by incorporating appropriate quantities into the soil and properly mixed to ensure even distribution within the soil.  All treatments were transferred into planting bags, perforated evenly and incubated. All treatments were watered at three days intervals with 40ml of tap water which was properly worked into the soil. The treatments were spread on polyethylene and aerated monthly by continuous mixing and watering for a duration of three days before re-transferring them into their respective planting bags. Monthly representative samples were collected from the respective treatments and control, labeled and transferred to the Laboratory for soil chemical properties analysis.

All soil chemical parameters  were analyzed  at the  Agricultural Laboratory in the Department of Soil/Crop Science and Forestry, and the Institute of Pollution Studies (I.P.S) Laboratory of the Rivers State University of Science and Technology Port Harcourt.   Pre-experimental and experimental soil samples were analyzed. Soil samples for analysis were air-dried, sieved through 2mm aperture sieve and stored in polyethylene bags with labels. Soil and amendment material were analyzed using various methods as indicated below: Soil pH and amendment material were determined by means of the MK20 model of pH meter.   Organic carbon and materials resulted in soil pH moving from acidity to alkalinity as could be shown from percentage increases. The observed alkalinity in amended soils was further observed to have re-adjusted slightly with amendment levels at two months post treatment. Residual experiment shows a slight acidic status at month 3 and 8 post-treatment for respective treatment levels, while the control indicated a  slight drop in acidity. The cumulative treatment experiment indicated an increase in soil alkalinity with increase in amendment rate. However, at 8 months post amendment, soil pH indicated slight acidic status against the control.

In summary, there is observable decrease in soil pH with passage of time at all amendment levels. The result of the effect of oil palm bunch ash (recovery material) on soil organic matter is presented in table 3.3

Similarly, the cumulative experiment indicated   high organic carbon content in respective treatment levels at 3 months post treatment. At 8 months post treatment organic carbon was observed to have generally reduced in the respective amended soils.

The analysis of variance for the above result indicated that the variability between amendment levels were significant at 0.05 probability which validate the observations obtained from the results.

The results of the effect of oil palm bunch ash (recovery material on soil percent total Nitrogen is presented in table 3.5.