Impact of Animal Dung from Goat, Pig, and Cow on the Physicochemical and Microbial Properties of Soil Contaminated with Spent Engine Oil

Spent engine oil is a common and toxic environmental contaminant. A preliminary investigation was conducted to determine soil properties (positive control), while spent oil-contaminated soil served as the negative control in a completely randomized experimental design featuring a 2*3*3*5 factorial combination. The analyzed parameters include pH, cation exchange capacity, moisture level, organic matter, organic carbon, particle composition, and soil temperature. Results indicated that soil physicochemical properties were significantly improved by using different animal waste as amendments at varying levels, regardless of time. The highest dose application (10% dung) yielded the best results. Goat dung at 10% (GD10) significantly increased soil pH (6.3), moisture level (17.0%), and clay (18.2%), but reduced soil silt (9.9%) and sand (72%) composition. Pig dung at 10% (PD10) significantly increased soil organic matter (13.48%) and organic carbon value (7.81%). Cow dung at 10% (CD10) significantly increased soil cation exchange capacity (5.09meq/100g) and temperature (31.9 °C), in addition to the organic matter (13.2%). Animal waste amendments had significant effects on soil microorganisms. The highest total viable counts (TVCs, 298.5cfu/mL) and total coliform counts (TCCs, 144.5cfu/mL) were recorded from 10% goat dung, while 5% cow dung produced the highest total fungal counts (TFCs, 122cfu/mL). Shigella spp. were present only in pig dung at 10% and cow dung at 3% and 5% while Escherichia coli, Enterobacter, and Shigella spp. were absent in control soil samples but present in all amended soils at all treatment levels. This cost-effective and simple method of soil remediation from spent engine oil may serve as a form of waste conversion into organic manure needed for plant growth.

Keywords:Spent engine oil; Cow dung; Pig dung; Goat dung; Soil contamination; Soil remediation

Soil is the uppermost weathered layer of the Earth’s crust, consisting of rocks that have been altered to bind chemically together with the remains of plants and animals that live on and in it. Soils have relatively high organic content in the form of organic compounds, plant roots, and soil microorganisms that make the soil come alive [1,2]. Any factor that interferes with the physical and chemical nature of the soil also derails the food production cycle. Soils form distinct natural kingdoms and can be distinguished based on their intrinsic properties, processes of formation, and patterns of distribution. Soil collectively constitutes a real entity in the natural environment where character, development, and distribution in space are governed by the natural laws of nature. The value of any soil for plant growth is therefore relative to the plant which can grow there. Owen [3] enumerated the characteristics of soils to include the following: soil structure, texture, hydrogen ion concentration (pH), temperature, moisture, micro-organisms, and organic matter among other properties. Research has shown that organic manure can be applied to improve the physicochemical properties of soil needed for the growth of plants as primary producers in a healthy ecosystem [4-7]. These include farmyard manure, green manure, and compost manure. Livestock is a huge source of organic manure. Several research has shown that soils amended with animal manure improved soil conditions and crop yields [5-7]. Waste excreted by goats, pigs, cows, and poultry is significant, although these animals are considered environmental pollutants. Organic manures are rich in organic matter and serve as a good substrate for the growth of soil microorganisms; they also positively impact the nutritional balance and physical properties of the soil [8].

Spent engine oil is a common and toxic environmental contaminant not naturally found. It is of great potential threat to the soil due to its nondegradable and persistent nature in the environment [9]. Livestock waste is another source of soil pollution due to the presence of pathogenic microorganisms and odorous substances emitted into the environment as well as leachates that contaminate underground water. Remediation technologies of toxic spent engine oil and nauseating livestock waste are becoming increasingly expensive, tedious, time-consuming, and rigorous. Improvements in treatment technologies are currently trending. Global attention has shifted to the potential conversion of agricultural waste from plants and animals into useful forms that offer solutions to environmental challenges. Various organic amendments have been utilized for the treatment of contaminated soil, including manures, biosolids, sawdust, wood ash, compost from different source materials, sewage sludge, bark chips, and wood chips. In the case of manure, only composted manure is suitable for soil treatment purposes, as fresh manure can harm plants due to high ammonia levels [10]. Livestock waste constitutes an environmental nuisance as it pollutes the soil, emits odors, and contaminates underground water sources with pathogenic microorganisms. Although animal waste is used as manures to increase soil nutrients, data are grossly insufficient on the comparative analysis spent engine oil-contaminated soils amended with wastes from pigs, cows, and goats. Thus, the present study aimed to compare the application of waste from goats, pigs, and cows as soil amendments for the potential improvement of soil contaminated with spent engine oil.

Study area

The study was carried out in Makurdi Local Government Area (7° 43′ 50″ North and 8° 32′ 10″ East) of Benue State, Nigeria (Figure 1). It falls within the Guinea Savanna agro-ecological zone of Northcentral Nigeria. It experiences a tropical climate with prominent wet and dry seasons with an average annual rainfall of 1290mm. It is characterized by the presence of the popular River Benue whose tributaries cover a substantial area of the town. Makurdi has a daily temperature range of between 22.5 °C minimum and 40.0 °C maximum. The soil type is sandy-loam and its supports agricultural practices [11].

Fgure 1:Map of Makurdi Local Government Area [11].

Sample collection and preparation

Goat dung was collected from the North Bank and Wadata markets in Makurdi. Pig dung was gathered from pen houses at North Bank in Makurdi, while cow dung was obtained from the livestock farm of Joseph Sarwuan Tarka University in Makurdi. Samples were sun dried, pelletized, ground into powdered form, and packaged in various polythene bags labeled with each animal type (GD=Goat dung, PD=Pig dung, CD=Cow dung). A total of 5kg of each type of waste was prepared. The bags were sealed and stored in the laboratory for later application. For the spent engine oil, the sample was procured from North Bank Mechanic Village, Makurdi. A total of 4L was kept in a 5 L-capacity gallon and stored in the laboratory [12]. For the soil sample, exactly 200g of sieved stored soil was preliminarily analyzed for physicochemical and bacteriological properties [13]. This served as positive control (soil without contaminant) and was coded as C1.

Determination of physicochemical parameters of soil sample

The procedure reported by Udo et al. [13] was followed for all determinations. Twenty (20g) of soil was weighed and transferred into a 100mL beaker containing 40mL of distilled water. The mixture was stirred with a glass rod and allowed to stand for half an hour (30 minutes). The electrode was immersed, and pH value was determined from the automatic display of the pH meter, Model 3510. To determine the cation exchange capacity, ten grams (10g) of soil sample in a folded filter paper was inserted in a funnel fixed on the leaching rack. Leached soil of 10g was poured into a 250mL volumetric flask containing 1N ammonium acetate (NH₄CH₃CO₂) (pH 7.0) and fixed on the rack. The residue in the filter paper/ filter funnel was allowed to dry by air for 24 hours. The residue treated with 75 to 150mL of methanol was allowed to dry again in air. Leaching was repeated in 0.1N potassium chloride (KCl) solution in a 250mL capacity. Thereafter, 1N NH₄CH₃CO₂ leachate was used to determine potassium (K) content while 0.1N KCl was also used to determine the CEC and expressed in meq/100g. The moisture content was determined by approximate loss in weight of soil at field capacity then air-dried by spreading the soil samples on a newspaper for a week. The weighing method was used. The moisture content was expressed in percentage water loss.

A mercury-in-glass thermometer calibrated in degrees Celsius (°C) was used to measure the soil temperature. Before collecting each soil sample, soil temperature was determined in situ by inserting the thermometer to about 5cm depth in the soil for 5 minutes of stabilization of the instrument before temperature readings were taken in °C in duplicates [13]. Organic matter and carbon were measured by wet-acid digestion, a procedure credited to Walkley and Black [14] while particle size analysis was determined by the hydrometer method using sodium hexametaphosphate (Na₆[(PO₃)₆]) and sodium carbonates (Na₂CO₃) as the dispersant. Textural class determination was done using the USDA textural triangle [15]. Percentages of clay, silt, and sand were obtained.

Preliminary determination of soil microbiological properties

Sample inoculation was done by inoculating 1.0mL of sample suspension on nutrient agar, MacConkey agar, and Salmonella- Shigella Agar (SSA). Incubation was done at 37 °C for 24 hours [16]. Morphological observations were recorded in the culture media. These include the colour, shape, and outline of the colony as well as the shape of each bacterium. The motility test was done by adding a drop of peptone water on a glass slide containing a bacterial colony covered with a slip and viewed under the microscope with a highpower objective lens [17]. Serial dilution, pour plates techniques, and incubation (37 °C for 24 hours) methods were employed for fungal count [17]. Visible colonies on the plates were counted using Colony Counter. Total viable Counts (TVC), total Coliform Count (TCC), and total fungal count were recorded in cful/mL (colony forming unit per milliliter [17]. Discreet bacterial colonies were sub-cultured on Nutrient agar plates for biochemical tests and identification [18]. Identification of bacteria species was done using standard microbiological procedures for each of the following biochemical tests: Gram staining, catalase, citrate, urease, indole, hydrogen sulfide, and oxidase tests [17]. All identified isolates were recorded per water and soil sample. For the contamination of Soil samples with Spent Engine Oil, about 10kg of soil sample was thoroughly mixed with 100mL of spent engine oil [19]. A total of 5g of this mixture served as the negative control (C2) and it was subjected to physicochemical and bacteriological analyses using the methods described previously.

Experimental design

The complete randomized experimental design was applied. It consisted of two factors: animal waste and spent engine oil contaminant. There were three treatments for animal waste: goat, pig, and cow dung. Each waste type was applied at three levels each (3%, 5%, and 10%) to spent engine oil-contaminated soil with 5 replications per treatment level [19]. The experiment was therefore a 2*3*3*5 factorial combination (90). The positive and negative control soil samples also had 5 replicates each. The total experimental units=100 units. A total of 100 plastic pots (each measuring 12cm in diameter and 7cm in height) were set up in a randomized design where 90 pots contained spent engine oil soils treated, each with any of the treatment combinations as given below in replicated forms: GD3=Goat dung applied at 3% to spent engine oil contaminated soil GD5=Goat dung applied at 5% to spent engine oil contaminated soil GD10=Goat dung applied at 10% to spent engine oil contaminated soil PD3=Pig dung applied at 3% to spent engine oil-contaminated soil PD5=Pig dung applied at 5% to spent engine oil-contaminated soil PD10=Pig dung applied at 10% to spent engine oil-contaminated soil CD3=Cow dung applied at 3% to spent engine oil-contaminated soil CD5=Cow dung applied at 5% to spent engine oil-contaminated soil CD10=Cow dung applied at 10% to spent engine oil-contaminated soil. Ten (10) pots were set up as positive (C1) and negative (C2) control pots as described below in replicated forms. C=Positive control soil (soil with neither spent engine oil nor animal waste treatment). C2=Negative control soil (soil with spent engine oil only without animal waste).

Analysis of contaminated and treated soil samples

Experimental soil samples were analyzed for physicochemical and microbial parameters at 7-, 14-, and 28-days post-treatment. The analyzed parameters and methods of analysis have been described above for pH (hydrogen ion concentration), cation exchange capacity, moisture level, organic matter, organic carbon, particle composition, and soil temperature for physicochemical parameters [20]. The following microbial analyses were carried out: identification of bacteria and fungi as well as estimation of total viable, coliform, and fungal counts from each experimental soil sample.

Data analysis

Minitab 17.0 was used. Log transformation was applied to transform selected percentage data to fulfill conditions for ANOVA (both one-way and two-way analysis of variance). Mean separation was done using the Fisher LSD (Least Significance Difference) at a 95% level of significance. The Kruskal-Wallace test was applied to count data at a 95% confidence level.

Physicochemical parameters of soil sample

Results showed that spent engine oil contributed to the acidity of the soil. This condition is capable of leaching away plant nutrients beyond the reach of the roots. The application of animal dung at different levels was shown to gradually reduce the soil acidity to a point where soil amended with 10% goat dung caused the highest reduction in acidity to a maximum pH value of 6.3 (Figure 2). Although pure soils have neutral pH [21], the level of hydrogen ion concentration recorded under 10% goat dung is considered suitable for the cultivation of crops on arable soils. Soil pH affects nutrient availability to plants. In general, the optimum availability of soil nutrients for plant uptake occurs between a soil pH of 6.0 and 7.0 [21,22]. The outcome of this study also agrees with Walker et al. (2004) who reported that cow manure was effective in increasing soil pH and supplying necessary plant nutrients. Many studies established a relationship between soil pH and the cation exchange capacity of the soil as both properties are important determinants of soil nutrients [22]. This outcome revealed that soil amended with 10% cow dung increased the power of the soil to exchange ions.

Fgure 2:Mean pH of Spent engine oil engine-contaminated soil Amended with Animal Wastes at Different Levels of Treatments.

Soil moisture is another crucial parameter needed to maintain a healthy soil for plant growth and function because plants absorb minerals and other nutrients in solution from the soil in a water medium [23]. The moisture level in soil was improved in soils amended with animal dung compared to control soils. The result aligns with studies by Mahdi and Lowery [24] who confirmed the efficacy of organic manure as a good soil conditioner that can maintain the moisture content of soil. The present work reported that spent engine oil-contaminated soil had the highest moisture value of 16.99% when amended with 10% goat dung (Figure 3).

Fgure 3:Overall moisture level of spent engine oil contaminated soil amended with animal wastes at different levels of treatments

Soil organic matter increases soil fertility by providing cation exchange sites and acting as a reserve of plant nutrients, especially Nitrogen, Phosphorus, and Sulphur along with micronutrients, which are slowly released upon soil organic matter mineralization [5-7]. As such, there is a significant correlation between soil organic matter content and soil fertility [4]. Among the three animal dungs investigated, contaminated soil amended with 10% pig dung had the highest organic matter and organic carbon followed by 10% cow dung, suggesting the usefulness of these wastes in soil fertility (Figure 4). Soil organic matter is regarded as being critical for soil functions and soil quality because, the positive impact on soil functioning includes improvement related to soil structure, aggregation, water retention, soil biodiversity, absorption and retention of pollutants, buffering capacity as well as cycling and storage of plant nutrients [7].

Fgure 4:Overall organic matter content of spent engine oil contaminated soil amended with animal wastes at different levels of treatments (a) and mean organic carbon content of spent engine oil contaminated soil amended with animal wastes at different levels of treatments (b).

The control experiment containing spent engine oil had a high amount of sand. A reduction in sand and silt levels and enhancement of clay content was noticeable when treated with animal dung especially goat waste at a 10% level (Figure 5). Particle size and distribution affect the soil’s capacity for holding water and nutrients. Fine textured soils generally have a higher capacity for water retention, whereas sandy soils contain large pore spaces that allow leaching [25]. This suggests the potential of goat waste in the formation of good soil structure. Data on soil composition complement soil moisture data since contaminated soil had the highest moisture when amended with 10% goat dung.

Fgure 5:Sand content of spent engine oil contaminated soil amended with animal wastes at different levels of treatments (a) and silt content of spent engine oil contaminated soil amended with animal wastes at different levels of treatments (b).

Soil temperature is an important property that is essential for many soil processes and reactions that may include water and nutrient uptakes, microbial activities, nutrient cycling, root growth, and many other processes [24]. Arable soil has an ideal temperature range of 18-24 °C [25,26]. Although contaminated soil amended with 10% cow dung recorded the highest temperature (Figure 6), there was no significant difference in temperature values of soil samples. This could be due to the influence of laboratory conditions on soil temperature devoid of natural climatic influences.

Fgure 6:Mean temperature of spent engine oil-contaminated soil amended with animal wastes at different levels of treatments

Soil microbiological properties

Soil microorganisms are normal components of healthy soils needed to decompose dead matter and aggregate mostly in the topsoil where they contribute to the fertility of the soil [8]. Goat dung at 10% applied to treat spent engine oil-contaminated soil maximally increased the total viable and coliform counts of bacteria while cow dung at 5% gave the highest total fungal count (Table 1). In other studies, pig waste was reported to contain a high volume of bacterial counts [8]. This disparity in bacterial load could be due to the nature of the treatment applied as pelletized forms were applied which might not give a true picture of ideal microbial load in animal wastes. However, microbial loads were highly enhanced in dung-amended samples than in control soils.

Table 1:Effects of animal waste amendments on total viable, coliform, and fungal counts (cfu/mL) of spent engine oil contaminated soil at different treatment levels (p<0.05).

*Treatment level showed no statistically significant difference (p>0.05).

The control soil samples contained 3-4 microbial species whereas soil amended with 10% pig dung and 3% cow dung contained 6-7 species (Figure 7). Shigella spp were found only in pig dung and cow dung. In addition, Escherichia coli, Enterobacter and Shigella spp were absent in the control soil samples but present in all amended soils at all treatment levels. Results showed that the addition of different animal wastes (goat, pig, and cow) to soil contaminated by spent engine oil influenced microbial diversity. This aligns with other findings where bacterial diversity was found to be high around livestock farms due to the presence of dung [27]. Results also agree with the report of Maheshbabu et al. [8] that rich soils are a good substrate for the growth of soil microorganisms, and they positively affect nutritional balance and the physical properties of soil.

Fgure 7:Number of microbial species in spent engine oil contaminated soil amended with animal wastes at day 7-28 of treatments.

Results of this study have shown the potential use of animal dung from goats, pigs, and cows in ameliorating soil conditions affected by spent engine oil contaminants. The study aligns with other reports confirming that deteriorated soils amended with animal manure improved soil conditions and crop yields [5-7]. The present outcome agrees with the view of Ayeni and Adetuji [28] & Gul et al. [10] who suggested the use of diverse amendments including manures, biosolids, sawdust, wood ash, and composts obtained from different source materials to improve soil conditions. Gul et al. [10] opined that only composted manure is used for soil treatment purposes as fresh manure may harm plants due to high ammonia levels. Therefore, powdered pelletized manure was used in this work to give the desired results. A study by researchers revealed that applying compost to contaminated soil facilitated the extraction of mineral (heavy metals) from the soil [10,20]. Although heavy metal investigation was not carried out in the present work, it was shown that the three animal wastes investigated performed better at 10% treatment levels than at lower levels (3% and 5%).

The study indicated that the properties of soil contaminated with spent engine oil were significantly enhanced using various animal wastes as amendments at different levels, regardless of the duration. The highest application dose (10% dung) resulted in the most favorable outcomes. Goat dung improved soil pH, moisture, and clay content while decreasing silt and sand composition. Pig dung contributed to increased organic matter and carbon levels. Cow dung enhanced the soil cation exchange capacity, temperature, and organic matter content. The amendment of animal waste affected microbial load and diversity. Soil treated with 10% pig dung hosted the highest number of species, ranging from 6 to 7. Each of the three types of animal waste demonstrated an influence on different soil properties. The combined effectiveness of the treatments is recommended at a 10% application level. This costeffective and straightforward method could be utilized as an amendment for the remediation of soil contaminated with spent engine oil. It may also facilitate the conversion of waste into organic manure, which is necessary for plant growth.

The authors declare no conflict of interest in this work.

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