Clean-up of mining-generated environmental waste in South Sudan using livestock excreta

Living in a clean and healthy environment is one of man’s greatest needs. Generally, it is a fundamental human right as reflected in resolution A/76/L.75 of the United Nations General Assembly (UNGA) (IISD, 2022). On the pathway to realizing this objective, there is a trade-off caused by necessary socio-economic activities. Such activities are sanctioned by the governments and supported by development partners to appropriate development goals. Mining is one of these strategic resources that must be exploited in mineral resource rich countries such as South Sudan. The country is prominent for oil and gas (Atim, 2023; Ruley, 2022; Ruley et al., 2020a, b). Most of South Sudan’s oil deposits are shared with Sudan (Atim, 2023). In terms of productivity, South Sudan has the third most prominent oil reserves in Africa with a production potential of about 3.5 million barrels per year (Mayar, 2021). Despite this endowment, about 90% of the gas and oil reserves remain untapped (Anadolu Agency, 2022; Mayar, 2021). Furthermore, although gas and oil are catapulting development in South Sudan, reports (such as Aurelio, 2019; Global Atlas of Environmental Justice, 2021; Ruley et al., 2020a, b; Ruley, 2022; SUSA Africa, 2020) have shown that South Sudan’s mining industry and particularly crude oil activities is not environmentally sensitive. Neethu et al. (2019) and Ruley et al. (2022) noted that much as petroleum derived products are an energy source and raw materials for strategic industries (such as petrochemical), environs where the extraction occurs are prone to accidental spill throughout the value chain. For instance, the soil is contaminated with PAHs, groundwater sources are equally contaminated as well as the air (Gotch, 2022). As a result, soil productivity has declined tremendously, wildlife and livestock mortality has been reported as well as strange skin diseases, coughing, birth deformities and miscarriages (Aurelio, 2019; Liam, 2020; Saturlino, 2023; Titmamer, 2022). The increasing nature of the above challenges has raised ire of South Sudanese who have organized protests and demonstrations in the past (Danga, 2020). This public outcry has attracted the attention of the government of South Sudan to carry out an audit of oil and gas companies in order to curb pollution (Reuters, 2020; Xinhua, 2021).

Irrespective of the negative environmental externalities reported above, mineral exploitation in South Sudan, oil inclusive must continue because mineral exploitation is the basis of national development. Given this fact that mining is necessary evil, the challenges ought to be ameliorated. While there is a score of chemicals, physical and electrical means of cleaning up mineral pollutants, PAHs inclusive, Ruley et al. (2022) established that deployment of these strategies is very expensive and therefore, the colossal sums of money to clean up the polluted areas is not available. This accounts for why biological means have been resorted to (Ruley et al., 2020a). The bioremediation of mining generated waste is eco-friendly and cheap compared to other remediation or clean-up approaches. Neethu et al. (2019) and Ruley (2023) recommended deployment of livestock waste and a cocktail or consortia of livestock waste for clean-up of total petroleum hydrocarbons (TPH). This study focused on cow dung because Heinrichs et al. (2023) reported that mature cows pass out dung every 1.5 to 2 hours and excrete a total of 45kgs per day, leading to more abundance.

South Sudan is a livestock rich nation (Report Linker, 2022). World Vision (2018) notes that the country has about 12 million heads of cattle, 20 million heads of sheep and about 25 million heads of goats. These numbers of cattle, sheep and goats (Atit, 2014) are higher than the human population which is estimated at 10,748,272 people in 2021 (World Bank, 2022). This abundance puts South Sudan in a strategic position as the number 1 country worldwide in terms of animal wealth per capita (World Vision, 2018) and in Africa (Doki, 2014). While income and food are the some of the key reasons why the range of livestock is enormous, the cultural norms especially marriage stand out as of the key determinants of raising large herds (FAO in South Sudan, 2021). According to World Vision (2018), the numbers of cows paid for bride price range between 30 and 100 heads and for this reason, households keep large numbers of livestock. The abundance of livestock in South Sudan implies that livestock waste is abundant. Thus, the purpose of the study was to assess the efficacy of livestock waste in cleaning up crude oil pollutants from oil extraction sites in South Sudan.

Data were obtained from a screen house experiment that was carried out ex situ at the University of Juba, South Sudan between January 2023 and October 2023. A blank soil sample was collected away from the crude oil extraction sites. At this area, the soil sample was considered to be natural and undisturbed. Crude oil samples were collected from Paloich Payam at the Dar Petroleum Operation Base Camp. The cow dung was collected from livestock farmers and fermented for two months to allow for partial decomposition. The blank soil samples were artificially contaminated crude oil at a rate of 75 gkg -1 soil. The treatments in three replicates were arranged in a Completely Randomized Design. The hydrocarbon components were analyzed using gas chromatography technique. The removal of TPH was confirmed using Total ion chromatograms (TIC) (Figure 1).

The application of cow dung to artificially contaminated blank soil degraded TPH. As seen in the control (Panel a), after artificial contamination of the blank soil with crude oil, 27 hydrocarbon ions were detected (from n-C13 to n-C40). When cow dung 5gkg -1 soil was introduced in the treatment, there was a reduction in the abundance and concentrations of hydrocarbon ions after 4 months (120 days) to 17 hydrocarbon ions (n-C22 to n-C37) (Panel b). After 8 months (240days), the cow dung further degraded TPH to 8 hydrocarbon ions (n-C25 to n-C33) (Panel c). The reduction in the numbers of hydrocarbon ions observed in this study could be attributed to the action of autochthonous bacteria resident in the applied cow dung. These bacteria have proven potential to scavenge on crude oil compounds and use them as food. Besides, they also breakdown hydrocarbon compounds into innocuous products that are less destructive to the environment. Mondal et al. (2021) confirmed that cow dung is a hot spot for various strains of bacteria. This was confirmed by Ruley (2022) who noted that cattle manure is a natural reservoir for bacteria genera, Bacillus, Luteimonas and Pseudomonas. Moreover, it was equally espoused by Manyi-Loh et al. (2016) that when cow dung is applied to the soil environment Firmicutes (and more especially Bacillus and Clostridium) are added. Moreover, Bhatt and Maheshwari (2019) and Mukhuba et al. (2018) equally reported that cow dung and digestate harbor Acinetobacter while Serratia and Pseudomonas were detected by Gupta et al. (2016). As well, the application of cow dung to the contaminated soil sample must have activated the resident strains of bacteria in the soil sample and empowering them to launch an invasive attack on the crude oil contaminants at 4 and 8 months respectively. This finding is in consonance with Roth et al. (2015) that the improvement in the environmental conditions is associated with an increase in richness of autochthonous microorganisms with K-strategist acquiring the ability to outgrow and survive the stressful environments.

As observed in the TIC diagram after 8 months, there were remnants of hydrocarbon compounds. The remaining 9 ions are classified as recalcitrant and therefore, these could not be completely eliminated by the cow dung. These must have been high molecular weight (ions) especially those that have more benzene rings such as pyrene and coronene. Okere and Semple (2012) reported that high molecular weight hydrocarbons exist in particulate form and therefore, their half-life is by far higher in a soil medium.

(a) No Treatment

(b) Treatement with cow dung 5gkg -1 soil after 4months

(c) Treatment with cow dung 5gkg -1 soil after 8 months

Figure 1 : Total ion chromatograms (TIC) showing removal of TPH from blank soil medium by cow dung treatment.

Given the reportedly high per capita animal wealth of South Sudan and the increased importance assigned to the mining industry, livestock excreta can become an excellent resource for riding the mining sites and their surroundings of contaminants especially those originating from crude oil extraction. The exemplar of cow dung has provided proof that livestock waste holds promise for enhancing the rejuvenation of mining-polluted environment. The study therefore concludes that deployment of cow dung should be prioritized in the ecorestoration of the crude oil contaminated environments in the country. It is recommended that more scientific studies be conducted to determine the most effective and efficient ways through the currently abundant cow dung in the different parts of South Sudan could be harnessed to invigorate the environment. Studies could also venture into deployment of a cocktail of various livestock excreta to establish whether the consortium could potentially sustain the complete elimination of the recalcitrant hydrocarbon ions reported by this study.

An invaluable credit is extended to Dar Petroleum Operating Company Limited for providing crude oil sample that were used for the experiments.