Waste management remains a critical environmental and public health issue, particularly in developing countries where inadequate methods such as open-air landfills and open burning predominate. These practices, as highlighted by Zhang etal. [1] and Anokye etal. [2], contribute to widespread contamination of water sources, the proliferation of diseases, and significant greenhouse gas emissions, all of which are the result of substandard waste management practices. Key problems include uncontrolled landfills, unregulated burning of waste materials, and inadequate management of leachate produced from the decomposition of waste. The situation is particularly dire in urban areas, exacerbated by high population density and rapid urbanization, which complicate the effective management of municipal solid waste. The ramifications of these issues manifest in various forms, including visual pollution, air quality deterioration, unpleasant odors, increased emissions of greenhouse gases, proliferation of disease vectors, and contamination of both surface and groundwater resources, confirming findings by Ferronato and Torretta [3].

Given the challenges surrounding municipal solid waste management in developing countries, considerable research has focused on household waste issues [1][2][4], disposal methods, and projections for future waste generation [5]-[7]. A significant yet often overlooked contributor to this problem is slaughterhouse waste, especially the rumen content from cattle. Poorly managed rumen waste leads to serious environmental issues, notably water and soil pollution, as improper disposal practices contaminate water sources, resulting in eutrophication and the degradation of water quality [8][9]. Additionally, the accumulation of organic waste in open areas attracts disease vectors such as flies and rodents, heightening the risk of waterborne and diarrheal diseases as well as respiratory illnesses among local populations. The unsightly odor from anaerobic decomposition poses an additional challenge, affecting air quality and causing discomfort in communities. Moreover, the solid waste can obstruct urban sewer systems, exacerbating the risk of flooding during heavy rainfall events [9][10].

To enhance the management of rumen waste and mitigate its adverse effects, several strategies can be pursued, including composting, utilizing it as animal feed, implementing controlled agricultural applications, and employing anaerobic digestion [11]. Specifically, anaerobic digestion stands out as a method that facilitates the conversion of ruminal contents into biogas, effectively reducing both the volume of waste produced and methane emissions. This process presents a viable alternative energy solution, particularly crucial given the continued reliance on fossil fuels, which contribute significantly to environmental degradation, climate change, and various public health challenges [12][13]. The integration of anaerobic digestion could thus play a pivotal role in addressing energy needs sustainably and reducing the ecological footprint associated with traditional energy sources [6][14].

In Côte d’Ivoire, annual meat consumption is roughly 13.0 kg per person, with beef constituting the most significant portion at 4.9 kg in 2016. Beef consumption saw a slight increase from 2.5 kg per capita in 2017 to 2.7 kg in 2018, reflecting both local production and cattle imports. This situation generates large amounts of organic byproducts, notably rumen contents, which are frequently mismanaged in slaughterhouses [15]. The resulting environmental challenges are particularly severe in the nation’s secondary cities, where insufficient political commitment and coordination hinder effective quality oversight by public authorities [16]. The municipal slaughterhouse in Man, the capital of the Tonkpi region, exemplifies this crisis. Established in 1945, the facility has deteriorated significantly and lacks adequate infrastructure to handle waste. Blood and rumen waste are carelessly discarded on an unpaved floor, ultimately polluting the nearby Koh River [17]. This research seeks to evaluate the quantity and quality of bio-waste produced at the Man municipal slaughterhouse, while also scrutinizing the environmental conditions of the site to better understand the on-site management of rumen waste.

The visit to the slaughterhouse in Man revealed an absence of a structured waste management process. This situation poses a significant environmental risk, primarily due to the disposal of carcasses behind the slaughtering area and the direct discharge of organic waste into the city’s main waterway. This poor waste management raises significant environmental and public health concerns and poses potential risks to aquatic resources and the safety of residents, as Zahui etal. [17] observed in this same river. Rumen contents consist of partially digested plant matter that is rich in water, biodegradable organic matter, nitrogen, and microorganisms. Without proper collection, storage, and treatment, they become a significant source of environmental and health pollution [24]. Paradoxically, rumen waste is a valuable resource rather than mere waste. Scientific studies have shown that rumen contents can be anaerobically digested alone or with other slaughterhouse waste. This process reduces pollution, produces renewable energy, and creates a digestate that can be used as an organic fertilizer [25].

Observation of slaughterhouse activities during the immersion period revealed significant figures regarding the number of cattle slaughtered. On average, the slaughterhouse processes between 18 and 24 cattle daily, with a steady average of 21 cattle per day. However, interviews with managers highlighted significant fluctuations during holiday periods. Christmas Day, New Year’s Day, Eid al-Fitr Day, and the day after Eid al-Adha show peaks in slaughter activity. The number of cattle slaughtered reaches 35 on Christmas Day, 39 on New Year’s Day, 43 during Eid al-Fitr Day, and 42 on the day after Eid al-Adha. These figures underscore the impact of cultural traditions and celebrations on slaughterhouse activity, revealing a seasonal pattern that may influence operations and resource management [26]. The observation of increased animal slaughter on the day after Eid al-Adha rather than on the holiday itself is explained by the Muslim tradition of sacrifice, which primarily takes place on that day. During Eid al-Adha, also known as Eid al-Kabir or the Feast of the Sacrifice, most of the consumed meat comes from family sacrifices. This ritual commemorates the sacrifice of Ibrahim (Abraham) and leads to a temporary pause in slaughterhouse operations [27]. However, starting the day after the festival, demand for meat increases significantly for several reasons. First, households that did not participate in the sacrifice—that is, those that did not slaughter an animal—seek to purchase meat through formal channels. Second, food service establishments, such as restaurants and hotels, must restock their meat reserves to meet customer demand [28].

Weighing the contents of the rumen at a slaughterhouse revealed non-significant differences in measured masses throughout the week. The results indicate that the daily average weight fluctuates between 19.8 kg and 28.5 kg, with a consolidated average of 25.9 kg. With the exception of the second day, which recorded a value of 19.8 kg, the other daily averages tend to be consistent, suggesting that the slaughtered cattle are similar in size. This consistency in weights indicates small variation in weight among animals, which contributes to consistency in slaughter operations [29]. However, the low weight on the second day may be due to farmers occasionally slaughtering heifers for economic reasons because raising heifers is considered unprofitable [30]. It is also important to note that the average weight observed in this study is lower than those measured in Cotonou and the slaughter areas of Porto-Novo and Abomey-Calavi in Benin [31]. This difference could be attributed to various livestock feeding practices, which highlights the potential impact of husbandry practices on animal weight at slaughter [29].

Analyses of the physicochemical parameters of rumen samples collected at the Man slaughterhouse reveal that the daily mean values do not show significant differences, with a p-value greater than 0.05. The rumen pH, generally close to neutral, ranges between 6.5 and 7.4, with an average of 6.9, consistent with the studies by Mutisi etal. [32]. This value is optimal for anaerobic digestion, which is indicated to be between 6.5 and 8.5 according to Moletta [33]. The near-neutral pH is linked to the physiological function of the rumen, which is a fermentation medium, highlighting a significant technical and economic advantage, as the rumen can be directly introduced into the digester without requiring pH adjustment, unlike other substrates [34]. The samples also exhibit a high moisture content of 81.5% to 85.5% (mean 84.1% ± 1.2%), corresponding to a relatively low dry matter content (14.5% to 18.5%, mean 15.9% ± 1.2%). These observations are corroborated by Selormey etal. [35], who report a dry matter content of approximately 15.06% ± 1.72% in ruminal contents. This high water content is essential for the hydration of feed particles and the functioning of the microorganisms responsible for the degradation of organic matter [36]. In wet anaerobic digestion systems, a dry matter content below 15% is typically sought to ensure effective mixing and prevent clogging [37]. Regarding volatile matter, the samples show a high content ranging from 86.8% to 89.3% (average of 88.1%), confirming a high richness in fermentable organic compounds, a key indicator of a substrate’s methanogenic potential [38]. This rate is corroborated by Selormey etal. [35], who reported a volatile matter content of 87.35% ± 5.52%. The high availability of volatile matter in the rumen, consisting of partially digested plant residues, volatile fatty acids, and microorganisms, presents an opportunity for biogas production through anaerobic digestion [36].

The analyzed samples reveal carbon and nitrogen levels that vary little, ranging from 49.9% to 51.3% (average of 50.6%) for carbon and from 3.4% to 3.6% (average of 3.5%) for nitrogen. The carbon-to-nitrogen (C/N) ratios range from 14 to 15, averaging 14.5. However, these ratios fall short of the recommended range of 20 to 30 for promoting anaerobic digestion, as indicated by Rajlakshmi etal. [39] and Zainudeen etal. [40]. Low C/N ratios indicate high nitrogen concentrations, which can lead to ammonia inhibition, as noted by Ihoeghian etal. [41]. However, Sittijunda [42] suggests co-digestion as a solution to rebalance the C/N ratio of substrates. Therefore, biogas conversion of rumen waste from the Man municipal slaughterhouse requires co-digestion with a carbon-richer substrate to optimize the C/N ratio. However, these results are inconsistent with those of Selormey etal. [35] and Mutisi etal. [32], who reported C/N values of 20.81 ± 3.96 and 23.5 ± 0.820, respectively. This discrepancy may be related to different livestock feeding regimens, which highlight the significant influence of diet on rumen content characteristics, as indicated by Zhang etal. [43].

Co-digestion using carbon-rich substrates in a local context in Côte d’Ivoire could involve cocoa shells, fruit and vegetable waste from markets, as well as certain food crop residues [44]. However, before being introduced into digesters, rumen waste requires pretreatment to optimize its biodegradability and ensure the system functions properly. These pretreatment steps are essential to ensure maximum efficiency in the anaerobic digestion process, which may include grinding, sorting, homogenization, or other methods aimed at improving the decomposition of organic materials. Paying close attention to these steps will help maximize biogas production and reduce the environmental impacts of organic waste [45].

The assessment of the theoretical biogas potential from the rumen waste of the Man slaughterhouse estimates an annual production of approximately 66683.01 m³. Daily production levels vary significantly throughout the year, with ordinary days averaging around 180.92 m³. Notably higher production occurs on specific occasions: 301.54 m³ on Christmas, 336.00 m³ on New Year’s, 370.46 m³ during Eid al-Fitr, and 361.85 m³ on the day following Eid al-Adha. This variation indicates that rumen waste can be an effective substrate for biogas production, particularly through anaerobic digestion, as supported by research from Klintenberg etal. [46]. However, it is important to note that no biochemical methane potential tests were conducted on the specific samples from the Man slaughterhouse. Thus, while the potential for biogas production appears robust based on the estimated volumes, further testing on the methane potential of these samples would be beneficial for more comprehensive insights.

An investigation at the municipal slaughterhouse in Man revealed inadequate waste management, resulting in significant environmental issues, including the discharge of organic waste into the city’s primary waterway, the Koh River, and the accumulation of carcasses.

The slaughterhouse generates an average of 25.90 kg of rumen content waste per cow and slaughters an average of 21 cows per day, 35 on Christmas Day, 39 on New Year’s Day, 43 during Eid al-Fitr day, and 42 the day after Eid al-Adha. Analysis of this waste revealed favorable physicochemical characteristics for methanization: an optimal pH, high volatile matter content, a low C/N ratio (which could be improved through co-digestion), and a suitable moisture content for wet anaerobic digestion. Furthermore, recovering rumen waste from the slaughterhouse could produce up to 66683.01 m³ of biomethane per year.

However, the current management of slaughterhouse waste poses risks to public health and the aquatic environment. Rumen contents are rich in biodegradable matter and could be valorized through anaerobic digestion. Therefore, biogas conversion of rumen waste from the Man municipal slaughterhouse requires co-digestion with a carbon-richer substrate to optimize the C/N ratio. This process would contribute to pollution reduction and the production of renewable energy.

The authors would like to express their gratitude to the Central Laboratory at the University of Man and to the laboratory at the Félix Houphouët-Boigny Polytechnic Institute in Yamoussoukro for their support. They would also like to thank the management of the Man slaughterhouse for their collaboration and invaluable assistance in collecting field data.