Geometry, Extent, and Chemistry of Fermentative Hot Spots in Municipal Waste Souk Sebt Landfill, Ouled Nemma, Beni Mellal, Morocco

Municipal waste landfills, true biological reactors, are the scene of fermentative processes closely linked to temperature, the nature of the waste, as well as the level of organic matter and moisture, the latter varying due to numerous factors such as climate, cultural and dietary norms, and the possible presence of waste selective sorting [1]. Municipal waste landfills also stand out due to a strong heterogeneity of deposited materials, varying according to their nature, water content, and the proportion of fermentable compounds [2]. The succession of deposits over time maintains this heterogeneity in the intensity of fermentative processes, depending on whether the deposit is recent and rich in fermentable compounds or old and has already undergone these processes. Furthermore, waste decomposition leads to the production of gas and leachate, as well as heat generation, due to continuous aerobic and anaerobic processes [3]. Although a wild landfill can generally be considered an anaerobic reactor, where organic matter degradation occurs, the composition of the leachates generated, which can contaminate groundwater resources due to their infiltration, varies considerably depending on the location [4,5,6].

Geophysical methods employing non-invasive approaches are highly adept at mapping the scope of fermentative activities. Among various geophysical methodologies, self-potential (SP) measurements have been applied for approximately three decades in research concerning landfill pollution [7,8,9]. In recent years, there has been a surge in research focusing on contamination, attributed to the remarkable sensitivity of self-potential measurements to redox conditions in shallow aquifers [10,11,12,13]. Notably, the detectable self-potential observed at the surface of the soil is responsive to spatial fluctuations in charge flux within the matrix, variations in redox gradients and temperature, signals generated by microorganisms, or other activities associated with the migration of contaminants [7,12,14,15,16,17]. Mapping of fermentative activity in a European landfill using the self-potential (SP) technique has highlighted the existence of “hot spots”, areas subject to intense fermentative processes under the control of microbial activities and geochemical reactions [9,18]. These phenomena, often studied in soil, intensify with the abundance of organic matter and aeration conditions. Fermentative processes there are intense, generating long-term heat, notably through gas escape, such as methane, which can spontaneously ignite [19]. Few studies have focused on these hot spots, with most merely mentioning their existence [18]. Are they present in all operating municipal waste landfills and distributed randomly or concentrated within recent waste? Analysis of these specific areas could provide crucial information to monitor landfill activities and estimate the location of unauthorized or unlisted landfills. The self-potential method has also been used outside landfills [20,21,22,23] to map pollution plumes in aquifers resulting from the arrival of leachates from landfill fermentations. These studies have also confirmed the existence of hot spots through very negative values, explained by the intensity of biogeochemical processes.