Exploring the biochemical methane potential of open market waste from Jordan and Tunisia for a future scale-up of anaerobic digestion in Amman and Sfax

Hundreds of local open markets, trading fruits and vegetables, are distributed across the Mediterranean region and produce large amounts of organic wastes. The advantages of the concentrated production of such leftovers as well as the absence of other organic wastes (such as meat/fish byproducts, manures etc) that would increase the pathogen content of the waste mixture, facilitate a waste management system aiming to produce energy and return a high quality digestate to the farmers, adopting the concept of the circular economy. The composition of the waste mixture produced in Mediterranean countries, such as Tunisia and Jordan, as well as its seasonal variability are crucial to the design and operation of a biogas plant exclusively fed on these feedstocks. After defining the waste mixture composition in three seasonal intervals (autumn-winter, spring, and summer), the biochemical methane potential (BMP) was determined by three European Institutions located in Spain, Italy, and Greece. The comparison of the BMP tests conducted on the same mixtures and expressed per COD mass added showed there are no significant differences among the various seasonal mixture wastes (0.303±0.022 NmL CH4/g CODadded) as determined by the three labs. The BMP expressed per mass of volatile solids added was not consistent among the labs, which is probably due to the different COD content of the mixture wastes. Nonetheless, all mixtures resulted in a BMP higher than approximately 270 NmL CH4/g VS, indicating that the operation of a full-scale digester along a whole year would benefit from the supplementation of a high-potential feedstock