Effect of attapulgite on anaerobic digestion of primary sludge and downstream valorization of produced biosolids

In the light of European Union's Green Deal, the aim of this study was the optimization of municipal primary sludge management, from biomethane production to the final valorization of the produced biosolids. The obtained results showed that the addition of attapulgite in the primary sludge favored the production of methane. The highest methane production was noted when attapulgite was used at a dose equal to 20 g/L. At this dose, methane production raised up to 378 mL CH4/g VS, 47% higher than that of the individual anaerobic digestion of primary sludge. Moreover, in this case, microbial community analysis revealed an increase in the relative abundance of Methanofastidiosaceae and a decrease of Methanocorpusculaceae, suggesting that attapulgite might induce a shift to a more methyl-thiol dominated hydrogenotrophic methanogenesis. In addition, the produced digestate demonstrated better behavior as regards dewaterability, since the normalized capillary suction time was about 54% lower than that of primary's sludge digestate, indicating that attapulgite diminished sludge's capacity to retain water. Finally, it is shown that the dried biosolids amended soil properties by augmenting organic matter content by about 20%, enhancing nutrients bioavailability, while also stimulated plant growth, unveiling their added value in green-based soil improvement solutions.