Dried Anaerobic Digestate from Slaughterhouse By-products: Emerging Cues for a Bio-Based Fertilization

The slaughterhouse and meat industry are worldwide rapidly growing and produce billions of tonnes of organic wastes annually. These materials can be used to produce biogas through anaerobic digestion and the resulting digestate represents a potential source of organic carbon and nutrients that could be applied to the soil as organic fertilizer. The present work aims to assess the fertilizing potential of a dried anaerobic digestate (DD) produced from beef slaughtering waste. DD was characterized at the physic-chemical level, particularly focusing on macro- and micronutrient contents, potentially toxic element and organic contaminants. Then, a short-term soil incubation experiment was performed on two different soils. After the incubation, DD released 10-26% of their total nitrogen (N) and 13-16% of total phosphorus (P), depending on the soils that had different characteristics and responded differently to the treatments. However, DD had positive effects on the principal soil fertility indicators, such as chitinase and phosphatases, stimulating the microbial activity and therefore exploiting a fertilizing potential as well as the other organic fertilizers tested. Moreover, DD had minor effects on soil extractable carbon (Cext) suggesting the presence of recalcitrant C forms in spite of soluble C, indicating a higher stability of slaughterhouse by-products after anaerobic digestion in respect to the other organic fertilizers. The results obtained in this work raise the concrete possibility use DD as a bio-based fertilizer.