Compost, digestate, and vermicompost from the recycling of urban biowaste have different impacts on earthworm behavior: A mesocosm study

Abstract

The valorization of Organic Fraction of Municipal Solid Waste (OFMSW) is mandatory in Europe since 2024. Composting, anaerobic digestion (AD), and vermicomposting are the techniques most commonly used for recycling OFMSW. When applied to soil, these products can have different effects on earthworms with either positive (food effect) or negative effects (toxic or repellent effect). We thus carried out a laboratory experiment to assess their influence on different facets of the earthworm behavior (bioturbation and cast production) for two earthworm species (Lumbricus terrestris and Aporrectodea caliginosa) currently found in arable lands. Mesocosms (30 cm depth and 16 cm diameter) were filled with soil from a field crop each product was mixed with soil at two doses: equivalent to 80 kg of N per hectare (normal practice for wheat crop) and 160 kg. N.ha⁻¹. Barium sulfate was also spread at 2.5 cm depth (i.e. between the two soil layers containing the products) as a contrast agent visible in X-ray tomography. After 2 months, the burrowing activity of earthworms within mesocosms was analyzed using X-ray tomography, surface casts were collected, and earthworms weighed. With compost, L. terrestris burrowed closer to the surface (in the 0–5 cm layer) compared to when in the presence of vermicompost and digestate (with 0.85, 0.55, and 0.29 cm³ of burrows, respectively). Moreover, signs of avoidance were detected for this species when digestate was present with deeper burrows (in a 15–25 cm layer). With compost, A. caliginosa burrowed more compared to when in the presence of vermicompost and digestate (with 3.22, 2.64, and 0.97 cm³, in the totality of mesocosm respectively). Digestate has no negative impact on the behavior of A. caliginosa. Barium enables the characterization of the ingestion and displacement of the soil layer containing the products. The displaced volumes were in the following order Compost > Vermicompost > Digestate with larger effects for the 160 than for the 80 kg.N.ha⁻¹ dose. Globally, compost had higher and positive effects for both species activities whereas digestate showed some negative impact on L. terrestris only. Vermicompost had positive effects but less marked than those of compost. These effects should however still be validated under field conditions.