A liming agent by recycling mollusc shells

The total EU fishery production amounted to around 4.5 million tonnes in 2022, of which 1.1 from aquaculture. This poses a challenge regarding the huge volume of wastes derived from seafood production and processing, in both economic and environmental terms. Anyway, these wastes contain valuable compounds that can be recovered in agriculture. The EU-funded SEA2LAND project, based on the circular economy model, explores the production of large-scale fertilisers in the EU from fishery and aquaculture wastes. In mollusc cultivation and fishery, the main waste is composed by shells, composed of CaCO3 and, at a lesser extent, of MgCO3, making them a promising source of liming agent for acidic soil correction. Several areas in Europe have low pH soils, due both to natural and anthropogenic processes, requiring lime distribution for agricultural production. Agricultural lime products are categorized as ‘EC Fertiliser Liming Materials’ in the EU Fertilizing Product Regulation (2022), the most used being ground limestone, dolomitic ground limestone, chalk, ground chalk, burnt lime and hydrated lime. However, although needed for soil quality and agricultural production, liming is often discarded due to its costs. The possibility to use waste products as liming agents allows to address both economic and environmental issues. The shellfish waste used in this work is a mixture of mussel, clam and murex shells discarded from a mollusc processing facility located in Ancona (Italy), whose production of discards accounts for about 1.4 ± 0.2 t·d-1. Waste was pre-treated by shredding the feedstock in the presence of water in a 1:3 (water: shellfish) ratio and the crushed shells (around 80% dry matter) were separated by gravity. The obtained shells were dried, milled and finally, sieved at 1 mm to obtain the liming agent with different particle sizes. These milled shells were first compared to reference liming agents (CaCO3 and CaO) in an incubation experiment to determine their effect on soil pH (UNI EN 14984:2006 method). Then the recycled liming agent was applied in two sites in northern Norway that needed liming, one with oceanic climate and one with more continental climate. The recycled liming agent was compared to conventional liming agent and no liming. Grass was sown at both sites. Results from the incubation trial suggest that the recycled liming agent has a high pH corrective power, similar to CaO and CaCO3. The results on soil pH and yield from the field trials will also be presented.