Abstract

Introduction: The salmon farming industry in Chile has grown significantly, positioning the country as a global leader in salmonid production. This growth has led to increased sludge generation from Recirculating Aquaculture Systems (RAS), primarily consisting of uneaten feed and fish feces. Due to its high organic matter and nutrient content, this waste offers an opportunity for circular economy practices, mainly through composting, to produce valuable soil amendments for agriculture. Purpose: This study evaluated the composting process of RAS salmon sludge as a sustainable waste management strategy in Chile. Methods: Composting was conducted in 200 L rotary bins over 120 days, with temperature and moisture levels monitored. The finished compost was analyzed following Chilean compost standards (NCh2880) and Test Methods for the Examination of Compost and Composting (TMECC) methodologies to assess nutrients, heavy metals, soluble ions, and pathogens. Maturity was evaluated via Solvita® tests, total polyphenol content, and germination tests with Lactuca sativa, Raphanus sativus, and Solanum lycopersicum. Results: During the thermophilic phase, temperatures exceeded 55 °C, aiding pathogen elimination and reducing weed seed viability. The mature compost showed high phosphorus (59.0 ± 3.1 g kg?¹) and organic matter (67.1 ± 0.4%) content. Maturity tests indicated a Solvita® index of 6, decreased polyphenols, and a 180% germination rate in R. sativus. Conclusions: This research presents the first report on aquaculture waste valorization in Chile, highlighting the potential of composting to produce phosphorus-rich amendments with high organic content. © The Author(s) under exclusive licence to Sociedad Chilena de la Ciencia del Suelo 2025.