Utilization of fish sludge and aquaculture effluent water from Norway for nutrient and energy recovery

Abstract

The Norwegian aquaculture industry is experiencing rapid growth. At the same time the demand for suitable aquaculture waste treatment is rising. This study aims to evaluate the environmental impacts of a waste-treatment process through anaerobic digestion and microalgae cultivation in Norway. This circular economy approach aims to recover nutrients and energy from an average land-based recirculating aquaculture system (RAS) with a production of 5000 tonnes of salmon yearly. In comparison, one of today's common solutions, the shipment of 50 % of the RAS fish sludge to Denmark for biogas production, was assessed as a baseline. A life cycle assessment showed that shipping 100 % of the fish sludge to Denmark for anaerobic digestion is more environmentally sustainable than releasing half of the fish sludge into the environment and only shipping 50 % to Denmark. Anaerobic co-digestion of fish sludge in Norway showed a lower environmental impact potential than the anaerobic digestion with fish sludge as the sole substrate (in Norway). The cultivation of microalgae in northern latitudes is highly energy demanding, which is one of the highest impact contributions of the value chain. National differences in the electricity grid composition (hydropower, other renewable energy, fossil energy) that is used for the respective scenarios in either Norway or Denmark, had a major impact on the assessment. A preliminary economic assessment showed that all scenarios had a decrease in operational costs compared to the baseline scenario due to the recycling of nutrients and produced energy from the RAS waste streams.