Estimated content of nutrients and energy in feed spill and faeces in Norwegian salmon culture

Summary

The annual production of 1.3 million tons of salmon in Norway consumes 1.5 million tons of feed. Some of the energy and nutrients from feed is not digested by the salmon, and ends up in the faeces. In addition, nutrients and energy from uneaten feed also end up in sludge. The total amount of energy and phosphorus in faeces and feed spill is estimated for land based smolt production and for the grow out phase in sea in Norwegian salmon farming. The energy content in faeces and feed spill from land based smolt production is estimated to 242,880 GJ, and 11,785,235 GJ from the grow out phase per year with today’s production volume. The corresponding figures for phosphorus are 225 tons and 9,096 tons, respectively. Currently, sludge is collected from land based smolt farms. Requirements for cleansing is generally based on reduction in concentration of total suspended solids. Consequently, the fish farmers main effort in sludge handling is technology and systems for such concentration reduction. However, the total flow of nutrients and energy in a fish farming system is poorly documented. To make wise priorities in investments and energy consumption (in e.g. filtering systems, dewatering and transport), in development of technology and making legislation for cleansing, detailed knowledge of the flow of nutrients and energy in salmon farming is required. This can serve as a guide for resource efficient prioritising of research and development in this area.