Abstract
The ability to collect waste feed and faeces from closed aquaculture systems in the sea (CCS) has been highlighted as an environmental advantage. Theoretical sludge collection efficiencies are available, yet efficiencies during commercial scale CCS production are almost nonexistent. Therefore, this was scientifically studied at a production site using parallel Ecomerd CCS systems connected to a sludge separator. The collection system utilizes a particle trap combined with mechanical filtration for separation of water and particles. Based on the analyzed concentrations in the sludge it was calculated that the system recaptures ~ 11% of the solids, 3 % of the nitrogen, 9 % of the phosphorous and 8% of the organic carbon from the produced waste. The collected sludge was classified as low in heavy metals, hence there are no restrictions in the agricultural/green areas where it could be used as a fertilizer. The study shows that CCS with sludge collection can reduce discharge to the recipient.