Life cycle assessment of phosphorous management for RAS sludge
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Phosphorous (P) is an essential nutrient and its recovery from aqua-culture sludge is the main core of this study. As the global reserves ofphosphate rock are likely to be depleted in the next 50-100 years, it iscrucial to investigate a more sustainable P management. The presentresearch first introduces the situation of aquaculture in the Norwe-gian context and describes the main characteristics of RecirculatingAquaculture Systems (RAS). Then, the role of Life Cycle Assess-ment (LCA) in assessing the environmental impacts of aquacultureand sewage sludge treatment is examined. Follows the design of ahypothetical RAS for harvesting Atlantic salmon in its whole life pro-duction cycle. Different technologies for the treatment of fish-basedsludge and phosphorous recovery are modelled in SimaPro, namelyanaerobic digestion (AD), thermal treatment (incineration) and en-hanced biological phosphorous removal (EBPR) with struvite crystal-lization. The different scenarios are considered in a local and in acentralized alternative. The functional unit (FU) chosen is 1t of rawsludge, which is treated and produces phosphorous (P)-rich fertilizer,or biogas. The different scenarios were compared with the referencescenario, consisting in land spreading of sludge without prior treat-ment or conditioning. The anaerobic digestion of fish-based sludgein the local scenario, to produce liquid fertilizer from digestate, andheat and electricity from biogas was proved to cause the lowest envi-ronmental impacts, especially in terms of human toxicity. The highestenvironmental impacts belong to the reference scenarios, both in thelocal and centralized option. The option of thermal treatment showedlower values compared to the EBPR method, due to the reuse of theheat produced in the incineration plant.