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Seaweed utilization for integrated bioenergy and fish feed production: Ecosystem services delivered by circular resource management

Research output: Book/anthology/dissertation/reportPh.D. thesis

  • Michele Seghetta
Linear production systems are not environmentally sustainable since they produce waste at a higher rate than nature is able to absorb.
Creation of closed-loop production processes aiming at generating zero-waste is the foundation for a circular economy. Offshore seaweed cultivation can play a key role to transform linear production systems into biobased circular flows. Seaweed can absorb manmade emissions to water, while producing valuable compounds that can re-enter the economic system. In the thesis, Life Cycle Assessment (LCA) methodology is used to analyze the environmental performance of different seaweed exploitation strategies. The main objectives are to identify and quantify the engineered ecosystems services delivered by circular management strategies and propose solutions to improve their environmental performance.
Improvement of Life Cycle Impact Assessment (LCIA) methodologies enables the identification and quantification of regulating services, i.e. eutrophication mitigation in aquatic systems. The methods are based on cradle-to-cradle approach, quantifying fate factors for nitrogen (N) and phosphorus (P) loss from agriculture fertilization to the aquatic environment (paper I). A LCIA method has been developed to
include both nitrogen- and phosphorus-limited marine eutrophication, thus providing a suitable instrument to assess suitability of seaweed cultivation in coastal areas. In a simple scenario, where seaweed is used as fertilizer, an eutrophication mitigation service of -25 kg N eq. and -3 kg P eq. per Mg seaweed dry weight is quantified.
A dynamic model of biogenic carbon has been created to describe the effect of uptake and harvest of CO 2
(HCO3−) by seaweed cultivation and processing system. The model quantifies the ability of the bio-economic value chain to create climate change mitigation (paper II). Specifically, LCA has been used to quantify the climate change mitigation service of three alternative seaweed exploitation strategies: use as feedstock for a biorefinery producing ethanol, protein-rich fish feed ingredient and biofertilizer; use in a biogas plant for production of energy and fertilizer; use as feedstock for a microalgae-based protein production (paper III and IV). All the production systems are carbon negative, meaning that they are
delivering climate mitigation. The service quantification varies between a minimum of -14 kg CO 2 eq. per ha of seawater cultivated, achieved when seaweed were used for combined production of ethanol, fish feed and fertilizer, and a maximum of -662 kg CO 2 eq./ha, obtained for biogas production. Productivity, i.e. harvested biomass per hectare, is an important element in relation to a competitive cultivation and processing of seaweed compared to other energies and protein production technologies.
Optimization of cultivation design could reduce externalities generated by the materials use. Optimization of storage methods, e.g. drying, is necessary to reduce the total energy consumption.
Improvement of the environmental and economical sustainability of seaweed production and biorefining may be obtained by optimized productivity. The latter can be achieved through selective breeding of species, identification of ideal cultivation sites according to environmental parameters and harvest time
designed for maximum output products.
Original languageEnglish
Number of pages140
Publication statusPublished - 2016

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