Bioextraction potential of seaweed in Denmark — An instrument for circular nutrient management

Abstract

The aim of the study is to assess the efficacy of seaweed for circular nutrient management to reduce eutrophication levels in the aquatic environment. We performed a comparative Life Cycle Assessment (LCA) of two reference waste management systems treating seaweed as biowaste, i.e. landfill disposal and combustion, and an alternative scenario using the seaweed Saccharina latissima as a resource for biobased fertilizer production. Life Cycle Impact Assessment (LCIA) methods were improved by using a cradle-to-cradle approach, quantifying fate factors for nitrogen and phosphorus loss from fertilized agriculture to the aquatic environment. We also differentiated between nitrogen- and phosphorus-limited marine water to improve the traditional freshwater impact category, making this indicator suitable for decision support in relation to coastal water management schemes. Offshore cultivation of Saccharina latissima with an average productivity of 150Mg/km(2) in Danish waters in 2014 was applied to a cultivation scenario of 208km(2). The bioresource scenario performs better than conventional biowaste management systems, delivering a net reduction in aquatic eutrophication levels of 32.29kgNeq. and 16.58kgPO4(3-)eq. per Mg (dry weight) of seaweed, quantified by the ReCiPe and CML impact assessment methods, respectively. Seaweed cultivation, harvest and reuse of excess nutrients from the aquatic environment is a promising approach for sustainable resource cycling in a future regenerative economy that exploits manmade emissions as a resource for closed loop biobased production while significantly reducing eutrophication levels in 3 out of 7 Danish river basin districts. We obtained at least 10% bioextraction of phosphorus manmade emissions (10%, 89% and >100%) and contributed significantly to local nitrogen reduction goals according to the Water Framework Directive (23%, 78% and >100% of the target).

Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation?

“…A stepwise approach to maximizing the benefits from seaweed aquaculture would include to sequentially extract high-value molecules used in the food, pharma or biotech industries, such as bioactive sulphated polysaccharides, pigments, and antioxidants (D'Orazio et al, 2012;Mak et al, 2014;Herrero and Ibáñez, 2015), and then convert-after extraction of carbohydrates for the hydrocollid industry or for biofuels production-the lowervalue residue to protein concentrates with value in the feed industry (Francavilla et al, 2015;Bikker et al, 2016;Seghetta et al, 2016). Algal biorefineries have evolved from concept and laboratory tests to pilot-scale plants involving a range of seaweed species and environments (e.g., Baghel et al, 2014;Lorbeer et al, 2015;Bikker et al, 2016;Masarin et al, 2016), and may soon become commercial operations.…”

“…Algal biorefineries have evolved from concept and laboratory tests to pilot-scale plants involving a range of seaweed species and environments (e.g., Baghel et al, 2014;Lorbeer et al, 2015;Bikker et al, 2016;Masarin et al, 2016), and may soon become commercial operations. The range of potential products also include using the nutrient-rich residues from a biofuel production for fertilizer, which may also serve for C retention in soil (Seghetta et al, 2016). New bioenergy concepts also use seaweed by-products and debris in energy production (Kaspersen et al, 2016).…”

Seaweed resources of the Baltic Sea, Kattegat and German and Danish North Sea coasts

“…Current research aims to identify new applications for these and other seaweed species that are present in the area. While the suboptimal conditions limit the profitability of the industry to some extent, seaweed harvesting and seaweed aquaculture are currently promoted as a way to decrease the nutrient load to eutrophic coastal areas and to mitigate the negative symptoms of eutrophication (Seghetta et al 2016). Seaweeds also gain in interest as a potential alternative to fossil fuels (Pechsiri et al 2016).…”

The Environmental Risks Associated With the Development of Seaweed Farming in Europe - Prioritizing Key Knowledge Gaps

“…Seaweeds in suspended cultivation remove inorganic nutrients from the marine environment during growth (Kerrison et al, 2015;Marinho et al, 2015). Positive remedial effects will occur when the quantity and proportion of nutrients removed are equal to those added by anthropogenic activities (Seghetta et al, 2016b). However, undesirable effects could occur if nutrient removal by cultivation results in concentrations which fall below that required for natural primary productivity, and very large-scale culture of macroalgae will extract proportionate amounts of nutrients from the surrounding water body (Lüning and Pang, 2003).…”

“…At larger regional scales, cultivation projects may contribute substantially to remediation of excess nitrogen if co-located in suitable areas of high anthropogenic nitrogen input. A Life Cycle Impact Assessment (LCIA) of seaweed cultivation and nutrient extraction in Europe, indicates that at large scales (208 km 2 ), seaweed cultivation can have a positive effect through bioextraction of N and P from anthropogenic activities in the marine environment and aid management strategies at the water body level (Seghetta et al, 2016b).…”