The use of algae for biofuel production is expected to play an important role in securing energy supply in the next decades. A consequential life cycle assessment (LCA) and an energy analysis of seaweed-based biofuel production were carried out in Nordic conditions to document and improve the sustainability of the process. Two scenarios were analyzed for the brown seaweed (Laminaria digitata), namely, biogas production (scenario 1) and bioethanol + biogas production (scenario 2). Potential environmental impact categories under investigation were Global Warming, Acidification and Terrestrial Eutrophication. The production of seaweed was identified to be the most energy intensive step. Scenario 1 showed better per- formance compared to scenario 2 for all impact categories, partly because of the energy intensive bioeth- anol separation process and the consequently lower overall efficiency of the system. For improved environmental performance, focus should be on optimization of seaweed production, bioethanol distilla- tion, and management of digestate on land.
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Recently,theuseofmathematicaltools,suchasthelifecycleassessment (LCA) methodology for ecologically sound processes, with the purpose of estab- lishing a process designer involving the limits of “cradle to grave” in an efficient and flexible way with less subjectivity, has become an ambitious challenge to be won. Therefore, to generate biofuels with low atmospheric emissions and minimal energy requirements has become crucial to commercial competitiveness. Thus, the objective of this chapter is to approach the current situation of the different sce- narios of microalgal biofuels production by an evaluation of them via a life cycle assessment. The chapter is based on three main topics: (1) fundamentals for structuring a life cycle assessment, (2) biofuels data set reported in the literature, and (3) application of LCA in microalgae biofuels.
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Algae are a promising source of industrial biomass for the future. In order to assess if aquacultured seaweed (macroalgae) could be considered an environmentally friendly source of biomass for bioenergy, life cycle assessments were performed for European countries, comparing methane as a biofuel from the anaerobic digestion (A) of whole seaweeds, (B) of alginate extraction residues, and (C) natural gas as a fossil fuel reference. These results clarify that the sources of electricity and energy used to heat the anaerobic digesters have an important impact. Recycling of materials and use of greenhouses at the nursery stage also allow environmental improvements for system (A). Ecodesign can make algal biomethane competitive in several categories compared to natural gas: a decrease of 21.9% and 54.2% in greenhouse gas (GHG) emissions and 58.6% and 68.7% in fossil depletion for systems (A) and (B), respectively, decrease in ozone depletion, and last but not least, improvement in the marine eutrophication index for system (A). For system (B), benefits are more arguable and dependent on the allocation. To conclude, seaweed could become competitive with terrestrial feedstock for biofuel production in the near future.
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We conducted surveys of six hatcheries and 18 farms for data inputs to complete a cradle-to-farm-gate life cycle assessment (LCA) to evaluate the environmental performance for intensive (for export markets in Chicago) and semi-intensive (for domestic markets in Shanghai) shrimp farming systems in Hainan Province, China. The relative contribution to overall environmental performance of processing and distribution to final markets were also evaluated from a cradle-to-destinationport perspective. Environmental impact categories included global warming, acidification, eutrophication, cumulative energy use, and biotic resource use. Our results indicated that intensive farming had significantly higher environmental impacts per unit production than semi-intensive farming in all impact categories. The grow-out stage contributed between 96.4% and 99.6% of the cradle-to-farm-gate impacts. These impacts were mainly caused by feed production, electricity use, and farm-level effluents. By averaging over intensive (15%) and semi-intensive (85%) farming systems, 1 metric ton (t) live-weight of shrimp production in China required 38.3±4.3 GJ of energy, as well as 40.4±1.7 t of net primary productivity, and generated 23.1±2.6 kg
of SO2 equiv, 36.9 ± 4.3 kg of PO4 equiv, and 3.1 ± 0.4 t of CO2 equiv. Processing made a higher contribution to cradle-todestination-port impacts than distribution of processed shrimp from farm gate to final markets in both supply chains. In 2008, the estimated total electricity consumption, energy consumption, and greenhouse gas emissions from Chinese white-leg shrimp production would be 1.1 billion kW 3 h, 49 million GJ, and 4 million metric tons, respectively. Improvements suggested for Chinese shrimp aquaculture include changes in feed composition, farm management, electricity-generating sources, and effluent treatment before discharge. Our results can be used to optimize market-oriented shrimp supply chains and promote more sustainable shrimp production and consumption.
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There has been a recent resurgence in research investigating bioenergy production from algal biomass due to the potential environmental benefits in comparison to conventional bioenergy crops and conventional fossil fuels. This life cycle assessment (LCA) considered the energy return and environmental impacts of the cultivation and processing of macroalgae (seaweed) to bioethanol and biogas with a particular focus on specific species (Gracilaria chilensis and Macrocystis pyrifera) and cultivation methods (bottom planting and long-line cultivation). The study was based mainly upon data obtained from research conducted in Chile but the results can be applied to other locations where similar cultivation is feasible. Speculative data were also included to test promising data obtained from research. The results suggested that using base case conditions the production of both bioethanol and biogas from bottom planted Gracilaria chilensis was the most sustainable option due to the low input method of cultivation. Using new advances in cultivation and processing methods of long-line cultivated Macrocystis pyrifera however resulted in a much more sustainable source of bioenergy. If these methods can be proven on a large scale, the generation of bioenergy from macroalgae could be highly competitive in terms of its sustainability compared to alternative feedstocks. Future research should bear in mind that the results of this study should however be considered highly optimistic given the early stage of research.
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Seaweed is a key biomass for the development of a biobased economy because it contains valuable components such as proteins, sugars, nitrogen and phosphorus. This paper analyses innovative offshore seaweed cultivation for the production of biorefinery feedstock. The biomass is converted into three products: bioethanol, liquid fertilizer and protein-rich ingredient for fish feed. We performed comparative life cycle assessment of a base case and six alternative production scenarios in order to maximize the benefits and minimize the trade-offs in environmental performance of future macroalgal biorefineries (MABs). The results show that the base case provides a net reduction in climate change factors, i.e. −0.1·10² kg CO2 eq. per ha of sea cultivated despite a cumulative net energy demand of 3.9·10⁴ MJ/ha, 13% of which originates from fossil sources. Regarding the environmental performance of the system, we obtained a reduction in marine eutrophication of −16.3 kg N eq./ha, thanks to bioextraction of nitrogen. For the base case the net impact on human toxicity (carcinogenic effects) was 2.1·10⁻⁴ comparative toxic units per ha of cultivation. The increase in human toxicity is seven times greater than the system can deal with, however reduction of materials for the cultivation lines, i.e. iron ballast, reduces human toxicity to 0.2·10⁻⁵ comparative toxic units. Externalities from the use of biofertilizer affect the non-carcinogenic effects of the system, resulting in 20.3·10⁻⁴ comparative toxic units per ha. Hotspots in the value chain show that biomass productivity is the main constraint against being competitive with other energy and protein producing technologies. Minor changes in plant design, i.e. use of stones instead of iron as ballast to weight the seeded lines, dramatically reduces human toxicity (cancer). Including engineered ecosystem services in the LCA significantly improves the results. As such, an increase in soil carbon stock represents 15% of the climate change mitigation provided by the MAB system. The study shows that MABs can contribute to a regenerative circular economy through environmental restoration and climate mitigation.
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Biomethane produced from seaweed is a third generation renewable gaseous fuel. The advantage of seaweed for biofuel is that it does not compete directly or indirectly for land with food, feed or fibre production. Furthermore, the integration of seaweed and salmon farming can increase the yield of seaweed per hectare, while reducing the eutrophication from fish farming. So far, full comprehensive life cycle assessment (LCA) studies of seaweed biofuel are scarce in the literature; current studies focus mainly on microalgal biofuels. The focus of this study is an assessment of the sustainability of seaweed biomethane, with seaweed sourced from an integrated seaweed and salmon farm in a north Atlantic island, namely Ireland. With this goal in mind, an attributional LCA principle was applied to analyse a seaweed biofuel system. The environmental impact categories assessed are: climate change, acidification, and marine, terrestrial and freshwater eutrophication. The seaweed Laminaria digitata is digested to produce biogas upgraded to natural gas standard, before being used as a transport biofuel. The baseline scenario shows high emissions in all impact categories. An optimal seaweed biomethane system can achieve 70% savings in GHG emissions as compared to gasoline with high yields per hectare, optimum seaweed composition and proper digestate management. Seaweed harvested in August proved to have higher methane yield. August seaweed biomethane delivers 22% lower impacts than biomethane from seaweed harvested in October. Seaweed characteristics are more significant for improvement of biomethane sustainability than an increase in seaweed yield per unit area.
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Life cycle assessment (LCA) is a holistic methodology that identifies the impacts of a production system on the environment. The results of an LCA are used to identify which processes can be improved to minimize impacts and optimize production.
LCA is composed of four phases: (1) goal and scope definition, (2) life cycle inventory analysis, (3) life cycle impact assessment, and (4) interpretation.
The goal and scope define the purpose of the analysis; describe the system and its function, establish a functional unit to collect data and present results, set the system boundaries, and explain the assumptions made and data quality requirements. Life cycle inventory analysis is the collection, processing and organization of data. Life cycle impact assessment associates the results from the inventory phase to one or multiple impacts on environment or human health. The interpretation evaluates the outcome of each phase of the analysis. In this phase the practitioner decides whether it is necessary to amend other phases, e.g., collection of more data or adjustments of goal of the analysis. In the interpretation, the practitioner draws conclusions, exposes the limitations, and provides recommendations to the readers.
The quality of LCA of seaweed production and conversion is based on data availability and detail level. Performing an LCA at the initial stage of seaweed production in Europe is an advantage: the recommended design improvements can be implemented without significant economic investments. The quality of LCA will keep improving with the increase of scientific publications, data sharing, and public reports.
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The invasive rhodophyte Grateloupia turuturu is a large perennial alga, discovered first in Narragansett Bay (Rhode Island) in 1994 and subsequently in the Long Island Sound estuary. The alga's low intertidal to shallow subtidal distribution overlaps that of the native Chondrus crispus. Our field measurements suggest that physical disturbance may promote increased substrate cover by G. turuturu. Molecular quantification of spore abundance suggests G. turuturu produces fewer spores, which also disperse shorter distances than spores of C. crispus. However, sporelings of G. turuturu grew faster than those of C. crispus at all environmentally relevant light levels, salinities and temperatures tested. In addition, the temperature tolerance of G. turuturu sporelings was broader; C. crispus sporelings died just after germination at 30°C; whereas, those of G. turuturu survived. The results have implications for community shifts as coastal waters continue to warm into the future.
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The life history of Porphyra hollenbergii Dawson, a species endemic to the Gulf of California (Mexico), was investigated in relation to temperature, photoperiod and photon fluence rates. The hypothesis was that its life history is controlled by extremes of temperature (< 10°C to > 30°C), photoperiod (short/neutral/long) and photon fluence levels (low/high light). Culture experiments were set up using a factorial 5 × 5 × 3 design with five photon fluence levels (10, 20, 40, 60 and 80) µmol photons m−2 s−1), five temperatures (10, 15, 20, 25 and 30°C) and three photoperiods [8:16, 12:12 and 16:8 light:dark (L:D)]. For the gametophyte phase, the optimal release of zygotospores was at 15°C, with photon fluence level of 60 µmol photons m−2 s−1 and long photoperiod 16:8 L:D. Germination was best at 20°C, a photon fluence level of 60 µmol photons m−2 s−1 and under a long photoperiod 16:8 L:D. The abundance of archeospores differed significantly at temperatures of 25 and 30°C. The number of archeospores mm−2 of the conchocelis tufts was significantly different in the long photoperiod 16:8 L:D when compared with the neutral 12:12 and short 8:16 L:D. The abundance of conchosporangia at temperatures of 15, 25 and 30°C were different and differed from the other conditions. In addition, abundance of conchosporangia mm−2 were significantly different in all photoperiod treatments. Conchospores were released after 6 weeks at 10°C, 20 µmol photons m−2 s−1 at 8:16 L:D. On the basis of our results, we found that water temperatures were the limiting factor for conchocelis growth. However, it is the combination of photoperiod and high water temperatures that are the environmental conditions that appear to control the development of archeospores and conchospores. Porphyra hollenbergii life history is controlled by an array of factors at each stage, strongly suggesting the environmental influence of the habitat on this species.
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