(41a) Life Cycle Assessment of Macro Algae as a Bio-Fuel Feedstock Source

The development of new technologies and methodologies for producing various petroleum substitutes from renewable materials is crucial in our attempts to improve environmental sustainability and limit dependence on foreign oil. In developing new renewable alternatives, it is important to fully understand the environmental implications of these technologies. Life Cycle Assessment (LCA) is a tool that can be used to explore and evaluate the full range of environmental, social and economic impacts that emerging technologies or processes may have. Providing this information to the scientific research community can inform ongoing debates regarding the relative environmental impacts of alternative energy sources that are currently being explored. This will help to focus the scientific, regulatory and investor communities on those technologies which appear the most promising.

The use of macro algae from an integrated multi-trophic aquaculture (IMTA) farm to produce biofuels appears to be a promising technology. While the macro algae removes waste products from fish farms and potentially inhibits eutrophication, it also has the potential to be a financially viable raw material for the development of commodity chemicals or renewable energy. An attributional LCA of a hypothetical process consisting of the cultivation and growth of macro algal species in an IMTA farm in coastal Maine through to the fermentation and purification of mixed organic acids at the University of Maine was performed.

The LCA was a cradle-to-gate analysis and the involved processes include the hatchery and cultivation of juvenile seaweed on nets, the grow-out process and harvesting of adult seaweed blades, a milling/grinding operation to produce an algae slurry, a pretreatment and acidogenic digestion process for converting the biomass to organic acids, and lastly, purification methods to obtain the desired product. The system boundaries of the study also included the transportation of juvenile seaweed from the hatchery facility in Franklin, ME to the grow-out phase in Cobscook Bay and Eastport, ME and transportation of adult seaweed blades from Cobscook Bay to the conversion process located at the University of Maine in Orono, ME.

The mixed organic acid product primarily consists of acetic acid with some propionic and butyric acids. Depending on the greatest economic feasibility, the mixed organic acid product can be further purified to be sold for vinegar production or for various industrial chemical applications. With further processing, the organic acids can be used to produce chemicals such as ketones or esters or mixed alcohol fuels, including ethanol, propanol, and higher chained alcohols. Alcohols are important solvents in many industrial and chemical applications, and mixtures of alcohols can be used as high octane gasoline additives or replacement energy resources.

Using macro algae to reduce the amount of nutrients emitted from fish facilities is of great interest for abating the eutrophication risk of aquaculture facilities. The concept of IMTA is to grow extractive species together with finfish in order to diversify the farm production and reduce environmental impacts. While all three of the products of a proposed IMTA (finfish, shellfish and macro algae) have existing markets for human consumption, the market for macro algae is small and would be over supplied if IMTA developed on any significant scale.

Because of the eutrophication risk, the ability to quantify the nitrogen and phosphorous removal potential of the cultured algae is of significant importance to the farm operators. LCA was used to fully understand the environmental impacts of these technologies by providing an analysis of the global warming potential and eutrophication potential of the processing technology and applied algal grow-out process. In reality, the modeled system has two modes of eutrophication. The first is the ability of the algae to remove nutrients from either the discharge stream of a land-based facility or from the surrounding waters of a netpen system. This has a potential benefit as it is removing nutrients from our coastal waters. The second mode of action is in the air eutrophication potential, primarily from the emission of NOx in the generation of the electrical energy and burning of fossil fuels needed to conduct operations. If the proposed process were implemented, operators of IMTA farms would benefit from the ability to sequester nutrient losses from their operations and derive additional value from the harvested macro algae.

Results

The system that was evaluated has multiple environmental impacts associated with it. However, those that are of prime importance include the uptake and emission of CO2, phosphorous and nitrogen. The uptake and emission of CO2 serves as a proxy for examining the potential impact on global warming from the production of macro-algal based biofuels. Typically, biofuels from algae are considered CO2 neutral, as any CO2 emitted from burning them is removed from the atmosphere or in this case, the oceans during their growth. However, a certain amount of energy is required to produce and refine the algae into useable alcohols, resulting in an additional contribution to global warming.

The energy consumption of the processes involved in the production of both algae and organic acids were also evaluated. The three processes that consumed the largest amount of energy were the juvenile grow-out phase, the marine grow-out phase, and the distillation process. The juvenile grow-out phase of the production of algae requires a significant amount of energy for pumping large quantities of water. The marine grow-out phase requires maintenance of the seaweed once a week for six weeks, which uses both diesel and gasoline for transportation vessels. The distillation process during the purification stage is identified as the most energy intensive processing step because of the large amount of required steam. Electricity was the form of energy that was consumed in the largest quantity, which is as expected since the majority of the processes require electricity for running equipment.

If a larger juvenile grow-out system was developed into an actual production of seeded juvenile nets on the scale of the proposed system, it would most likely consume considerably less energy than our model predicted. This result is supported by two main considerations. First, an appropriately scaled facility would utilize larger, more energy efficient pumps to move the required volume of water, rather than using many small pumps as assumed by our model. Most aquaculture facilities attempt to take advantage of gravity as much as possible by pumping water to a high point and then allowing the water to flow to the required processes either in series or parallel as needed. By integrating the juvenile net grow-out raceways with the effluent water of a marine finfish hatchery, the juvenile raceways would be located downstream of other fish processes and would share the energy requirements for pumps. Second, it is likely that larger raceways could be constructed so that a larger volume of nets could be grown with a lower amount of energy required per area of net. It is also likely that the density of nets in the existing raceways could be increased to grow more juvenile biomass while using the same amount of energy.

While the ability for biomass resource development to occur in a sustainable manner is of great concern, macro algae appears to be a promising potential source of renewable energy. The economic benefits of producing a valuable end product by reducing a potential source of waste are apparent. The growth of macro algal species to abate the eutrophication potential of fisheries will enable farmers to have a lower environmental impact and more efficient processes. The use of macro algae as a source of biomass for the production of mixed organic acids and alcohols will potentially increase the financial viability of biofuel production without competing with food production, as do many current sources of biomass.