The estimation of maximum macroalgae production is calculated by converting from available of total marine fish production. To produce 158,018 tonnes of marine fish, with feed conversion ratio of 1.25:1 (Jackson, 2012), require 197,522.5 tonnes of feed. Therefore, DIN and DIP release are accounted for 45% of total release N and 18% of total release P. The available of DIN is approximately 55,109 tonnes and DIP is about 24,888 tonnes. The macroalgae productivity can be found by calculate with brown macroalgae yield. However, yields from scaled-up experiences are lacking, especially from Europe, so in this project will use a yield 120 tonnes wet weight of Saccharina Latissima per hectare per year and a value of 15% dry weight (Holdt & Edwards, 2014) since there is only available yield of brown macroalgae. The yields of 120 tonnes wet weight will be assimilate 576 kg N with 3.2% N dry weight (Holdt & Edwards, 2014). The macroalgae production of this yield is approximately 11,480,995 tonnes. In addition, the amount of maximum macroalgae production with 11,480,995 tonnes is done by assuming 100% of nitrogen absorption during macroalgae cultivation.
In comparison, the calculation by James (2010) suggests that 40.3 tonnes of nitrogen will go into environment per 1,000 tonnes of salmon produced and assuming that the nitrogen is between 1% and 2% of dry weight of seaweed with 90% of water content. This could equal to 40,300 tonnes of wet seaweed per 1,000 tonnes of salmon produced (James, 2010). The maximum macroalgae production, which calculated by James concepts, is equal to 6,368,125.4 tonnes. Since there are two amounting different of maximum production, which is accounted for 55.4% difference. It is certainly that the amounts of nitrogen concentrations are difference, which may cause the different output. Since the estimation of macroalgae in report by James (2010) did not put much detail of macroalgae species, which could be red, green or brown algae, so the biochemical will be different and the performance of nitrogen absorption would be different also. In other words, it is obviously that the availability and efficiency of recapture of nitrogen would, in the middle of other things affect final yields.
In addition, an idea of IMTA concept actually can use with both saltwater fish aquaculture and freshwater fish aquaculture. It appears in figure 1 that mainly aquaculture in England and Wales have been flavor with freshwater fish aquaculture than seawater fish aquaculture. Considering freshwater fish, it also has potential to adapt with IMTA and can produce more macroalgae as it may be an optional choice to get more macroalgae production as much as possible. Even though, this report is focused on marine macroalgae production in the UK, if there is a change to pursue more macroalgae production by adapting IMTA concept with freshwater fish aquaculture in the UK. It would be better for the future of macroalgae-derived biofuel to have many chances to derive as much as possible. To estimate the macroalgae production potentially from freshwater fish aquaculture in the UK, assuming all the conversion and nitrogen absorption are same as saltwater fish aquaculture. From Facts & figures sheet by the marine Socio-Economics Project (MSEP), showed that freshwater fish productions in 2012 are accounted for 11,276 tonnes (Williams, 2014) and 97% of total freshwater fish productions are rainbow trout. With the same condition and calculation as saltwater fish aquaculture, the maximum macroalgae production by adapting IMTA concept in all freshwater fish aquaculture in the UK, then they will able to produce 819,271 tonnes of macroalgae. Comparing to macroalgae production by adapting IMTA system with saltwater fish productions, the production from IMTA with freshwater fish aquaculute are much lower due to the freshwater fish productions are not major market in the UK. Additionally, it is well known that Scotland is dominated by saltwater fish aquacultures and massive salmon productions are commonly exported to the USA. The salmon markets are increasing every year (Department for Environment Food & Rural Affairs, 2015). In contrast, English finfish aquaculture has not developed as same level as Scottish. Moreover, trout farms in the UK have no major centre or hub and the salmon farming in England is really small due to focusing on specialist hatcheries rather than food producers (Williams, 2014).
2.3.2 The integration of offshore seaweed production
Offshore development has been raising attention to many countries, especially in regards to renewable energy sources (Allard, 2009). Offshore aquaculture activities are highlighted as one of the areas, where further growth is possible (Jansen et al., 2016). The use of wind turbines as structures on macroalgae cultivation, likely offer essential benefits. The preliminary advantage of macroalgae offshore cultivation is that there is less competition for agricultural land. However, there is relatively little research into offshore cultivation due to the technical challenges and cost effective. The development of aquaculture facilities in conjunction with offshore wind farms by using wind turbines as structures for seaweed cultivation offer its benefits (Saeid & Chojnacka, 2015). Additionally, the concept of using offshore wind farms for aquaculture is promising, although algae cultivation with economics for this approach needs further investigation (Carlsson et al., 2007).
According to a report from Sustainable Energy Ireland (SEI) marks that it is currently not known the level of salinity, turbidity and other conditions surrounding wind farms would be able to support algae cultivation as effective production (Roberts, 2012), so this requires further research to prove if it is possible and can be commercial. The idea of offshore wind farm combined with mussel farming and macroalgae cultivation could accelerate the development due to cost sharing (Kapetsky, Manjarrez & Jenness, 2013). In other words, as long as offshore wind farms require frequent visits for maintenance and monitoring. It might possible to schedule routine maintenance of the wind farm alongside maintenance of integrated aquaculture. It is an advantage for other to use marine areas as integrated aquaculture. A figure 4 shows the concept of offshore wind farm cultivation as an idea that offers potential cultivation for the future. Remarkably, the experts interviewed also represented that this concept was deserving of further investigation (Roberts, 2012).
Figure 4. The concept of multi-use installations for offshore wind and seaweed
(Burg et al., 2013)
Furthermore, there are a few case studies within this kind of concept by EU-funded research project, known as Innovative Multi-purpose offshore platforms: Planing, design and operation (MERMAID). They are developing the next generation of offshore platforms and also developing a multi-use offshore platform (MUP), purpose to integrate energy extraction with aquaculture activities (Yttervik, et al., 2015). The project will planning and design MUP to proficiency use ocean space in order to exploiting renewable energy and aquaculture (MERMAID, 2014). Initially, MERMAID has four different infrastructures on sites, including the Baltic Sea site, the transboundary area of the North Sea site, the Atlantic Ocean site and the Mediterranean Sea site (offshore WIND staff, 2014). All sites have four different environmental conditions, which are focused on specific challenges as following:
• The Baltic Sea site is focused on a typical estuarine area between fresh water and marine water.
• The North Sea site is focused on a typical active morphology.
• The Atlantic Ocean site is focused on a typical open deep-water site.
• The Mediterranean Sea site is focused on a typical sheltered deep-water site.
However, there are no public authorities at national level and no plans by the national government have decided to realise MUP in the Baltic Sea, Atlantic Ocean and Mediterranean Sea. While MERMAID project has brought wind energy sector and aquaculture sector together in order to learn and discuss MUP (Stuiver et al., 2016). Various government agencies have been associated in the process as well, but there still is much hesitancy to invest in MUP. Due to the oscillation of the offshore wind sector to invest MUP, the Dutch government is exploring risks and opportunities to prepare for potential legal regulations such as opening up wind farm areas for co-use (Stuiver et al., 2016). For instance, there is MUP case at North Sea site that represented in EWEA Offshore 2015 in Copenhagen. It is estimated of 1,000 MW offshore wind farm, consists of 100 units of 10 MW wind turbine. The design layout shows in figure 5 and the estimation of the annual salmon production is predicted to be 60,000 to 70,000 tons and accounts for 73-85% of electricity yield for this case (Yttervik, et al., 2015).
Figure 5. Layout of MUP case at North Sea site (Yttervik, et al., 2015).
To estimate the macroalgae production in the UK by the multi-use offshore platform (MUP), regarding to the previous estimation by Yttervik et al., 1,000 MW installations of offshore wind turbines can produce 60,000-70,000 tonnes annually. Since there are 5,053 MW installed in the UK with 1452 turbines (Wikipedia, 2016: the Wind Power, 2016), which can theoretically produce 353,710 tonnes of salmons per annum by MUP concept. This can be estimated the macroalgae production by using calculation as same as IMTA concept, which assume that salmon release waste material, consists of nitrogen and phosphorus. Then the maximum macroalgae production can produce in the UK by integration of offshore wind farm is approximately 25,699,242 tonnes per annum. However, there was a study that showed the difficult operation of fish aquaculture in the North Sea during each season and the relative shallowness of the southern North Sea does not allow fish cages to be submerged due to the compensation for temperature conditions (Jansen et al., 2016). There are also argument about the placing fish cages within the offshore wind farm might cause conflict within the operation and maintenance and also conflicts between the offshore wind turbines operation and aquaculture farms during their installation (Yttervik et al., 2015). Even though the maximum production potential is massive, there will face lots of issues, as it is very sensitive with environmental impacts, operations, infrastructures and its regulations. Nevertheless, the integration of offshore wind farms with aquaculture activities need more investigation in order to prove that it is reliability for technical and economic feasibility. To attract investors, it is current uncertain due to a level of development and it requires considerable strategies to make it happen for commercial scale. It still needs more researches and analysis to be done and proved. This case study presents promising example of future innovative multi-use offshore wind farms with aquaculture.