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  • 1.
    Björn, Erik
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    A circular production of fish and vegetables in Guatemala: An in-depth analysis of the nitrogen cycle in the Maya Chay aquaponic systems2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study was done with the aim of deepening the understanding of the Maya Chay aquaponic systems. To meet the aim, a literature study on aquaponics, with an emphasis on the nitrogen metabolism in such systems, was conducted. Furthermore, a deep investigation of the specific Maya Chay systems was made to understand how these systems might be different from the general aquaponic designs. Finally, two nitrogen balances were developed with the purpose of examining the dynamics of the nitrogen transformations in two Maya Chay aquaponic systems. The measurements for the nitrogen balances was made between Mars 2017 to July 2017, and the model for the nitrogen balances evaluated the amount of nitrogen as:

    i) nitrogen input to the system through the feed,

    ii) nitrogen assimilated by the fish and the plants,

    iii) nitrogen accumulated in the sludge, and

    iv) nitrogen lost to the atmosphere through denitrification and similar processes such as anammox.

    The resulting nitrogen balances showed some interesting differences in the dynamics of nitrogen distribution. In the smaller Maya Chay XS system in Antigua, only 36 % of the nitrogen input was assimilated by the fish (30 %) and the plants (6 %) and 64 % of the nitrogen input could be regarded as lost, either to the atmosphere (46 %) or in the sludge (18 %). The other nitrogen balance showed that the distribution of nitrogen in the Maya Chay S system in Chinautla is much more efficient in taking care of the nitrogen input. In this system 70 % was assimilated by the fish (33 %) and the vegetables (37 %) and the remaining 30 % was lost, either to the atmosphere (14 %) or in the sludge (16 %).

    The nitrogen balances also showed that both systems are almost equally efficient in terms of nitrogen assimilation by the fish, and that the big differences lie in the rate of nitrogen assimilation by the plants (6 % vs. 30 %) and in the nitrogen loss to the atmosphere (46 % vs. 14 %). A likely explanation for these differences is the difference in design of the vegetable beds, where the less efficient system in Antigua has a large surface area for the vegetable bed, but only a small portion of this could be utilized for vegetable growth. Furthermore, a consequence of the larger surface is a larger anoxic zone in the bottom of the vegetable bed, which promotes the growth of denitrifying and anammox bacteria. These kinds of bacteria convert the dissolved ammonia, nitrite and nitrate to gas forms of nitrogen, such as nitrogen gas and nitrous oxide and thus nitrogen is lost from the system to the atmosphere.

    Finally, this study also showed a great difference in the ratio of vegetable to fish production between the systems, where the ratio was 0.43 in Antigua and 2.7 in Chinautla. This ratio further indicates the difference in design between the systems, especially regarding the vegetable beds, has an impact on how well they perform, both in terms in economic and productivity terms, but also in terms of the release of greenhouse gases (nitrous oxide). It can therefore be concluded that the original design of the Maya Chay system (i.e. the Chinautla system) is the preferable one.

    Even though the accuracy of the measurements in the experiments could be improved for future studies, this study has demonstrated the value of making nitrogen balances for aquaponic systems. Nitrogen balances increase the knowledge of the performance of the system and they increase the understanding of the dynamics of nitrogen transformations that takes place in the system. This knowledge can then be utilized to adjust the design and/or verify if either the aquaculture or hydroponic system is properly designed.

  • 2.
    Johansson, Fredrik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Strategic Sustainability Studies.
    Tornberg, Patrik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies. WSP, Sweden.
    Fernström, Astrid
    A function-oriented approach to transport planning in Sweden: Limits and possibilities from a policy perspective2018In: Transport Policy, ISSN 0967-070X, E-ISSN 1879-310X, Vol. 63, p. 30-38Article in journal (Refereed)
    Abstract [en]

    Research on sustainability and transport has paid increasing attention to how the purpose of the transport system is framed, often arguing that there is a need to shift the focus of transport planning and policy from the physical infrastructure to mobility and accessibility. Sweden's national transport policy also has elements of this shift, most noticeable in the so-called four step principle, where the possibility to affect the need for transport and choice of transport mode (step 1) and the possibility to use existing infrastructure more efficiently (step 2) should be considered before large reconstructions (step 3) or new infrastructure (step 4) is chosen as the solution to transport related problems. The aim of this article is to study whether the practical implications of Swedish national transport policy are consistent with the ambitions expressed in the four step principle, with particular focus on the Swedish Transport Administration's (STA) mandate to finance different measures. Based on an analysis of policy documents and semi-structured interviews the main finding of the analysis is that many step 1 and 2 measures do not fall within the financial mandate of the STA. The implementation of the four step principle therefore depends on the commitment among other actors than the STA to implement step 1 and 2 measures. Furthermore, it is concluded that the limits to the STA mandate has consequences for the ability of the STA to engage in collaboration with the actors on which it depends, and that strengthening the STA's mandate to finance a desired function rather than physical infrastructure is likely to increase commitment among other stakeholders to work with these measures. Such a step would imply a different regulatory framework than the current, more in line with ”the sustainable mobility paradigm” (Banister 2008) and could contribute to a good accessibility to different amenities at the same time as negative environmental impacts are reduced.

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