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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.
    Vedin, Felix
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Sandström, Camilla
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    A comparison study of PV and battery technologies for EWB off-grid electrification projects in Sub-Saharan Africa2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Only 10 % of the rural population in Sub-Saharan Africa has access to electricity. At the same time the Sub-Saharan countries are close to the equator and get many sun hours a day, leading to a huge potential for solar energy. This report aims to compare different PV system components for use in Sub-Saharan Africa to facilitate EWB for their work in electrification projects in the areas. The PV system will be compared with the following factors: economic, adoptability, scalability, environmental impact and efficiency, weighed in that order. A case simulation was made for a village around Nairobi were 20 households would be supplied with solar power. Both Polycrystalline silicon cells and thin filmed CIGS were simulated were the Poly c-Si cell was both the cost-efficient and scalable choice. Poly c-Si cells was also concluded to be advantageous of the crystalline cells by the chosen factors. Pb-acid batteries are best suited for off grid PV systems in rural areas. Different types of Pb-acid batteries can be used depending on the area’s typology. Off grid solar powered microgrids could be the solutions for an increased socioeconomic wellbeing for communities in rural areas.

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