Internship report Jiska van Vliet -...
Transcript of Internship report Jiska van Vliet -...
Aquaponics
Internship report
Jiska van Vliet
Internship provider: TGS | Business and Development Initiatives
Supervisor TGS: Klaas Evers
Supervisor WUR: Peter Leffelaar
Contents Introduction ............................................................................................................................................. 1
Activities .................................................................................................................................................. 3
Projects ................................................................................................................................................ 3
Driel ................................................................................................................................................. 3
Iraq .................................................................................................................................................. 4
Indonesia ......................................................................................................................................... 4
Almelo ............................................................................................................................................. 6
Other ............................................................................................................................................... 6
Miscellaneous ...................................................................................................................................... 7
Screening of funding opportunities ................................................................................................. 7
Informative publications ................................................................................................................. 7
Networking ...................................................................................................................................... 7
Meetings .......................................................................................................................................... 8
Answering various questions .......................................................................................................... 8
Literature reviews ............................................................................................................................... 8
Reflection ................................................................................................................................................ 9
Acknowledgements ............................................................................................................................... 11
Appendix I ‐ Photo overview of the system in Driel..............................................................................13
Appendix II ‐ Aquaponics ‐ A literature review......................................................................................17
Appendix III ‐ Feasibility of saline aquaponics ‐ A literature review......................................................43
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Introduction
For my internship, I have worked at TGS | Business and Development Initiatives for four months. TGS is a small Dutch organisation which is involved in initiating and supporting various business activities worldwide. These businesses can facilitate positive economic and social change on a community level. TGS believes that entrepreneurship must be encouraged. TGS is involved in the businesses through project development, conducting feasibility studies and market research, giving advice on business administration and strategy development, connecting them to relevant partners and developing plans for social activities. Examples of business activities in which TGS is involved are a Cashew nut processing factory in Côte d’Ivoire and a chicken business in Central Asia. Currently, TGS is working with various aquaponics projects. Aquaponics is a highly efficient sustainable food production method, in which cultivation of fish and vegetables is integrated into one system (Figure 1, for more information, please refer to Appendix II – Aquaponics ‐ A literature review). TGS believes that aquaponics can play a major role in improving
the access to sufficient healthy food especially for marginalised groups and can contribute to food security and development. TGS has already established such systems in both Egypt and The Netherlands. However, the knowledge base for aquaponics needs to be expanded in order to prevent future problems in new projects. In addition, the starting of new projects requires a high time investment, while the current employees of TGS were also involved in other time consuming projects. Hence, TGS was looking for someone who would be able to do more research regarding the biological functioning of the system, and also support the TGS staff in the initiation of new aquaponics projects. This vacancy was ideal for my internship placement. When I heard about aquaponics, it immediately sparked my interest and I was highly motivated to find out more about the functioning, the opportunities and threats of this system. With my
scientific background in Biology and Plant Science, I could contribute to the technical knowledge required for the development of aquaponics systems. As a WUR student, I could more easily access information both through the University library and through contacting experts. Moreover, in this working environment, I would gain more experience with all stages of project development and execution. Through my involvement I would gain many insights, skills and competencies which are required for working on a project basis, but also for working in an organisation in general. Moreover, the projects in which TGS is involved are largely aimed at development. As I am highly attracted to development work, this would be a very valuable working experience for me. I was not assigned to one clear, delineated task. Rather, just as my colleagues, I contributed to projects as part of the team. Responsibilities were shared between us; however, mutual feedback was always part of the process. Below, the activities in which I was involved during my internship are described. TGS works on a project basis and I have been involved in different phases of several projects. Activities directly related to a specific project, such as designing the project and applying for funds, have been described per project under ‘Projects’. Throughout the internship I have worked on many other tasks for TGS, which are described under ‘Miscellaneous’. As part of the internship, I also conducted literature research and wrote two reviews. This is described under ‘Literature reviews’, and the reviews can be found in the Appendices. The report ends with a final personal reflection on the internship and the acknowledgements.
Figure 1: Simple
representation of aquaponics
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Activities
Projects
Driel
One of the projects was to set up an aquaponics system at AquaVita in Driel. TGS had already established good contacts with AquaVita. AquaVita has been involved in the establishment of fish farms and the organising of training courses in fish management, and exploits a shop for fish farm supplies and a fishpond. AquaVita is owned by ir. Dicky van Zanten, who is a Wageningen Fisheries and Aquaculture graduate and is an expert in fish management. Mr. van Zanten was very interested in aquaponics, and had agreed to the building of a system in a greenhouse on his property in cooperation with TGS. The objectives of the system would be to gain more practical knowledge on aquaponics, be able to do some experimental research on the system, and use the system for demonstration purposes. Mr. van Zanten would be able to monitor the system closely, and his expertise on fish management was very welcome. Two funds were applied to for this project. Both funds were aimed at SME’s (Small and Medium sized Enterprises, or MKB in Dutch). So‐called innovation vouchers could be obtained which allowed SME’s to hire knowledge partners to do research on an innovation which would stimulate the business opportunities of the enterprise. The first application I filed was for an MIT (MKB Innovatiestimulering Topsectoren) innovation voucher issued by AgentschapNL. This application consisted of filling in an application form. Most of the form consisted of formal questions regarding previous subsidies and details of the applicant in order to check eligibility. Only a small paragraph describing the project was required. Hence, this application was quite straight forward. After submitting the application I was called by someone from AgentschapNL. He informed me that the subsidy would be granted on the condition that we would find another knowledge partner because AquaVita did not meet the formal requirements of ‘knowledge institute’ set for the voucher. As we were already working together with AquaVita, we could not meet this condition, hence, the application was rejected. A similar innovation voucher was available for SME’s in Gelderland, issued by FoodValley. A colleague was working on this application and made an appointment with someone at FoodValley. This was a useful meeting, in which we explained the plans TGS had with aquaponics in general and the system in Driel specifically. FoodValley was very enthusiastic about the ideas, and we got some useful insights in the assessment criteria that were used by FoodValley. After this meeting, the application form was filled in by a colleague. This application form was a lot more elaborate than that of the MIT innovation voucher. The information we obtained during the meeting was quite useful and I helped with answering the questions in such a way that it met the assessment criteria as much as possible. Shortly after the application, the subsidy was granted. In the project design, I contributed by designing a research plan. This included, for instance, listing the variables which should be monitored and at what frequency, and listing the variables which could be manipulated. I also advised on cold‐resistant plant species which could be used, and other mostly plant related technical aspects of the system. The specific design for the system was primarily made by a colleague in consultation with mr. Van Zanten, and little contribution from my part was necessary (Figure 2). My colleague, mr. Van Zanten, and I started building the system in November and after a short period of cycling the fish and pre‐grown seedlings were introduced at the end of December/beginning of January (for an overview in pictures, see Appendix I – Photo overview of the system in Driel).
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Figure 2: Design of the Aquaponics center in Driel (by Rutger Toorman)
Iraq
Another project I was involved in was a project in Iraq. The starting point of this project was a local contact who was in the process of building an aquaponics system in Basra with help of the local University. He had contacted us to seek technical advice and suggested to work together to expand his project, and in September I was assigned as his primary contact. However, he did not have very specific ideas about what this expansion would imply and asked for our suggestions. Also, it was not known whether any funds would be available. Hence, there was little framework available for designing the project. However, we designed a very basic project in which an aquaponics training and distribution centre would be set up. This kind of centre would be very much in line with the objectives of TGS. This basic project design could be easily adapted in case the local partner in Iraq would be able to provide us with a better defined project context. However, it could also be adapted to other projects in other countries. I wrote a draft for a proposal for the designed project. The proposal included, amongst others, an explanation of the functioning and opportunities of food production using aquaponics, a description of TGS and their past experiences with aquaponics, the objectives of building an aquaponics centre, a description of some of the steps necessary for implementing the project (e.g. feasibility study), etc. Initially, this proposal was aimed at the Iraqi context. Hence, I did some literature research concerning this context (for instance regarding agro‐ecological conditions, current agricultural production, food security and consumption, employment levels, business climate). One paragraph in the proposal was specifically about the Iraqi context, and how aquaponics systems would fit in here. In other paragraphs, references were made to the Iraqi context. I also was involved in searching for funding resources for this project. For this purpose, I contacted the Dutch Embassy in Iraq, but I was redirected to AgentschapNL. Currently, there were no funding opportunities available for such a project in Iraq. However, a new fund would open up for Iraq, and could be applied for in 2014. Other funding opportunities did not come to any results yet, either.
Indonesia
A specific fund which could be applicable for an aquaponics project was brought under our attention through the Dutch Embassy in Indonesia. Based on an initial screening of the call for proposals in which some of the requirements were identified, contacts were sought with existing partners in Indonesia. As these partners were enthusiastic, it was decided to aim at implementing a large aquaponics project there.
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The requirements for the specific call for proposals gave a framework for designing the project for instance in terms of some broad objectives and partnering requirements. In consultation with the local partners, the objectives of the project were established based on both the local context of constraints and resources and local demands and the objectives of TGS concerning entrepreneurship and social change. Information on the local context was partially received through the local partners, and partially obtained through literature review, largely using internet resources. I was involved in this project from the start. Based on the call for proposals, I made a summary of the requirements of the fund, which provided a clear overview to be used in designing the project. Also, I did a lot of background research which we used in the design phase. During the brainstorm sessions I made valuable contributions through bringing in own ideas and critically assessing others (Figure 3).
Figure 3: Result of one of the brainstorm sessions on the Indonesia project
The project would be a research project. Apart from TGS and the known local partners (who were involved in community development), the University of Palangka Raya would also be a partner in this project. In an experimental setup, aquaponics pilot systems varying in size, design, and level and type of input would be built in order to gain knowledge on aspects such as obtainable production levels, nutrient balances, required inputs such as fish feed, construction materials and technical equipment, and management strategies for different fish and vegetables in the different experimental systems. Through participatory focus group meetings with the identified target groups, the different systems would be demonstrated and evaluated, discussing the objectives, preferences and constraints of the target groups. Also, market research would be executed. Based on the research outputs, suitable aquaponics systems would be designed for the target groups. Consequently, an aquaponics centre would be established where systems will be demonstrated and produced. People would be able to buy all necessary inputs and receive training and advice for starting and maintaining an aquaponics system at the centre.
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I wrote a project proposal for this project design. The proposal was quite comprehensive. It was meant to use as a starting point for funding applications, but also for internal use in the consortium. The project had been designed in consultation with the different partners. However, this proposal was written entirely by TGS. It would be sent to all consortium members for feedback and approval, therefore, all plans were explained in as much detail as possible. For writing the proposal, background information was gained through consulting the consortium partners and literature research. As part of the project proposal, a budget was made by a colleague. The proposal was critically reviewed by colleagues of TGS at various stages. As mentioned, the proposal was quite elaborate. It was not written to meet the requirements of the proposal as stated in the call for proposals for the Applied Research Fund, issued by Wotro, on which the project was based. Although the proposal largely followed the required paragraphs, it had to be rewritten, especially to meet the criteria of word count limitations. To achieve this, it was important to determine which of the information Wotro would require in order to positively evaluate the project. Many details had to be removed, and what remained had to be drastically reformulated. This proved to be a notorious job, but with some input from colleagues, I managed to write the project description as required for the fund application. Other components of the application (a Consortium Agreement, the budget, and some other appendices such as CV’s of consortium members) were prepared by colleagues and/or provided by the consortium partners, after which I sent the full application to Indonesia for submission. Decisions regarding the approval of the grant will be made known in April. For the same project, a USAID grant ‘Securing Water For Food’ was found to be appropriate. Application for this grant occurs in several stages. In January, a concept note can be submitted. After evaluation of all submitted concept notes, USAID will make a selection of projects for submitting a full project proposal, which will again be evaluated, followed by a round of interviews, etc. Fortunately, the requirements for the concept note are not very complicated, and for a large part, the project proposal as used for the ARF can be used. This concept note will be submitted before the end of January.
Almelo
When I started at TGS, a promising project was a project in cooperation with a green college and the food bank in Almelo. A system would be set up at the school. Students and teachers would be involved from the start and the project would be integrated into the curriculum. Produce would partially be sold at certain occasions at the school, but most of the produce would go to the food bank. Volunteers of the food bank would also contribute to the management of the system (e.g. feeding the fish and harvesting of vegetables) during weekends and school holidays. A declaration of intention was signed by TGS, the school, and the food bank in October. Some questions were raised by the school during the meeting regarding the economic feasibility of the projects, and it was agreed that TGS would provide some more information for instance on the possibilities of marketing the fish. Also, the food bank had applied for a fund and was awaiting reply. Hence, the final decision regarding execution of the project was postponed. Unfortunately, the school apparently was not as interested in the project as suggested by the representative with whom the project plan had been initiated. Also, the fund was refused. Although the project has not officially been refused by the school, it does not seem that it will be executed.
Other
As described under ‘Iraq’, I wrote a project proposal for an aquaponics centre. I adapted this proposal for similar projects in other countries. For this purpose, I did research regarding the local context of the country or region in question and integrated the finding in the proposal.
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Through a contact of my supervisor, I got an email address from somebody working in the Middle East for Caritas. I contacted her, initially proposing the aquaponics centre project for Iraq. She was enthusiastic about the potential of aqauponics and we made a Skype appointment. During this conversation, she suggested that aquaponics might be very suitable for projects in cities in Gaza and the West Bank, where natural resources were scarce, import of food expensive, and people quite entrepreneurial and open to start new businesses. We sent her more documentation regarding aquaponics, for which we wrote a very to‐the‐point proposal with some of the possibilities of different projects with different systems. She would present the options on her visits to different local partners in December, and also applied for an internal fund of Caritas for innovative projects. The fund was assigned; however, it is not clear yet whether the local partners are interested.
Miscellaneous
Screening of funding opportunities
In order to be able to implement projects, TGS is largely dependent on external funding. Sometimes this funding can be found through partnering with other companies or institutions. In many cases, TGS applies for additional funding through various subsidies and grants. I did a screening of funding options. The screening was primarily based on internet research of companies who issue funds, agencies like AgentschapNL and Dienst Regelingen, and a broad range of development foundations. I also looked into the possibilities of acquiring funding through various crowd funding platforms. I made a list of all options with their key characteristics (eg eligible countries of implementation, maximum award, duration of the project, main themes for which the application could be filed, procedure), and a short document broadly describing how to find funds and a broad definition of options. The list should be kept up to date regularly.
Informative publications
I was involved in composing various publications such as flyers, brochures, internship vacancies, and website texts. Sometimes I was the person responsible for the publication, other times I fulfilled a revising task. The publications were written for various purposes and people, and the style of writing was adjusted accordingly.
Networking
Networking is of crucial importance for TGS. Through networking, contacts are made with experts, potential partners, potential funders, etc. I contacted existing contacts of TGS for various projects. This happened mainly through email, and sometimes resulted in Skype appointments (as many contacts are abroad). I also established new contacts. For the research I was doing regarding Saline Aquaponics, I contacted various experts from research institutes and companies that I came across during the research. Through these contacts, I gained some valuable information both through reports and through my conversations with them. Similarly, after reading an article by two WUR scientists involved in aquaponics related projects, I made an appointment with them in which we received some valuable input. Contacts like these will remain useful, as many of them are open to future questions and possibly even cooperation in research projects. I also contacted Wetlands International for possibilities of cooperation in the Indonesia project, and we have arranged a meeting at the end of January. I also approached other people for funding, both from governmental agencies and private companies. Often these contacts did not directly lead to funding opportunities, but they may prove to be valuable in the future.
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In November, I attended a day organised by Cordaid (the Dutch Caritas) for people aiming to start a Private Initiative. This was a very interesting day with workshops (for instance about fundraising in the Netherlands, or about starting a project in a particular country) and plenty of time for networking. Apart from the valuable input from the workshops, I also established some useful contacts on this day.
Meetings
During my time at TGS, I attended various meetings. During internal meetings the progress of various running projects was discussed, updates were given, future steps were identified and tasks were divided. External meetings included meetings with experts, a business breakfast in Rotterdam, the presentation of an aquaponics project in Alphen a/d Rijn, a meeting at FoodValley Wageningen, etc.
Answering various questions
Sometimes, questions arose for instance during meetings or project design. I have answered several research questions on different topics, some of which were not related to aquaponics. Topics included the possibilities of integrating sea cucumber into an aquaponics system, biological certification of aquaponically produced vegetables, marketing options of fish, certification requirements of fish production and processing, credibility of claims of a biological soil enhancer, levels of evaporation from aquaponics systems, etc. These questions were answered through literature and internet research, but also through talking to people at the local fish store, the open market, and a local biological supermarket.
Literature reviews
Although TGS had already established several aquaponics systems, there were still many questions regarding the biological functioning of the system. Most of the information that TGS used was obtained through forums on the internet, and a ‘How‐to‐guide’ for building home systems. Therefore, I conducted a literature study about the functioning and application of aquaponics. The resulting review can be found in Appendix II – Aquaponics – A literature review. Following some problems and suggestions we encountered during several projects, questions arose regarding the possibilities of establishing saline aquaponics systems. TGS did not know anything about this topic yet, and it was unknown what, if any, the possibilities would be. Therefore, the research was quite broad. Results can be found in the review about Saline aquaponics (Appendix III – Feasibility of saline aquaponics – A literature review).
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Reflection
During the first meeting that I had with my internship supervisor of TGS (Klaas Evers), he told me about the work of TGS and how this is mainly done on project base. This kind of project work includes many aspects such as fund raising, networking, and writing project proposals, with which I had little experience. My supervisor mentioned that I would probably get quite some responsibilities and would be expected to work quite independently on all aspects of a project. This both frightened and excited me, and it would definitely be challenging. Moreover, these were actual projects, where something real was at stake! I realised that, especially by crossing my own boundaries, I would be able to acquire and improve many skills and competencies during this internship which I had not drawn that much upon during my studies. During the first days and even weeks of my internship, I was not very confident and asked for quite some feedback and confirmation from my supervisor. I even had him read my emails before I actually sent them! Gradually, however, I noticed that I gained more confidence. I started working more independently and also dared to take more initiatives without consulting my supervisor first. Of course, this depended on the implications of the initiative. I found a balance between working independently, doing as I was told, and taking initiatives, in which I also asked for feedback when appropriate. I also gained confidence in the interaction with contacts such as experts, project partners, and potential funders. This interaction consisted of emailing, telephone and Skype conversations, and actual meetings. Especially at first, I preferred emailing people. That way, I had as much time as I needed to carefully weigh and reweigh my words, and could reread and if necessary rewrite my emails prior to sending them. Also, I would not have to be afraid to be confronted with an unexpected question to which I would not have an answer immediately. Slowly, I started to take less time for my emails, as I realised that my first version of an email was usually fine, and with that, most people could care less about the exact words I was using. I did not like telephone calls. I was always quite hesitant to call someone, and I would always take a deep breath first while feeling my heart thumping. This was especially the case because these telephone calls could be quite important, and I thought that they could mean the difference between getting funding or not, or being able to partner with someone or not. Fortunately, this improved drastically during the course of my internship. Partially, this was because I realised that these telephone calls were not as important as I had made myself believe. For a large part, it was simply because I learned that I was actually not that bad at talking to people, explaining them the objectives of TGS, explaining aquaponics, and explaining why I had called them. Also, I always prepared myself prior to making a call by identifying exactly what my purpose of contacting this person was and what objectives that person might have regarding that purpose, and I made some notes regarding the questions that I needed to ask and things that I needed to explain. Prior to an actual meeting, I made similar preparations. For one meeting, my supervisor had asked me the day before to lead that meeting. I was happy with getting this opportunity and learned a lot from it, especially after evaluating the meeting with my supervisor. During the meeting, I could have taken more initiative in leading the conversation. Although all the aspects which I had on my ‘agenda’ had been covered, this could have been done more efficiently if I had dared to interrupt the speakers to politely direct them to specific topics of concern. It wasn’t that what was being discussed was not useful or interesting, but it is good if somebody takes a leading role in such a meeting and in this case that someone should have been me. Although this partly is a matter of style and preferences, I should take a bit more initiative in such meetings. During my internship, the importance of ‘staying on top of things’ when it comes to contacts was confirmed. Very regularly, I needed to email and/or call people to confirm whether they had received
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my emails, to remind them to follow up, and just to keep in touch. Personal contacts may be tedious in this respect, however, they often offer more opportunities than, for instance, formal online registration forms. As I already knew, structure is quite important for me in several ways. Especially during the first weeks of my internship, I did not have a clear overview of what I should be working on within the projects to which I was assigned. This caused me to work relatively inefficiently. Later, I started dividing the work that needed to be done into more delineated tasks. I made weekly plannings in which I wrote what tasks I was planning to work on per half day, and set deadlines for myself. This way, I could also work towards tangible results, which fits to my working style. When writing a document, I also need to start with structuring. First, the objective(s) of the document need to be established. What message needs to be conveyed, and to whom? Then, a draft can be made of the structure of the document, for instance by indicating the paragraph titles, to establish a logical order in which all aspects that need to be covered can be presented. The actual writing is far easier once this structure is present. I used this method for writing documents such as project proposals, but also when writing the reviews it was very useful. This is especially clear when comparing my way of working between the two reviews. For the general Aquaponics review, I worked according to the method as described above. I formulated the research question that I would like to answer through the review, designed a structure for the review, and approached the review accordingly. For the review on Saline aquaponics, I worked less structured. This led to some extra work as, after writing several more or less separate paragraphs, it was not that straight forward to turn them into one logical story. It was very clear that I was the one responsible for the reviews. Although I could ask for feedback, involvement of others was nearly absent. For many other documents, however, we were involved in the writing as a team. I found that in this case it needs to be clear who is the main author and who gives feedback, and whether feedback implying making changes to the document is given as an advice or as a direct call for change. During this internship, I learned a lot about project based work and the world of networking and funding. One thing which struck me, for instance, was how one project design could be presented in very different way according to the public and their objectives and preferences. Emphasis of an aquaponics project could be on themes such as food security, water saving, or employment. A proposal could emphasise the research component of the project, the innovativeness of aquaponics, or the economic benefit that either the local community or the SME‐sector of Gelderland could gain with the project. Especially for fund applications it was important to fit the presentation of the project into the application requirements, resulting in quite different proposals for the same project. Of course, I also learned a lot about aquaponics during my internship. I had never heard of it before. It was interesting to apply a lot of knowledge that I obtained during my studies in Biology (BSc) and Plant Sciences (MSc) to this new concept. Although I was often confronted with questions to which I had no answer, I understood the biological principles of the system. Therefore I could more easily understand information available on aquaponics and apply other information regarding the different components.
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Acknowledgements
I would like to thank Hans Hamoen, Klaas Evers and Rutger Toorman of TGS for giving me the opportunity to work with them, giving me feedback, and sharing their stories, experiences and knowledge. I would also like to thank Peter Leffelaar for giving me his comments and feedback, often outside office hours. Furthermore, gratitude goes to the experts who were willing to share their knowledge, the people who I contacted for various projects, and others who have supported me during this internship in various ways.
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Appendix I – Photo overview of the system in Driel
The building of the system Top left: the bottom of the raft bed was covered with isolation material Top right: sowing the beams for the media grow bed Bottom, from left to right: construction of the media grow bed, inside of the filter, and some of the plumbing of the system with pipes from the fish tanks to the solids filter to the media grow bed
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Cleaning the lava stones Left and below: almost one whole m3 of lava stones had to be rinsed to remove lava dust prior to inclusion in the media grow bed of the system.
Above left: filling the system with water Above right: the fish tanks, with netting to prevent fish from jumping out
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Above
left: the whole
system. Above
right from top to bottom: pre‐growth of seedlings, the water thermometer, and the first water sample to be sent for analysis. Below: the spinach in a raft, and a net pot clearly showing the emerging plant roots
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Appendix II
Aquaponics – A literature review
J.A. van Vliet
Contents Abstract ................................................................................................................................................. 18
Introduction ........................................................................................................................................... 20
Aquaponics: the system ........................................................................................................................ 22
Fish tank(s) .................................................................................................................................... 22
Solids filter ..................................................................................................................................... 22
Media grow bed ............................................................................................................................ 23
Raft grow bed ................................................................................................................................ 24
Nutrient Film Technique ................................................................................................................ 24
Sump tank ...................................................................................................................................... 24
Water pump .................................................................................................................................. 25
Aeration pump .............................................................................................................................. 25
Aquaponics: biological background ....................................................................................................... 26
Nitrogen ......................................................................................................................................... 26
Other nutrients .............................................................................................................................. 26
Solids ............................................................................................................................................. 27
Oxygen ........................................................................................................................................... 28
pH .................................................................................................................................................. 29
Ratio plant‐fish .............................................................................................................................. 29
Temperature .................................................................................................................................. 29
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Irradiance ...................................................................................................................................... 30
Plant and fish diseases .................................................................................................................. 30
Production ............................................................................................................................................. 31
Application ............................................................................................................................................ 33
Current technical knowledge gaps ........................................................................................................ 37
Conclusions and recommendations ...................................................................................................... 39
Bibliography ........................................................................................................................................... 41
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Abstract
Aquaponics is a recirculation system in which the production of fish is combined with the production
of vegetables. In the system, the fish waste water is biologically filtered through the use of bacteria,
and the nutrients are extracted and utilised by the vegetables after which the water can flow back to
the fish. Fish and vegetable production using aquaponics systems can be high and requires only small
amounts of water, no fertile soil, and no additional (chemical) fertilisers. Aquaponics is thus argued
to be a very efficient and sustainable food production method. An aquaponics system consists of
several components such as fish tanks, vegetable grow beds, and pumps. The design of a system will
depend on the objectives to be reached with the system and the resources available for building and
maintaining it. For appropriate biological functioning, aspects such as nitrification requirements, solid
removal and temperature within the system will have to be taken into account in the system design.
Currently, large scale commercial production does not seem to be economically feasible. Urban
agriculture with high interaction with the consumer, and introduction of aquaponics in developing
countries may both be suitable applications of the technology. Part of the problem of designing
profitable large scale commercial systems is the lack of thorough understanding of the functioning of
aquaponics systems. The integration of aquaculture with horticulture leads to interactions which are
not well understood. More research is necessary in order to develop this technology to its full
potential.
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Introduction
The world’s population is predicted to increase to 9 billion people by 2050. Competition over natural
resources, such as land and water, is intensifying. Increasing resource use efficiency in food
production is crucial in meeting global food demands. Innovative approaches are needed across the
agricultural sector to increase productivity while conserving natural resources and using inputs
sustainably and efficiently (FAO, 2013b). This report will focus on the production of vegetable crops
and fish.
In conventional crop production, major problems arise from the availability of fertile agricultural land
and water. Adverse climatic conditions such as erratic and/or limited rainfall have aggravated over
the last decades, while erosion and soil nutrient depletion further decrease the area which can be
readily used for crop cultivation (IPCC, 2007; Bossio, 2013). Irrigation and fertilisation may offer
solutions, and other technologies such as use of pesticides can also increase production levels
(Murshed‐E‐Jahan and Pemsl, 2011). However, these technologies may not be environmentally
sustainable, and are often inaccessible to many farmers due to the required high capital and
technological investment associated with these technologies (Murshed‐E‐Jahan and Pemsl, 2011).
In many countries, fish are the main source of protein. Aquacultural production is increasing and now
provides nearly 50% of the world’s consumption fish (FAO, 2013a). In aquaculture, waste water
management is of crucial concern. Aquacultural practices can negatively impact the adjacent
environment through the discharge of output effluents into the surrounding area (Martins et al.,
2010). The effluents contain suspended solids, treatment chemicals and excess nutrients from fish
waste and leftover fish feed, leading to problems of salinity, eutrophication and chemical pollution
(Cheng, 2010). Other problems involve the high use of medication and antibiotics in aquaculture
(Boyd et al., 2005).
Several technologies have been developed that address the above issues. The most relevant of these
technologies for this review are hydroponics, Recirculation Aquaculture Systems, and Integrated
Aquaculture‐Agriculture.
In hydroponics, crops are grown on nutrient solutions. Hence, soil is no longer required, and the use
of water and nutrients is much more efficient than in conventional agriculture (Grewal et al., 2011),
while production is higher both spatially and temporally (AquaponicsUK, 2013). However, input of
water and nutrients is still required, and may not always be at hand.
The problems of waste water management in aquaculture have led to the development of various
solutions. In Recirculating Aquaculture Systems (RAS), the waste water undergoes treatment to
enable recirculation of the water to the fish. Depending on the efficiency of the treatment methods,
the water exchange rate can be reduced from over 50 m3 to less than 0.1 m3 per kg of fish feed
(Martins et al., 2010). However, the more efficient treatment methods require higher investments in
technology and capital. Also, the products that remain after treatment (such as sludge and water
with high concentrations of contaminants), though of potential value, often remain unutilised and
may cause environmental problems if discharged (Martins et al., 2010).
21
A method to discharge the waste water is through the use of Integrated Aquaculture‐Agriculture
(IAA), in which the waste water is applied as irrigation water to field crops. This method increases
resource use efficiency (Murshed‐E‐Jahan and Pemsl, 2011). However, some of the problems
mentioned above still apply, as many of the valuable nutrients and water, but also harmful
contaminants, will be lost through leaching (Brown et al., 1999).
Aquaponics is a combination of integrated aquaculture‐agriculture (IAA) and recirculation
aquaculture systems (RAS) in which hydroponics is incorporated into an RAS as part of the treatment
of the waste water prior to recirculation (Rakocy et al., 2006). Through the combination of several
technologies and the high level of integration between the different subsystems, aquaponics can be
a highly efficient and sustainable system for the production of both vegetables and fish as several of
the problems of different methods are solved while the major benefits are retained (Bernstein,
2011).
22
Aquaponics: the system
Aquaponics is a recirculation system in which the production of fish is combined with the production
of vegetables (Figure 1).
Figure 1: Various aquaponics systems varying in size and complexity (from left to right:
www.kickstarter.com, www.growingpower.org, www.jandjaquafarms.com).
In the system, the fish water is biologically filtered through the use of bacteria, and the nutrients are
extracted and utilised by the vegetables after which the water can flow back to the fish. Hence, use
of nutrients and water is highly efficient. An aquaponics system may consist of several components.
Fish tank(s)
The fish tanks have to contain an adequate amount of water for the amount of fish that is
maintained in the system. The appropriate stocking density will differ between fish species. For
Tilapia, a stocking density of about 60 kg of fish per m3 is often applied (Losordo et al., 1998; Rakocy
et al., 2006). Stocking density also depends on the objectives of the system. In conventional
aquaculture achieving high production levels, Tilapia densities may reach 200 kg m‐3. In biological
Tilapia cultures, a maximum stocking density of 20 kg m‐3 is allowed (Schuilenburg, 2012). Sometimes
one tank is used; other systems make use of multiple tanks. This allows for sequential rearing of
batches of fish or having different kinds of fish in one system.
Solids filter
For the removal of solids from the fish effluent (see below under Solids), usually some sort of filter is
installed between the fish tank and the media grow bed. Methods mostly used for the removal of
solids are based on settling and sieving, for instance using settling basins, screen filters, or swirl
separators (Figure 2, Danaher et al., 2013).
23
Figure 2: From left to right: examples of a settling basin (water.me.vccs.edu), a screen filter (www.process‐
controls.com) and a swirl separator (api.ning)
Media grow bed
The media grow bed is filled with gravel or pebble‐like media to provide support to the plant roots,
act as a solid waste filter, and for air and water exchange (Figure 3). The media also provide growing
surface for bacteria. Often, gravel, lava rock or expanded clay is used. The media should not alter the
pH of the water, shouldn’t break down or decompose and be of the proper size. If the media are too
small, it will easily get clogged by solid waste and is too compact for air and water exchange. Media
that are too large will create large empty spaces, making them unsuitable for root establishment.
Media of about 12‐18 mm in diameter are considered the right size, and the media bed is usually
about 30 cm deep (Bernstein, 2011).
Figure 3: A media bed with expanded clay pellets (usaquaponics.files.wordpress)
In the media bed, an ebb‐and‐flow system can be created through the use of an auto siphon or a
timed pump, depending on the arrangement of the system. The tank is filled up with water from the
fish tank(s) and then drained to the raft grow bed, the sump tank, or directly back to the fish tank(s)
(depending on system design) at intervals. This ebb‐and‐flow system allows for proper aeration of
the plant roots.
24
Raft grow bed
A raft grow bed does not contain media, only water. Rafts (often made of polystyrene) float on the
water or are placed just above the water to allow for more aeration. Pots containing the plants are
placed in holes in the rafts, with their roots largely submerged in the water (Figure 4).
Figure 4: Vegetable production on a raft grow bed (aquaponics.com)
Nutrient Film Technique
Another hydroponic technique sometimes used in aquaponics systems is the Nutrient Film Technique
(NFT, Figure 5). NFT systems consist of narrow plastic channels for plant support with a film of
nutrient solution flowing through them (Rakocy et al., 2006).
Figure 5: Vegetable production using Nutrient Film Technique (people.morrisville.edu)
Sump tank
A sump tank is sometimes added to the system. It is placed at the lowest point of the system, and
water flows into the tank through gravity, while a pump carries the water back to the fish tank(s) or
the grow beds. The sump tank acts as a buffer to prevent water level fluctuations in the fish tank as a
consequence of water loss and the ebb‐and‐flow system (if present) (Rakocy et al., 2006; Bernstein,
25
2011). The sump is also a good location for the addition of base to increase the pH in the system
without creating a rapid increase to toxic pH levels in the fish tank (Rakocy et al., 2006). In small scale
systems, the sump tank is often omitted.
Water pump
Usually, the water is transported through the system largely based on gravity. A water pump is only
needed to bring the water back from the lowest point of the system to the highest component. The
arrangement of the components of the system determines where the pump should be placed. The
entire water body in the system is usually cycled every hour. This is especially important to provide
the fish with clean, filtered water. Plants are less susceptible to a low rate of water circulation
(Bernstein, 2011).
Aeration pump
Oxygen is needed by plants, bacteria and fish (see below). Although some oxygen is added to the
water through the ebb‐and‐flow system in the media grow bed and the pumping of the water, more
oxygen can be added to the fish tanks and the raft grow bed to ensure optimal production. This is
usually done through installing an aeration pump connected to several aeration stones on the
bottom of the tanks and beds.
Many different sizes, combinations and arrangements of these components are possible. Some
systems do not have both a raft bed and a media bed, some systems do not make use of aeration
pumps, or sump tanks, and so on. Other systems include other components, such as degassing units
(which won’t be described in this review). The design of a system will depend on the objectives to be
reached with the system and the resources available for building and maintaining it. Below, the most
important aspects for proper functioning of an aquaponics system are explained. Any system has to
be designed in such a way that all these aspects are taken into consideration.
26
Aquaponics: biological background
Several biological aspects are of crucial importance in an aquaponics system and need to be well
balanced for the system to function properly.
Nitrogen
Fish excrete nitrogen in the form of ammonia into the water through their gills (Rakocy et al., 2006).
This ammonia is highly toxic to the fish. A group of nitrifying bacteria (Nitrosomonas) utilises the
ammonia as an energy source for growth and produce nitrite as a by‐product. This nitrite is still toxic,
but is readily oxidised to nitrate by a second group of nitrifying bacteria (Nitrobacter).
Nitrosomonas: 2 NH4+ + 3 O2 2 NO2
‐ + 4 H+ + 2 H2O
Nitrobacter: 2 NO2‐ + O2 2 NO3
‐
In conventional RAS, biological filtering is most commonly used to convert ammonia into nitrate, and
this is also used in aquaponics. The biological filters consist of a substrate with a large surface area
where the nitrifying bacteria attach and grow. Commonly used substrates in RAS are gravel; sand;
and plastic beads, rings, tubes and plates (Losordo et al., 1998). Within aquaponics systems, part of
the surface area is provided by the media bed and/or the rafts, as well as in the sedimentation filter.
Nitrate is not highly toxic, but high levels of nitrate will eventually negatively influence fish
production. In conventional RAS with nitrification filters, the concentration of nitrate is a determining
factor for the water exchange rate, as high levels of nitrate eventually negatively influence fish
production (Martins et al., 2010). Denitrification reactors may be installed, but these anoxic reactors
are expensive, high‐tech and knowledge intensive (Martins et al., 2010). In aquaponics systems, the
nitrate which is formed through nitrification is utilised directly by the plants, eliminating the
necessity of installing these reactors to reduce water exchange. In addition, many other dissolved
nutrients from the waste water are utilised by the plants (Rakocy et al., 2006).
Ako and Baker (2009) indicate that, at a pH of 8, ammonia is toxic at a concentration of 17 mg L‐1 and
nitrite at 8 mg L‐1. Nitrate levels should be maintained at about 47 mg L‐1.
Other nutrients
Plants require a range of nutrients in different concentrations (Raven et al., 2005). Some nutrients
may be toxic at high levels. Acceptable nutrient levels depend on the plants’ ability to extract and
tolerate different concentrations of nutrients (Savidov, 2004). The fish in the system do not rely on
the nutrients present in the water as their nutrient uptake occurs through the feeding on fish feed.
However, high levels of certain nutrients may be toxic to fish.
The essential nutrients for plants are represented in Table 1.
27
Table 1: Essential nutrients for most vascular plants and internal concentrations considered adequate (Raven et al., 2005)
Element Chemical Symbol Form Available to Plants Adequate Concentration in
Dry Tissue (mg/kg)
Micronutrients
Molybdenum Mo MoO42‐ 0.1
Nickel Ni Ni2+ ?
Copper Cu Cu‐, Cu2‐ 6
Zinc Zn Zn2+ 20
Manganese Mn Mn2+ 50
Boron B H3BO3 20
Iron Fe Fe3+, Fe2+ 100
Chlorine Cl Cl‐ 100
Macronutrients
Sulfur S SO42‐ 1000
Phosphorus P H2PO4‐, H2PO4
2‐ 2000
Magnesium Mg Mg2+ 2000
Calcium Ca Ca2+ 5000
Potassium K K+ 10,000
Nitrogen N NO32‐, NH4
+ 15,000
Oxygen O O2, H2O, CO2 450,000
Carbon C CO2 450,000
Hydrogen H H2O 60,000
Nutrient availability depends not only on concentration, but also on water conditions such as
temperature and pH. These factors influence the form in which the nutrient is present and the
solubility of the nutrient.
Solids
The plants in the system remove most dissolved fish wastes and products of microbial breakdown of
fish wastes. However, removal of solids from the system is still necessary to sustain fish and plant
health (Rakocy et al., 2006; Danaher et al., 2013). The solid waste consists of faecal waste from the
28
fish, uneaten feed, and organisms (eg bacteria, fungi and algae) that grow in the system. If this
organic material is left in the system, in the process of decay it will reduce oxygen levels, while
increasing levels of carbon dioxide and ammonia. When no solids would be removed and deep
deposits of sludge are allowed to form in the system, anaerobic decomposition may even lead to
production of methane and hydrogen sulphide, both highly toxic to fish. Solids may also accumulate
on plant roots in an aquaponics system, creating anaerobic zones that prevent nutrient uptake by
active transport as this process requires oxygen (Rakocy et al., 2006). Small amounts of solids in the
system may be beneficial, though. Decomposition releases inorganic nutrients into the water. This
process, mineralisation, supplies several nutrients essential to plant growth. Lack of solids may thus
lead to a lack of these nutrients, necessitating nutrient supplementation. Hence, an optimum balance
of solid removal and retention is required (Rakocy et al., 2006).
Most solid removal occurs through installed filters and the media bed, if present (see above under
Solids filter). Mineralisation of retained solids is enhanced if an ebb‐and‐flood system is used, which
increases oxygen availability. Inoculation with red worms (Eisenia foetida) further improves bed
aeration and assimilation of organic matter. However, occasional cleaning of the medium will be
required to prevent clogging (Rakocy et al., 2006).
Removed solids may be used for associated land agriculture (Rakocy et al., 2000).
Oxygen
Plants, fish and most bacteria require oxygen. Plant roots require oxygen for respiration used for
water absorption and nutrient uptake, and to maintain root cell tissue (Rakocy et al., 2006). Under
normal conditions, this occurs through proper aeration of the soil around the roots (Raven et al.,
2005). However, in hydroponics as well as in aquaponics, the water has to provide the oxygen.
Hence, the dissolved oxygen (DO) concentration of the water is of crucial importance. For instance,
DO concentrations of at least 4 mg L‐1 are recommended for optimum growth of lettuce in
hydroponics systems, and severe plant stress was observed at DO concentrations below 2 mg L‐1
(Both, date unknown). Levels are usually maintained at around 8 mg L‐1 in commercial hydroponics
(Brechner and Both, date unknown).
Oxygen requirements of fish are highly variable between species. Some fish, such as catfish and
tilapia, are not very vulnerable to low oxygen levels. Others, such as trout, require higher levels of
oxygen (Bernstein, 2011). Oxygen demands also depend on food consumption. According to Priva
(2009), Tilapia needs 600 g of oxygen per kg of feed consumed.
Both the bacteria involved in the aerobic breakdown of solids (mineralisation) and those involved in
nitrification require oxygen, which is another reason for maintaining adequate oxygen levels
(Losordo et al., 1998). This is also one of the reasons why at least some solid removal is
recommended: a high amount of solids in the system will increase mineralisation and hence lead to
depletion of oxygen.
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pH
Efficiency of nitrification is higher in an alkaline solution, pH 7.5‐8.0, which is the reason for a
relatively high pH in most aquaculture facilities (Savidov, 2004). A high pH also increases solubility
and consequently availability of phosphor, calcium, magnesium and molybdenum. However, a higher
pH decreases solubility of various other nutrients essential for plant growth, such as iron,
manganese, copper, zinc and boron (Rakocy et al., 2006). Commercial hydroponics systems
producing lettuce often maintain a pH between 5.6 and 6.0 (Both, date unknown), but a pH between
5.0 and 7.0 is suitable for most plants (Bernstein, 2011). Tilapia is reported to survive in water with
pH levels between 5.0 and 10.0 (Kotzen and Appelbaum, 2010). Priva (2009) uses a pH between 6.5
and 8.0 for Tilapia. Optimum growth of freshwater fish in general occurs at pH levels of 6.8‐7.5
(European Inland Fisheries Advisory Commission 1969 in Edwards and Twomey (1982)). It is argued
that the optimal pH of an aquaponics system is a compromise between the optimum pH of the
plants, fish and bacteria at a pH of about 6.8‐7.0 (Bernstein, 2011). The pH in aquaponics systems is
often adjusted through adding KOH or other salts leading to a pH increase. The nutrient component
of the salt may be utilised by the plants (Ako and Baker, 2009).
Ratio plant‐fish
The ratio between the amount of fish and the amount of plants in the system is crucial for achieving
an appropriate nutrient balance (Rakocy et al., 2006). Nutrient levels in the water will depend on the
level of excretion of the fish and the absorption by the plants, which may differ between fish and
plant species, and depend on other factors such as feeding rate (Seawright et al., 1998; Rakocy et al.,
2006). The total amount of water in the system also influences nutrient concentrations (Rakocy et al.,
2006). Hence, optimal ratios between fish and plants will depend on different factors. However,
some rules of thumb are frequently used. For raft aquaponics, (Rakocy et al., 2006) advise a ratio of
60‐100 grams of fish feed per day per m2 of plant growing area with Tilapia being raised to a final
density of 60 kg per m3. Although the balance between the fish tank size and the area of plant
production within an aquaponics system differs between plant and fish species, it lies in the order of
magnitude of 1:10‐30 fish production (m3):plant production (m2) (Vermeulen and Kamstra, 2013).
Temperature
Although the optimum temperature for many plants is around 23oC, most common garden crops will
still produce at 15oC, and some winter crops such as cabbage can withstand even lower temperatures
(Rakocy et al., 2006). The temperature of the water is more important than that of the air in
aquaponics systems. In the tropics, high water temperatures reduce the concentration of dissolved
oxygen in the water for plant respiration (Sikawa and Yakupitiyage, 2010). Although the temperature
tolerance range of Tilapia is wide, optimum temperature is between 28oC and 30oC (Kotzen and
Appelbaum, 2010). Other fish, such as carp, will grow optimally at lower temperatures (Edwards and
Twomey, 1982; Bernstein, 2011). Under suboptimal water temperature conditions, feeding of fish
will decrease (Kotzen and Appelbaum, 2010).
In order to maintain the best water temperature, heating in winter may be needed in temperate
regions, while cooling may be necessary in the tropics (Rakocy et al., 2006).
30
Irradiance
The amount of available light is a determining factor for plant productivity. Production is best at
maximum intensity and daily duration of light. Even in heated greenhouses, production may
decrease substantially in winter if radiation is low (Savidov, 2004; Rakocy et al., 2006).
Plant and fish diseases
Pesticides and fish treatment chemicals should not be used in aquaponic systems as these could pose
a threat to fish, and crops and bacteria, respectively (Rakocy et al., 2006; Blidariu and Grozea, 2011).
Accumulation of chemicals, even if not directly affecting the production of the system, may deem the
production unsuitable for human consumption. Treatment of fish diseases using salt is also
detrimental to plant crops (Rakocy et al., 2006).
Nonchemical methods of integrated pest management (IPM) must be used (Rakocy et al., 2006;
Blidariu and Grozea, 2011). Parasitic wasps and ladybugs can be used to control white flies and
aphids. Caterpillars and moth larvae can be controlled through spraying with Bacillus thuringiensis
(Seawright et al., 1998; Rakocy et al., 2006). Thrips can be controlled with the parasitic spider mite
Encarsia formosa (Seawright et al., 1998). Although the use of neem oil to repel pests has been
suggested, this may block fish gills and be an antibiotic and should hence not come into contact with
the water (Bernstein, 2011; BackyardAquaponics, 2013). Insecticidal soaps are also used to control
insect pests, however, as neem oil, these soaps can harm the fish (Seawright et al., 1998; Bernstein,
2011).
A benefit of growing plants hydroponically is that crops are less susceptible to attack from soil borne
diseases (Blidariu and Grozea, 2011). It is argued that an additional benefit of growing crops
aquaponically over hydroponically is an increased resistance to diseases due to the higher level of
biological activity (Rakocy et al., 2006).
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Production
Production levels vary per system. Savidov (2004) reports yearly yields of Genovese basil to reach 42
kg m‐2 within two years, cucumber yields of 33 kg plant‐1 year‐1, and tomato production 21 kg plant‐1
year‐1, which is 10‐15% higher than average yield in the hydroponics industry. Rakocy et al. (2006)
observe that the income from herbs such as basil and mint is much higher (1700%) than that from
fruiting crops such as tomatoes and cucumber. Lettuce is widely used in aquaponics systems, as it
has a short growing time (3‐4 weeks) and, as a consequence, has relatively few pest problems. Also, a
larger portion of the biomass is edible and thus marketable than from fruiting crops (Rakocy et al.,
2006). According to many studies (ao Graber and Junge (2009); Seawright et al. (1998); (Graber and
Junge, 2009)), lettuce and other vegetable production in aquaponics is equal to or higher than
production in hydroponics, although others (see Blidariu and Grozea (2011)) claim production is
lower. Many other crops are reported to be suitable for aquaponics systems, such as flowers, a
variety of herbs, eggplant, Chinese cabbage, strawberries and watercress (ao Savidov (2004); Rakocy
et al. (2006); Bernstein (2011)).
Fish production can equal that of conventional aquaculture (Savidov, 2004; Graber and Junge, 2009;
Vermeulen and Kamstra, 2013). Production can vary strongly between fish species. Vermeulen and
Kamstra (2013) mention that the productivity of eel, African catfish and Tilapia can be 200, 1000 and
300 kg m‐2 year‐1, respectively.
32
33
Application
Currently, although gaining in popularity, the use of aquaponics systems is not widespread (Rakocy et
al., 2006). Most working aquaponics systems are small scale, and more meant for ‘fun’ than for
making a living.
Researchers have claimed that there is a business case for aquaponics (ao Rakocy et al. (2000);
Savidov (2004); Rakocy et al. (2006); Rakocy (2007); Blidariu and Grozea (2011). However, there are
few examples of successful commercial aquaponics ventures.
A major incentive for starting a commercial aquaponics venture may be the anticipated cost
reductions compared to other agricultural and aquacultural production systems. These cost
reductions would arise due to a decrease in the use of resources such as water, land and nutrients,
shared operating and infrastructural costs, and wastewater clean‐up cost abatement (Blidariu and
Grozea, 2011). However, some argue that cost reductions as a result of integration of hydroponics
and RAS are low, and that the economic incentive of using aquaponics is not high enough to justify
the extra inputs necessary for further development of this system (see Vermeulen and Kamstra
(2013)). Currently, in western countries, importing frozen fish and horticultural products using
current methods are still considered to be cheaper, less risky and of higher quality than aquaponics
by many (Vermeulen and Kamstra, 2013).
It is argued that the incentives for using aquaponics should be sought in value adding rather than
only in cost reduction (Vermeulen and Kamstra, 2013). One opportunity to add value to the produce
is to have it certified as Organic. Consumers are increasingly attracted by terms such as ‘natural’,
environmentally friendly’, ‘pesticide free’ and ‘organic’, and are willing to pay extra for organically
certified products (Blidariu and Grozea, 2011). However, certification may be expensive. Also, organic
certification of aquaponically produced vegetables may not be possible in all countries. Although it is
a possibility in at least the USA and Canada (Savidov, 2004; Blidariu and Grozea, 2011), in other
countries such as The Netherlands certification of aquaponically produced vegetables is impossible.
Here, production on soil is a requirement for certification (Skal, 2013). Without the certification label
on the package, a costumer may not realise that aquaponics products meet their personal demands
of environmentally friendly production. Although they are willing to pay extra for products that meet
these demands, they will not do this for the unlabeled aquaponcis products.
Interaction with the consumers is another possibility of value‐adding to aquaponic products. Based
on interviews with current users, Vermeulen and Kamstra (2013) found that the advantages of
aquaponics are its ability to produce fresh produce in the vicinity of consumers with the charm of
being able to let these consumers witness the production process. Through small scale production,
direct sales and close interaction with consumers, aquaponic producers may enter a niche market
and be able to achieve high‐margin sales (Vermeulen and Kamstra, 2013). This concept may be most
suitable in an urban setting. In cities, aquaponics farms will allow the consumers to (re‐)connect to
the production of the food they consume and systems can be set up on rooftops, in basements, and
in other city locations which are not suitable for conventional agriculture (Blidariu and Grozea, 2011;
Vermeulen and Kamstra, 2013).
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These findings are exemplified by a quick scan of aquaponics ventures that have started in the last
few years in the USA1,2,3,4,5,6,7,8. Four out of the 8 ventures found were out of business by now1,4,5,8,
most likely due to financial and marketing problems. One of these ventures was taken over by a non‐
profit organisation for educational purposes8. The highest costs in most ventures arise from the
energy costs necessary to heat the greenhouses. One of the successful ventures is in Hawaii3, where
these costs can be eliminated. The primary distribution channel of most ventures still in existence is
direct sales to local restaurants, though some have found a niche market for local, organic produce.
Many of the ventures work with volunteers. These ventures, though operating at a larger scale, are
closely related to private so‐called ‘backyard systems’ which have arisen all over Australia and the
USA. They are more meant to bring consumers closer to the producer, to other consumers and to the
products under the flag of environmentally sustainable production, than that they are meant to
supply the main‐stream market of fish and vegetables. For this purpose, more highly commercialised,
large‐scale aquaponics would be needed. Following from this review, this may not (yet) be achievable
for several reasons. It may not be economically attractive to produce vegetables and fish where both
of these commodities are already available in large quantities of high quality at low prices
(Vermeulen and Kamstra, 2013). As Chris Newman, the founder of Santa Cruz Aquaponics, said:
“From a biosustainable point of view, I was trying to do something responsible. But the market's not
paying attention. The market pays attention to price”. With that, he adds: “It does seem like a great
idea, but I'm not convinced the vegetable world is ready for it” (Jones, 2013). This problem of lack of
acceptance of this new technology is frequently encountered. As it took a long time for hydroponic
production systems to be accepted by the horticultural community, it may take a longer time before
actors in the food production sector are willing to accept aquaponics (Jones, 1982).
One of the potentials of aquaponics is its capability to produce vegetables and fish in locations where
this is not possible with more conventional methods. As described above, this may be the case in
urban areas, where there is no agricultural land available. However, this may also be the case in both
rural and urban areas in developing countries (FAO; FoodSource; AquaponicsUK, 2013; Salam et al.,
2013). As soon as there is a lack of access to fresh vegetables and/or fish, aquaponics may be an
option. Aquaponics systems can be designed using high tech equipment for optimal control of the
system, and hence optimal production and growth of both fish and plants is possible (see for instance
Priva (2009)). However, low input systems can also be designed which are better suited to local
1 Santa Cruz Aquaponics, Watsonville (http://www.polishpartnerships.com/santa‐cruz‐aquaponics/;
http://www.linkedin.com/company/santa‐cruz‐aquaponics) 2 Viridis Aquaponics, Watsonville (http://www.santacruzsentinel.com/ci_23836792/future‐agriculture‐venture‐
aims‐be‐worlds‐largest‐aquaponics, http://viridisaquaponicgrowers.com) 3 Friendly Aquaponics Inc., Hawaii (http://news.medill.northwestern.edu/chicago/news.aspx?id=186175,
http://www.friendlyaquaponics.com/) 4 312 Aquaponics, Chicago (http://www.plantchicago.com/welcome‐312‐aquaponics/,
http://www.linkedin.com/company/312‐aquaponics) 5 City Micro Farms LLC, Chicago (http://articles.chicagotribune.com/2011‐05‐25/news/ct‐x‐c‐fish‐farming‐0525‐
20110525_1_meatpacking‐plant‐farming‐aquaponic) 6 Farmedhere, Chicago (http://farmedhere.com/) 7 Greens and Gills, Chicago (greensandgills.com) 8 Sweet Water Organics, Milwaukee (http://sweetwater‐organic.com/)
35
conditions in developing countries such as problems with electricity supply, lack of technical and
financial resources, and low availability of inputs such as fish feed. Systems have been developed
that function without grid electricity through the use of solar energy or foot pumps. Systems can be
built using locally available materials, such as cement and empty barrels. Fish feed may be produced
on‐farm, using ingredients such as worms, flies, duckweed, chicken dung and plant wastes (FAO;
FoodSource; AquaponicsUK, 2013). Aquaponics systems may be used for domestic and commercial
production of fish and vegetables in developing countries. This can lead to an increase of
consumption of essential proteins, vitamins and minerals and potentially provide the owner of the
system with additional income (Essa et al., 2008; Murshed‐E‐Jahan and Pemsl, 2011). Adequate
training of adopters is crucial in achieving the potential benefits of new technologies such as
aquaponics (Murshed‐E‐Jahan and Pemsl, 2011). Adoption constraints of aquaponics in developing
countries may be found in lack of knowledge and limited access to information, lack of market
facilities, and poor availability of quality fish fingerlings and vegetable seeds (Murshed‐E‐Jahan and
Pemsl, 2011).
36
37
Current technical knowledge gaps
A lot of information available on modern aquaponics is developed and spread through non‐scientific
sources. Some aquaponics ‘pioneers’ started exploring aquaponics, based on academic research in
the nineties by, amongst others, Dr. James Rakocy of the University of the Virgin Islands and Dr. Nick
Savidov from Alberta. They used guidelines following from this research to start experimenting with
aquaponics themselves, and developed guides and handbooks which have contributed to the spread
of small‐scale aquaponics systems especially in the USA and Australia (Bernstein, 2011). Many
aquaponics practioners have gathered in online platforms (for instance backyardaquaponics.com;
aquaponicscommunity.com; and aquaponics.net.au). These platforms lead to the continuous
production of more experience based rules of thumb and advice concerning aquaponics systems
(Bernstein, 2011). Most of the information thus available is knowledge on what works, and not so
much on how or why it works. This is usually sufficient for anyone to start their own aquaponics
system. However, a more solid scientific knowledge base on the functioning of this complex system
would contribute to further development of the system. Scientific literature on hydroponics is quite
widely available. Technologies such as Recirculation Aquaculture Systems and the use of aquacultural
waste water for irrigation have gained increasing attention. However, the range of scientific
publications on the combination of these components, aquaponics, is limited, and there are many
knowledge gaps remaining.
Little is known about responsible biological fish management within aquaponics systems.
Conventional antibiotic or salt treatments are not applicable in aquaponics systems (Rakocy et al.,
2006). It is sometimes argued that the fish will remain healthy as long as other factors such as
temperature, pH and feed availability are kept in the right range, as it is mostly stress that will cause
diseases to develop (Dicky van Zanten, personal communication November 2013). Also, it is advised
to use hardy fish species such as Tilapia (Rakocy, 2007). However, in the case that diseases do occur,
these often remain unidentified and may result in partial or total loss of the fish in the system
(Rakocy et al., 2000). Although this problem is acknowledged in scientific literature, no alternatives
are offered (ao Rakocy et al. (2000)).
Data is available on recommended nutrient concentrations for crop production of several crops in
hydroponics. However, these recommendations might not be applicable to aquaponics systems, as
there is continuous nutrient generation and water circulation in these systems (Rakocy et al., 2006).
The concentration of several nutrients is different in most aquaponics systems compared to standard
nutrient formulations, without any apparent problems to either crops or fish (Rakocy et al., 2006).
According to some authors (see Seawright et al. (1998)) it is not possible to maintain sufficient
nutrient levels and prevent excessive salt accumulation in recirculating aquaponics systems
regardless of the ratio of plants to fish. In order to prevent yield reduction, nutrient supplementation
and water replacement are unavoidable. Especially iron is often reported to be insufficiently
38
available, and is supplemented through addition of chelated Fe2+ to a concentration of 2.0 mg L‐1
(Rakocy et al., 2006; Ako and Baker, 2009). Others (ao Savidov (2004)) argue that aquaponics systems
have an intrinsic capacity of self‐regulation and balancing nutrients in the solution, diminishing the
need of nutrient supplementation. However, this increased system resilience has not been formally
researched.
Theoretically, it is possible to manipulate the relative proportions of nutrients present in fish
excrements through manipulating the nutrient content of the fish diet (Seawright et al., 1998).
However, little research has been done to further explore this possibility.
Seawright et al. (1998) noticed persistent tip burn on lettuce in their aquaponics trials, indicating Ca‐
deficiency. However, when analysing water samples, no nutritional deficiencies were apparent. It
was suggested the tip‐burn was caused by Na accumulation, inhibiting Ca uptake, although no
mineral imbalances were found in the lettuce tissue. In the same experiment, calculations were
made to determine the appropriate amount of fish in the system to result in an equilibrium between
N assimilation by the plants and N excretion by the fish. However, N concentrations decreased,
apparently due to denitrification.
The examples from this experiment stress the difficulty of evaluation of nutrient levels due to the
interactions between the nutrients, but also due to the influence of physical factors such as
temperature and pH, and biological factors such as the rates of bacterial denitrification and
nitrification.
Most scientific data and recommendations available are based on either the aquacultural or the
hydroponical component. Even articles written about the combination of these components
(aquaponics) are usually written from the point of view of an expert of either of the components. For
proper research on aquaponics, however, expertise of both sectors will be necessary (Vermeulen and
Kamstra, 2013). Moreover, new expertise concerning the integration of the two components is
necessary. The dynamics within the integrated system are not readily explained even through
combining the knowledge on both components. In the case of aquaponics, one plus one does not
necessarily equal two as a consequence of the interactions of so many physical and biological factors.
39
Conclusions and recommendations
Based on the results of this literature review, several conclusions can be drawn regarding the
functioning and potential of aquaponics.
The basic functioning of aquaponics systems is understood and aquaponics systems can be designed
using the information that is currently available. The technology seems to offer large benefits
compared to other production methods of fish and vegetables. These two commodities can be
sustainably produced with a high resource use efficiency and low environmental impact. However, it
seems that it is currently not economically feasible to produce fish and vegetables on a large,
commercial scale using aquaponics. In Western countries, aquaponic production may be most
suitable for relatively small scale urban agriculture. Aquaponically produced fish and vegetables can
distinguish themselves from the products available at low cost in supermarkets through small scale
production, direct sales and close interaction with consumers. The product can thus occupy a niche
market, allowing for high‐margin sales and hence economic feasibility. There also is a potential for
using aquaponics systems to increase the consumption of fish and vegetables in developing countries
where these commodities are often expensive. Low‐tech systems can be designed which function
well in regions with limited access to resources such as fertile soil, water and chemical fertilisers.
Increased research efforts concerning aquaponics will lead to a better understanding of the
functioning of aquaponics systems. Aquaponics system design may then improve, and this may lead
to production increases and/or cost reduction, allowing for economic feasibility of large, commercial
scale systems. A lot of knowledge on different aspects of aquaponics systems, such as bacterial
nitrification and nutrient balances in both horticultural and aquacultural systems, already exists.
Experts from both the aquacultural and the horticultural background will need to collaborate closely
in joint research projects in order to understand the integration of these two components and the
interaction effects that arise in this integrated system. Experimental research will be able to shed
more light on the interactions that occur in aquaponics system. A comprehensive computer model of
aquaponic systems may be developed, in which available knowledge is brought together in an
organised way. Only when the functioning of aquaponics is better understood, the technology may
be further developed in order for it to meet its potential for sustainable food production on a large
scale.
40
41
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44
Appendix III Feasibility of saline aquaponics ‐ A literature review J.A. van Vliet
Contents Abstract ................................................................................................................................................. 46
Introduction ........................................................................................................................................... 48
The living components of aquaponics ................................................................................................... 51
Bacteria .............................................................................................................................................. 51
Plants ................................................................................................................................................. 51
Fish .................................................................................................................................................... 55
Plant use in saline aquaculture ............................................................................................................. 57
An example of aquaponics under ‘saline’ conditions ........................................................................ 57
Use of halophytes for treatment of saline aquaculture effluents..................................................... 57
Current use of halophytes as biofilters in open systems .............................................................. 57
Potential use of halophytes as biofilters of Recirculating Aquaculture Systems waste water ..... 59
Discussion regarding plant use in saline aquaponics ........................................................................ 60
Potential crop and fish alternatives ...................................................................................................... 63
Sea weed ........................................................................................................................................... 63
Sea cucumbers .................................................................................................................................. 66
Shrimps .............................................................................................................................................. 67
Other research regarding integrated salt water systems ..................................................................... 70
Conclusions ............................................................................................................................................ 72
Bibliography ........................................................................................................................................... 75
45
46
Abstract
In aquaponics systems, the production of vegetables is combined with the cultivation of fish. Through
recirculation of the water in the system, aquacultural effluent discharge is limited and necessary
inputs other than fish feed are limited. Aquaponics systems may enable the production of fish and
vegetables in areas where there is scarcity of water, fertile land and/or (chemical) fertilisers.
Currently, in most aquaponic systems, fresh water is used. In some cases systems using water with a
higher salinity may offer opportunities. Examples are regions where fresh water is scarce while saline
ground water is largely available or where marine aquacultural effluent discharge causes
environmental problems. A range of options for systems of varying salinities are possible. Various
vegetables and fish that are known to be suitable for fresh water aquaponics systems may also
tolerate higher salinities and can thus be included in saline aquaponics system designs very similar to
their fresh water counterparts. At higher salinities, marine fish species which are known to be
suitable for recirculation aquacultural systems may be used. Selection of suitable plant to be included
in high salinity systems may require more research. Although plants are known which tolerate high
salinities, it is often not known whether these halophytes are suitable for growth in recirculation
systems. Moreover, economic value of many halophytes is yet to be determined. Systems may also
be designed for inclusion of other species such as shrimp or sea weed. Currently, more research is
needed in order to select species suitable for saline aquaponics systems and determine appropriate
designs of these systems. Under some circumstances, it may be more feasible to design non‐
circulation systems as these systems are less complex and more research has been performed on
them. Feasibility of any system will depend on many conditions such as the objectives to be reached
and the resources available.
47
48
Introduction
Aquaponics is a recirculation system in which the cultivation of vegetables is combined with the
cultivation of fish. What is normally considered to be waste water from the fish is now directed to
vegetable grow beds. The vegetables use the nutrients from the waste water, either directly or after
bacterial conversion depending on the nutrient. Crucial is the two step bacterial nitrification of
ammonia into nitrate. Ammonia is excreted by fish, but is toxic to them at low levels, while nitrate is
an essential plant nutrient. When combined with a simple solids filter, the water is cleaned and can
be recirculated to the fish, while the vegetables require little to no additional nutrients for growth.
Aquaponics can thus be described as a combination of Recirculation Aquaculture Systems and
Hydroponics. The main inputs of the system are fish feed, electricity for the water and air pumps, and
a limited amount of water to replenish losses due to evapotranspiration and flushing of the filter.
Outputs are fish and vegetables. No aquacultural waste water, which causes negative impact on the
environment, needs to be discharged.
Various designs of aquaponics systems are possible, varying from small scale domestic systems to
large scale commercial systems. Common components are a fish tank, a raft and/or media grow bed
for vegetable production, and pumps for both water and air (Figure 1). Usually, an additional filter is
included for removal of solids. Other components may vary. For more information about the
functioning and design of aquaponics systems,
please refer to van Vliet (2014).
It is argued that it is possible to set up
sustainable systems gaining a high production of
vegetables and fish at low costs in areas where
conventional agriculture is difficult due to a lack
of arable land, water and/or chemical fertilisers.
The system thus may be applied for food
production in cities, but may also offer
opportunities for many developing countries
with scarce natural resources (van Vliet, 2014).
Most examples of aquaponics systems are based
on fresh water. However, in some situations
saline systems may offer opportunities. Effluent
discharge issues of marine aquaculture are
similar to that of fresh water aquaculture and
may be mitigated using aquaponics (Webb et al.,
2012). Also, in some areas, access to fresh water
is highly limited while saline ground water is
widely available. In order to gain more
knowledge on the possibility of designing sustainable saline aquaponics systems, this literature
review was executed.
49
Figure 1: Example of a small scale aquaponics systems
including both a raft grow bed and a media grow bed for vegetable production (api.ning.com).
50
51
The living components of aquaponics
Although variations in species composition are possible, in a common aquaponics system three
groups of organisms are crucial for the functioning of the system. These are the bacteria, the plants,
and the fish. Below, the potential of these three groups of organisms for use under saline conditions
is discussed.
Bacteria
A crucial step in the functioning of an aquaponic system is the biological nitrification of ammonia
through nitrite to nitrate. The species of bacteria responsible for nitrification in soils and fresh water
systems may differ from those in marine environments. Little is known about the abundance and
diversity of these marine species (Gaag et al., 2010). Nevertheless, their existence has been
demonstrated (Gaag et al., 2010) and it is assumed that nitrification will take place in saline
aquaponics systems as it does in fresh water systems.
Plants
The next living component of aquaponics systems is the plant. In a hydroponic experimental setup,
Schwarz (1963) used brackish water of 2.5‐3.5 ppt9. This is a higher salinity than in conventional
hydroponics but cannot truly be called saline. Common crops for hydroponics such as lettuce,
tomato, carnations and cucumber were successfully produced. Schwarz mentions that more frequent
irrigation and replacement of nutrient solutions is needed than with non‐saline hydroponics. Water
use is thus higher when using brackish water, although not as high as when irrigating soil to achieve
the same amounts of production (Schwarz, 1963). For use in an aquaponics system, this would mean
that part of the water needs to be replaced on a regular basis. Production is higher when plants are
first grown in non‐saline solution for four weeks before transfer to a saline solution (Schwarz, 1963).
Hence, the time before transplant of seedlings to the aquaponics system could be slightly extended
to increase production.
The salinity level in this experiment, although higher than in conventional hydro‐ or aquaponics, is
still low as it is only about 10% the salinity of sea water10. Little is known about truly saline
hydroponic growth of vegetables. More substantial research has been done on the crop potential of
different plants on saline soils, or using saline water for irrigation. Aronson (1989) has compiled a
comprehensive list of plants that are able to grow under saline conditions to various degrees, which
is now accessible online with constant updates (eHALOPH). These plants are called halophytes,
meaning salt loving. There is a variety of mechanisms employed by halophytes to tolerate different
salinity levels, and some halophytes tolerate much higher salinity levels than others (Glenn et al.,
1999). Halophytes have been tested as vegetable, forage, and oilseed crops in agronomic field trials
(Glenn et al., 1999).
9 All salinity indicators used in cited articles are calculated to the salinity equivalent of the indicator in parts per
thousand (ppt) for ease of comparison. 10 Sea water salinity is usually around 35 ppt (NIO, 2006; Cheng, 2010) . This salinity level is used in this review.
52
At the low end of the salt‐tolerance scale, some crop plants such as sugar beet (Beta vulgaris,
Chenopodiaceae), date palm (Phoenix dactylifera, Arecacea) and barley (Hordeum vulgaris, Poaceae)
(Figure 2) can be cultivated on irrigation water approaching a salinity of 5 ppt (Ayers and Westcot,
1989).
Figure 2: From left to right: Beta vulgaris (sugar beet, www.rna‐seqblog.com), Phoenix dactylifera (date
palm, commons.wikimedia.org) and Hordeum vulgaris (barley, commons.wikimedia.org)
At the upper end, species such as Salicornia bigelovii (Chenopodiaceae, Figure 3) can yield as much
biomass and seed as conventional crops even when salinity of the soil solution exceeds 70 ppt, which
is around twice seawater salinity (Glenn et al., 1999).
The most sensitive crops include rice and bean, which are harmed by salinity levels of 1.1‐2.7 ppt
(Greenway and Munns, 1980).
In various field trials, halophytes such as Salicornia bigelovii, Distichlis palmeri and several species of
Atriplex (Figure 3), gave yields within the same range as from conventional forage grasses using
irrigation water with a salinity equivalent to sea water (Gallagher, 1985; Glenn et al., 1999; Glenn et
al., 2013). Most research has been done on fodder crops (Glenn et al., 1999). There are also some
crops which are able to grow under such high salinity which are potential human food crops. Atriplex
triangularis, a halophyte vegetable, can yield 21.3 t ha‐1 fresh weight per harvest (Gallagher, 1985).
Several halophyte seeds may be of value for use as grains (eg Distichlis palmeri) or for oil (Salicornia
bigelovii) (Glenn et al., 2013).
53
54
Figure 3: Top left: Distichlis palmeri (nipa grass, www.sciencedirect.com), top right: Suaeda (seeblite,
www.wildseedtasmania.com.au), bottom left: Salicornia (glasswort or samphire, commons.wikimedia.org),
bottom right: Atriplex triangularis (saltbush, calphotos.berkeley.edu).
The high yields obtained under full sea water irrigation are not optimal; even the most tolerant
species perform best at a salinity of 11.4‐19.4 ppt, which is between 25 and 50% sea water (Glenn et
al., 1999). When water of lower salinity is used for irrigation, yields could be even higher. Brown et
al. (1999) tested Suaeda, Salicornia and Atriplex at salinity levels of 0.5, 15 and 35 ppt. Suaeda and
Atriplex performed better than Salicornia at low salinity, while Atriplex performed very poorly
relative to the other two species on high salinity water. For all three species, plant dry matter
production, and the amount of nitrogen and phosphorus removed from the irrigation water,
55
decreased with increasing salinity. A higher irrigation rate would decrease salinity in the root zone,
reducing growth inhibition, but leaching would be substantially higher in that case.
Hence, plants are available which tolerate a wide range of salinity levels, but the circumstances
under which they tolerate these levels may be different from the circumstances in aquaponics
systems.
Fish
The third crucial living component in most aquaponics systems is the fish. Some fish have quite broad
ranges of salinity tolerance. The closer all other circumstances are to their optimum, the broader the
range of salinity tolerance will be. Especially temperature plays an important role in salinity
tolerance. For instance, Tilapia fish (Figure 4) grown in their optimal temperature range may survive
salinity levels of up to 40 ppt (Schofield et al., 2011; Iqbal et al., 2012), while they die at salinity levels
above 10 ppt when they are grown at 14oC which is below their temperature optimum. Also, even
though the fish at optimum temperatures survived at 40 ppt, reproduction and growth may be
reduced at salinities above 30 ppt (Schofield et al., 2011). Tilapia is frequently used in freshwater
aquaponics systems, but the above illustrates that, when other conditions are kept within their
optimum range, they may also be used in salt water systems. Common carp (Figure 4), on the other
hand, which is quite commonly used in fresh water aquaponics systems in temperate regions, cannot
tolerate such high salinity levels even under otherwise optimum conditions as indicated by an
experiment by Kasim (1983) in which common carp died at 8.1 ppt.
Figure 4: Left: Tilapia (downtownpala.blogspot.com), right: common carp (www.fcps.edu)
While fresh water species are likely to suffer from too high salinity levels (Wu and Woo, 1983), for
some marine species it is more likely that problems arise if salinity levels are too low. Marine species
will commonly be adapted to the saline conditions of the environment in which they live, which is
commonly around 35 ppt (NIO, 2006; Cheng, 2010).
As for fresh water fish, other factors such as optimum temperature range, growing time, optimal
stocking density and oxygen requirements will also have to be considered when determining
suitability of various marine fish for saline aquaponic systems. It can be assumed that any fish which
56
is suitable for more conventional saline aquacultural systems will be suitable for aquaponics systems
of a similar size.
57
Plant use in saline aquaculture
An example of aquaponics under ‘saline’ conditions
Kotzen and Appelbaum (2010) have done research using brackish geothermal ground water for
aquaponics systems in the Negev Desert. The salinity of the water they used was between 2.7 and
4.4 ppt, so the salinity of the water used in the experiment was quite low.
Brackish aquaponics raft and medium systems were compared to fresh water systems. The raft
system consisted of a fish and a plant tank of equal dimensions (2 m2, 1.17 m3), filters (total volume
0.35 m3), and a sump tank. Total water volume in the system was 2.73 m3. Aeration occurred in the
filters at the sump tank and through two aerators in the plant tank. 25 Nile tilapia fish were used. The
brackish water used at the start of the experiment had a salinity of 2.9 ppt, a pH of 7.0 and a
temperature of 19.3oC. The design of the fresh water system was essentially the same as that of the
brackish system except that two smaller fish tanks (1.0 m2, 0.627 m3 and 1.0 m2, 0.424 m3) were
used instead of one large one due to logistical constraints. Total water volume of the fresh water
system was 2.87 m3, with a salinity of 0.4 ppt, a pH of 6.5 and a temperature of 21.0oC. Water flow in
the systems was 12 L min‐1.
A variety of plants was used. Celery, chard, kohlrabi and parsley were grown successfully in both the
brackish system and the control system. Strawberry performed better in the control system, though
it survived in the brackish system. Chives, lettuce and mint had problems related to growing
conditions other than salinity in both systems. Addition of some nutrients (especially iron) is required
for healthy plant growth depending on plant species. Nitrification was successful: ammonium in the
brackish system remained at undetectable levels throughout the trial. Nitrate content was higher in
the freshwater system than in the brackish system. In both systems, nitrate was a limiting factor for
plant growth. Therefore, a Tilapia density increase to more than 50 fish per system was advised in
order to increase nitrogen input into the system. The fish in both the brackish and the freshwater
system remained healthy. Average weight increases in brackish and fresh water were 167 and 149
grams in 101 days, respectively. Weight increase was dependent on temperature and can be
considered reasonable especially since the aquaculture regime focused only on maintaining fish
health and monitoring the experiment, not on achieving optimal production levels.
Use of halophytes for treatment of saline aquaculture effluents
Current use of halophytes as biofilters in open systems
Marine and coastal aquaculture systems are often open systems which can discharge high volumes of
waste water containing suspended solids and dissolved metabolites in the form of organic matter
and inorganic nitrogen and phosphorus (Webb et al., 2012). Halophytes may be used as a biofilter for
aquaculture effluents (Gaag et al., 2010; Buhmann and Papenbrock, 2013). Popular, for instance, is
the use of (constructed) wetlands and mangrove forests, in which the halophytes play an important
role in the complex interactions between vegetation, soil and micro‐organisms which contribute to
water purification (Gaag et al., 2010; Buhmann and Papenbrock, 2013). Water may be recirculated
58
within the system. However, the main function of the system is the removal of nutrients from the
waste water (Buhmann and Papenbrock, 2013). In most cases, little attention is paid to the
commercial value of the crops. Some research is mentioned regarding the feasibility of different
halophytes with potential as forage or oilseed crops as biofilter for saline aquaculture effluents
(Buhmann and Papenbrock, 2013). Brown et al. (1999) have tested several halophytes and concluded
that constructed wetlands are efficient in removing solid waste from aquacultural effluent. Still,
most inorganic nutrients remain in the water and often there is no economic return from the plants.
The authors also mention that, when using the aquacultural effluent for irrigation of halophytes, it is
possible that nutrients leach past the plant root zone, causing contamination when reaching high
amounts in the aquifer.
59
Potential use of halophytes as biofilters of Recirculating Aquaculture Systems waste water
To reduce the amount of waste water produced in aquaculture, Recirculating Aquaculture Systems
(RAS) have been developed. In RAS, the waste water undergoes treatment to enable recirculation of
the water to the fish. Depending on the efficiency of the treatment methods, the water exchange
rate can be reduced from over 50 m3 to less than 0.1 m3 per kg of fish feed (Martins et al., 2010).
However, the recirculation loop will never be entirely closed, and the water which has to be
discharged may still contain high nutrient loads and may cause environmental problems if discharged
(Martins et al., 2010). Webb et al. (2012) have
tested the use of the commercially‐valuable
halophytic plant Salicornia europaea agg (L) for
treatment of waste water from a marine RAS. In
this system, the halophyte filter is not part of the
recirculation loop. Rather, the filter is used to
clean the waste water which remains after the
treatments that make the waste water from the
fish suitable for recirculation. The waste water is
first drained to a settlement pond. From here it
is pumped into a header tank through a vortex
separation tank containing plastic biofilter media
removing suspended particulate matter (Figure
5). The waste water is then pumped to filter beds
growing Salicornia using a flood and drain regime
of 24 h. This regime simulates the tidal
immersion cycles experienced by saltmarsh
plants. It allows for aeration at the root zone for
several hours before re‐submergence, thus
reducing the build‐up of anaerobic conditions
usually accountable for low nitrification. A
constant sub‐surface flow through the length of
the beds is maintained using a pump to improve
nutrient flow across the root zone whilst
reducing the build‐up of anoxic zones within the
substrate. Large pore spaces within the stone
layer reduce clogging (Figure 6).
The system proved to be a highly effective
biofilter, removing 97‐99% of influent total
dissolved inorganic nitrogen and 41‐88% of
influent dissolved inorganic phosphate.
Figure 5: Overview of the pilot system (Webb et al., 2012)
60
Figure 6: Cross section of pilot filter bed (a) Lengthwise and (b) width wise (Webb et al., 2012)
Discussion regarding plant use in saline aquaponics
Although the system as described by Kotzen and Appelbaum (2010) is truly a recirculation
aquaponics system, it is not truly saline. As in the hydroponic experiments by Schwarz (1963) salinity
is low. The plants used in the system are not true halophytes, so although they performed relatively
well under the low salinity circumstances of this aquaponics system, they will probably not cope with
higher salinity levels. This means that these plants are not suitable for aquaponics systems using truly
marine fish species. Notwithstanding, the experiment shows the potential of the plants in hydro‐ and
aquaponics systems under lower salinity levels. This allows for integration with other (fish) species
which do not require such high salinity levels but thrive well under low salinity, such as Tilapia (see
Fish above), but also shrimps (see also Shrimps below).
The examples of the use of halophytes for the treatment of waste water from saline aquaculture
systems are promising for the potential use of halophytes in high salinity aquaponics systems.
However, in both systems, the aim of the halophyte treatment is not to recirculate the water to the
fish. Also, in the second system, the water which is directed to the halophytes is pretreated. These
differences between the two systems and a recirculation aquaponics system do not allow for a direct
comparison of the systems.
It seems that there is a potential for plant production in saline aquaponics systems, although the
choice of suitable plants for different systems remains a challenge. Certain economically interesting
crops are known to thrive well under aquaponic conditions, such as lettuce and tomatoes. The
experiments described above indicate that these crops may also tolerate higher salinity levels than
conventionally used in these systems. Unfortunately, very little research has been done regarding the
salt tolerance of these species under recirculating conditions.
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This is also the case with highly salt tolerant halophytes. It is unclear whether all halophytes that are
suitable for growth under high salinity soil conditions are also suitable for saline hydroponic growth,
let alone saline hydroponic growth in a recirculation system. Irrigation dynamics is very different
from the dynamics in hydroponics (or aquaponics). In irrigation, factors such as leaching, differences
between the salinity of irrigation water and soil solution and irrigation depth play a role (Glenn et al.,
1999). As a consequence, the salinity levels of irrigation water which are tolerated by different
halophytes may not be the same levels as those which are tolerated within hydroponics systems. Salt
marsh plants, which are not only salt tolerant but can thrive in poorly drained soil (Glenn et al., 1999)
may be most suitable for hydro‐ or aquaponic growth. The roots of many salt marsh species possess
aerenchyma allowing exchange of gases between the shoot and the root and indirectly aerate the
surrounding soil zone potentially resulting in increased nitrification/denitrification efficiency (Gaag et
al., 2010; Webb et al., 2012). Other suitable plants may be those that have adapted to growth in tidal
zones. Here, the plants are constantly or occasionally flooded with salt water, which resembles
circumstances in raft and media bed culturing, respectively (personal communication Sander
Ruizeveld de Winter, PRI, 10‐12‐2013).
Another factor that needs to be taken into account is the economic value of the plant. For plants
such as tomato and lettuce this economic value is evident in its use as a consumption crop. As
described above, halophytes may have economic value as a consumption or fodder crop, or for use
as biofuel. Still, most of the halophytes are currently not widely used and known for these purposes,
decreasing market potential of the crops.
Taking these factors into account, an example of a potential plant for use in high salinity aquaponics
systems is Salicornia spp, or samphire. This is an edible succulent leafless genus that grows in
saltmarshes and saline environments and has commercial value as an oil seed crop, as food or fodder
and potential use in health, beauty and nutraceutical industries (Gaag et al., 2010; Webb et al.,
2012).
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63
Potential crop and fish alternatives
Sea weed
Above, various higher vascular plants are considered for use in saline aquaponics systems. For use
under highly saline conditions, sea weed may also be considered. Sea weed is fast growing and may
be cultured in a sustainable way without being in competition with other food crops. Hence, sea
weed is a promising biomass product (Hortimare; Noordzeeboerderij). It may be used as a biofuel, in
feed, as fertiliser, it can function to catch phosphate flowing to the sea through rivers, it can clean
water, and it can be used for human consumption as well (Hortimare; Noordzeeboerderij). With
that, growing sea weed may be combined with aquaculture (Hortimare; Noordzeeboerderij). In The
Netherlands, research is being done on growing sea weed in the North Sea (Noordzeeboerderij).
Under the name ‘Noordzeeboerderij’ (North Sea Farm) several institutes are working together with
various knowledge partners (amongst others, WUR) and have established a ‘farm’ in the North Sea.
This farm is used for research, development, testing and demonstrating concepts for amongst others
the culturing of sea weed, fish, shellfish and other flora and fauna. The current projects do not
include any aquaponics using a recirculation system. Under one project, aquaculture is combined
with the culturing of sea weed in the Oosterschelde. The Plant Research Institute of Wageningen
University and Research Centre is performing tests here. In this project, the culturing is done in semi‐
open systems, with lining systems for protection from waves (Noordzeeboerderij). However, it may
be possible to use sea weed in closed systems as well. Hortimare, one of the project partners, is
involved in exploiting this possibility. Hortimare offers aquaculturalists to provide their system with
sea weed and harvest for them, so that the aquaculturalist can focus on the fish (Hortimare).
Recirculation systems using sea weed to treat aquacultural waste water may be considered to be a
form of aquaponics. As part of the research project ‘Vis, Schelp & Wier’, led by Hortimare,
bioreactors using Ulva lactuca (Figure 7) were successfully included in marine RAS systems in which
turbot was cultured (Hortimare, 2012a). Various characteristics of Ulva make this macro alga highly
suitable for use in such systems. Aquacultural effluents can typically reach nutrient concentrations
100 times higher than normal concentration in open sea (Hortimare, 2012a). Unlike other
macroalgae such as Saccharina and Laminaria (Figure 7), Ulva can tolerate these extremely high
nutrient concentrations (Hortimare, 2012a). The nutrient uptake potential of Ulva is high. Under
optimal conditions, nitrogen uptake is 2‐3 mg L−1 day−1 in a system with 5 kg of Ulva biomass per m3
(Hortimare, 2012a). Biomass growth averages 5‐8%/day (Hortimare, 2012a) and it is easily harvested
(Hortimare, 2012b). The Ulva biomass produced may be most suitably applied in bio refinery, for
instance for use as biofuel or fish feed (Hortimare, 2012a). Also, Ulva produces high amounts of
oxygen. One kg of Ulva daily supplies enough oxygen for two kg of fish (Hortimare, 2012b).
64
Figure 7: From left to right: Ulva lactuca, Saccharina and Lamanaria (Hortimare, 2012a)
Initially, the ‘Vis, Schelp & Wier’ project used deep tanks with a volume up to 2.5 m3 and a surface of
about 2.0 m2 for cultivation of the Ulva (Figure 8). This caused problems due to light interception by
the uppermost Ulva layers, which could not easily be solved through inducing circulation of the
water, especially if the volume of the tanks would increase. It was found that a higher
surface:volume ratio would increase efficiency of the Ulva cultivation. A more appropriate design of
the tanks would be 40‐50 cm deep raceways (Figure 8). Initially, paddle wheels were used to induce
circulation. As the paddle wheels caused high losses of Ulva, they were later replaced by waterjets
(Hortimare, 2012a).
Figure 8: Left: Tanks used by Hortimare in the Vis, Schelp & Wier research. Right: Raceways with paddle
wheels (Hortimare, 2012a).
65
In the final design that resulted from the project, three raceways were placed in series. The volume
of the second raceway is half the amount of that in the first raceway, thus the water flow is twice as
high and residence time is twice as short as in the first raceway. Similarly, the volume of the third
raceway is half the amount of that of the second raceway, with a water flow twice as high and a
residence twice as short as in the second raceway. Hence, in each tank an equal amount of nutrients
will pass a certain mass of sea weed per unit of time so that the flux remains equal. Using this system
about half of the nutrients is already captured in the first day in the first raceway. In the next
raceways, each time half of the remaining nutrients is captured within the same time (Hortimare,
2012a). As the concentration of nutrients in the second and third raceway is much lower than in the
first raceway, it may be possible to cultivate other sea weeds such as Saccharina and Laminaria in
these tanks (Hortimare, 2012a).
The raceway design as described above is suitable to use in a recirculation system combining
cultivation of fish with cultivation of sea weed, which may be considered a form of aquaponics.
However, economic sustainability of this model is questionable. Currently, the price that can be
obtained for sea weed is low (Hortimare, 2012a). Although the potential use of sea weeds in bio
refinery is large and gaining attention, it is currently in need of more innovation and research before
it becomes economically interesting (Noordzeeboerderij). The same is the case for the cultivation of
the sea weeds. In the project described above, many unforeseen problems were encountered in
growth and reproduction of the sea weeds, many of which remained unsolved. More research is
needed to optimise sea weed cultivation in general and in recirculation systems specifically.
Moreover, the methods for optimisation which are already available need further innovation in order
to reduce their costs and technical complexity. For instance, in the system designed as a result of the
Vis, Schelp & Wier project, complex and expensive components such as UV filters, CO2 reaction
chambers, temperature control units are included (Figure 9). Although a smaller, less complex system
is currently being piloted, extensive research will be necessary before the technology can be
disseminated to a larger audience (personal communication Freek van den Heuvel, Hortimare, 06‐12‐
2013).
66
Figure 9: Design of the three phase filtration system (Hortimare, 2012a).
Sea cucumbers
As sea cucumbers are of great commercial value in Asia, where they are a popular luxury food item,
some research was done for this review regarding the feasibility of including sea cucumbers in an
aquaponics system. The information below is retrieved from a review by Purcell et al. (2012).
Of sea cucumbers, sandfish (Holothuria scabra, Figure 10) is most commonly cultured in tropical
areas. In culture, usually 30‐50 brood stock are used for spawning, with equal numbers of males and
females. The brood stock is kept in ponds or tanks, and fertility decreases with increased time in the
tanks. Only a small proportion of the brood stock will be successfully induced to spawn, and
problems caused by a lack of genetic variety frequently arise.
Usually the larval tanks contain between 0.3 to 1.0 larvae per mL. Survival rate of larvae is low,
especially in the first stage from larva to transfer to nurseries, during which time survival rate is only
1%.
Nursery of juveniles is space intensive and usually occurs in tanks or alternatively in mesh enclosures
in earthen ponds. This may take several months.
Further culturing usually is either in earthen culture
ponds (for sandfish, which are amenable to pond
conditions) or by using sea ranching in sheltered bays.
67
Sea cucumbers are usually harvested after 12‐18 months. Prices for sea cucumbers tend to rise
exponentially with increasing body size. For example, a 300 g sandfish can be sold dried for about
US$2.4, which is US$8 per kg, while a sandfish of 1 kg can be sold for US$18. This is a relative price
increase of 125% per kg. Maximum absolute growth rate is achieved when the sea cucumber is
between 300 and 800 g. The most profitable size for harvesting tropical sea cucumbers will vary
between climatic conditions, market conditions, and management practices.
Figure 10: Holothuria scabra (sea cucumber, echinoblog.blogspot.com)
Little is known about the relation between survival rate and hatchery practices such as stocking
density in different larval stages, water exchange regimes, transfer method, and dietary components.
Sea cucumbers in culture are currently fed with a variety of algal pastes, waste and faeces from
aquaculture, planktonic microalgae and other forms of organic detritus.
Sea cucumber cultivation may be part of a system with other aquacultural production (e.g. fish or
shrimps), as sea cucumbers can eat the solid waste from the aquacultural water.
Based on the information above, however, it does not seem viable to include sea cucumbers in
simple aquaponics systems. The low survival rates, the long growing time until a profitable size is
reached, the various different stages of cultivation each with their own conditions, and the use of
ponds or sea enclosures are all factors complicating this inclusion. Apart from technical and
economic constraints, the knowledge intensive nature of sea cucumber cultivation can pose
problems. There are still many knowledge gaps regarding the cultivation of sea cucumber in general,
even less is known about cultivation in co‐culturing systems, and nothing is known about including
sea cucumbers in recirculation systems as would be the case in aquaponics.
Shrimps
Effluent discharge of saltwater shrimp farming (Figure 11) currently causes large environmental
problems, especially in regions where the expansion of shrimp farming in coastal ecosystems has
been developed (Cheng, 2010; Mariscal‐Lagarda et al., 2012). New innovations are being developed
to mitigate the impact of shrimp pond effluents, such as recirculating systems and constructed
wetlands (Mariscal‐Lagarda et al., 2012). As for other aquacultural production, aquaponics may offer
solutions, but little scientific research has been done considering the use of shrimp in aquaponics.
There is a report from a student who grew Atriplex hortensis hydroponically in aquaria containing
shrimp (Cheng, 2010). Regrettably, the setup was very small, and some shortcomings in the
experimental design negatively influenced growth and
development of the plants. Also, the salinity in
commercial shrimp ponds usually is 5 to 10 ppt, while
in the experiment a salinity of 20 ppt was used. Plant
growth and development might be higher under the
68
lower salinity conditions of commercial shrimp ponds. Also, only Atriplex was used as a plant species
in the experiment, while it is unclear whether Atriplex is suitable for growth under hydroponic
conditions. Figure 11: Shrimp (liveblue.net)
Another article describes the use of shrimp waste water for irrigating tomatoes, without recirculation
(Mariscal‐Lagarda et al., 2012). Stocking rate of the shrimp was 50 post larvae per m2 and 15 plants
per fish tank (4.9 plants m‐2). Prior to placement in the experimental tanks, the shrimp were
acclimated in a raceway in which salinity was decreased from 35 ppt to 0.6 ppt in six days and was
retained at 0.6 ppt for another six days. The water used in the experimental tanks was low salinity
ground water (0.65 ppt). During the trial, additional KCl and MgNO3 fertilizer applications were made
if the primary productivity in the pond water was low. During the 19 weeks of culture in the trial, the
water temperature, dissolved oxygen, and pH of the shrimp tanks fluctuated between 20.4 and 32.3
°C, 8.1 to 10.6 mg L‐1, and 7.7 and 9.6, respectively. Salinity of the water applied to the tomatoes
varied between 0.80‐0.97 ppt. Tomatoes were grown in pots with a zeolite base, maintaining
nitrogen availability. Tomato yield using shrimp effluent water for irrigation was similar to that using
nutritive solution and significantly higher than using ground water. In the shrimp setup, water not
used by the plants was recirculated to the shrimps. Although it is unclear how well the system would
perform in absence of the KCl and MgNO3 fertilizer applications, this experiment indicates that there
is a potential for using low salinity water in a recirculating aquaponics system in which cultivation
vegetables is combined with cultivation of shrimps.
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Other research regarding integrated salt water systems
On various locations in Zeeland, The Netherlands, research on integrated salt water systems is being
performed by Stichting Zeeuwse Tong (KNDW). This foundation is a development project from
businesses, research institutes and education institutes for an integrated, within the dykes
(‘binnendijks’) system combining culturing of sandworm (Alitta virens), fish such as sole (Solea solea),
shell fish, algae, and saline crops (Figure 12).
Figure 12: From left to right: Alitta virens (sandworm, www.marinespecies.com), Solea solea (sole,
commons.wikimedia.org) and Aster tripolium (sea aster, www.floracyberia.net).
The sandworms are used as feed for the fish, the excrements of the fish stimulate the production of
algae and saline crops, while algae are the food of shell fish and sandworms. All nutrients that are
taken from the system in the form of harvest are replaced, for instance through feeding the
sandworms. Currently, the whole system functions within the dykes. Water is taken in from the
Oosterschelde and filtered, after which it flows to a basin in which the sandworms and soles are
cultured. The nutrient rich water flows to an adjacent basin, where algae are cultured. Next, the
water flows to a third basin, in which shell fish are kept. These shell fish filter the water. Currently,
saline crops are not yet integrated into the system. Among the crops under research are sea aster
(Aster tripolium, Figure 12) and glasswort (Salicornia europaea, Figure 3). Several pilots are running in
order to further develop this integrated system. The foundation is aiming at demonstrating and
promoting the possibilities of salt water systems, both in The Netherlands and worldwide. The
foundation also offers trainings to entrepreneurs who are interested in starting to exploit this
integrated system.
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Conclusions
Some conclusions can be drawn regarding the possibilities of designing saline aquaponics systems,
taking into account low salinity aquaponics, high salinity aquaponics, and other forms of integrated
systems.
In some areas, access to fresh water is highly limited while saline ground water is widely available.
Low salinity aquaponics systems may offer opportunities for the production of crops and fish in such
areas. Certain crops and fish are known to be both biologically and economically suitable for fresh
water aquaponics. Some of these crops and fish also show a relatively high degree of salt tolerance
and can therefore potentially be used in designing sustainable low salinity aquaponics systems. Other
species that thrive under low salinity, such as shrimp, may also be included. However, more research
is needed to establish salt tolerance of different crops, fish, and other organisms in recirculation
systems. This will allow to select the appropriate combination of species that is suitable for the
salinity of the water which is available.
High salinity aquaponics systems would limit the environmental impact of culturing marine fish
species. Most likely, fish which are currently used in inland marine aquaculture are also suitable for
recirculation aquaponics systems with similar fish tank size. For a ‘conventional’ aquaponics design,
using raft and/or media grow beds, halophytes will need to be identified that are biologically suitable
for these systems. Moreover, these halophytes would preferably have an economic value apart from
their environmental value in reducing waste water. More research is needed to identify species
suitable for this purpose. Another possibility of high salinity aquaponics is to divert from the
commonly used raft and media grow beds. Cultivation of sea weed in a system using raceways offers
potential to be included in an aquaponics system. However, the cultivation of sea weed in
recirculation systems is currently too complex and expensive and will need to be developed further
prior to uptake in aquaponics systems.
In regions where there is no water scarcity, it may not be necessary to design recirculating systems.
In that case, saline aquaculture effluent may be used for irrigation of hydroponic or soil grown salt
tolerant species. The plant component will function as a filter for the waste water. Open systems are
less complex than recirculation systems, and more research has been done on using saline ground
water and saline aquacultural effluent for irrigation in open systems than in closed systems.
Based on this review, it is not possible to draw final conclusions on ‘the feasibility of saline
aquaponics’. Saline aquaponics is a very vague term, and a variety of systems may be described using
this header. Moreover, feasibility is highly dependent on the objectives of the system and the local
context of limited resources and constraints (Graaskamp, 1972). For different specified cases, this
local context and the objectives of a potential project will first need to be established. Examples of
questions to be answered are: Should food or another economically valuable crop be produced or is
73
filtering of effluent the main objective?; Is there already a form of aquaculture taking place and if so,
what are related constraints?; What type of water (of which salinity) will be the source of the
system?; Are there water constraints?; Is there market potential for fish/crops/sea weed/shrimps/?;
etc. After analysis, it can be determined whether feasible saline systems can be designed to meet the
objectives and which can function in the local context of limited resources and constraints.
74
75
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