Universiteit van Amsterdam (UvA) Faculty of Science
School of Life and Earth Sciences
Internship Report – Aquaponics
MSc Earth Sciences, Environmental Management Internship Earth Sciences (5264INT24Y)
Master Student: Vera Catalano, 12047422 Examiner: prof. dr. Albert Tietema Co-assessor: dr. Elly Morrien
Weekly supervisor: Saro van Cleynenbreugel
Amsterdam, The Netherlands 30th September 2020
Table of Content
1. Thematic Summary of the Internship 4
2. Company and Internship Activities 5
2.2. Mediamatic company 5 2.3. Internship extent 5 2.4. Internship activities 5 3. Personal Reflection 7 4. Detailed Report 9 4.1. Aquaponic system 9 4.2. Why aquaponic 9
4.3. Aim of the project 10
4.4. Aquaponics team and meetings 10
4.5. Aquaponic at Mediamatic 10
4.5.1. Fish species 12
4.5.2. Plants and grow beds 12
4.5.3. Biological filter 13 4.6. Internship activities 14 4.6.1. Introduction 14 4.6.2. Daily activities 15 4.6.2.1. Checking the pH 15 4.6.2.2. Add nutrients 15
4.6.2.3. Check sump tank water 18
4.6.2.4. Check waterflow 18
4.6.2.5. Feeding fish 18
4.6.2.6. Plant trimming 19
4.6.2.7. Research 19
4.7. Weekly activities 19
4.7.1. Monitoring water quality 19
4.7.2. Tours to the public 22
4.8. Monthly activities 22
4.8.1. Water test to the lab 22
4.8.2. Cleaning pipes 23
4.9. Occasional activities 23
4.9.1. Weighting fish and calculating fish feeding rates 23
4.9.2. Checking plant pests, diseases, molds 23
4.9.3. Plant planting plan 24
4.9.4. Aquaponics workshop 25
4.9.5. Blog posts, interviews, podcasts 26
4.10 Setbacks in the aquaponic greenhouse 26
4.10.2. Ammonia buildup in the fish tanks 27
4.11. Side project: biodegradable material with mycelium 27
1. Thematic Summary of the Internship
In my internship, I managed an aquaponic system at the company Mediamatic, in Amsterdam. I worked full-time for 8 hours a day, 4 days a week for 6 months. Aquaponic is a circular and close cultivating system which combines aquaculture, the breeding of fish, and hydroponic, the cultivation of plants in water with no soil. The system is based on the equilibrium of three living components: fish, bacteria and plants. Fish produce waste, which nitrifying bacteria convert into nutrients and which plants use for growth. The delicate equilibrium so created by the system needs constant monitoring of, for example, the water quality to prevent undesired imbalances detrimental for one or the other living component. It is part of my internship to monitor water quality parameters such as ammonia, pH and temperature, research on optimal nutrient amounts, counteract plant nutrient deficiency and naturally control plant pests, research ways to improve the efficiency of the system and the suitability of fish and plant types for aquaponic among others. The aim of this aquaponic project is to research on new innovative potential techniques of producing local food in a sustainable way and within an urban context, facilitating the circular economy and creating opportunities for climate change adaptation. On the one hand, in an aquaculture system the water becomes toxic for fish due to ammonia buildup from fish waste, requiring a constant renewal and waste of water. Hydroponic requires the addition of chemical fertilisers. On the other hand, aquaponic prevents water waste and chemical input. Through the circularity, the system produces the majority of plant nutrients, recycles water and produces two food products at once.
2. Company and Internship Activities 2.2. Mediamatic company
In my quest to find an internship that focuses on sustainable innovative technologies that preserve natural resources and improve efficiency, like circular economy or sustainable agriculture, I came across Mediamatic in Amsterdam. Mediamatic is a dutch cultural institution founded in 1983 in Amsterdam and is considered a small enterprise (up to 50 employees). The daily management of the Mediamatic Foundation is led by Willem Velthoven, founder and Jans Possel, director. Mediamatic started with the production of media art and it is now a meeting place for exhibitions, seminars and workshops on media, technology, art, nature, biotechnology and society. The company is interested in innovative developments in society that combine art, design and science. The projects are based on sustainable principles making their contribution to the circular economy. The company has a Myco Design Lab where they experiment on biodegradable materials with living organisms. They are focusing on the use of mycelium, the root system of mushrooms, to create biodegradable materials as an alternative to plastic. For example, they are working on making an insulating material to isolate a nineteenth century barn where they held public events. Another biotechnology project is exploring sustainable ways of food production with aquaponic. Aquaponic is a semi-closed circular system where fish and plants are cultivated together. Aquaponic is based on principles of ecosystem functioning and it utilises the nitrogen-cycle where the ammonia from fish excretions is converted into nitrite and then into nitrate. Nitrate, the available form of nitrogen for plant uptake, is a macronutrient vital for plant growth and survival. This process also serves as a biological filter reducing the water ammonia levels and making water suitable again for fish. Aquaponic is a sustainable way of cultivating food as it reduces significantly the amount of water required and is suitable for urban environments as it takes up hardly any space. Mediamatic also opened a restaurant in which they use the food grown in the aquaponic farm. The organisational structure is built up in such a way that both the Myco-Lab team and the Aquaponics team have one coordinator or department leader and 2-5 interns.
2.3. Internship extent
The internship lasts 6 months from May to October 2020. I worked 4 days a week for 8 hours a day from 9:30 to 18:00. This internship counts towards 24 EC.
2.4. Internship activities
During my internship I was responsible with another intern to manage the aquaponic farm. An aquaponic system requires regular checks and maintenance works. The water system has to be cleared from any fish excretions or plant residues that stop the water flow. If the water flow stops the fish don’t receive fresh water and would soon die of water toxicity. Similarly, the water quality needs to be checked daily for pH and weekly for ammonia levels. These two factors must stay within a certain level range to be suitable for fish survival. In regards to plants, the water quality needs to be checked weekly for nutrient levels. Also the water flow
needs to be adjusted daily with the addition of some nutrients to complement the role of nitrogen and give a more complete set of nutrients to plants.
3. Personal Reflection
When I started my internship at Mediamatic I quickly realised that working at Mediamatic requires a hands-on and self-initiative mentality. Interns at aquaponics are assigned an external coordinator who comes to meet us once a week. During my first day the coordinator explained the basic tasks that had to be performed daily, weekly and monthly, the key tasks, and introduced to the different sites where to get information. Thereafter we had to learn ourselves how to perform the tasks and how to solve any issue. None of the other colleagues and nor the founder and the director could help us in aquaponics as only our external supervisor knows about the system. Thus, at first, I wasn’t given extensive training and I had to find my way through the work. However, this setting made me proactive and independent in understanding the working environment, the managerial tasks to maintain aquaponic in equilibrium and learning the most of it. This was facilitated by the many interns that work at Mediamatic: we worked and collaborated together, we trained each other perfecting our tasks, we shared what we learnt, and quickly learned how to deal with the working environment. Before I started at Mediamatic I didn’t know about aquaponic besides the information provided on the Mediamatic website regarding the internship activities. Now, five months later, I know how to maintain an aquaponic system at a suitable equilibrium for both fish and plants, I know how to fix technical problems, I give tours where I am able to share technical and scientific information to a varied public on various depth levels of knowledge and I am able to perfectly train the new interns that will soon substitute me.
I realised that I had to take initiative if I wanted to learn more besides the activities assigned by the coordinator. In this I saw the possibility of developing my own assignments. Nevertheless, often there were high priority tasks that required immediate attention as an aquaponics system works on a nutrient-cycle that has to be maintained at suitable conditions for the fish, bacteria and plant survival. Over time there was more room to formulate my assignments, collaborate with my colleagues and learn from each other’s projects. During my internship I took the initiative to rethink the plant plan of aquaponics in terms of ensuring a proper amount of harvest for the restaurant use. The issue that I found is that for some herbs there is not a suitable amount of harvest to be used in the kitchen. Thus, some herbs are of no use for the restaurant and will be trimmed and composted while the restaurant will need to purchase herbs somewhere else. If the variety of herbs is reduced but the quantity of each herb is increased aquaponic will be more productive. Also, to maintain biodiversity the different plants can be planted together in every single growbed so also as to increase the plant resilience to pests and diseases. My idea will be considered in the new year’s plant sowing plan.
The internship and the activities were of great use and relevance for my learning goals at a personal, professional and technico-scientific level. For example, on a personal level I learnt to quickly become accustomed to the working place and make the most out of my experience even with little initial training. I was pushed to be proactive and independent, I learnt my curiosities through self-learning and develop interpersonal skills through cooperation with others. In the end, I am glad this was the case because that initial situation made me develop myself on a personal level and professional level.
On a more practical level, ensuring the continuity of the circular system improved my problem solving skills. On a daily basis, new issues arise that need to be fixed with a methodological approach and immediate problem solving and accuracy were mandatory. Practicing this skill helps me in my future career as any science related job will involve applying problem solving skills. Giving tours to a wide audience trained me in the capacity to transfer scientific knowledge in an easy, accessible, comprehensible and also enthusiastic manner. This also gave me insights on my skills of presenting and talking to the public. Furthermore, the monitoring of the water quality is linked to gaining particular technico-scientific knowledge about aquaponic and more broadly as a basic knowledge for circular systems. Since aquaponic is a circulating system, monitoring the water quality parameters is key for a suitable system functioning and for the prevention of dangerous imbalances in pH, ammonia or nitrate levels. Performing this task made me aware of how important it is to regularly monitor parameters in a circular system as well as to act promptly when imbalances occur as the system hosts living creatures.
4. Detailed Report 4.1. Aquaponic system
Aquaponic is a sustainable cultivation method that utilises principles of ecosystem functioning to cultivate fish and vegetables in a circulating closed environment. It combines aquaculture, the breeding of fish with hydroponics, growing plants without soil in water. By combining the two it is possible to reduce water waste and limit the addition of chemical fertilisers. Aquaponic works by creating a constant water flow between the fish tanks and the growbed. The water in the fish tanks becomes enriched with ammonia due to the fish excretions. When the water is pumped into the grow beds, two types of nitrifying bacterias convert ammonia into nitrite and then into nitrate, the available form of nitrogen for plant uptake, setting the conditions for a continuous nitrogen-cycle. This process makes nitrogen from fish waste available for plant uptake, one of the macronutrients for plant survival. In aquaculture, fish are grown in tanks but the accumulation of ammonia from the fish excretions builds up with time generating a toxic environment for the fish. Thus, in this system wastewater has to be discharged and new clean water has to be added into the system. In hydroponics, chemical fertilisers need to be regularly added to the water medium in order to grow plants. By combining aquaculture and hydroponics into aquaponics, the water from one type of cultivating system is recycled through the other, hardly any water needs to be added over time, no water needs to be wasted and nitrogen does not need to be added from a chemical form. Aquaponics create a circulating system that can be closed or semi-closed as in the case of the farm at Mediamatic as the fish food is added. Additionally, whereas some nutrients are added to the water flow to combine nitrogen, no chemical pesticides can be used in the farm as these will endanger fish health and survival.
There are two types of aquaponic designs: deepwater culture and media-based systems. Both work on the principle of the nitrogen-cycle, whereby the roots host nitrifying bacteria-cultures and fish provide plants with essential nutrients. Mediamatic chose the media-based method, growing plants in large containers filled with media from lava rocks and clay pebbles. The media helps to break down the solid waste acting as an additional filter. However, this method does not maximise output of plant growth compared to other aquaponic techniques. In a deep-water culture, roots are suspended in the water and produce the highest harvest, therefore, being more suitable for commercial and mass production (FAO, 2014). In fact, the media-based method served Mediamatic's purpose of engineering and installing a small scale aquaponic farm for experimenting and researching, educating the public on sustainable urban farming, and producing vegetables and herbs for their restaurant. 4.2. Why aquaponic
Mediamatic focuses on current concerns of our society and on alternative technologies that can offer sustainable solutions. With the rising concern of sufficient food production to feed the growing population throughout the precariousness of the future given by climate change, it is vital to develop new ways of sustainable farming. These should use little space, make use of unfertile lands, eliminate the need for clearing land, recycle resources, use little and
renewable resources, utilise principles of ecosystem functionings, be suitable for an urban setting and decrease transportation needs. Aquaponic is a system that can provide a local source of food within an urban context, with sustainable methods that can facilitate the circular economy and create opportunities for climate change adaptation (Estim et al., 2020). Mediamatic decided to explore new sustainable urban farming techniques and was suggested to research and experiment with an aquaponic system, which they designed and built in 2012. 4.3. Aim of the project
Mediamatic is a cultural foundation which serves the scope of educating, sharing ideas, developing projects, inspiring and raising ecological awareness amongst society. With aquaponic, Mediamatic aims to explore and research innovative and unconventional ways of farming based on sustainable principles. The public is invited to learn through blog posts, workshops and guided tours. The company aims at providing examples of sustainable farming in the city so as to increase the public consciousness about food production, food transportation and consider alternatives to traditional agriculture.
4.4. Aquaponics team and meetings
During my internship at Mediamatic I am part of the aquaponic team together with one other intern under the supervision of Saro van Cleynenbreugel, the aquaponic coordinator. The aquaponic team is responsible for managing, maintaining and improving the aquaponic system, giving tours and facilitating workshops. Daily, weekly and monthly activities are the responsibility of the interns, whereas the coordinator is available for consultation. Saro engineered and built the aquaponic system himself with the help of previous interns, thus, he is the most experienced with aquaponic within Mediamatic. Every Friday, there is a meeting with the aquaponic team where we share the latest developments, technical issues and future steps. If there is an urgent technical matter we get in contact with Saro remotely. Other means of communication are done through emails especially with the boss and director, or by oral consultation among interns. Every Wednesday, we have a meeting with all the employees where we discuss upcoming events, news, updates and we finish with communal tasks like setting up spaces for events. The small scale nature of the company allows for informal and accessible communication amongst employees and interns.
4.5. Aquaponic at Mediamatic
The aquaponics system is a vertical semi-closed farm system placed in a greenhouse at the Biotoop Dijksgracht at the Mediamatic site. The vertical structure is divided into 3 separate metal structures each containing 12 grow beds with 3 grow beds placed vertically above one another (Fig.1). There are 36 aquaponic grow beds (40m2) at Mediamatic. This vertical
structure is placed into a greenhouse. The fish tanks are not below the grow beds as illustrated in the figure but are placed inside a container which is also inside the same greenhouse. There are five different fish tanks that contain 1200 litres of water each and 152 fish in total. The fish are placed separately in each tank depending on the different life stage, fish size and weight: in the first tank there are a higher number of small fish whereas in the
last one there are a fewer number of bigger fish. The smallest weighs 680g on average and are the largest population - 50 small fish. In the other four tanks the sizes vary from 1000 to 2500 grams and they are much less in number between 20 and 32. When the fish grow bigger they are moved to the next tank so to regulate the amount of food fed to the fish.
Figure 1. Vertical structure for aquaponics at Mediamatic (Engels, 2012a)
A continuous flow of water connects the fish tanks to the grow beds hosting plants, earthworms and bacteria (Fig.2). The pump pumps up the water simultaneously into the fish tanks and into the top grow beds. There are two pumps which work similarly, the only difference between the two is that one irrigates one half of the upper grow beds and the other the other half of the upper grow beds.
Water from a sump tank (containing 500 litres of water) is pumped to the five fish tanks. The waste water in the fish tanks flows to a solid filter., which flushes the water back into the sump tank. The water from the sump tank is pumped with electricity only to the upper grow beds. The top grow beds fill until halfway and a bell syphon regulates the amount of water by emptying a certain amount of water down into the lower grow beds. From the upper grow beds water therefore flows down mechanically by gravity. Through bell syphons it is possible to create a ‘low- and high-tide’ system in the grow beds. The syphon is triggered when the water in the growbed reaches the overflow level. At this point, the vacuum formed in the grow beds draws the water into the next growbed. This system however has some glitches, such as a syphon that does not stop flushing (generally because of a too high water inflow) or that it does not flush properly because of obstructions. Lastly, from the bottom grow beds the syphon flushes down water into a drainage pipe that runs the water back into the sump tank.
Figure 2. Aquaponic at Mediamatic. Plumbing design connecting the vertical structure divided into three components of grow beds with the sump tank and fish tanks (van Cleynenbreugel, 2015).
A fail safe system safeguards the waterflow with a flow sensor. The sensor gives a realtime waterflow on a display located in the fish container. Two GSM Power Alarm modules are installed to send a text message to employees when the power fails on one of the pumps. The alarm is also triggered when the waterflow is lower than 250 l/hr from one minute. In this case, water might be leaking out of the system or the pipes are not well maintained and the water is consequently filling up the grow beds. A short circuit can happen because of a faulty heater or with water in one of the socket boxes.
4.5.1. Fish species
The aquaponic farm has African catfish (Clarias gariepinus). Mediamatic decided on African catfish because of their high resilience. They can withstand changes in pH, temperature, and oxygen levels and are resistant to many diseases and parasites. Catfish are also air breathers and thus are very suitable for aquaponics as if the oxygen level suddenly drops they survive. The optimal water temperature is 26°C and they stop growing at 20-22°C (Thomas and Wellborn, 1987).
4.5.2. Plants and grow beds
Plants grown in aquaponics are all edible and are mostly high value herbs, vegetables and flowers that can be used as additions to food recipes in the restaurant (Fig.3). Examples are edible flowers like begonia, Szechuan flowers, malva flowers and nasturtium, herbs lemon verbena, vietnamese coriander and red basil, while greens New Zealand spinach, kale and blood sorrel.
The medium of the grow beds consist of volcanic rocks and expanded clay pebbles or a mix of the two. These mediums are chosen because they have a high surface area to volume ratio, meaning they can provide space for bacteria-colonies and increase the oxygen content in the water beneficial for bacteria (FAO, 2014). With volcanic rocks woody plants can be planted
in the aquaponic grow beds as they provide sufficient strength for root holding (e.g. pineapple sage, patchouli, peppers). In clay pebbles more fragile plants can be grown like dill and nasturtium.
In order to be able to provide a proper amount of plants for the restaurant, we decided on planting a fewer number of plants so as to harvest a good quantity of each plant. In doing so we want to maintain a high biodiversity - as opposed to a monoculture - by sowing the different plants together in each grow bed. Some plants are more tolerant than others to pests and can repel pests. For example, we planted tobacco plants, Vietnamese coriander and onions next to the most vulnerable plants, persley, moroccan mint and Szechuan flowers.
Figure 3. Aquaponic farm at Mediamatic. 4.5.3. Biological filter
Biological filtration is a natural mechanism on which aquaponic is based (Fig.4). The ammonia that builds up in the water of the fishtanks from the fish waste is balanced by this mechanism. The ammonia in the system is reduced thanks to nitrifying bacteria, that live around the roots of the plants in the grow beds, that convert ammonia into nitrate nitrogen with the combination of two processes known as nitrification. Firstly, ammonia and ammonium are transformed into nitrite (NO2) by Nitrosomonas bacteria. Through this
process, oxygen is required, pH is lowered and acid (H+) is released. Secondly, nitrite (NO2),
a highly toxic form for fish, is converted to nitrate (NO3) by Nitrobacter bacteria. This
process also uses oxygen and decreases pH. This non-toxic nitrate is the bioavailable nitrogen form that plants can uptake as nutrient. When the dissolved oxygen content is high and the organic matter is low, nitrification performs at best. Alternatively, with low oxygen content the nitrification slows down or ceases, causing an excessive buildup of ammonia toxic for
fish. The balancing of ammonia through the biofiltration links fish, bacteria and plants in the aquaponic circular system. If the biological filter is not performing well, the fish waste accumulates leading to toxic water, inconsistency in plant nutrients, and deficient system.
Figure 4. The aquaponics cycle with a close look at the biological filter process by nitrifying bacteria (Engels, 2013). In order to establish the biological filter in a newly developed aquaponic system, between 4 weeks and 6 weeks are required to allow the bacterial populations to develop. Ammonia and nitrite need to be monitored daily to prevent toxic levels for fish. By feeding the fish, ammonia levels increase in the initial absence of sufficient nitrifying bacteria to transform ammonia into nitrite. Then, as Nitrosomonas bacteria increase, ammonia levels will be reduced with the conversion of ammonia to nitrite. Next, high nitrite levels decrease as soon as Nitrobacter bacteria convert nitrite to nitrate. When both ammonia and nitrite levels drop below 0.5 ppm the biofilter is settled and the system is cycled and able to support the establishment and growth of plants (FAO, 2014).
4.6. Internship activities 4.6.1. Introduction
The aquaponic farm needs daily, weekly and monthly checks and maintenance works. Aquaponic requires constant attention as it functions on a delicate equilibrium that requires problem solving through understanding the cause of the problem and deriving an immediate solution by trial and error. In this section I describe the activities performed on a daily, weekly, monthly and occasional basis.
4.6.2. Daily activities 4.6.2.1. Checking the pH
The first thing to do every day is checking the pH with an electric pH meter from the water that flows into the fish tanks. Measuring the pH is crucial because in addition to indicating whether the living conditions are still suitable for the fish, it also indicates problems in the system such as if fish excrements are not filtered out well or if there is a dead fish in the tank. Also, if the pH is too low, the nitrification slows down or stops leading to high ammonia concentration in the fish water. The suitable pH range is between 6.2 and 6.8 with 6.2 being the optimal level. If the pH is equal or under 6.0 the water is too acidic for the fish and we add 10g of potassium hydroxide (KOH) to increase the pH; if the pH is higher than 6.0 we add 13g of potassium sulfate (K2SO4). These are strong bases and should be added at low doses aiming for lowering pH slowly (FAO, 2014). One problem that can occur in an aquaponic system is a constant high pH that does not decline, stabilises at high levels or starts increasing. This phenomenon can be traced to the presence of hard water or other mineral sources for example from water snail shells that can accumulate in the sump tank. A high or stable pH can also be the cause of anaerobic conditions (absence of oxygen) due to denitrification - the microbial process whereby nitrate and nitrite are converted to gaseous forms of nitrogen such as nitrous oxide (N2O) and nitrogen (N2). Denitrification increases pH and stabilises it. This is also the reason why filter tanks and pipes need to be cleaned (Section 4.8.2.) and organic matter deposits in the hydroponic medium should be removed. 4.6.2.2. Add nutrients
In an aquaponic system, the fish food and fish waste produce the majority of the essential macronutrients and micronutrients for plant growth. These include the macronutrients nitrogen (N), phosphorous (P), sulfur (S), magnesium (Mg) and the micronutrients chlorine (Cl), boron (B), zinc (Zn), copper (Cu) and molybdenum (Mo). The exceptions are the two macronutrients calcium (Ca) and potassium (K) and the micronutrient iron (Fe). These we add in the system. Potassium is also supplied when potassium hydroxide is added to the water to regulate the pH.
For every nutrient we research the optimal amount not just for plant growth but also for an aquaponic system on the account of the fish. Daily, we add 9g of iron (from a 7% solution) and either 10g of potassium hydroxide or 13g of potassium sulfate depending on the pH (see Section 4.6.2.1.) (Fig.5). During the weekends no intern works in the aquaponic and so every Monday we triple the amount of nutrients to add in the waterflow. These provide plants with iron and potassium which are not produced by the aquaponic system.
The third element not produced by aquaponics is calcium. However, while we once used to add calcium to the waterflow, we then noticed an excessively high concentration of calcium. We then stopped adding calcium for a week to then check the levels with a water test and discover that the amount was still rising. The coordinator Saro asked to investigate the issue. I reconducted the rising calcium to the presence of numerous small water snails which found
their way to and now live in the sump tank. The species seems to be the invasive New Zealand mud snail. It could be that the accumulation of shells from dead water snails releases calcium in the water. Now being two consecutive months the calcium concentration is still high, thus, eliminating the need to add the nutrient.
From time to time, we also add 7g of epsom salt (a source of magnesium) on a weekly basis. Although an aquaponic system produces magnesium, sometimes low pH conditions or a high amount of competing elements such as potassium and calcium can decrease the availability of magnesium for plants. The specific amounts of nutrients that we give to aquaponic are calculated on the optimal levels of nutrients for aquaponic. When first setting up an aquaponic farm, we research the optimal nutrient amounts. Then, based on the total amount of water in the system, it is possible to calculate the quantity required to derive the optimal percentage amount in the whole system. Below is an example of the calculation for the addition of chelated iron.
The standard UVI system rate of chelated iron is 2mg/L every three weeks (FAO, 2014). This is the starting point. Chelated iron is not pure, thus it provides only a percentage of iron usually between 6% and 12%, which in the case of our chelated iron is 7%. Assuming we add 7% (0.07) of iron in our system, to get 2mg of iron per liter in the system, we divide 2 by 0.07 which gives 28.6mg/L. This is the amount of power required to get 2mg of pure iron per liter in the system. Thus, this number is multiplied by the volume of water of the system: 28.6mg/L * 6500L = 185.900mg/system. Converting this value in grams, 185.9g of powder is the amount to add in the system every three weeks to maintain the iron level at the recommended standard. This amount is then divided to derive a smaller dose to add daily. The equation is therefore as follows:
Chelated iron (7%): 2mg/L * 3 weeks; 2/0.07 = 28.6mg/L; 28.6mg/L * 6500/L = 185.900mg/system; 185.9g / 3 weeks = 62g/3weeks; 62g/7 days = 8.9g daily amount of chelated iron which we average to 9 grams a day.
Figure 5. Adding chelated iron in the aquaponic waterflow at Mediamatic
Once the quantity is calculated, the key thing to consider is that aquaponic, by hosting fish, requires extra attention regarding the frequency and quantity of nutrients released in the system as well as the effect that these have on fish. On the latter note, an experiment needs to be performed before starting to add the nutrients in the system. Premising that the non-toxicity of the nutrients to fish is confirmed, to ensure the safety of the nutrient quantity to add, one fish is isolated from the others in a fish tank to test the reaction of small doses of nutrients. The amount of nutrient is increased until reaching the desired amount; if the fish survives the nutrient quantity is suitable for the aquaponic system. In our system, these trials were always successful. This is especially important with nutrient fertilisers that are not in the pure mineral form. For example, potassium hydroxide is a potential toxic element for fish, however, in its pure form, it is safe for an aquaponic system (FAO, 2014). As previously anticipated, the frequency and quantity are also important factors. In order not to stress the fish or create water quality imbalances, it is advisable to give a smaller amount of nutrients daily rather than a higher quantity of nutrients weekly or less frequently. Thus, the total quantity of nutrients to be added is divided per day. This is also the result of trials and errors: when the aquaponic farm was settled, the nutrients were added weekly, however, this resulted in high imbalances in the chemical water quality. Thereafter, the nutrients were added daily in smaller amounts. Furthermore, now we add the nutrients into the water flow directly, however, at the beginning nutrients were added directly in the grow beds so as to further decrease the stress to the fish. However, this led to an alkaline state, which is known to inhibit the plant uptake mechanism and increase the likelihood of plant diseases. Thus, it was concluded to add the nutrients in the water in small daily doses.
Through experimenting, as soon as the desired nutrients level adjusts in the system, the amount of nutrients to supply is calculated from the average quantity of nutrients given in the preceding three months. As the aquaponic stabilises and the nutrient quantity in the water reaches the optimal levels, the quantity of nutrients becomes the average of all the preceding months since the starting of the aquaponic farm.
4.6.2.3. Check sump tank water
The sump tank water needs to be filled with water orelse the fish in the tanks will not receive fresh water and they risk to die from high water levels of ammonia. The sump tank empties slowly and gradually into the fish tanks within a couple of days, thus, on Fridays and Mondays we fill in the sump tank completely to cover for the weekend.
4.6.2.4. Check waterflow
The waterflow that runs to the grow beds needs to be checked daily because if it becomes clogged with some particles there is a risk of fish death from water toxicity. The waterflow can be obstructed with fish excretions and the syphons with plant residues or plant roots. Making sure that the waterflow is in the right order is also important because a leakage of water could provoke a short circuit as there are lights on top of each grow bed. When there is only a little stream or no water is coming out, the first thing to check is the syphon that regulates the water in every grow bed and clear it from any organic matter residue. If the syphon is clear and the water still does not come out, the issue is solved by either cleaning the pipes or cleaning the filters on the pumps in the sump tank.
The water flows into the grow bed through one single tube per each grow bed. This was first thought to decrease the oxygen level in the grow beds, thus, a bar spray was first installed in each grow bed instead of one single flow so to maintain oxygen levels high. However, no changes in the dissolved oxygen (DO) were observed. Thus, it was decided to opt for one single water flow to each grow bed and the DO remained generally high. This is also due to the medium chosen, clay pebbles and volcanic rocks.
4.6.2.5. Feeding fish
African catfish are very resilient as, in their natural environment, they can easily switch from one feeding mode to another: they can consume both living and dead matter, from phytoplankton to plants to other fish to individuals of their own species. Also they can feed at the bottom as well as at the water surface (Thomas and Wellborn, 1987). In our fish tanks, we feed them with floating fish food in order to monitor their feeding behavior. We take account of how much they eat, how fast and how enthusiastic they are. This could give an indication of how well they are. Not eating could indicate that the water in the fish tanks is acidic, which could be a sign of a waterflow malfunction or of fish waste moving back to the fish tanks when the pipes are getting cleared. Every three months we weigh the fish to derive the average weight per tank and adjust the amount of fish food accordingly also depending on the season. Every tank receives different amounts of food. On Fridays and Mondays we feed the fish the double amount to cover for the weekend.
4.6.2.6. Plant trimming
Being plants sowed in a vertical structure, they have to be trimmed regularly to maintain a suitable size. Plants are either harvested for the restaurant or trimmed and composted (Fig.6). Also it is important to keep the hydroponic medium clean in order to remove excessive plant residues and organic matter which can lead to pH changes but also be favourable for pests.
Figure 6. Pepper harvested for the Mediamatic restaurant.
4.6.2.7. Research
Aside to practical tasks we research on different topics as part of both assigned tasks and independent work. The former include researching and observing suitable plants to sow for the new planting season, natural pest controls, plant nutrient deficiencies, optimal nutrient levels. The latter include researching catfish behaviour, sustainability of aquaponics (resource use, renewable sources, enhancing circularity), bioethics of aquaponics, pros and cons of the system within different urban and rural settings, and lastly biodegradable material with mycelium. As I was new to aquaponic, becoming knowledgeable about the system required extensive learning through practice, observations and experimenting and independent research. Some of these topics are discussed throughout the sections of this chapter.
4.7. Weekly activities
4.7.1. Monitoring water quality
The water quality needs to be monitored weekly to ensure suitable pH and ammonia levels as well as to regulate the amount of nutrients based on potential imbalances and plant nutrient
deficiencies. When the system was first set up the water quality had to be tested daily in order to adjust parameters as required. For example, with high ammonia levels the fish feeding amounts can be reduced or water can be diluted. Once the nutrient cycles are balanced, testing weekly is sufficient. Monitoring the water quality is essential in a closed system because any elements that enter the circle remain until they get taken up by plants or digested by microbial life or earthworms that inhabit the system.
We test the water of the fish tanks. We use JBL freshwater test-kits (Fig.7) which are liquid colorimetric indicators which change colour in accordance with the parameters of the water with which they are mixed. The colour that develops is then compared with a printed card. Colorimetric methods are reasonably simple and ours are accurate to about 0.05 ppm. This value is adequate for the aquaponics system as the toxic parameters such as nitrite should always be 0 and macro-nutrient concentrations are measured only up to one decimal. All the water quality measurements are recorded in an Excel file to facilitate the observation of trends and diagnose future issues.
With these tests we determine the chemical water quality, the most important index in the aquaponic system. We examine the following parameters and aim for the following optimal concentrations:
- Temperature for fish 26°C, for bacteria 17-34°C - pH; 6.0-6.8 - optimal 6.2 - Ammonia (NH3); 0.0-0.1 (ppm) - Ammonium (NH4); 0.0-0.1 (ppm) - Nitrite (NO2); 0.0-0.1 (ppm) - Nitrate (NO3); 40-80 (ppm) - Potassium (K); 100-400 (ppm) - Calcium (Ca); 100-500 (ppm) - Magnesium (Mg); 50-100 (ppm) - Iron (Fe); 0.5-5.0 (ppm) - Oxygen (O2); 4-8 (ppm) - Phosphate (PO4); 50-100 (ppm)
Ammonia, temperature and pH are the most crucial parameters that require constant monitoring. Whereas due to the grow bed medium there is good aeration and so oxygen is at suitable levels at all times and does not need to be checked. Fish constantly release ammonia through their gills, urine and solid waste. Uneaten food and other decaying organic residues also increase the ammonia concentrations. The biological filter is a natural mechanism that balances the ammonia levels. Nevertheless, imbalances can occur so testing is essential. Ammonia damages gill membranes and prevents fish from breathing normally eventually leading to fish death. Even trace amounts stress fish and harm their immune system increasing the likelihood of disease. Ammonia exist in two forms: un-ionized (NH3) and
ionized or ammonium ion (NH4+). NH3 ammonia is toxic to fish, while NH4+ is not, apart at
extremely high levels. The ratio of NH3 to NH4+ in water varies according to water pH and
temperature. At pH 7.0 or lower, most ammonia (>95%) is present as NH4+, the non-toxic
form. With higher pH, the proportion of NH4 to NH3 rises. Water temperature also affects this
ratio: in warmer water NH3 is present at any given pH compared to cooler water. For
instance, at 28°C, the percentage of NH3 is 2% at pH 7.5 and 18% at pH 8.5. Ammonia in the
NH3 and NH4 forms must be maintained below 0.1 ppm in an aquaponic system. Fish tolerate
higher ammonia levels at <7.0 pH (FAO, 2014).
Ammonia levels may build up when the ammonia produced is too high to be handled by the biofilters. This may be caused by an overfeeding, too high fishing stocks or improper aeration. An easy way out would be to clear the pumps, reduce the feeding amount and test the oxygen levels. However, a more durable solution is decreasing the fish density, weighting the fish and adjusting the feeding rates accordingly (see Section 4.9.1.). If plants are not growing this could be linked to low ammonia levels. Low ammonia occurs when there are only few fish or when the water is too much for the number of plants. This can be solved by increasing the fish density or using a smaller tank.
The water temperature is important not just for fish but also for bacteria and the aquaponic in general. For bacteria’s growth the ideal temperature range is 17-34°C. If the temperature of the water is lower than 17°C, the bacteria productivity decreases and below 10°C the productivity is shrinked by half or more. Low temperatures have major impacts during winter times (FAO, 2014). The water in the fish tanks is heated to desired levels with heaters, however, the water in the grow beds is not. Therefore, during winter the lower temperature decreases the metabolism of bacteria while that of fish remains stable. This would imbalance the aquaponic cycle. One solution is giving winter food to fish which has a lower protein content, therefore, leading to less fish waste or decreasing the feeding rates. High nitrate concentrations (>150 ppm) indicate that there is an insufficient number of plants in the grow beds to take up the nitrate produced. To address this, grow beds could be filled with more plants, one grow bed could be added, or more fish could be harvested to reduce the ammonia produced.
4.7.2. Tours to the public
On Fridays we give tours to the public in the aquaponics greenhouse. We provide detailed knowledge on the function of the system regarding water, nitrogen-cycle and water system. We explain the function of the syphons and filters as well as the purpose of clay pebbles and volcanic rocks. We also explain the reason behind the choice of African catfish with specific details on fish size, amount of food, health, behaviour and natural habitat. In addition we discuss the sustainability of the aquaponic system, its suitability for being scaled-up to a commercial level and its environmental advantages in terms of resource use, input, land area required, crop production and applications. These are topics that I research based on literature throughout the internship. Giving these tours requires the ability to communicate abstract and technical knowledge in a very basic and accessible form. During my internship I gave several tours to a very varying audience from highschool students interested in building an aquaponic structure for a school project to people that had no knowledge about the system and who knew something about it and wanted to learn more.
4.8. Monthly activities 4.8.1. Water test to the lab
Monthly, we send a water sample from the fish tank to a laboratory external to Mediamatic to inspect our water quality measurements. The laboratory is the SGS laboratorium within the Agricultural Food Life in Spijkenisse. We send 100ml of water sample in a small glass container and send it through post mail. This is performed on the same day in which we test the water ourselves so to compare the results of the same water sample. In addition to the values we test, the lab gives values for boron (B), zinc (Zn), copper (Cu) and molybdenum (Mo), sulfur (S) and manganese (Mn). Since the colorimetric method is not very accurate and requires a subjective assessment of colour, it is important to check the results with a laboratory.
4.8.2. Cleaning pipes
To maintain the continuous waterflow of the system the pipes need to be clean monthly. The fish waste can accumulate in the pipes and block the waterflow. With a special brush we clean all the pipes linking grow beds, the sump tank and fish tanks. One issue that can occur by cleaning pipes by the fish tanks, is that the fish waste residues in the pipes can be pushed back into the fish tanks. The residues soon after increase the ammonia levels endangering the fish and this is also why it is important to clean the pipes regularly before too many residues buildup and imbalance the water quality.
4.9. Occasional activities
4.9.1. Weighting fish and calculating fish feeding rates
Once every four to six months, we weigh the fish to make any required adjustment in the fish tanks in regards to fish feeding and fish size. This task is important because if the feeding rates are higher than required, the uneaten food increases the ammonia levels. In fact, after weighting, the feeding rates are re-calculated depending on the average weight of the fish in each fish tank. To weigh the fish we use the water displacement method; since a fish has a similar density to the water in which it swims, the buoyant force on an object is equal to the weight of the water it displaces. We perform this by filling three transportation tanks with water to a certain level which is then marked. The fish are then loaded into the different tanks depending on their average size (this step is useful because we want to group together fish of a similar size when we put the fish back in the original fish tanks). Then we make a second mark where the water has reached due to the fish loading. We measure the weight of the water between the first and second mark. This value is then multiplied by the water density; from this we derive the average weight of the fish (g). We also keep track of the number of fish per tank. With these values we multiply the number of fish by the average weight per tank (g) and we divide it by 1000 to derive the biomass (kg) per tank. Then to calculate the new feeding rates we look at the data from the weighting, the data from the feeding rates and the different temperature. The equation is as follow:
Ration = biomass (kg) * 1000 * feeding rate (%)
Example: biomass 10 (kg/tank), average weight 100(g), temperature 23°C, pellets size 4.5(mm), feeding rate 2.0% = 20000.0% daily ration (g). At a water temperature of 23°C we would feed the fish in this fish tank with 200g of fish food a day.
This task is also important to keep track of the fish size as the fish are moved from one tank to the next depending on their average size and life stage; when the fish are too big for the fish tank size they are removed.
4.9.2. Checking plant pests, diseases, molds
The plants are regularly checked for pests, diseases and mold. As we monitor the pests in the aquaponic farm we record which pests have been found on which plants, the treatment
attempted and its success. An aquaponic system in a greenhouse generates a lot of humidity and combined with the medium they provide perfect environmental conditions for pests. In fact, particularly important is providing a good ventilation system so as to generate airflow that can help in preventing mold formation. In the greenhouse a big van is set on a timer so that every 2-3 hours it provides a strong airflow for about 30 minutes. Whereas to control some pests it is sufficient to spray the plants directly with a hose. For instance, this practice can deter white flies. Infested branches can be trimmed and for example with aphids this can be very efficient.
The most common pests we find are aphids (e.g. attacking mint, Szechuan flowers, nasturtium, parsley), snails (e.g. eating patchouli, basil, strawberries), white flies (e.g. on patchouli), ants (nourishing aphids to feed on them), and spider mites. Mold develops extensively on lemon balm and apple mint. As part of our job we identify the pests and research on natural pest controls such as natural insecticides made with garlic or pepper. The substances cannot be chemical as these will harm the bacteria colonies and fish. For instance, neem oil is toxic for fish and in case it should be carefully used only on foliage (FAO, 2014). We then investigate the efficiency by observations and experimenting. An example is creating a beer trap for snails by filling small containers with 2cm of beer and placing it on a grow bed directly under an affected plant. The snails are attracted by the smell and taste and as they drink the beer they eventually drown in the beer. This solution was very effective for example with patchouli. As another natural pest control method, I researched tolerant plants that can protect other plants and planted them next to infected plants. Coriander, garlic, tobacco plants and other pest repellent plants were placed next to infected plants. This solution however did not prove successful with for example aphids which can infect a parsley next to a Vietnamese coriander and not being affected at all.
When we do not recognise certain pests we can send them in petri dishes to a laboratory for accurate identification. The lab can provide us with natural predators (e.g. ladybirds, wasps) to be introduced in our system to control the pest infestation. Ladybirds were introduced as they and their larvae feed on aphids. Since their introduction they reproduced and lived in the greenhouse for months and proved very effective in keeping under control the aphid infestation. Another enemy of aphids and ants is the ichneumon wasp, a parasitic wasp. Especially during summer months, these find easily their way into the greenhouse and can cut back the ant population. However, when the pest infestations are not excessively damaging the plants, we usually rely on light/heavy trimming, cold water or natural insecticides.
4.9.3. Plant planting plan
Through observing how plants grow in aquaponic we examine the plant suitability. Based on these observations we make a new planting plan for the next season. For example lacinato kale does not particularly thrive in an aquaponic environment also probably because of the vertical cultivating structure that prevents it from building a tall woody stem. When a plant dies (e.g. accidental high waterflow) or needs to be removed due to diseases, we substitute these plants with new plants. This is also important to maintain the system equilibrium in
terms of the nutrient cycle and plants uptake. With a vertical structure it is relevant to consider shade, light exposure and distance as well as the medium in which the plants are grown (clay pebbles for plants that grow thin stems or lava rocks plants that need stability). Also we plant certain plants for the scope of controlling pest infestations next to more vulnerable plants. The plan is done on a shared excel file which we update by adding new suitable plants, deleting or noting down plants that proved unsuitable and select plants to sow for each coming month. The plants are divided by flowering plants, herbs, greens and fruits. We research planting methods for each plant for example if the seeds are too small they cannot be sowed directly in the medium and must be first sowed in a rockwool medium. We note down when they can be transplanted into the grow beds, their growing time, blooming time, harvest time. We also provide harvest tips. This document is important also as part of passing our knowledge on to future interns commencing their work in the aquaponic farm. 4.9.4. Aquaponics workshop
Every three months we give workshops to educate the public on how to build a mini aquaponic system, a ‘miniponics’ (Fig.8). This system was developed at Mediamatic and is suitable to be placed in an apartment. During the workshop we teach the basics of biology, plumbing and carpentry required for developing an aquaponic system, then we build the miniponics together. By the end, the participants should be sufficiently educated on how to build their own system at home. We want to ensure that the key and crucial tasks required to set up, maintain and regulate an aquaponic system have been passed through.
4.9.5. Blog posts, interviews, podcasts
Throughout the internship we also occasionally write blogs about aquaponics and post them on the Mediamatic webpage. These are meant to inform and educate the public. Topics discussed are the system functioning, daily activities in aquaponic, issues encountered and
various curiosities.
Furthermore, from time to time, some external visitors come to interview on the different projects run at Mediamatic for journal articles, news, videos or podcasts. A group of reporters from Germany, interested in the aquaponic system, interviewed me on technical and scientific aspects of the farming technique. Another day, a group of master students from Utrecht interviewed Saro and me for an Irish podcast. They had questions on not just the technical and scientific side of the farming technique but also on its sustainability and potential usefulness in the present context of the coronavirus pandemic. On this latter note, aquaponic could be an interesting farming technique to provide a local source of food as it can be established in an urban context and can create a form of indepence as it can be designed for both exteriors and interiors in gardens or homes.
4.10 Setbacks in the aquaponic greenhouse 4.10.1 Burned growbed
One day we found one of the upper grow beds burned and melted halfway with water dripping on the floor (Fig.9). The cause of the accident could be a technical failure in the LED lights. Luckily, aquaponics could be considered a self-extinguishing system as the fire extinguished once it reached the water level in the grow bed melting only the plastic on the upper side of the grow bed. Facing the issue we quickly realised that the melted plastic could enter the waterflow system and endanger the fish. Thus, we removed the grow bed, saved the plants that survived and proceeded with cleaning the grow beds below from plastic residues. We removed the lava rocks and washed them from the mud that formed and the plastic particles. Then we used an old 1000L IBC tank at Mediamatic and cut it similar to the others. Then we ordered new bamboo sticks, cut them to the desired length and replaced the grow bed filling it with lava rocks and new plants. When one whole grow bed is missing, the aquaponic cycle can be disturbed as there is less nutrient uptake. Therefore it is important to not only replace the grow bed but also plant new plants to maintain the existing cycle.
Figure 9. Burned and melted upper grow bed in the aquaponic greenhouse at Mediamatic. 4.10.2. Ammonia buildup in the fish tanks
As previously briefly anticipated, when cleaning the pipes the brush can push some of the fish waste back into the fish tanks. On one occasion, after cleaning the pipes, I noticed that the water in the fish tanks became turbid with waste and it was difficult to see the fish clearly. I saw the fish disappearing to the bottom of the fish tanks and then coming up to the surface to try and breath from the air (as African catfish are capable of doing so). Although they are able to breath some oxygen from the air, I started worrying about the ammonia buildup. I quickly took a water sample from the fish tanks and tested ammonia level which was very high 0.5ppm. At these concentrations the water is toxic and even lethal for fish. Next, I immediately researched the toxicity of ammonia and found that ammonia toxicity is also dependent on pH and temperature levels. If the pH was higher than 7.0 the fish would risk to die (Thomas and Wellborn, 1987). I quickly tested the pH and found that it was 6.5, thus, the conditions were still safe. This showed the importance to clean the pipes regularly so as to prevent any toxic ammonia buildup.
4.11. Side project: biodegradable material with mycelium
In the myco-lab at Mediamatic they research and build biodegradable materials with mycelium, the rooting system of fungi. To broaden my learning experience I follow my colleagues closely in the projects they are developing (e.g. pigeon tour, insulating materials..). I participated in a workshop in the myco-lab about how to grow mycelium and
mushrooms. I wanted to learn more and develop practical and technical skills in building biodegradable materials. Together with my aquaponic colleague and the myco-lab interns we brainstormed some ideas around biodegradable plant pots. Growing biodegradable materials with mycelium is reasonably simple and straightforward. Mycelium grows under the soil therefore in a dark environment and requires a medium on which to grow (e.g. straw, hemp straw), and humidity. The key is to ensure a clean/sterilised environment so that no other microorganisms can grow. The equipment is always sterilised with alcohol. The straw is boiled or steamed as a form of sterilisation and it is left to cool down. The straw can then be mixed with fungi spores in a clean bag. To give the mycelium a shape, in the case of our pot we covered the internal surface of one big pot with foil and placed a 1.5cm layer on the bottom of the pot. Then we covered the external surface of a smaller pot in foil, inserted it in the bigger pot and distributed the remaining mix until the top. Then we closed the top surface with another layer of foil (Fig.10). We placed the pot in a dark and clean space and waited for the mycelium to grow.
Figure 10. Building a biodegradable plant pot with mycelium
After 1 week the mycelium had fully grown in a plant pot (Fig.11). This type of pot can be placed directly in the soil, in which it will eventually degarde. As water affects the mycelium properties (e.g. other microorganisms can grow on it), I researched more and developed more ideas to for example create a waterproof pot that can be used in homes. I thought of using a wax and discovered carnauba wax which is vegan and has a melting point 82°C, therefore suitable for interiors. And to make the waterproofing even safer I learned that a cotton or hemp cloth can be waxed to the pot. At the moment, we are in the process of making a new pot to test the waterproof idea with carnauba wax. I am very satisfied to have acquired this technical and scientific knowledge and gained the necessary practical skills to make
biodegradable materials with mycelium as these are enlarging my wealth of knowledge that complement my university background.
5. References
Engels, E. (2013a). The Aquaponics Cycle. Retrieved at:
https://www.mediamatic.net/en/page/74430/aquaponics-cycle-v2
Engels, E. (2013b). Miniponics system. Retrieved at:
https://www.mediamatic.net/en/page/80361/miniponics-systeem
Engels, E. (2012a). The tower system. Retrieved at:
https://www.mediamatic.net/en/page/46740/aquaponics-tower-graphic
Estim, A., M. Shaleh, S., Shapawi, R., Saufie, S., & Mustafa, S. (2020). Maximizing Efficiency and Sustainability of Aquatic Food Production from Aquaponics Systems - A Critical Review of Challenges and Solution Options. Aquaculture Studies, 20(1). Retrieved at: http://www.aquast.org/abstract.php?lang=en&id=497
FAO (Food and Agricultural Organisation of the United Nations) (2014). Small-scale aquaponic food production. Integrated fish and plant farming. Authors: Somerville, C., Cohen, M., Pantanella, E., Stankus, A., Lovatelli, A., Italy, pp. 1-262. Retrieved from Mediamatic library.
Thomas, L. and Wellborn, Jr. (1987). Catfish farmer’s book. Extension Wildlife and Fisheries
Department, Mississippi State University. Retrieved at:
