Aquaponics using PU foam could be a sustainable way to feed the world, argues Dr Anastasia Kottara. Here she explains why and describes her aquaponic experiments.
Conventional agriculture aims to maximise yield and profit but this comes with terrific cost for the environment. Soil degradation, excessive use of water and loss of biodiversity all result from this way of doing things. And with a projected global population of 9.8 billion by 2050, the need for sustainable agriculture is urgent. What we need is new way of growing food. And our world-leading aquaponics research program aims to provide just this.
Recently, soil-less culture systems have been a major focus of agriculture research. In these systems plants grow without soil, either in a nutrient solution or a porous substrate. So far 2 soil-less systems have been tried, hydroponics and aeroponics. Hydroponic systems provide nutrients in water. Alternatively, aeroponics provide nutrients in the air as mist.
However, whilst hydroponics and aeroponics can achieve high yields, they can also require a heavy chemical load. Therefore it is debatable whether hydroponic and aeroponic systems are ultimately environmentally sustainable.
Our experiment looks at an alternative system, aquaponics using PU foam as a growth media.
Aquaponic systems use fish wastewater as a nutrient solution for plant growth. While in hydroponic systems plant growth depends on a chemical supply, in aquaponic systems plant and fish growth are interdependent. Fish supply bio-nutrients to the plants, while the plants uptake these nutrients and clean the water for the fish.
Positives of aquaponics include the fact it does not depend on a chemical supply for the plants to grow. Plus it only requires only 10-15% of the water used for food production. And it can produce 4 times more food per acre compared to conventional farming.
However, there are key challenges that need to be overcome in order to achieve easy maintenance and high productivity of aquaponics.
A general challenge of all soil-less culture systems is the development of a growing substrate. We need a substrate that has a high water holding capacity, does not decompose, and does not alter the water pH.
An even bigger challenge is the biological complexity of the system. Three different biological levels co-exist (microbes, plants and fish) and failure of one component can lead to failure of the whole system. As a result, water quality needs constant monitoring. And fish and plant mass needs to be in optimum equilibrium. Plus microbial composition and activity need to be frequently assessed.
Me and my colleagues have been tackling these challenges. Joint experiments are being conducted in the University of Sheffield’s AWEC (a world-leading facility representing investment of £4.5 million by TUoS) and at Sohar University in Oman.
The design of our aquaponic system is simple. It consists of a fish tank with a water filter and plant beds with a water sub-tank.
We are examining innovations in soil-less, enhanced growth media made of polyurethane (PU) foam to use as a substrate in our aquaponic system.
Currently, expanded clay pebbles are the standard aquaponic growing substrate. But these pebbles are not ideal. Firstly, they have a very low water holding capacity. Secondly, they are made in a process that involves roasting the clay (to expand) in rotary kilns under extremely high heat (500 to 1,000 °C). Overall, these pebbles are not an ideal candidate for sustainable agriculture.
In order to find a good replacement for these pebbles, we turned to PU foams. We are optimising PU foams to be used as synthetic soils for the cultivation of high value horticultural crops (e.g. tomato plants). And pilot experiments testing PU foams with high water holding capacity versus expanded clay pebbles have already started. Results of these experiments will indicate the performance parameters of our substrate.
Future research will be focused on growing tomato plants alongside multiple herbs (e.g. mint, basil) and leaf vegetables (e.g. lettuce) in a matrix made of PU foam. We will determine which set of microbial composition and conditions return the highest yield for each crop.
Following these experiments, we will try to enhance the microbial activity in our system by inoculating microbial communities beneficial to the plant growth. With this final step, we aim to further optimise our system in order to achieve higher crop yields.
In this world-leading research project, we aim to design and optimise a sustainable agricultural system for food production. Looking at the past and the methods of conventional agriculture that have led us to water scarcity and soil degradation, we have designed a system which keeps a close eye on parameters that increase environmental sustainability.
Soil-less culture systems like aquaponics are often biologically complex systems but the good news is that once they are fully understood and optimised, such systems may be able to feed 10 billion people. Keep up to date with our aquaponics and PU foam experiments on my Twitter account!
Anastasia works on a collaborative project between Grantham Centre Director Tony Ryan, Grantham management board member Duncan Cameron and the University of Sohar, Sultanate of Oman. This project is funded by a UK-Gulf Countries Institutional Links award to develop capability and demonstrate innovations in protected growing (greenhouses) for increased water use efficiency and food security in Oman and other hot, dry climates.
Edited by Claire Moran.