The field of hydroponics has been evolving in recent years as growers and researchers seek to make these soilless growing systems more sustainable and less resource-intensive. This progression has followed a pathway from fully inorganic (also known as “mineral hydroponics”, actively aerated and/or recirculated systems, to more organic, passive approaches requiring fewer external inputs (1).

Energy & Nutrient sources

Early hydroponic systems relied on inorganic/mineral nutrient solutions typically with active aeration and recirculation of such solution. The obvious first-step would be to simply switch the energy source to fully renewable, for example with the use of photovoltaic panels or wind turbines, or by connecting to an energy grid with less carbon-intensive energy sources such as hydroelectric or nuclear. A more elegant solution, however, is to simply avoid needing the use of energy at all. Passive inorganic systems, like the so-called Kratky method, can eliminate the need for aeration and pumping, reducing energy demands and material (2).

Focus then shifted to the source of fertility. Aquaponic systems use fish waste to provide nutrients, moving away from synthetic fertilizers (3). Anthroponics takes this a step further, relying on human urine, although treatment with aeration and biofilters is still needed (4). Bioponic arrangements allow a wider range of organic waste to be utilized as a nutrient source, though typically still requiring some sort of energy input to transform the compounds in the waste to plant-available nutrients (5).

Pollution

Another significant driver in the pursuit of sustainable hydroponics is the issue of pollution. Nutrient runoff from hydroponic systems can contaminate water sources if not properly managed (6). Microplastics from growing containers and equipment can accumulate in the environment and food chain (7). Solid waste, such as spent growing media and plant debris, also poses a disposal challenge. Shifting to organic nutrient sources, biodegradable or reusable non-plastic containers, and minimum-input systems that minimize waste and runoff are key strategies for addressing these pollution concerns.

Simple diagram of conventional hydroponic flows and potential recycling

The ultimate goal for sustainable hydroponics would be a fully passive, organic system in which fertility is generated in a near closed-loop, “circular” manner without requiring imported nutrients or energy-intensive processing. Traditional growing containers made from clay, ceramics or treated wood could replace plastics, further reducing the environmental footprint.

“Circular” Economy

It’s important to cast a critical eye on claims of “circularity”, whether in hydroponics or the wider economy. True closed-loop systems are extremely difficult to achieve. For starters, modern products are too complex to recycle efficiently. The diversity of materials used, including many synthetics, microchips, batteries etc. makes it impossible to recover all the resources. Recycling processes are never 100% efficient. 20% of global resource use is fossil fuels, over 98% of which is burned for energy and cannot be recycled or reused at all. Renewable energy infrastructure also requires resource inputs that are not easily recyclable. There will always be a need for some new resource extraction. Finally, global resource use keeps increasing every year due to economic growth. Even with 100% recycling, the amount of recycled materials available would always lag behind the material demands of growth. As long as material stocks keep accumulating in infrastructure, buildings, and goods, achieving a fully closed loop is impossible (8).

Climate Change

The urgent motive driving innovations in hydroponics and agriculture more broadly is the looming specter of catastrophic climate change. Greenhouse gas emissions continue to rise in spite of international accords and commitments (9). Global temperatures are increasing faster than anticipated, and the second-order effects of droughts, floods, wildfires and ecosystem disruptions are becoming alarmingly evident (10).

Second Order Consequeces: Climate Change

Our society’s default response is often to put faith in technological solutions – a tendency some dub “techno-hopium”. But the dramatic emissions cuts needed to avert the worst climate scenarios may demand a more fundamental rethinking of consumption, growth and resource use (11). Concepts of “deep adaptation” and mitigation are entering the conversation (12).

It’s understandable to feel overwhelmed, even doomed, by the sheer scale of the climate predicament. But we mustn’t succumb to fatalism or inaction. Every effort to reduce emissions and build resilience matters. Every fraction of a degree of warming we can avoid will reduce future suffering. In that light, the quest for sustainable hydroponics is a small but meaningful part of the vital work of remaking humanity’s relationship with the planet that sustains us.

References:

[1] Nguyen, N. T., McInturf, S. A., & Mendoza-Cózatl, D. G. (2016). Hydroponics: A versatile system to study nutrient allocation and plant responses to nutrient availability and exposure to toxic elements. Journal of visualized experiments: JoVE, (113).

[2] Kratky, B. A. (2004). A suspended pot, non-circulating hydroponic method. Acta Horticulturae, 648, 83-89.

[3] Goddek, S., Delaide, B., Mankasingh, U., Ragnarsdottir, K. V., Jijakli, H., & Thorarinsdottir, R. (2015). Challenges of sustainable and commercial aquaponics. Sustainability, 7(4), 4199-4224.

[4]  Sánchez, Henrique (2014). Aquaponics and its potential aquaculture wastewater treatment and human urine treatment. Faculty of Sciences and Technology, New University of Lisbon, Portugal.

[5] Sánchez, Henrique (2022). Using green waste biogas slurry as nutrient source for a NFT hydroponics system combined with an MBBR [Technical report]. ResearchGate.

[6] Gorito, A. M., Pinto, T., Ribeiro, A. R., Almeida, C. M. R., & Silva, A. M. T. (2021). Assessing nutrient recovery from hydroponics wastewater using biochar substrate and tomato plant uptake. Journal of Environmental Management, 277, 111445. https://doi.org/10.1016/j.jenvman.2020.111445.

[7] De Souza Machado, A. A., Kloas, W., Zarfl, C., Hempel, S., & Rillig, M. C. (2018). Microplastics as an emerging threat to terrestrial ecosystems. Global change biology, 24(4), 1405-1416.

[8] Haas, W., Krausmann, F., Wiedenhofer, D., & Heinz, M. (2015). How circular is the global economy?: An assessment of material flows, waste production, and recycling in the European Union and the world in 2005. Journal of Industrial Ecology, 19(5), 765-777.

[9] IPCC. (2018). IPCC Press Release – Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C approved by governments.

[10] Leggett, J. (2020). Winning the carbon war: power and politics on the front lines of climate and clean energy. Routledge.

[11] Hickel, J., & Kallis, G. (2020). Is green growth possible?. New political economy, 25(4), 469-486.

[12] Bendell, J. (2018). Deep adaptation: a map for navigating climate tragedy.

Disclaimer: The information above has been partially aided in its drafting and/or editing with LLM tools.

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