Do We Expect Too Much from Aquaponics?
Decreasing Dependencies
In June 2010, one year after the Honduran Constitutional Crisis, I found myself standing among the wreckage of a barren, vine-laden, hydroponic greenhouse, in the mountains of Tegucigalpa. The steel and plastic of a once state-of-the-art shade-house, had been reclaimed by the earth and bramble. Poking around at the briars and cracking pipes, my utopian views on the role of hydroponics in addressing global food security took a massive blow.
During the year prior to my arrival in Tegucigalpa, political disputes led to the detention and exile of then-President Manuel Zelaya, which resulted in civil unrest, suspension of Honduras from the Organization of American States, and degradation of international relations, humanitarian aid, and trade. As could be expected during such times, shipments of fertilizers and nutrient additives halted, and the hydroponic shade-house quickly became nutrient deficient, and was shut down.
A short distance from the battered hydroponic system, was an earthen tilapia pond; one of the oldest features of the mountain property. Perched on the grassy knoll between the shade-house and the pond, I threw bits of torn grass into the water, and watched as the fish splashed and swirled. Indifferent to constitutions or elections, and unmoved by coups, those fish reproduced, ate, and produced waste- and the banks of that pond were always green. It was in that moment that my focus shifted from conventional hydroponics, to bioponics and aquaponics.
Upon returning to the United States, Dr. David Foster, my close friend and research partner, and I began assessing the viability of aquaponic crop production as a tool for international development and food security; focusing on eliminating major nutrient inputs, developing alternatives to manufactured fish feeds, conducting growth rate trials on various commercial crops, and evaluating other agro-industrial waste streams as inputs into soilless growing systems.
Over the past ten years, our work has afforded me the opportunities to travel the globe, consulting on agricultural development plans and CEA implementations across East and West Africa, and overseeing industry-leading research into nutrient reclamation from agro-industrial waste streams, in the United States and the European Union. Having spent a decade straddling the divide between technology-driven vertical farming, and boot-strapped solutions for developing nations, global crises like those we are facing today, still leave me wondering if aquaponics, as conventionally discussed and constructed, is capable of meeting the industry-pressures of high-production factory farming, and the implementation struggles of deployment in developing nations.
The Fight is with Food-Insecurity, Not Hydroponics…
Before jumping into a discussion about the benefits and considerations of aquaponic growing relative to conventional hydroponic, or even soil-based, farming methods, we need to define what burdens we expect this technology to bear.
Looking at the domestic food insecurity, the U.S. Bureau of Labor Statistics has posted a 0.7% increase in food prices in June, on the heels of a 1% increase in May. This marks a six-month run of increases, contributing to a 5.6% rise in food prices at grocery stores since this time last year, the largest annual increase in nearly a decade. These rates drastically outpace the U.S. inflation rate, which Statista forecasts to be ~0.6% for 2020.
These sudden increases in food prices have had a hard impact on households across the country, with 1 in 5 households reporting food insecurity, up nearly two-fold from prior to the outbreak of COVID-19. Surveys conducted by The Hamilton Project note that over 17% of mothers with children ages twelve and under are unable to afford the proper food to meet their families needs; this is up from 7.4% according to a USDA survey in 2018.
Though food prices have climbed steadily over the past few months, the National Farmers Union notes that these increases do not trickle down to growers. On average, farmers are selling produce at prices averaging 4.8% lower than this time last year.
For many developing nations, the novel coronavirus is just one of many recent disasters threatening food production and economic stability. Aside from the regular battering of cyclical droughts and floods, swarms of locust are decimating crops across 23 countries, from East Africa, through the Middle East, and into Southern Asia.
According to the Food and Agriculture Organization of the United Nations (FAO), at the end of 2019, roughly 135 million people, across 55 countries, were reported to be experiencing ‘crisis levels of acute food insecurity.’ Given recent health, climate, and environmental disasters, it is estimated that this number could climb to 265 million people by the end of 2020.
While The World Bank notes that global production of rice, wheat, and maize are at near-record highs, the production of many vegetable crops, which are a critical source of rural livelihoods, has declined in response to a decrease in global demand.
Mitigating the carry-over impacts of these depressions on next-season’s production will require continued global cooperation in maintaining open trade and stable supply-chains for both agricultural inputs, such as seeds, fertilizers, and pesticides, and product off-take.
Unfortunately, as we saw in the 2007 food crisis, it is often the case that in global crises, countries tend to become protectionist. This trend has once again been working its way around the globe, as countries close borders and limit exports, jeopardizing global supply chains and agricultural trade. These global disruptions often disproportionately impact import-dependent countries, especially those facing depreciation of currency, or an inability to bring commodity crops to market at stable prices, in light of the dominance and projected appreciation of the U.S. dollar.
Whenever global crises arise, whether environmental or geopolitical, a national obsession with food-security and homesteading tends to follow. Aside from the national shortages of pullets and chicks during the spring of 2020, amid the early weeks of the COVID-19 outbreak, Google Trends shows nearly twice as many searches related to gardening and homesteading during April and May of 2020, relative to previous years. Working in Controlled Environment Agriculture (CEA), these trends tend to renew discussions about the role that soilless growing can play in safe-guarding urban communities against food-insecurity, and often rekindle debates between hydroponic and aquaponic growers about resource management, sustainability, and production potential.
Fundamentals of Conventional Aquaponics
Underpinning many arguments in favor of soilless farming are statistics related to global population growth, decreases in arable land per capita, and resource efficiency. Industry surveys, comparing soilless growing methods with conventional farming, validate the claims that soilless cultivation can utilize up to 90% less water per yielded crop unit, and that technology-driven vertical farms produce 35–300 times the harvestable produce per square meter, while mitigating incidences of food contamination, and fluctuations in output from pests and seasonality.
Further narrowing the discussion, those championing aquaponics, where plant nutrients are derived from fish waste, over conventional hydroponics, where fertilizer solutions consist of nutrient salts or synthetic nutrient additives, will often cite decreased dependency on inputs, increased water efficiencies, given that aquaponic systems do not require the purging of saline water, as is common in hydroponic production, and the overall naturalness of aquaponics, as reasons why they believe that aquaponics is the ideal form of crop production; for both commercial factory farming, and for deployment in developing nations as a means to increase food security.
In other posts, we will dig into some of the scenarios where I have strongly advised either for or against the implementation of aquaponic or bioponic technologies, but for this discussion, I want to focus on some of the broad, technical struggles that tend to limit the adoption of aquaponics, and to walk through some characteristics common to successful aquaponic facilities, whether high-end commercial growers or systems constructed in developing nations.
Though today, many people are attracted to the simplicity and sustainability of aquaponic growing, the proliferation of aquaponics in the 90’s can be partially attributed to the crackdown of regulatory and law-enforcement agencies on the production of hydroponic cannabis. The alleged tracking of growing equipment and crop fertilizers lead growers to evaluate and refine aquaponic cultivation methods, as a means to drive stable, quality crop production. In the years to follow, aquaponics moved from basements, to backyards, as tens of thousands of growers around the world have constructed small- to mid-scale systems.
Despite the fact that some aquaponic growers have demonstrated commercial viability, the technology is still seen by much of the CEA industry as novel and untested, lacking sufficient long-term production data and predictability to warrant a transition away from conventional nutrient sources. Given that the primary differences between aquaponic and hydroponic crop production relate to the sources from which nutrients are derived, and the protocols used for maintaining fertilizer solutions, positioning aquaponics as a viable alternative to industrial hydroponics requires that processes continue to be developed that ensure the efficient utilization of aquaculture sludge waste, through the operation of low-discharge aquaponic systems, while allowing for fertilizer solutions to be formulated and maintained within optimal parameters for plant uptake and crop growth, through the decoupling of the aquaculture and growing portions of the system loop.
Many conventional aquaponic systems are designed as continuous loops, carrying mixed-stream waste-water from fish tanks, into plant growing equipment. This flow of water often passes through filtration equipment and bacterial culture tanks, to separate out heavy sludge and to ensure that the harmful ammonia nitrogen in the water is converted into usable nitrate nitrogen, prior to entering the plant growing equipment. As the nitrate-rich solution moves through the growing equipment, plants pull nutrients from the water, decreasing the nutrient load of the stream that flows back into the fish tanks.
While these single-loop systems are easy to construct and operate, they depend on inherent compromises between the water quality requirements of the fish populations, and the ideal water quality for consistent, competitive crop production; primarily as it relates to pH, temperature, and nutrient loads.
Testing water from conventional aquaponics systems has shown that aquaponic nutrient solutions are less than optimal for plant growth, leading to variability of crop quality across the aquaponic industry. As a result of sludge discharge, and the low nutrient composition of fish feed, mass balance analysis has demonstrated that concentrations of phosphorus and many micronutrients are regularly limited, and that potassium-nitrogen and phosphorus-nitrogen ratios do not meet suggested levels for reliable plant growth.
Decoupled aquaponic configurations, where an aquaculture circuit produces waste that can be translocated into separate growing systems, allow the growers to manipulate the temperature and pH of the plant fertilizer solution, maximizing the bioavailability of nutrients. Additionally, nutrient concentrations can be increased well-above those typically maintained in stable aquaponic circuits.
Steps to Achieving Industry Adoption
Positioning aquaculture-derived nutrients, and other natural nutrient sources, as viable alternatives to industrial hydroponic fertilizers requires digestion processes that can adequately and consistently, break down sludge waste streams, mineralize the contained nutrients, and increase the bioavailability of those nutrients for plant uptake. These technologies not only facilitate the low-discharge operation of single-loop aquaponic systems, but allow for truly decoupled crop production from a range of agro-industrial waste streams.
Research conducted by the University of Liege shows that sludge discharge can account for the loss of 50–90% of the available nutrients from a conventional aquaponic system. Sludge waste is often discharged because the nutrients contained in feces and uneaten feed are insoluble, and not readily available for plant uptake.
Furthermore, industry surveys have shown that while aquaponic and hydroponic lettuces have similar growth rates, nutrient content of conventional aquaponic produce averages 35% less than hydroponic produce. Based on the nutrient profile of mineralized aquaculture sludge, however, aquaponic systems that successfully incorporate sludge waste into plant growth, can achieve a 39% increase in fresh mass yields over hydroponic and conventional aquaponic production. Comparative studies conducted by Dr. Dongyun Ru and Dr. Subhrajit Saha have demonstrated that low-discharge systems can produce fresh basil with 58% gains in weight compared to hydroponics, and bok choy with 83.6% increases in yield.
The ability to recycle the nutrients contained in sludge back into the growing system improves plant health and production potential of the overall system, positioning natural nutrient solutions as a viable input for industrial hydroponic growing. Due to the high processing rates, elevated dissolved oxygen, and stable pH that can be achieved by aerobic digestion processes, where dissolved oxygen concentrations are actively maintained to facilitate the growth of certain microorganisms, this is where Dr. Foster and I have focused our recent research.
In partnership with Integrated Agriculture Systems Inc. (INTAG), Pennsylvania, Dr. Foster and I have developed the INTAG Natural Nutrient System (INNS), a single-stage, aerobic digester that is capable of converting a wide range of agro-industrial wastes into liquid fertilizers that can be fertigated into industrial hydroponic equipment.
Operating this aerobic process at pH 6.4–6.8, far lower than can be achieved by methanogenic-dependent anaerobic processes, the INNS facilitates the rapid mineralization of macro and micro-elements in sludge waste. As this process maintains a pH similar to that of optimal plant fertilizer solutions, nutrient-rich effluent from these aerobic digesters can be integrated directly into plant growing circuits.
Over the past four years, we have implemented these digesters on three continents, and have pushed the technology to process a range of agricultural wastes. Preliminary tissue testing, by third-party labs, shows that aquaponic systems utilizing these aerobic digesters to eliminate sludge discharge, and to mineralize the contained nutrients for plant growth, can cultivate lettuce crops with 24% more protein, 88% more calcium, 37% more magnesium, 18% more phosphorus, 41% more potassium, and 109% more zinc than reported averages for lettuce cultivated in soil. Similar testing of kale and collards showed increases in protein of 48% and 241%, 341% and 63% more calcium, 134% and 162% more magnesium, 41% and 167% more phosphorus, 33% and 84% more potassium, and 243% and 353% more zinc, respectively.
Last year, conducting research for INTAG, I had the opportunity to travel to Groen Agro Control, in the Netherlands, to conduct comparative growth rate trials on tomato plants utilizing INNS-produced natural fertilizer from aquaculture waste, and tomato plants supplied conventional hydroponic fertilizers. Ard Jan Grimbergen, lead scientist at Groen Agro Control, noted that the team was surprised that the INNS fertilizer was capable of yielding comparable biomass to the hydroponic solution, while the quality of fruit was improved in both taste and weight; even though the nutrient concentrations in the INNS fertilizer were up to ten times lower than those maintained in the hydroponic fertilizer.
These trials demonstrated the ability for hydroponic crops to be cultivated using natural, renewable sources of fertilizer, while maintaining lower nutrient concentrations, and eliminating the need to discharge saline waste-water. Decouplable, sludge-handling technologies, such as the INNS, play an important role in shifting the CEA industry from viewing aquaponics as a novel experiment, to accepting natural fertilizers as economically feasible alternatives to conventional hydroponics solutions. These same technologies allow for aquaponic growing methods to be deployed in development settings, where minimizing energy consumption, eliminating waste-water discharge, and maximizing crop production potential is critical to off-setting implementation costs and operating risks.
While there are a number of market pressures, food-safety concerns, and regulatory considerations that aquaponics is facing as it competes for industry adoption, checking the boxes of quality and consistency seems to be the first gate; and ensuring proper nutrient concentrations and bioavailability in fertilizer solutions are critical to meeting those benchmarks.
As we continue discussing the role of soilless technologies in industrial agriculture, and assessing the viability of aquaponic growing for increasing global food security, particularly in developing nations, we will look at a number of projects that I have been a part of over the years, and will evaluate different strategies that tend to separate successful implementations from less successful ones.
