In November 2025, a team at the United Arab Emirates University published Current technologies for nutrient recovery in aquaponic systems: a review in Frontiers in Sustainable Food Systems. The paper presents nutrient recovery as a major unsolved problem in aquaponics, surveys physical, chemical, and biological recovery methods, and concludes that hybrid approaches combining all three are the way forward. It calls itself “comprehensive.”
It does not mention the Integrated Aqua-Vegeculture System (iAVs). It does not mention McMurtry, Dr. Douglas C. Sanders, or NCSU. It does not cite the foundational research showing that a properly designed sand biofilter can retain and utilise fish solids in place, without separate sludge handling infrastructure. Five of its seven authors had co-authored papers on these same topics in the preceding twelve months.
That is not a minor oversight. It is a review article presenting a field-wide problem while excluding the best-known system that directly contradicts its framing. More than that, five of its seven authors had already co-authored a 2024 sandponics paper that explicitly identified sandponics as iAVs, cited McMurtry, and stated that sand can sustain productivity for up to 25 years without substrate replacement.
What the Review Says
The review’s central claim is that aquaponic systems have a waste problem. It states that “nutrient recovery in aquaponic systems faces major challenges such as imbalances in nutrients, inefficiencies in nutrient extraction, and scalability constraints”. It describes solid aquaculture sludge as something “often removed and discarded”. It calls waste and nutrient management “one major drawback of existing aquaponic systems”.
The paper then surveys a long list of recovery technologies: drum filters, mesh screens, sedimentation tanks, struvite precipitation, ion exchange, ammonia stripping, nanofiltration, aerobic and anaerobic mineralization, vermicomposting, algal bioconversion, and various combinations. It concludes that “hybrid systems, which integrate physical, biological, and chemical approaches emerge as the most promising avenue” and that “no single method is sufficient”.
When it finally mentions sand and gravel as growing media, the review says they “can also effectively remove solid waste by intercepting solids as aquaculture effluent passes through the hydroponic bed while decomposing leftover organic matter (Rakocy, 2012).” It then adds: “However, to sustain system efficiency, regular bed tillage or replacement is necessary to prevent the clogging of media (Rakocy, 2012)”. That is the full extent of its treatment of sand-based nutrient retention.
The review’s framing is not only textual. Its Figure 1 schematic presents a sediment tank and sludge collection component as standard elements of an aquaponic system. No sand biofilter configuration is shown. The sludge-removal architecture is therefore built into the review’s visual model before the argument has even been made that such infrastructure is universally necessary.
What iAVs Actually Does
iAVs is a closed-loop system in which fish effluent is pumped directly onto sand biofilters through shallow furrows. Solid waste is deposited on the sand surface and mineralised aerobically in place. In this configuration, the sand serves simultaneously as a mechanical filter, a biological filter, and a plant growth medium, after which the treated water returns to the fish tank by gravity. The system does not rely on a separate mechanical filter, clarifier, sludge collection stage, or supplemental fertilisation. That distinction matters, because the review treats sludge handling and nutrient recovery as though they are universal unresolved problems in aquaponics. iAVs is relevant precisely because it was developed to address those problems by design.
The review cites Rakocy to suggest that sand beds require regular tillage or replacement to prevent clogging. That is not a valid generalisation. The iAVs system developed by McMurtry et al. was specifically designed to prevent clogging. As the authors explained, the introduction of the reciprocating biofilter “reduced problems of clogging, channelization and low oxygen,” thereby making it possible to retain solids in place as a nutrient resource for plant growth. The sand medium itself was also deliberately specified to avoid failure: “Composition of the medium, which was optimized to avoid clogging, was 99.25% quartz sand and 0.75% clay,” with “0.0% silt.” In other words, clogging was not treated in this work as an inevitable feature of sand-based culture. It was treated as a design problem to be addressed through correct media selection and hydraulic operation.
Rakocy is cited as if he directly established the limits of sand biofilters, yet his published aquaponic work was centred on gravel and later, raft systems, not sand itself as a media. That makes his sand caution a poor basis for generalising, especially where McMurtry’s own trials repeatedly reported no clogging.
The empirical findings are even more important. The papers by McMurtry et al. did not merely propose that clogging could be avoided. They repeatedly reported that it was avoided. The studies explicitly evaluated “signs of clogging” and found that “No clogging was observed in the sand beds.” Elsewhere, the authors state, “At no time was clogging or channeling observed in the biofilters,” “Clogging was never observed,” and “Clogging was not a problem, and water quality measures were good in all ratio treatments.” One report goes further: “In fact, these biofilters were run for three years without clogging after this work.” This is direct primary-source evidence from the iAVs literature itself, and it materially weakens any blanket claim that sand biofilters inherently require routine tillage or replacement.
For that reason, the review’s treatment of sand is not merely incomplete but misleading. The authors had already published a 2024 sandponics paper containing an unresolved internal contradiction. In Section 3, that paper states that sand can remain physically stable for decades, maintain excellent air permeability, and sustain productivity for up to 25 years without substrate replacement. In Section 5, however, it states that sand may clog over time and that periodic cleaning and replacement are essential, (incorrectly) citing McMurtry et al. 1990 alongside Rakocy 2012. Those positions were never reconciled. The November 2025 review carries forward only the negative side of that contradiction. It preserves the replacement framing while omitting the evidence that undermines it, including the repeated findings by McMurtry et al. that clogging was not observed under the actual iAVs design. That omission is not minor. It removes the central evidence required for a fair assessment of whether sand-based systems can solve the very sludge and nutrient-recovery problems the review presents as unresolved.
What the Authors Had Already Published
The strongest evidence here is no longer mere prior exposure. It is prior authorship.
The November 2025 review was authored by Drishya Nishanth, Chythra Somanathan Nair, Ramya Manoharan, Radhakrishnan Subramanian, Irfan Salim, Sajid Maqsood, and Abdul Jaleel. Before that review was submitted on 7 August 2025, five of those seven authors had already co-authored Sandponics: A Sustainable Agriculture Solution for Food Security and Resource Efficiency in Arid Regions (Nair et al., 2024). That paper does not merely allude to related ideas. It opens its system description by stating: “Sandponics, also referred to as iAVs.” It also cites McMurtry.
A second relevant publication, Sustainable leafy green production in sand media based integrated aqua vegeculture system under salinity, appeared on Research Square on 29 April 2024 and included Subramanian, Nair, Manoharan, and Jaleel. Public comments posted on that preprint in June 2024 specifically identified the absent McMurtry references and the iAVs lineage questions, placing that gap on the public record before the 2025 review was submitted.
A further 2025 paper by Nishanth et al. compared microgreens growth in desert sand against rockwool as a production medium — demonstrating that the group’s engagement with sand as a substrate was active and ongoing at the same time the review was being prepared. This reinforces the same point: the author group was not merely adjacent to sand-media work. It was producing it across multiple papers, in multiple journals, while the review they submitted treated sand-based system history as though it did not exist.
The pattern extends further. The review’s biological methods section identifies algal bioconversion as a promising approach to nutrient recovery requiring further research. One of the review’s authors co-authored a 2025 paper specifically on harnessing microalgae for nutrient cycling in aquaponic systems (Manoharan, 2025). Yet the McMurtry et al. iAVs research documented decades ago that algae grew naturally on the sand biofilter surfaces as part of normal system operation, contributing dead biomass as a nutrient source for vegetable crops alongside fish metabolites and uneaten feed, and disappearing spontaneously as plant canopy developed without any separate management or infrastructure. Algal nutrient cycling in sand-based systems is not an ‘open research question’ requiring new funding. It was observed, documented, and solved in the iAVs literature decades ago – the very literature these authors omitted.
What This Does to the Literature
A review article does more than summarise papers. It tells later researchers what the field is, what its core problems are, and which solutions are worth taking seriously.
When a review calls itself comprehensive while omitting a system that directly addresses its central problem, the damage is not confined to one paper. It changes the map.
This review makes sludge handling and nutrient recovery appear to be universal unsolved problems in aquaponics. They are not universal. iAVs addressed them through system design decades ago. In this case, the distortion is especially clear because the omitted counterexample was not buried in obscure literature. It was present in a paper five of the review authors had themselves published the year before. Readers relying on the review will not learn that. They will instead be directed toward drum filters, struvite reactors, membrane systems, digesters, and increasingly elaborate hybrid recovery architectures.
The paper’s treatment of sand media also reinforces a misconception that discourages investigation of sand-based nutrient retention. That matters even more because this research cluster presents itself as working in arid-region conditions, where sand is not an exotic material but an obvious one.
Because the paper is open access in a Frontiers journal, its framing is likely to travel. Future papers citing it as evidence that nutrient recovery is a major unresolved challenge in aquaponics may inherit that distortion without ever encountering the omitted design pathway.
The Core Problem
This is not a case of obscure literature being missed. It is a case of a review article presenting itself as comprehensive while omitting a directly relevant paper five of its seven authors had co-authored, selectively inheriting only the portion of that paper’s citation trail that supported its own framing, and dropping the citation that most clearly pointed back to McMurtry.
That description does not require speculation about motive. The documentary problem is already serious enough: the review presents sludge handling and nutrient recovery as universal unresolved problems, cites Rakocy to support routine sand replacement, omits the same-author paper that explicitly equated sandponics with iAVs and stated 25-year substrate longevity, and reproduces only the negative half of that record.
The wider structural issue is also clear. Academic systems often reward fundable complexity more readily than low-cost, already-functioning design. That does not prove intent in any individual case. It does describe an environment in which omissions of this kind can be normalised and reproduced.
Why This Matters Beyond One Review
This matters because review articles influence what gets studied, funded, taught, and built.
If a low-cost sand-based approach is left out of the literature map, researchers are nudged toward more complicated and expensive paths. That has practical consequences, especially in regions facing water constraints, high input costs, and pressure to produce food with locally available materials.
The point is not that one review has single-handedly determined the future of food security. The point is narrower and stronger. Literature distortion has downstream effects. When simple and relevant design history is omitted, the field becomes more expensive, more confused, and less honest about what has already been demonstrated.
That is reason enough to take this seriously.
Institutional Amnesia and the UAE Context
This omission is especially striking because the review comes from a university in a region where sand-based agriculture is not a theoretical curiosity – it is the literal foundation of their national food security.
In the UAE and across the arid world, the basic question is how to produce food under conditions of extreme heat, water constraint, and barren soil. A sand-based, closed-loop system is not marginal to that discussion; it belongs at the absolute center of it.
Yet, the significance of this academic suppression goes far beyond a missing citation. By burying iAVs, the authors at the United Arab Emirates University are actively erasing the foundational history of their own nation’s agricultural miracles.
Long before these UAEU authors published their review, the late Sheikh Zayed bin Sultan Al Nahyan – the founding father of the UAE – personally invited a pioneering American scientist to Abu Dhabi to solve the crisis of the desert. That scientist was Dr. Merle Jensen.
Beginning in 1969 at the Arid Lands Research Center on Saadiyat Island, Dr. Jensen proved to the world that massive, sustainable agricultural yields could be achieved in the harshest environments using the sand beneath their feet. His revolutionary work established that sand was not an obstacle to food production, but a highly viable substrate.
The lineage of that desert research is directly tied to the birth of iAVs.
In 1983, Dr. Mark McMurtry established a professional association with Dr. Jensen, who was applying his mastery of sand culture to the design of the Land Pavilion at Walt Disney World’s EPCOT Center. Through this relationship, McMurtry discovered that the massive 5.7-million-gallon aquarium at EPCOT was maintained using fluidized-bed sand filters.
This revelation was the catalyst. Inspired by Jensen’s sand-filtration application, Dr. McMurtry took the concept to North Carolina State University (NCSU). There, working with botanical experts like Dr. Paul V. Nelson, McMurtry evolved the concept into the Integrated Aqua-Vegeculture System (iAVs). He proved that a reciprocating sand biofilter could completely eliminate expensive mechanical filters, retaining 100% of the nutrient solids, and outperforming inorganic hydroponics by 200% to 300%.
Furthermore, Dr. McMurtry specifically designed his 1986 village-scale iAVs demonstration to simulate the exact environmental conditions of the Middle East and Northern Africa.
For a research team sitting at UAEU – a university birthed from Sheikh Zayed’s vision—to publish a “comprehensive” review that deliberately ignores iAVs and dismisses sand media is breathtaking in its arrogance. They are omitting a system that was explicitly designed for their climate, sparked by the very pioneer (Dr. Jensen) who built the agricultural heritage of their own region.
They are not just ignoring a competing system. They are suppressing a lineage of science born from the sand they stand on. When an institution excludes a system that perfectly addresses solids retention and low-cost production in arid conditions, it steers its people toward expensive, complex recovery architectures while making the simpler, proven pathway disappear.
That is not a neutral scholarly choice. It is a distortion with profound human consequences.
Conclusion
The November 2025 UAEU review presented nutrient recovery in aquaponics as a major unresolved problem and called itself comprehensive. The record now shows five documentable failures. It cites Rakocy to support regular tillage or replacement of sand media, even though Rakocy’s own discussion notes that coarse sand reduces clogging potential. It omits the 2024 sandponics paper’s contrary claim that sand can remain productive for up to 25 years without replacement. It drops McMurtry from the citation chain even though the same-author sandponics paper cited McMurtry et al. 1990 alongside Rakocy. And it omits a paper co-authored by five of its seven authors that explicitly states: “Sandponics, also referred to as iAVs.” This pattern of omission violates the core tenets of academic integrity. We formally call upon Frontiers in Sustainable Food Systems to investigate this selective citation and require a correction to the public record.
The issue is not merely that relevant literature was missed. It is that a review article claiming breadth excluded a directly relevant system already present in its own authors’ recent publication record, while preserving only the portion of that record that supported its preferred framing.
When review articles distort what the field has already demonstrated, the effects do not stop at citation practice. They shape what later researchers study, what institutions fund, and what growers are told is possible. In a world of water scarcity, input stress, and food-security pressure, that is not a minor scholarly lapse. It is a distortion with practical consequences.
Learn more about Dr. Merle Jensen’s work in UAE at https://iAVs.info/spotlight-on-dr-merle-jensen-key-member-of-the-iAVs-research-group-known-worldwide-for-decades-of-research-into-sand-culture/
References
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- Icba. “ICBA Plays Host to Veteran US Biosaline Agriculture Scientist.” International Center for Biosaline Agriculture, 28 Mar. 2019, www.biosaline.org/news/2019-03-26-6773.
- Manoharan, Ramya, et al. “Harnessing microalgae for sustainable nutrition and ecosystem services in aquaponic systems: a blue–green approach to ecosystem health.” Frontiers in Marine Science 12 (2025): 1661042.
- McMurtry, M. R., et al. “Sand culture of vegetables using recirculated aquacultural effluents.” Applied Agricultural Research 5.4 (1990): 280-284.
- McMurtry, M. R., et al. “Efficiency of water use of an integrated fish/vegetable co‐culture system.” Journal of the world aquaculture society 28.4 (1997): 420-428.
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- Nair, Chythra Somanathan, et al. “Sandponics: a sustainable agriculture solution for food security and resource efficiency in arid regions.” Journal of Sustainable Agriculture and Environment 3.4 (2024): e70033.
- Nair, Chythra Somanathan, et al. “Recent advancements in aquaponics with special emphasis on its sustainability.” Journal of the World Aquaculture Society 56.1 (2025): e13116.
- Nishanth, Drishya, et al. “Current technologies for nutrient recovery in aquaponic systems: a review.” Frontiers in Sustainable Food Systems 9 (2025): 1681638.
- Nishanth, Drishya, et al. “Harnessing desert resources: a comparative study of microgreens growth, nutrient dynamics, and performance in desert sand and rockwool.” Frontiers in Plant Science 16 (2025): 1677009.
- Rakocy, James E. “Aquaponics—integrating fish and plant culture.” Aquaculture production systems (2012): 344-386.
- Subramanian, Radhakrishnan, et al. “Integrating desert sand utilization in saltwater aqua-vegeculture production: performance evaluation of yield and biochemical composition.” Animals 15.9 (2025): 1246.
- Subramanian, Radhakrishnan, et al. “Sustainable leafy green production in sand media based integrated aqua vegeculture system under salinity.” (2024).