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A Numerical Comparison of Two Approaches to Commercial-Scale Aquaponics

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Dr Mark McMurtry's comparison of the two schools of aquaponics shows that the media-based, 'flood/drain' approach outperforms, by a wide margin, the hydroponic raft system. Dr McMurtry is widely acknowledged as the creator of the science of aquaponics when he was at NC State University in the mid-eighties to early nineties, writes Bevan Suits, AquaPlanet.

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His method, which he called IAVS, (Integrated AquaVegeculture System), is better known today as flood-­and-­drain. It is favored by backyard practitioners around the world, with a few examples of commercial systems.

Prior to the mid-eighties, aquaponics was merely a sketchy concept of plants growing in fish tanks, originated at The New Alchemy Institute1. There had been little, if any research and development. Since then the concept has developed into various forms, methods and sizes, branching off around the world, but limited to hobbyists, universities and the occasional entrepreneur. Today it is variously described as an “industry” or “movement”. There is clearly positive growth in various regions, as well as occasional setbacks, due to prominent missteps. Yet considering the real and proven value of this technology it is something of a mystery as to why it is not further advanced, creating new economic opportunities and jobs based on locally-­?grown organic fish and vegetables.

How big is that opportunity? A recent detailed study2 by Karp Resources indicates that in Louisville, KY, with a population of about 1.2 million, “Total demand for local foods... is $258 million among consumers and $353 million among commercial buyers.” This exhaustive survey and analysis clearly puts a target value that can be scaled to other metro areas and begin to figure in to investor spreadsheets.

Two Approaches, One Goal: More Food Faster

Aquaponics is a broad term that covers two approaches, both of which involve converting fish waste to nutrients for plants. There are two distinct paths, or methods, that today’s systems follow. One is the floating raft system by Dr Rakocy at the Virgin Islands. The other is Dr McMurtry’s IAVS, which closely mimics a tidal wetland, with plants growing in sand, gravel or other non-soil medium.

Some commercial systems today are beginning to integrate the two methods.

The UVI raft method is a hybrid of traditional hydroponics and aquaculture. In large-scale hydroponic systems, shallow troughs full of water support floating foam panels with plants in net pots, with the roots extending into the water. The water is amended with nutrients (whether purchased or produced by fish waste, or both). The water troughs require their own aeration system. The UVI aquaculture component consists of large tanks, above ground, with water that is recirculated through various filters and plumbing systems to refine the fish waste before its basic nutrients are introduced to the hydroponic ponds. After the water is passed through the ponds, it drains to a sump tank, where it is pumped back to the fish tank.

The IAVS system, by contrast, is far simpler. Fish tanks below ground3 are adjacent to grow beds (or “biofilters”) containing grow media, such as sand, gravel or any other small mineral particle with high surface area, where the aerobic bacteria population can flourish. The beds are lined with pond liner. The plants are positioned directly into this media without pots, and the fish tank water is flushed across the surface, trickling to a drain that returns to the fish tank. There are no filters, degassing columns, sumps, Styrofoam panels, pots or aeration for the grow beds. Obviously the cost is far lower to implement and to operate, with fewer components to manage or risk failure.


As far as similiarites, each system:

  • Is considered a form of Recirculating Aquaculture System (RAS).
  • Relies on the nitrification process of aerobic bacteria converting fish waste solids and liquids to usable nutrients for plants.
  • Uses fish food as the sole nutrient input.
  • Relies on system aeration in various forms to enable microbial growth.
  • Is able to produce impressive yields of fish and vegetables.
  • Relies on existing technologies of water pumps, plumbing, pond liners, plastic tanks, etc.

System Differences

The UVI system requires more labor, with regular cleaning of its filters and excess waste discarded or used in soil farming. It is far more complex and costly to build and to operate, especially in cold climates. The skill level and potential for equipment failure is also increased. All of these factors add up to a system that is less scalable and more risky for operators and investors. Of course the UVI system is very successful as a producer of fish and vegetables, even compared to traditional hydroponics. However technology evolves toward simplicity. Less efficient systems are eventually modified or abandoned.

The IAVS system demonstrates simplicity, especially the low-­?tech concept for export to remote areas of the world. It is as close in design to a natural wetland ecosystem as possible. With a single pump, a solar panel and some pond liner it is quite possible to create a low-budget, off- grid system.

Larger “high-tech” commercial IAVS designs build on the original simplicity. Lower development cost allows for creative variations in tank placement and configuration, water heating systems (crucial for tilapia in cold climates) and grow bed construction. Warm water, heated by natural gas, solar or biomass also can serve to heat ambient air in greenhouses far more efficiently than traditional forced air. Advanced sensors and control systems, found in state-of-the-art greenhouses are more affordable with IAVS. Many higher-end solutions exist to enable remote 24/7 monitoring, resulting in greater yield predictability and less risk. Other cutting edge materials include greenhouse components such as glass panel products that generate electricity while allowing light to pass.

The relatively low system cost of IAVS allows for the greenhouse to be included as an integral component of the operation, as they should be. Many of the new aquaponics companies in the upper Midwest do not even use greenhouses, opting for retrofitting of warehouses, with high infrastructure and artificial lighting costs. And the design of a Hawaii greenhouse is not the same as it is in Georgia, Vermont or the high deserts of Afghanistan.

Although the IAVS system has been limited mostly to the small-­?scale backyard growers around the world, it has been successfully proven on a commercial greenhouse scale at least twice. In the mid-­?nineties, a public health doctor, Dr Boone Mora worked with USDA (NRCS) representative Tim Garrett in Eastern North Carolina. They received a $100,000 government grant to develop a 10,000 square foot greenhouse using Dr McMurtry’s method. It operated successfully for 16 months and was documented by Dr Mora and affirmed by Mr Garrett as a viable and effective method.4 It was toured by thousands of curious visitors and its flavorful tomatoes and cucumbers were in extremely high demand at local markets.5

A better-known example, in Missouri, was started also in the mid-nineties by Tom Speraneo and his family. They operated S&S Aqua Farms as a modest greenhouse operation for about ten years before Tom died in 2004.6 It received impressive reviews in the horticulture press and was perhaps an inspiration to the early backyard enthusiasts who have been successful in creating even smaller and simpler systems.

The point here is that there is great opportunity for innovation in integrating aquaponics and greenhouses, based on the simplicity of flood/drain IAVS. The resulting yields in a properly designed system can easily go far beyond what amazes us today with even the basic aquaponics systems. This brings up the concept of system optimization.

System Optimization

Any engineered system is designed with a goal of optimal results, with greatest results from minimum input, also known as efficiency. Car engines, for example, have been continuously evaluated and updated for over one hundred years with a goal of more power, less fuel at a reasonable price. The difference is that car engines are far easier to engineer for optimal performance than an agricultural biosystem, with so many variables and changing dynamics, including:

  • Climate
  • Seasons
  • Energy costs and methods
  • Pathogens & pests
  • Human factors
  • Untested crop performance

With proper peer-reviewed research and development, we will begin to see real examples of optimized production.

Scalability Factors

A key factor towards encouraging industrial growth is scalability, which, in our opinion, has been lacking in aquaponics. The term is most often used in computing, as in “capable of being easily expanded or upgraded on demand” or “the ability to enhance a system by adding new functionality at minimal effort or cost.” The dominant model of commercial aquaponics, the raft system, in its current design, is far less scalable than the IAVS.

According to Dr McMurtry, the IAVS method also greatly improves on the yields, and with significantly lower operating costs. This adds further weight to the advantages of IAVS, even with a large margin of error. Without side-by-side comparisons, of course, we can only speculate, based on published numbers. We present this data with a goal of more scientific comparisons in the future.

This is not to dismiss the raft system out of hand, as it will likely continue to prove its value as a specialized enhancement. For example, it is more closely compatible with the existing commercial hydroponic greenhouse industry, which has its own unique efficiencies for producing greens in ponds and NFT systems (nutrient film technology). It appears, however, that the raft system needs to continue evolving towards simplicity and modularity to be truly scalable.

Dr McMurtry’s intricate methodologies in measuring the many parameters of an aquaponics system warrant further investigation. We maintain that his work will serve as an industry benchmark, and that additional R&D funding should be applied to replicate and improve on it.

If there are other models that approach this level of detail, in terms of development costs, operating efficiency, production yields, energy consumption, labor costs and nutrition value, we invite comparisons.

The Tables

Dr McMurtry recently produced an intricately detailed spreadsheet of the numbers comparing the floating raft aquaponics method with IAVS. His numbers show that the two systems are quite distinct in many variables, and that the published volume and depth of parameters of the UVI system does not come close to IAVS. It should be noted that his work at NC State University was supported and reviewed by a world-class ag research team.7

The Excel spreadsheet, called UVI vs IAVS extends to 250 rows and includes highly detailed calculations, notes and qualifications. We have slightly edited and reformatted the document here for public review and comment.

Dr McMurtry refers to two variations of IAVS, one low-tech, one high tech. The low-tech design is for remote areas using minimal resources, solar PV to operate the pumps, aeration accomplished by return water splashing.

3 Above ground tanks are also possible.
4 Documentation available from AquaPlanet.
5 One lesson learned: Maintain limited public access through a controlled environment greenhouse or it will introduce pathogens. Boone Mora is available for further comment.
6 Numerous attempts to contact the Speraneo family have not been successful.
7 See list of supporting scientists at End Notes

Further Reading

You can view the tables mentioned in this article and the AquaPlanet website by clicking here.

August 2013