Can Biogas Make Aquaponics Even More Efficient?

Image credit: Friendly Aquaponics & Makine Mekanik

While some folks may be busy debating whether soil-less agriculture can be organic or not, there's a lot of momentum behind aquaponics. As the name suggests, aquaponics is a system of food cultivation that combines hydroponics with fish farming, and which uses the waste from the fish to feed the plants, and the plants to filter the waste from the fish. From Worldwide Aquaculture's plans for industrial-scale aquaponics to Growing Power's urban aquaponics, many people believe that it holds at least one of the keys to feeding a growing population in a world of diminished resources. But as I've asked before, given the required energy inputs, from feed to heating and lighting, is aquaponics really an efficient way to feed ourselves? Now one farm in Hawaii is hoping to make that question a little easier to answer—experimenting with small-scale biogas to power its systems. As I argued in my original post on the efficiency of aquaponics, even with the energy inputs for heat and supplemental light, aquaponics has a lot to recommend it: it doesn't involve cultivation of soil; fish are much more efficient at converting feed into protein than land animals are (of course the sustainability of fish food, and the animal welfare issues related to aquaponics are another debate!); and even though energy is required to run these systems, it's much easier to run a pump and a water/space heater on renewable energy than it is a tractor.

That's why Friendly Aquaponics, the folks who rather provocatively argued that aquaponics kits are a rip-off, are now experimenting with small-scale biogas production to fuel their farm. Here's an excerpt from their newsletter as to why they think this is so important:

"We're lucky to have a 365-day growing season at our farm in Hawaii, but most farmers in cold climates have a short growing season of only 5 to 7 months. They have to make all their income during this short time while having expenses that last for a full year. The two major problems these farmers face if trying to grow during wintertime are that heating greenhouses is expensive, and there's not enough sunlight for good plant growth, resulting in a need for expensive supplemental lighting. Thus, they never even bother to build the greenhouses because ultimately the cost to produce the vegetables is not tied to the cost of the greenhouses but rather to unpredictable and continually rising petroleum-based energy costs for their heating and electricity."

Biogas, they say, is the perfect solution as it uses up waste biomass that is readily available on most farms, it produces both electricity and 65% waste heat that can be used to heat your greenhouse (instead of propane or other fossil fuels), and it also produces a waste slurry that makes a great fertilizer—though presumably that fertilizer would be unnecessary for the plants in an aquaponics system.

However, most biogas installations in the US are geared toward large-scale use of municipal sewage and/or swine/dairy farm waste, and are priced way above most small-scale farmers' realm of affordability. So before building their system, Friendly Aquaponics are first experimenting with several small-scale biogas digestors to optimize production for family farms and small aquaponics set ups. Their core challenge is to figure out a means of producing biogas from high-solids input streams (10% solids, rather than 2% solids more typically used in larger systems), and to work with mixed inputs, rather than a steady stream of cow, hog or human waste:

"To accomplish the most research economically in a short time, the lab has ten 5-gallon size digesters, six 6-gallon size digesters, and a single 500-gallon digester, with instrumentation to measure total gas production from each digester, plus analysis capabilities to measure the makeup and quality of the biogas we are generating. There are heat exchanger elements inside the digesters that circulate hot water captured from the waste heat of the electrical generator's diesel exhaust so we can run the digesters in mesophilic mode (105-115 degrees F) as well as psychrophilic (65-85 degrees F) mode."

Looks like fascinating stuff. And to share their knowledge, Friendly Aquaponics are holding their first ever biogas workshop on April 23rd rhosted and taught by David House, the author of the Biogas Handbook. Sign up on their website.

Tags: Agriculture | Alternative Energy | Farming | Fish | Hawaii | Renewable Energy | United States

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