Aquaponics operations combine aquaculture and hydroponics, with nutrient-rich water from the former being used to fertilize plants in the latter. Soon, such systems could also be powered by methane biogas derived from their own fish feces.
In a typical aquaponics setup, fish are raised in land-based pens which are connected (by pipes) to soil-less hydroponics grow beds in which vegetables are growing. As water is pumped from the one to the other, fish waste in that water fertilizes the plants. Additionally, bacteria in the grow beds break down the waste, helping to clean the water before it's recirculated back into the fish pens.
Now, scientists at Sweden's University of Gothenburg have come up with a new use for the heavier solid fish waste which would otherwise go unused in some aquaponics operations.
After fish feces have settled to the bottom of a separate tank, they can be collected and converted into a concentrated gas mixture which is 70% methane. The conversion technique utilizes a process known as anaerobic digestion, in which bacteria break down biodegradable material in the absence of oxygen.
In a real-world usage scenario, the biogas could subsequently be used to power the electrical systems in the aquaponics system, lowering both its carbon footprint and operational costs.
And as an added bonus, nutrients released from the waste during the digestion process could be used to further fertilize the plants. What's more, the carbon dioxide which is produced when the biogas is burned could be utilized to boost the growth of plants in enclosed environments such as greenhouses.
Although the system has only been tested in a lab setting so far, plans call for it to be trialled in a commercial aquaponics operation later this summer.
"Fish waste contains a lot of nutrients," said the lead scientist, Victor Lobanov. "These should also be usable in aquaponics to enable even more sustainable food production than today."
Source: University of Gothenburg