When fish are filleted in a seafood-processing plant, or when shrimp and shellfish are boiled, a lot of wastewater is generated. Currently, that water is simply discarded. An experimental new system, however, is able to draw much of the nutrients from it – and those nutrients could have a number of uses.

According to Sweden's Chalmers University, about 7,000 to 8,000 liters of water (1,849 to 2,113 US gal) are used when processing one ton (0.9 tonnes) of marinated herring. Around 50,000 liters (13,209 US gal) are utilized when boiling and peeling one ton of shrimp, or when processing three tons of raw shrimp.

Led by Chalmers' Prof. Ingrid Undeland, a research team from the multi-partner NoVAqua project analyzed such water, and found that it contained up to 7 percent protein and 2.5 percent omega-3 fatty acids. Utilizing a unique two-step process, the scientists were able to recover as much as 98 percent of the protein from the water, and 99 percent of the fats.

In a nutshell, the process involves first treating the water in such a way that the proteins and fats clump together. In the presence of air bubbles, those clumps then float to the surface, where they can be retrieved. The end products consist of a nutrient-rich liquid and semi-solid biomass.

When tested on farmed salmon, that biomass showed promise as a fish feed. The liquid, on the other hand, was shown to be more effective than water as a protective glaze to help keep frozen fish from spoiling. It also enhanced the growth of two types of microalgae, which could in turn be used in biofuels, nutritional supplements or animal feeds.

Although the NoVAqua (Extracting Novel Values from Aqueous Seafood Side Streams) project wrapped up earlier this year, the follow-up AquaStream stream project is now looking into ways of bringing down the cost of the process, and implementing it into commercial seafood-processing centers.

"It's very important to help the industry understand that the side streams don't need to be wasted," says Undeland. "Instead, they should be treated as really exciting raw material."