FISH FARMING TECHNOLOGY
FISH FARMING TECHNOLOGY #2 by Henning Gatz, President, Aquacare Environment Inc., USA
Having been involved in fish farm design, construction and support since 1987, I have seen many new technologies come and go. Often a vendor offers a 'black box' that is intended to solve problems for fish farmers and reduce risk. Many of these are backed by slick brochures and hefty advertising budgets, but still fail to become adopted by the aquaculture industry. The reason is usually that the 'black box' does not live up to its promise, is too complicated, too expensive, and too unreliable.
Oxygenation in intensive commercial fish farms using Oxyflow速 One of the key process technologies required for intensive fish farming is dissolving oxygen gas into the farm water. There are many technologies available to accomplish this, ranging from simple low head oxygenators (LHO) to very elaborate, multi-stage processes operating at elevated pressures and controlled by computers. What the commercial fish farmer really wants and needs is a simple, reliable process for dissolving oxygen gas into the water that does not cost more than necessary and can be maintained by farm personnel without a huge time requirement. Above all it needs to be reliable, even during disruptive events like power failures. In 2010, JLH Consulting and Aquacare began an initiative to lower the cost of land-based intensive fish farming operations. This initiative focused on two of the largest cost factors: pumping head and oxygenation. The pumping head has now been reduced by several meters by lowering the bio filter and CO2 strippers to a level where gravity can supply them, and only pumping clean filtered water back to the fish tanks with high flow, low head pumps. This reduction in pumping head led to another challenge; oxygenation with lower head. In 2012, we had the good fortune to meet the people at France Oxygenation (FOX) who have developed and marketed a simple, reliable and efficient oxygen saturator under the name of Oxyflow速. Upon closer examination, this unit process technology was exactly what we were seeking to lower the cost of dissolving large amounts of oxygen into the fish farm water, reliably and efficiently. Fox Oxygenation was established as a specialist oxygenation technology company in 2005, after founder Bohumil Sevic developed the technology in 1977 as a research engineer for Air Liquide in France. He was able to retain the I.P. after leaving Air Liquide. Since then Mr Sevic has continued to refine and evolve the technology to where it is today. Essentially, the Oxyflow速 is an LHO that operates in a sealed vessel thus not breaking head pressure. Process water enters the top of the unit under mild pressure of about 0.3 bars. The water next passes through a horizontal drilled plate with specially shaped orifice holes (number and size determined by flow rate required), which jets the water downward through an oxygen atmosphere approximately 20 cm deep. When the jets strike the water surface below, they cause a high turbulence and create a bubble cloud of pure oxygen that extends downwards to 40cm below the surface of the water. These buoyant bubbles flow upwards, counter to the downward water flow in such a way that the downward velocity is not strong enough to carry the bubbles out of the chamber, hence the only way the oxygen gas can escape the Oxyflow速 unit is to become dissolved in the water. Bubbles that break the water surface inside the unit are again subjected to the turbulence of the downward jets until they become dissolved. 38 | August 2017 - International Aquafeed