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Solids Removal by Foam Fractionation


									40 >>NOVEMBER/DECEMBER 2007                                                                                                                  HATC HE RY I NTE R NATI ONAL

                              Solids Removal by
                              Foam Fractionation
                                        here are many options       or a venturi injection system.
                                T       for removing solids
                                        from aquaculture water
                                                                    Although achieving fine enough
                                                                    bubbles can be problematic, this
                              such as pressurized media             is the easiest and most reliable
                              filters, microscreen filters,           technology, and is the one most
                              gravity separation, and flotation.     commonly used in aquaculture
                              The choice of technology will         facilities.
                              depend on the water quality               Flotation systems tend to be
                              and the treatment process.            highly mechanical. Effectiveness
                              Each technology deserves its          is very dependent on the type of
                              own article so we will start with     particulate matter, characteristics
                              particle removal via flotation.        of the water, the bubble size and
                                  Flotation systems operate         the air/solids ratio. Generating
                              by introducing bubbles into           fine bubbles is relatively easy in
                              the liquid. Particulate matter        salt water, but can be harder in
                              attaches to the surface of the        fresh water systems. Although
                              bubble as they rise through the       flotation system performance
                              water to the surface, where they      can be enhanced by the addition
                              can be skimmed off. Flotation         of chemicals, which change the
                              technology is most appropriate        surface tension of the water, these
                              for removing fine- and low-            chemicals are not typically used        Clear RK2 fractionator system.
                              density particles that are difficult   in aquaculture facilities.
                              to remove through sedimentation.          Foam fractionation is also
                              A small but significant percentage     known as protein skimming
                              of the wastes generated in            since it also allows the removal
                              aquaculture systems are too fine       of suspended and dissolved waste
                              to be removed by conventional         such as proteins before they
                              filtration systems. Normally,          decompose to toxic compounds.
                              these fine solids are flushed away      Dissolved or suspended organic
                              with effluent water, however, in       particles are drawn by polar
                              tight recirculating systems, they     charges on the particle to an air/
                              can build up, providing food for      water interface. One end is drawn
                              bacteria, which consume oxygen        to the water while the other end
                              and release toxins into the water.    is drawn to the air. The bubbles
                              Foam Fractionators are often used     rising to the water surface form
                              to remove these fine organics.         a layer of foam. Skimming off
                                  There are three basic types of    the foam therefore removes the
                              flotation system:                      attached solids. Tiny bubbles
                                  • Dissolved-air flotation          are more effective than large
                                  • Vacuum flotation                 bubbles because they maximize
                                  • Air flotation                    the surface area of the air/water
                                  In dissolved-air flotation,        interface and the length of time
                              gas is dissolved under pressure       that it takes for the bubbles to rise
                              into the water. When the water        to the water surface. A venturi is
                              is discharged into a vessel           commonly used to create the fine
                              at atmospheric pressure, the          bubbles.
                              dissolved gases come out of               The foam is usually collected
                              solution as fine bubbles. As           in a chamber at the top of the
                              air is most commonly used,            vessel and is then directed to
                              this technology is rarely used        waste, carrying the fine particles
                              in aquaculture facilities as the      with it.
                              increased gas pressure may create
                              problems with super-saturation.                                               RK2 system at Monterey Bay Aquarium.
                                  In a vacuum flotation system,
                                                                    The use of Ozone
                              the water is passed into a vacuum         Foam fractionators can also
                              chamber and the existing              be used for ozone injection,
                              dissolved gases are drawn from        rather than using air. Ozone
                              solution as bubbles, due to the       enhances the process by oxidizing
                              reduced pressure within the           potentially dangerous organisms
                              vessel. This technology is usually    including bacteria and viruses,
                              more complex and difficult to          thereby destroying these
                              execute than the other options,       pathogens. Ozone also works well
                              and so, is the least likely to be     as a water clarifier and will make
                              used.                                 the particles easier to be captured
                                  Air flotation systems involve      by the bubbles.
                              injecting gas bubbles into the                                                Sander protein skimmers.
                              water column using diffusers                      continued on page 43                RK2 Foam Fractionator System.
H ATC HERY I N T E R N AT I O N A L                                                                                                                NOVE MBE R / DE C E MBE R 2007 >> 43

                                                                       Larval Fish and Feeds
New feed for rotifers
Reed Mariculture recently

                                     The new diet is specially
introduced an addition to its
Instant Algae™ product line
                                     formulated for use in rotifer
                                     production systems such as the                                                           Fish Egg Sorters • Fish Egg & Fry Counters
– Rotifer Diet 2™. Rotifer           Aquatic Eco-Systems (AES) High
Diet 2 is a combination of the       Density Rotifer System pictured.                                                                          Sales • Rentals • Service
microalgae Nannochloropsis,
Tetraselmis, and Chlorella and                                                                                                           We supply dependable, reasonably priced
is specifically formulated for use                                                                                                      and innovative equipment to fish hatcheries
in rotifer production systems,
such as the Aquatic Eco-                                                                                                                                       around the world.
Systems (AES) High Density
Rotifer System.
    According to a press release                                                                                                      20756 High Desert Court, Suite 6, Bend, OR 97701
from AES, Rotifer Diet 2 is a                                                                                                             Voice: 1-541-389-3591 Fax: 1-541-389-0050
high energy feed for rotifers
that helps them reproduce at
peak levels. The release notes
that: “Typical production
yields in an AES Rotifer
System using RD2 are 5,000
rotifers per ml and a 50% daily
harvest, however the system can be pushed to significantly higher yields as needed.”
Nannochloropsis is the primary component in RD2 and the addition of Tetraselmis helps
to increase the metabolism of the rotifers, while the Chlorella helps to provide a balanced
    “RD2 is an exceptionally ‘clean’ feed which helps increase performance in high density
systems which rely on screens to contain the rotifers,” adds the company. “Clean feeds
like microalgae result in low bacterial content so the rotifers and their droppings are less
sticky and much less prone to fouling the system or screens.”
    RD2 is packed in 10 liter bags and has a minimum eight week refrigerated shelf life.

                                                                                                 Site Manager Atlantic salmon hatchery
                                                                                               • Competitive Salary Package                     • Be fully conversant with smolt hatchery
                                                                                               • Tasmanian Location                             operations from ova incubation to smolt delivery
                   continued from page 40                                                      • Excellent career opportunities                 and have a minimum of 5 years practical
                                                                                                                                                experience in hatchery operations of Atlantic
      Here are some good reasons to                  Is the application for fresh or salt      This is an excellent opportunity to join an      Salmon.
  incorporate a foam fractionator into your     water? The foam removal skimmers are           Australian market leader who has                 • Have proven experience in the management of
  system:                                       usually different, depending on water          experienced considerable change and is           staff, production planning and budgetary
      • Reduces system cleaning                 characteristics.                               about to embark on tremendous growth.            requirements.
        requirements by reducing the                 What is the desired flow rate through                                                      • Hold tertiary qualifications in Aquaculture
                                                                                               Tassal Group Ltd is the largest aquaculture
        growth of bacteria on tank and pipe     the unit? Is it a side-loop arrangement        company in Australia, employing over 450
                                                                                                                                                • Commit to continual business improvement,
        walls, drum filter screens, etc.        or for full flow usage? If it is a side-loop   people and marketing 60% of the Tasmanian
                                                                                                                                                exceeding production targets and the production
      • Reduces oxygen demand by                a recirculation pump may have to be            salmon industry’s production. Tassal is a
                                                                                                                                                of the highest quality smolt.
        reducing heterotrophic bacteria         incorporated as well as the venturi pump.      vertically integrated company from hatchery
        concentrations.                              Foam fractionation is a tried and                                                          In return for the above you will be rewarded with
                                                                                               through to farming, processing, value-
      • Reduces loading on biofilters by        tested method of removing small                adding, distribution, sales and marketing.
                                                                                                                                                a comprehensive salary package and excellent
                                                                                                                                                career opportunities.
        minimizing heterotrophic bacteria       particles and is relatively inexpensive        For more information on Tassal visit
      • Improves water clarity.                 if incorporated with other filtration
                                                                                                                                                For more information please contact Danielle
      • Improves transmissivity of UV           methods. Together they will reduce                                                              Foster or forward your applications or enquiries
        light from sterilizer units, reducing   turbidity and organics from the culture        Heading up a small dynamic team this
        power requirements.                     water, which benefits the culturist            position will be located at the Russel Falls
      • Is easy to incorporate in an existing   since cleaning tanks and equipment is
                                                                                               As an operational role it is expected that the
        treatment train.                        made easier. It also benefits the fish by
                                                                                               successful candidate will;
      • Requires very little maintenance        reducing bacterial growth and improving
        and has low operating cost.             oxygen concentrations and overall water
      When purchasing a foam fractionator       quality.
  some information needs to be passed
  onto the supplier, as material and design     Genny West is a Mechanical Engineering
  modifications are often optional:             Technologist with PR Aqua, Nanaimo, BC.
      Will ozone be used? If so, ozone-
  resistant materials will need to be
                                                For more ideas and information contact her
                                                                                               Check out the online Suppliers Guide

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