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Purifying wastewater using algae
  • Starting at household scale, our daily sewage sent to a treatment plant with solids removed is called secondary effluent, floccing chemicals are used to remove the nutrients because they cause algae blooms if released to a river or other body of water.

    If algae are used instead of chemicals they take longer but do a bettter job so make full recycling relatively cheap by greatly reducing the purification needed by the final step, the chemicals leave too much so it's expensive and full recycling is used only at places like Lake Tahoe where it's mandatory.

    Ponds aren't practical for this so bioreactors are the only way grow algae 24x7, the basic one in labs is two glass plates with water & algae and lights with aeration from the bottom in a temperature controlled room. So my unit is 24 glass plates that separate the water with lighting, aeration is better; these are cubes a 1/2-meter on a side that stack to about 6-7 high. Lighting is fiber optics to the glass and each unit needs 12-watt equivalent, using spectra LED's the power for this is half that or about 24-watts per person continuous to grow. 

    Algae cling to the glass so there's a squeegee that's pumped to clean them. And, for the past year I've adding in tries for continuous harvesting instead of using centrifuges, the common technique for micro-algae and one that takes a lot of electricity so trying to avoid it. However it's done the slurry goes to a small biodiesel press-refining unit to gain about 7.5L/2gal per person on a city system, that's a lot of fuel, and, you get the water back.

    Then, tests in Egypt found my favorite Spirogyra jumped wheat yields 25%, tests ongoing to see if that was from other factors but that's the potential of this overall, to digest solids for methane to use in the kitchen or shop, recycle the water, gain biodiesel for the car or tractor and get a good fertilizer from the pressed algae cakes.

    It all boils down to the unit, once a basic model works in simulation software my job is then to create a prototype assembly-line that makes them from sub-assemblies, those each needing a supply-chain, standardized parts & connectors; then near the end service-people for the units which are simple to maintain but not to fix if something breaks.

    For certification I have a small Oklahoma utility that does wastewater & farm remediation so likes that this will work on most farm waste as well and willing to help development of a reliable unit that can enter building codes, that allows homeowners to install them.

    To point out that there are sewage solids digesters for household scale to buy today, a difference is that this is intended to include all steps of sewage treatment for full recycling as a coherent product system to supply a home, ranch or farm with biofuels and pure water from their own sewage.

    From the type of projects on opensourceecology to me sewage treatment seemed to fit the goals, none of this class of bioreactors have been made before, most bioreactors are quite different and designed to large scale so not fitting the needs of a single-family home, ranch or farm.

    In any case, the topic is open for all.

  • 3 Comments sorted by
  • Vote Up0Vote Down
    November 2012
    Hi, tmallard,
    I'm really interested in this field and I would like to ask you to post some pictures or plans for your installation so I can have an idea about it.
  • Vote Up0Vote Down
    December 2012
    Very cool work. It sounds like you are describing a flat panel bioreactor for medium scale cultivation. Are you inoculating with strains or just seeing what grows? I am an algal biochemistry researcher and interested discussing more.
  • Vote Up0Vote Down
    January 2013
    I have a suggestion.

    Instead of using a glass container full of fiber optics. What do you think about using a water tight hopper full of glass or plastic beads for the light source?
    When the beads pack and touch, the points of intersection will create paths for light to transmit. The Algae will of course, grow all around the bead surface. To harvest the Algae, you "harvest" the bead with the mechanism of your choice. I suggest an Archimedes screw from the bottom of the hopper. Clean beads will be deposited on the top.

    Production of transparent beads is probably easier to produce than glass panels. The harvesting of the beads can be done by rolling the bead around until the algae comes off.

    What I like about this idea, is the ability to scale it up by adding more beads. At a certain volume, you'll need a second or third light bar, and there may be some dead zones. However, as the beads get cycled in and out, the zones will change.

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