Re: constructed wetland for Aquaculture wastewater

>From: "John Doe" <DNITZ at VALINET_COM>
>Date: Fri, 20 Dec 1996 22:53:32 -0500
>I am overseeing the operation of a constructed wetlands for Aquaculture
>wastewater. Specifically, Tilapia (freshwater) fish wastewater.  
>Currently my flow is 6 gal./min. but soon to go to 15 gal./min. and within
>3 months up to 24 gal./min.
>Our main objective is to remove nitrate-N and phosphate.
>Currently the plant we chose to help is Phalaris arundinacea (Canary
>The media we are using is peat moss, rockwool "stonewool" and a
>of the two.

One minor bit of information that we're missing is where on the planet
you're located.  Hopefully, we can give you an indigenous selection of goot
marsh plants to use.

>Q:  What plants might do well in this wastewater, media and/or treatment

If I were in Texas, I'd look seriously into cattails.  There's a
possibility, depending on what you feed your Tilapia, that you might wind
up with an nutrient imbalance going in that will result in an excess of one
or more nutrient on the other end.  If you monitor the output and add
whatever macro nutrients you *don't* find in the output, you will probably
adjust the ratio favorably so the plants can consume all the nutrients.
Micro nutrients may be necessary as well.

I'm recommending cattails because I know they're major producers, meaning
they're also major consumers.  Optimally, you'd want a plant that doesn't
need a lot of fuss, and I'm suggesting bog (emersed) plants for that
because they have ready access to CO2 when they're out of the water.

If you're in Asia, you might look into Hygrophila stricta or an
Alternathera species.  These are also very fast growers.  I don't know much
about what to pick from South America, Australia, Africa, Europe, or any

>Q:  How can I help the plant density (for increased hydraulic conductivity
>through the media) establish quickly?

Give them full sunlight and make sure they aren't deficient in any

>Q:  What combination of plants might work best?

This really depends on where you are, again.  The cattails might be only
good for removal of say, the first 2/3 of the nutrients from the water, but
they starve below that (speculation for the sake of argument).  After that,
you might pick the grass that grows in the Everglades, or maybe some native
Echinodorus that will grow up out of the water.  Water Hyacinth is another
good producer, but you'll need to very carefully contain it and use the
waste compost well away from streams or lakes.  Water Hyacinth may also be
illegal where you live.

Duckweed and salvinia will probably also be good choices for rapidly
reproducing floating plants.  In full sunlight, with plenty of nutrients,
they will probably need to be harvested daily.  Depending on your needs in
your tilapia tanks, these plants may be suitable for growing as a
head-start in the same water as the tilapia (serving as a food supplement
in addition).  Once you add them to the water, don't expect to get
completely rid of them easily.

>Thank you in advance.	Dan  
>My e-mail address is DNITZ at VALINET_COM

I hope this helps.

David W. Webb           Corporate Business Systems
Texas Instruments Inc.  Dallas, TX USA
(972) 575-3443 (voice)  MSGID:       DAWB
(972) 575-4853 (fax)    Internet:    dwebb at ti_com
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