John Harris [jfhdally@agn.net.au] asked
> Is there any reason other than accurate flow rates for analysis that
> you used peristaltic pumps ? It would appear to be excessively
> expensive for a commercial system.

The only reason that we used peristalotic pumps was to have good control of
the flow rate, since this was a research project, just as you thought.

> What were the reasons for selecting Lettuce & Basil for the project ?

Lettuce and basil are 2 of the most common crops grown by commercial
hydroponic companies. Our goal for this study was to test the technology,
rather than experiment with other crops and see if there was a market for them.

> With a 72 foot trough was there any effect from oxygen depletion in  the effluent ?

We didn't do a side by side test with a conventional system, so I can't
tell you if these plants were growing at the maximum rate possible. However,
the product was very good, as I think you can see in the pictures.

> Was the BOD measured after microfiltering ? and
> could high BOD cause problems considering the effluent is only
> in the system for  around 150  minutes (assuming 2mm film)?

The BOD of the effluent was low, but solids do collect in the troughs,
since there are about 6mg solids/L.But the roots and plants
were very healthy looking and you can see the good growth rates we
observed. The question is good, but I didn't make any obsevations that
would lead me to think that the plants were stressed in any way.

Paul Adler
USDA-ARS, 45 Wiltshire Road,
Kearneysville, WV 25430 USA