Dr Zecarias Russom Tesfasion FEPA/ZERI [fepazeri@cyberspace.net.ng] wrote:
> 1.    The major objective of the paper was to reduce the level of P
> from an effluent of Rainbow trout by growing plants such as
> lettuce in the effluent. Then the water with low P level can
> be used again with a bonus of marketable lettuce. If that was
> the case, what will be the effect of P to the Rainbow
> trout when they are grown in water with high level of P? The
> introduction did not give solid reasons as to why P has
> to be reduced to low level.
>
> Knowing this, I might then understand the justification for this
> study. In fact, under the heading, "Rainbow trout effluent
characteristics," the
> effluent had the lowest P value (0.7 mg/L) when compared with the
> content of
> NO3-N, K, Ca, Mg and S. So, why was P targeted for reduction?

Zecarias,

I tried to briefly state the problem in the first paragraph of the paper,
but I guess I didn't state the problem clear enough. So I will
try again and have included the excerpt from the paper below.

It is easier to treat effluents that have high nutrient concentrations and
lower volume, than low concentrations and high volume. P is the most
limiting nutrient in US freshwater so is the most critical to reduce to
minimize eutrophication. We know that in a stream, it is the total quantity
of P, that is important, not concentration alone (e.g. 100L of 10mg P/L
gives same amount of P as 10,000L of 0.1mg P/L). That was the rationale for
our work.

"Aquacultural effluents are difficult to treat because they contain
large volume flows carrying relatively dilute nutrients (< 1 mg/L P).
However, it may be important to treat the nutrients in aquaculture
effluents because, depending upon the receiving water, the total
nutrient mass loading can contribute significantly to environmental
degradation."
 

> 2.    In characterizing the effluent the following values were given:
>             NO3-N = 25 mg/L
>                     P = 0.7 mg/L
>                     K = 5 mg/L
>                    Mg = 20 mg/L
>                     S = 9 mg/L
> These values do not mean much without stating the number of samples
> taken and the value of the standard error.

The values, as listed, serve our purpose in giving the readers an idea
regarding the concentration of nutrients in our water, which I believe is
valuable information. But, you are right, if one wants to know what kind of
variability we observed, you will not be able to determine that from these
data.

Paul