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At 15:07 08/05/2006, Martin Weiss wrote:
>Yes it is however, there is a paucity of details. Are these just shells or 
>intact organisms scallops? The report says, in part, "They discovered the 
>shells' shape and chemical makeup neutralizes pH and also helps filter out 
>coliform bacteria, sediment and heavy metals." (Emphasis added).
>
>Anyone have any insights?

I can't get the web-link to work. However, what you've quoted sounds just 
like the low-tech biological filters we built many years ago when I was 
setting up low-budget public marine aquarium attractions in Wales. We would 
fill large tanks either with crushed cockle-shell or with "3/4-inch" 
limestone gravel and pump seawater in through a network of perforated pipes 
at the bottom of the gravel. The water flowed slowly upwards then out 
through an overflow pipe at the top.

It's an amazingly simple and beneficial setup for improving the quality of 
aquarium water on a large scale. The more irregular the shape of the gravel 
or shell particles, the greater the surface area: that's the most important 
factor. After running for a week or so, a sticky biological film of 
bacteria and other bugs forms on all the surfaces in contact with the 
moving water. The treatment works biologically, physically and chemically.

In biological filtration, denitrifying bacteria feed on toxic ammonia 
excreted by fish and other water creatures, converting it to less toxic 
nitrates.

Physical filtration happened, I used to reckon, partly because of millions 
of tiny 'eddies' among the bits of gravel where suspended silt and organic 
particles could settle, and partly because of the stickiness of the 
gravel's biological coating. Physical filtration only worked well when the 
flow-rate was slow enough, but not so slow that oxygen levels dropped too 
low to support our beneficial bacteria before reaching the surface. The 
filtration was incredibly efficient, though. Muddy, opaque water quickly 
became crystal clear. While I was a postgraduate student, we set up a 
filter using a plastic rubbish-bin full of coarse beach sand and were 
staggered to find that it effectively removed almost all suspended bacteria 
from the water.

Chemically, the benefit of using shell or limestone gravel was the 
neutralising effect of the calcium carbonate on old aquarium water which 
normally tends to become too acid.

I don't know about removal of heavy metals. I guess it's some kind of 
'adsorption' process onto the huge surface area of organic material. 
Periodically, to keep the physical filtration effective, you have to dig in 
and flush out the thick soup of mud that collects in the gravel, so that 
would probably remove accumulating heavy metals. This was a long, filthy 
job that we always seemed to do on freezing cold winter days...


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