Flocculation
Flocc Growth
A Fractal Process
So what we have at the moment are small spheres of joint up polycations floating around in water. What happens next? I could just tell you but first I would like to briefly discuss fractals or fractal structures. In simple terms, fractals are structures that are self-similar. What does this mean. Well, for example,if you were to look at a fractal structure under a microscope you see the same structure as you can see with the naked eye, if you used a more powerful microscope you still see the same structure.
Floccs approximate fractal structures. It is very difficult to look at a photograph of a flocc and tell what size it is. Why? Because of the repeating process in which they are formed. I have already told you what this repeating process (or fractal process) is:
RULE 3: Floccs are formed by a repeating process of spheres attaching to each other forming chains/networks. These chains/networks than curl up on themselves forming a much larger sphere.
The photograph on the front page illustrates this very well and I have repeated it below:
In this photograph (which took me about two years to take, just in case you think this is easy) you can clearly see small spheres, about 30 nm in diameter which have small tendrils sticking out. These tendrils themselves seem to be made up from small spheres about 2-5 nm in diameter. In contrast the 30 nm spheres have formed a much larger sphere of 2 micrometer, of which two have joined together.
The interesting thing here is that scientist have predicted the size of a aluminum polycation to be 1.6 nm. So what you can see in this image all they way from the basic building bloc, the polycation, to almost visible size.
Almost as interesting is that in this image there seem to be particles of about 200-400 nm present. They are not quite dominating the structure but are clearly there. So it can be argued that we have two competing scenarios:
Scenario A:
- 2 nm size
- 30 nm size
- 300 nm size
- 2000 nm size
Scenario B:
- 2 nm size
- 30 nm size
- 2000 nm size
Scenario A sounds like the way things should be, nice and regular, each progression about 10 times larger than the previous one. Scenario B instinctively feels like there is something wrong, there is a size missing. I think that small changes in parameter such as concentrations, temperature and stirring regime regime can cause small changes in each progression and on occasion a situation can exist where a size-range or progression is missing. This may explain the phenomenon that all operators are familiar with, where a plant, for no apparent reason at all all of a sudden has a dramatic reduction in treatment efficiency.