Membrane filters (1 Viewer)

[annie_sinc]

Could someone please help me.. im a bit confused..

Why is the water made to flow ACROSS the membrane and not THROUGH it? What is the difference??

thanks!

 

[l-mercedes-l]

Hey. i didnt really understand dot point either, so i did some research and heres what i understand it to mean.

Water flows across which prevents the filters getting clogged, nanofiltration can filter as small as 1um so theres going to be lots of stuff in the water thats isnt going to pass through (eg impurities like protozoans, bacteria, etc)

Therefore by the water flowing across the membrane rather than along it something like this happens (see dodge paint picture!) What i think happens is water can diffuse through into the membrane but bigger molecules kind of 'bounce off' which would prevent clogging up.

that is kind of how i understand it but i too am open to others interpretations. theres not very much info on the net that isnt in german or way too deep.

(this is my interpretation, i made the pic up from my head.. dont make the mistake of accepting this as fact. ppl make mistakes and im just a hsc student the same as everyone else!)

 

[serge]

ions wont be filtered out

Could someone please help me.. im a bit confused..

Why is the water made to flow ACROSS the membrane and not THROUGH it? What is the difference??

thanks!

tell us what you mean,
are you talking about the MC in the HSC paper?

 

[annie_sinc]

thanks so much mercedes!! that's really helpful, it's a bit more clearer now. thanks for the paint diagram haha it helped

 

[l-mercedes-l]

Ions wont be filtered out

hmmm no ions wont be filtered out. i meant to write something else but i dont remember what as an example.

*edited post ^*

 

[annie_sinc]

Well my notes say "water is made to flow across the membrane not through it. This reduces the blockage factor". However, I don't really understand the difference between across/through/along ... don't they all mean the same thing!?

 

[serge]

Well my notes say "water is made to flow across the membrane not through it. This reduces the blockage factor". However, I don't really understand the difference between across/through/along ... don't they all mean the same thing!?

some go THROUGH the nanometre thick pores... and then you can blow air
in from the opposite way to clean it, called backflushing

there are a few different types i think...
so ur notes are probably right

 

[l-mercedes-l]

Well my notes say "water is made to flow across the membrane not through it. This reduces the blockage factor". However, I don't really understand the difference between across/through/along ... don't they all mean the same thing!?

wouldnt through be like this
__________________________________________________________
<---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <----
__________________________________________________________
<---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <----
__________________________________________________________
<---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <----
__________________________________________________________

so it could get blocked more easily (key 0=blockage)
__________________________________________________________
______________________0<---- <---- <---- <---- <---- <---- <----
__________________________________________________________
<---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <----
__________________________________________________________
<---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <---- <----
__________________________________________________________

im a visual learner. if i cant see it i dont get it

Across the membrane would be like

/ / / /
l/_ l/_ l/_ l/_
________________________________________________________
<--- <---- <---- <-----
________________________________________________________

(sorry for the dodgy diagrams but weve established paint is not my forte)

 

[serge]

I think blockage is good
its how it filters out bad bacteria

if the point of a filter was to let
water through easily, it wouldnt
filter very much at all?

 

[l-mercedes-l]

but you want water to get thru and other crap to be left outside. if that stays completely out of the filter then all the beter its only going to clog up the tiny pores and make filtering less effiicient.

Serge i dont know if u looked at my dodge paint pic, u mite have an opinion but the more i think about it the more logical it seems

ideas?

 

[serge]

if that stays completely out of the filter then all the beter its only going to clog up the tiny pores and make filtering less effiicient.

its 1 nm thick pore 1 x10^-9 metres thick (probably less cause CC says 0.2nm thick) the picture in CC shows a crazy amount of wirey plastic things

efficiency will be just fine with a few clogged pores, i reckon

until of course you filter a huge amount of dirty water

but membrane filters are tertiary treatments anyway
so when you put tap water through it it'll already be pretty clean

(if the water goes ALONG the filter and the dirty bits get stuck in the pores
thats fine, aslong as the pores filter out the unwanted parts... thats all that matters)