happy new year, everyone.   ...

happy new year, everyone.

 slow sand filters would work really well.

if you do an up flow one, it will also help denitrify.  

you will need to back wash from time to time.  but you can use air to back wash.  the up flow ones

so you will need two lines.

also you want the biofilm.  and if it clogs, thats the time you till it in.  in a low wage country like india.  it should work out well.  ( this is the down flow one.)

the biofilm can come in different colors.  from red, to yellow to green.  And sure in the down flow ones, you can see worms develop from helminth eggs.  but the water at the end will be clean.   sure, you will find all sorts of worms and insects feasting on the biolfilm.  

for a small one, all you need is a rake to till it down.  kill the worms, its okay.  they are nematodes.  

20 years ago, I built one for a city for their drinking water.  land was cheaper then.

the main advantages is that, it world real well and opex is real low.  and its very good in disinfecting.  better than uv, chlorine or ozone.  

disadvantage is it takes a lot more space.  there will be no odor.  

one more thing.  you want large grains of sand.  more than 1 mm.

and you may want a mix of pea  gravel and sand bed.  pea gravel is another wonderful medium.  

good luck.