Pause Period (idle Time)
Idle time typically accounts for greater than 80% of the daily cycle whereupon various microbial attenuation processes are likely to be significant. In other words, most removal occurs during the point where water is in contact with the biofilm (also referred to as schmutzdecke). Unfortunately the exact processes that occur in the biofilm have not been identified and require further study.
When the standing water layer reaches the same height as the outlet tube, the flow stops. Ideally, this should be at a level that is high enough to keep the biofilm in the sand layer wet, but also allow oxygen from the air to diffuse through the standing water to the biolayer.
The pause period allows time for microorganisms in the biolayer to consume the pathogens and nutrients in the water. The flow rate through the filter is restored as they are consumed. If the pause period is too long, the biolayer will eventually consume all of the pathogens and nutrients and die off. This will reduce the removal efficiency of the filter when it is used again. The pause period should be a minimum of 1 hour after the water has stopped flowing up to a maximum of 48 hours.
Pathogens in the non-biological zone die off due to the lack of nutrients and oxygen.
Read more about this topic: Bio Sand Filter, Filtration Process
Famous quotes containing the words pause and/or period:
“O, my offense is rank, it smells to heaven;
It hath the primal eldest curse upon ‘t,
A brother’s murder. Pray can I not,
Though inclination be as sharp as will;
My stronger guilt defeats my strong intent,
And like a man to double business bound
I stand in pause where I shall first begin,
And both neglect. What if this cursed hand
Were thicker than itself with brother’s blood,
Is there not rain enough in the sweet heavens
To wash it white as snow?”
—William Shakespeare (1564–1616)
“Stupid word, that. Period. In America it means “full stop” like in punctuation. That’s stupid as well. A period isn’t a full stop. It’s a new beginning. I don’t mean all that creativity, life-giving force, earth-mother stuff, I mean it’s a new beginning to the month, relief that you’re not pregnant, when you don’t have to have a child.”
—Michelene Wandor (b. 1940)