Sump Depth and Retention Time

[Burton & Cherstin Sparks]

Does the depth of the sump matter as long as the volume is the same ?  Should the volume of the sump be based on retention time?

The reason I'm asking is because in my climate we can get to about -50F (-45C) with windchill, so the plan is to bury the system under a greenhouse and include the warm greywater to keep the temperature high enough for the worms, but when the inlet is already several feet down the hole you have to dig can get pretty deep.  A shallower sump would reduce how deep we'd need to dig.  The thought was to keep the same volume as a 55gallon (208L) drum but spread it over a wide area.

PS. To avoid the risk of flooding the worms I'll have a large diameter emergency overflow pipe above the surge capacity that passively routes to subsurface infiltration chambers downhill, since I'll need subsurface discharge for winter anyways.

[Dean Satchell]

What is the purpose of your sump? Is it the primary digester sump? If so, divide the volume into what is above equilibrium water level and the water volume at equilibrium water level. With an overflow pipe surge capacity isn't as important, but its good to have as dealing with overflow effluent isn't desirable. If you are using the sump to settle fine solids it will need sufficient volume to slow the water flow through it. A diagram would be useful... a sump mightn't be necessary.

Cheers

Dean

[Burton & Cherstin Sparks]

Dean,

Sorry for the delay.  I was thinking the overflow would only be needed on the primary sump, and hoping to flatten the primary, secondary, and tertiary sumps (less height but same volume if needed).  Here is a notional diagram.  Except for the solar panels, the entire system would be installed in an underground room.  The goal is to have surface discharge quality after a tertiary vermifilter.

Burton

[Dean Satchell]

Hi Burton,

I don't see why you can't flatten the sumps. You'd want to save vertical space in the primary vermifilter and primary sump setup. You could have one chamber:

The baskets are raised above the floor of the sump, with sufficient surge capacity provided. If the effluent volume is insufficient there is a risk that sediment will go through into the secondary vermifilter sump and clog the secondary recirculation pump. If the sump is wide and shallow, the primary recirculation pump (which is to pump sediment back into the primary digester) might not pick up that sediment, so perhaps most important will be to have sufficient slope in the sump floor so the sediment settles where your recirculation pump picks up the sediment at the bottom: