Stormwater/Wastewater 4

[3Hugger]

There is a farmers market which needs to direct the wash water that generated at the end of the day to the sanitary sewer while directing any water from precipitation events to the storm sewer. This needs to be done so as to reduce the burden on the water treatment plant. So far I have come up with a holding tank for the washwater and/or that the sewer lids need to have no gaps and as such need to be manually opened during a storm event or wash down. Thank you for your thoughts on this matter.

 

[Ussuri]

I assume from your posting that the area you washdown is outside and therefore exposed to the elements.

Usually where stormwater is separated there will be two distinct pipe networks, unless you happen to be particulary close to a river.

I would be wary about having a holding tank for your washwater. I would expect this will contain animal faeces (the reason the washwater needs to reach the sewer) and depending on the size and retention time of your tank this will give solids the chance to settle out in the tank.

Your statement about manually opening during a storm event is also a problem. I take it you dont have someone sitting around 24 hours a day waiting for it to rain?

To my way of thinking the simplest way to do it would be to have one network, used for both washwater and rainwater draining to a single point, a manhole say. In the manhole you have one entry and two exits. Each exit has a penstock (manual or hydraulic actuated), one connects to your sewer line the other to your storm water system.

So for day to day when no market is running and night time (default) the flow goes to stormwater. When your market is open and animals are defecating, followed by washdown the flow goes to sewer (you will obviously get some rainwater in the sewer if the market is open and raining, would that be a problem?). You could link the switch over between penstocks to something that happens when the market is being prepared for business (auctioneers lectern, lights, doors, etc) so this does the change automatically.

Alternatively, stick a roof over your market with downpipes.

 

[LHA]

I don't know the site conditions, but if it is feasable, I would look into diverting the washdown water form the site runoff before it enters the system.

Can you run troughs and/or trench drains immediately downgradient of the areas where the animals eat and spend most of their time? These could be fairly small in diameter, staff could probably install themselves. These would go directly into a manhole then to WWTP. I would imagine spot cleaning would suffice in the rest of the areas, where occasionally animals are walked. This (presumably) much larger area could then just rely on conventional pipes and swales to whereever the storm runoff goes.

Then, you don't have to bother with some type of mechanical separation scenario, any of which will have to rely on some type of human or instrumentation control.

Engineering is the practice of the art of science - Steve

 

[bimr]

Ussuri has provided a good post. Put a roof over the market. Drain everything under the roof to the sanitary drain and grade everything else to storm.

 

[blueoak]

Your operation is the biggest selection criteria.

I have seen blocking the stormdrains at the bottom of a manhole and then just pumping to the sanitary (you could even put in switches to automize it (however you have the whole power and safety issues) pretty easy for just a weekly use.

If you can plumb a line to the sanitary from a storm drain manhole they have pretty good switches. For just washing situations you can attach the switch to the hose control so you don't leave the sanitary open to storms. Just as Ussuri stated.

A roof and connection to sanitary is great, but sometimes requires harder to get permits and your sanitary fees may be higher than an "incidental use" type agreement. I think getting most is good, but the assumption that stormdrains aren't filled with animals and birds don't migrate over rivers can be a little difficult to believe.

 

[DazzaNZ]

On our site at work we have an automated system that diverts all of our storm water to our waste-water treatment plant.
This is set-up with a rain gauge so that if there is a rain event it allows the initial rain to flush the system and then diverts the remaining water to stormwater, when the rain stops it remains diverted to allow the ground water to drain away.
If there is a second rain event a short time after the first, it bypasses the flush delay.
The system was put in to prevent spills from contaminating the stormwater.
There is also the ability to prevent the system from diverting to stormwater if a spill occurs during a rain event.
I think that this type of system could be suitable for your application with a simple timer set up to divert the water during market and wash-down
The system is based on the manhole with one in and 2 out and a single control valve, the storm water outlet is higher than the waste water so when you close the valve on the waste the sump fills up and then the water flows to the storm drain, this also has the advantage of trapping sediment which is then flushed to the waste system when the valve reopens.