Septic Tank Gauge

[Seagoon]

Those of us living in rural areas are often all too familiar with the problem of getting sh*t to flow downhill. Generally there is some kind of holding tank near (but not too near) the house. All the household waste water + contents drains into the tank. In simple installations it just sits there until someone comes to pump it out and take it away. If one has a "septic field" in addition to the tank, an outlet pipe from near the top of the tank will allow water to travel slightly further downhill into a perforated pipe buried in a gravel bed buried in the soil. Bacterial action will eventually convert quite a lot of the solid matter into liquid which drains out in this manner. The remaining solids sink and accumulate. There comes a point when the level of solids reaches the outlet pipe, and then one runs the risk of plugging up the perforated pipe in the gravel bed, which necessitates digging the whole mess up at great expense and considerable inconvenience. However, cleaning out the tank too often screws up the bacteria which do the solid-to-liquid breakdown; in fact, when they pump out the tank they always leave a little sediment to get the process going again.

What would be very useful to know is the level of the sediment relative to the outlet pipe. Ideally one would not have to open the tank for this purpose.

An alarm ("you're getting close!") would be good. A gauge which could be probed from time to time (say, every few months) might be better.

I own many clothes pegs and am willing to conduct limited sampling and testing experiments.

This is NOT a joke, and date is NOT April 1st, just for the record

[rickj]

This has a lot in common with the Open Automatic Tank Gauge, which was raised as a reddit topic recently.

We need two things, a depth gauge to detect the amount of fluid in the tank, and a reporting mechanism.

The depth gauge can be readily implemented with ultrasonics. This may be adversely affected by foam floating on the surface, if that is something which may happen. Perhaps septic-tank owners with strong stomachs could sneak a peek, and let me know. If there is often foam, we need a different principle - perhaps RF measurement.

It may be neccesary to rate this as a Class 1 Zone 2 hazardous environment, since I would imagine there is sometimes methane in the tank, in which case we have all the usual certification hassles (which add to development costs). I have no idea how certification for a hazardous environment interacts with open-source hardware, but I'll find out and post the answer.

Reporting is easy if the septic tank is within wi-fi range of the dwelling. It can send a signal from time to time to say it is alive, and email a warning as the tank becomes full enough to justify a pump-out. If it is out of range, you may have to stroll by with your Bluetooth-enabled laptop once a month and interrogate it. Probably still more fun than uncapping the tank and wielding a dipstick. Would a few septic-tank equipped laptop users wander out to the tank top and report if the wi-fi works?

Battery life is going to be the big design criterion here. Ideally, you should not need to replace the battery between pumpings. How often do people pump their tanks?

[Seagoon]

The frequency of pump-outs is usually measured in years - say, 2 to 4. It depends a lot on how many people are making use of it, how big the tank is, and whether or not there is a septic field. I want to stress that a septic field system does not need to be pumped out until the level of more-or-less solids nears the outlet pipe, so it is not just a fluid level gauge that is needed.

As for a power source, and given the infrequent need to test the level, I wondered whether it is possible to supply power externally (e.g. inductively) as needed, or do something really clever with the heat generated by the bacterial action. In the winter you can readily spot the septic tank by the lack of overlying snow.

[rickj]

It seems that the determination of the need to pump is predicated on both the level of sludge in the base of the tank, and the level of scum at the top, with the total depth remaining pretty much unchanged in normal operation. A good deal of detail is given at: http://inspectapedia.com/septic/Septic_ ... ements.htm.

There seems to be at least one gauge on the market which measures these variables, http://www.atsgreasewatch.com/Home/FeaturedProducts. Does this meet your needs?

[Seagoon]

The ATS Greasewatch monitor would certainly do what I want - and then a whole lot more! It sounds like it is designed for much larger installations than mine, probably of a commercial nature. Probably beyond my budget, or that of most of the people I can think of who might otherwise be interested. If it were possible to do something in the <$350 price range I think that might catch on.

[rickj]

So the challenge is to duplicate the functionality of the ATS device at a much lower price. I'm not clear on which features we might get away with deleting, and which must be retained. Can you be a bit more explicit?

[hso]

The frequency of pump-outs is usually measured in years - say, 2 to 4.

I have a tank where the pump-outs is usually measured in hours - say, 4 to 8.
I do not need a battery in the tank. I can use a cable. (12V / 24V) If we use 12V, its' possible to run it on a cheap car battery, probaly for a long time.

[rickj]

As soon as a cable is a possibility we can run low-voltage power from any source on the cable, even mains-derived power. If the pump-out time is only hours, you will need frequent readings, perhaps every 15 minutes or so. This will mean greater power consumption. In a case where the time is in years, weekly readings should be adequate, and a small battery may well suffice.

[rickj]

On further thought, I wonder if we have an ambiguity in terminology here.

Seagoon is using "Pump Out" to mean intervention by a truck-mounted set of equipment to remove the scum, and the bulk of the sediment, perhaps leaving a little sediment to re-establish appropriate bacteria.

I'm hard put to believe that hso has this done every four hours. Could it be that in hso's case, we are referring to the removal of the liquid portion of the tank content to the septic field?

[hso]

I use the " Septic Tank" as a short storage tank, before it get moved to anoter location. I do have a system to day that start and stops the pump. I wold like to add anoter system that is separate from the current, to give me some indications / correction on the other system.