details of Bobs drain field

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rickeldridge
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Joined: Sat Feb 03, 2007 2:16 pm
Location: Orono Maine

details of Bobs drain field

Postby rickeldridge » Mon Feb 05, 2007 6:44 pm

Bob

Your Photo seems to inciate that the water fall from the constructed wetland to the pond. Is the water being pumped back from the pond to the wet land. What are the dimensions of the wetland. As the water fall down throught the garden soil how many layers of of soil/ sand/ gravel does it fall through. What are the detentions times of each of your treatment units? Have you had any sample analyzed for. Does your 5000 gallon sictern remain aerobic??

My inital test bed for an eclogical engineered water recycle system will be an 18'ft saliboat. My water consumption will be 5 gal/day. I'll shower with a misting system to acheive such a small water useage.

Thanks in advance for providing this info

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Bob
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Postby Bob » Tue Feb 06, 2007 5:22 pm

Your Photo seems to inciate that the water fall from the constructed wetland to the pond.

The waterfall is not part of the pond/wetland system. It is part of a secondary system which is primarily aesthetic (a lower pond, not shown, and flowing stream fed by recirc pump in pond), but which can also be used as a secondary redundant system if the first one fails.

Is the water being pumped back from the pond to the wet land.

Yes. But, as noted above, not with the waterfall visible in the picture. A small fractional hp submersible pump in the pond recirculates water from the pond to one end of the root-zone filter.

What are the dimensions of the wetland.

The pond is about 5' diameter. The 'wetland' (more properly, a subsurface flow root-zone filter?) is a lined trench about 16" wide by 12" deep around 1/2 (or a bit more, say closer to 2/3?) the circumference of the pond, filled with pea gravel. The plants include pickerel weed, umbrella palm, dwarf papyrus, duckweed and some grasses. Fish in the pond are my water quality monitors (canaries in the mine).

As the water fall down throught the garden soil how many layers of of soil/ sand/ gravel does it fall through.

Two. The "indoor leachfield" is 12' wide by 30' long with a sloping bottom varying between 4' and 8' depth. It is filled with sand and gravel (pit run) to about 18" from the surface, which is covered with geofabric, and topped with soil. Water from the pond overflows to perforated drain pipe laid in the soil layer.

What are the detentions times of each of your treatment units?

OK. Thinking out loud here.... Average daily flow is < 50 gpd. But it can be as high as 100+ (if, say, run a load of wash, plus dishwasher plus 2 showers, etc.).

The primary treatment unit (current design, anyway) consists of three 55 gal drums, so let's say it holds about 150 gallons. (HRT: avg: 3d, peak flow: 1d)

The pond is about 5' diameter by avg 24' deep, so that's about 40 cu ft, or ~ 300 gallons. Volume of the root-zone is about 5' x 3.416 / 2 x 1 x 1.5 = 12.8 cu ft. Assuming, say, 20% voids in the gravel, lets say it holds about 2.5 x 7.48 ~ 20 gallons (HRT: avg ~6d, peak flow: 3d -- for entire pond/root-zone system)

Volume of the 'leach-field' is 12' x 30' x 6' x ~.1 (a wild guess as to void space?) x 7.48 gal/cu ft ~ 1,600 gallons. (hrt not valid concept for this system, as there is some channelization. Next time, I would replace the pit run gravel with better graded sand, or make other design changes)

Volume of storage cistern is about 5,000 gallons, though depending on rainfall, time of year and usage patterns it is often less than full.

Have you had any sample analyzed for.

Yes. It has consistently tested bacteria-free. In the 20 years we have lived here, the system has evolved. At first we didn't drink the water, using the recycled water for everything but (including washing dishes and brushing teeth, but not actually consuming). Then, as we gained experience and confidence in it, we installed a RO unit at one kitchen sink just for potable water. Then after a few years of that we replaced the RO with a capillary membrane filter (0.35 micron absolute) -- which offers distinct advantages.

Does your 5000 gallon sictern remain aerobic??

I assume so, though I've not checked DO levels. But I bubble air in it continuously. Again, as an ongoing experiment, I have also bubbled ozone through it, though not currently doing so.

My inital test bed for an eclogical engineered water recycle system will be an 18'ft saliboat. My water consumption will be 5 gal/day. I'll shower with a misting system to acheive such a small water useage.

Whoa. Very interesting, but way different from my system, and I'm not sure how well my system parameters would scale. Are you familiar with NASA's CELSS? Probably way more high-tech and complex than what you are after, but maybe some good ideas that could be borrowed.

My first thought would be to enlarge the scope of your question from "How can I convert sewage to drinking water?" to include other things like reducing BOD at the source. If you can avoid putting your shit, piss and food scraps in it in the first place, it becomes a lot easier to treat back to drinking water quality.

rickeldridge
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Joined: Sat Feb 03, 2007 2:16 pm
Location: Orono Maine

Bob thanks for the information

Postby rickeldridge » Wed Feb 07, 2007 9:40 pm

My experieince validates yours concering the cistern. If you're bubbling air through water that clean the D.O. is proably very near saturation. Again thanks for the informantion. By the way to you know how much air your bubbling through the cistern. If your concerned about the energy cost, my experience sugguests the could go from continious to intermittent areation.

What do you do with the sludge that accumulated in the preliminay treatment system?

My experince with scaling activates suldge and fixed film reactor systems is that they scale very well until the less forceful hydraulics associated with low flow changes the influent distribution and reactor hydraulics. Pliot activated sludge reators can be on the order of gallons. Fixed film pilot plants{more akin but not identical to your system} can't be scaled below about 20 gallons.

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Bob
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Postby Bob » Thu Feb 08, 2007 4:33 pm

By the way to you know how much air your bubbling through the cistern. If your concerned about the energy cost, my experience sugguests the could go from continious to intermittent areation.

I don't have the specs at hand, Rick, but it's really small -- a 6-watt aquarium air pump -- just enough flow to keep it moving around a little. At local rates it costs less than $0.02/day to run -- about $5/year.

What do you do with the sludge that accumulated in the preliminay treatment system?

The current system has only been in place since October. So, so far, nothing. I seeded it with sludge taken from the last experiment -- a 150 gal reactor with air-driven RBC which I replaced. It was in place from 1994 -- 2006, and also never *really* cleaned out, though it certainly should have been. It was not a fun job. Here's a screenshot from a slide presentation. The vertical pipes sticking up out of the RBC tank extend to the bottom, and were intended as sludge suction connections.

Image

But in answer to your question, part of the reason for the 55 gal drum design was to make the job easier. Based on previous experience I'm anticipating that it will involve pumping out, say, 50% of the contents of the middle drum, then 2-3 shop-vac-fulls of denser sludge, to be emptied in the flower garden or on/around tree or shrub roots. Maybe once/year, maybe even every 2 years? Don't know, yet.

(I've got a bunch of war stories about how not to do it -- like letting sludge build up under biodek fixed film media until it becomes impermeable to gas bubbles, which then cause it to float until it interferes with the RBC rotation, which then becomes much harder to restart, etc. etc.)
Last edited by Bob on Fri Feb 09, 2007 2:51 pm, edited 1 time in total.

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Bob
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Postby Bob » Thu Feb 08, 2007 4:54 pm

My experince with scaling activates suldge and fixed film reactor systems is that they scale very well until the less forceful hydraulics associated with low flow changes the influent distribution and reactor hydraulics. Pliot activated sludge reators can be on the order of gallons. Fixed film pilot plants{more akin but not identical to your system} can't be scaled below about 20 gallons.

I guess I wasn't thinking so much about scaling per se, but more about the quite different set of design requirements between a house and an 18' sailboat.

How much space do you have aboard for the whole treatment system? And how light would it need to be? (Or is that an issue, with such a small system?) In my (stationary) system I use gravity for settling, but it seems like that too would be out of the question for a boat.

I'm intrigued by your idea, Rick. I hope you will keep us posted.


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