14 replies to this topic

[TheArchitect]

Hello all, I'm new to these forums and I hoped that someone smarter than me could help me with an eco-engineering issue.

I've been designing an off-grid home for the last few months, and I mean ENTIRELY off-grid. It produces its own water, electricity, and food, and it recycles everything in a nearly closed system for maximum efficiency. I'm currently designing the waste-recycling system, and this is where the problem starts.

The house is underground, and it contains a dedicated section for growing food and plants that can be processed on-site into various necessary consumables by means of aeroponics. I've read about composting toilets, and since the house is designed to be almost entirely independent of any external commercial input I can't buy nutrient solution. I would like to compost the organic and human waste from the inhabitants into the needed nutrients for the aeroponics farm, but I'm unsure of how to do this effectively. The system must be continuous and fairly rapid, ensuring a constant supply of nutrients to the plants. It must be mechanically simple and low-energy if possible. It must be absolutely clean, and ideally low-maintenance.

So far, a vacuum pulls solud waste from the toilet into a holding chamber. Effluent and filtrate from the house water filter (which includes urea from filtered wastewater), kitchen scraps, and other organic wastes also exits into this tank. Once the tank is reaching capacity, the collected waste is released into some sort of digester to produce compost. My thoughts beyond this are vague and uncertain. Does anyone know of methods that could satisfy the above criteria, in whole or in part? My research has led me down dead ends.

[Shortpoet-GTD]

First off-welcome to the forums-
Second; these links might help.

http://www.motherear...x#axzz32pNu8lpL

http://www.npr.org/b...ted-human-waste

http://news.national...ost-fertilizer/

[Dustoffer]

I built my independent Earthship 16 to 14 years ago.  It has rainwater catchment and tank, solar electricity, a 12VDC pump, compost toilet, and real dirt gardens that will accept the compost.  There is a big problem with closing it entirely, because the humidity buildup has caused the need for painting with mildew resistant paint, and gotten through the seals on insulated tempered glass large windows. It also has rusted out the flue of my backup wood stove, and still ruined paint in some areas.
Hydroponics are a nice thought but not close to natural, and do not get necessary micro-nutrients that come with healthy soil.
Even my interior gardens are composters with fungi, nematodes and several kinds of worms.  The outdoor composters have compost mix, a compost turner, and the two hold around 250 gallons of compost.  This gets mixed with garden soils when it is fully composted.
The main problem is in winter, when venting loses too much solar thermal gain.  Then the humidity is 80 to 90%.  When I can vent, it goes down to 40%.  The high humidity is hard on amps and speakers, and makes my guitar necks sticky.  There also has been fights with aphids and white flies, that cost plenty to get rid of in this partially buried  greenhouse.
About the only thing for hydroponics possible is a worm composter where you add the worm excrement to the hydroponic water with the regular fertilizer mix.
Once your tank is full of human waste, it will be too late to be able to use it again until the waste is composted.  It could have been like a regular septic system with Rid-X or the like added monthly and a leach field to take the treated water and hopefully it will go down to an aquifer.  The "white water" system can go to regular ground water, or be filtered more and re-used.
The composters can work in as little as 6 weeks in summer to a whole year.  Sounds like yours will take a couple years.
Mike Reynolds developed systems of interior swamplands to close up the system, plus he designed solar toilets that cook the stuff to grit and powder that can be used for added minerals in soil.  It depends on your interior heat, solar input, or ability to get rid of the excess interior humidity by venting or dehumidifier.
The gross part is transferring untreated sewage to a compost system.

[TheArchitect]

The system is two-tank, one for collection and one for processing. It's the processing step that's driving me up the wall.

I guess a better question is: how do I grow enough food to feed two people give or take in a small space with minimum resources? The reason I originally went with the aeroponics idea was because it satisfied those requirements. The issue was how to get sufficient nutrients to grow the plants without commercial mix, since the home is off-grid (in the additional sense of being independent of commercial systems beyond the point of construction). The home is entirely underground, not partially buried like some earthships. This is due partly to the lovely energy savings of an entirely buried home, but mostly it's for reasons of survival. I designed the thing as part eco-home, part apocalypse shelter. I probably should have mentioned that to begin with :P

So if aeroponics is out, is there a way to grow food under those conditions, to the criteria stated above? If not, is there a way to recycle waste into plant nutrient suitable for aeroponics applications?

[Dustoffer]

You must be in a warm place to have a decent underground temperature.  In my experience of Earthship piloting for 14 years, it would take at least 200 sq. ft. of garden per person.  You will have to put out for more power for dehumidifier use.  You must have a drain for black water, or system flush or overflow.  With 12" annual rainfall you would need 1500 square feet of rainwater catchment per person.
With double/half.  Black water is from detergent and grease buildup.  Basically you have to design in two drain systems along with the catchment system.   There has to be an outlet for black water to a septic system, at least to be legal in most places.
Living entirely underground is not good for plants without grow lights.  They work, but the scale would cost too much when you can build a greenhouse large enough for two (about 20 x 60).
There was an old book I've got "Five Acres and Independence".   Best bet is to compost on the surface and not in your underground house, same with gardens which of course will need a water system.
Have a 5 gallon pail emergency toilet in the house and empty it into the composter often.  Don't try to grow underground, and then you also won't need a dehumidifier.
It would take a huge nuclear powered underground fortress with aquifer and grow rooms to last past 2020 to mid century.  Even then, the surface will not be good to live on for some time, probably in the millions of years.

[TheArchitect]

My home is designed for desert use, to be built in the Middle of Nowhere. Power isn't an issue (solar in the Mojave desert is the energy equivalent of a firehose), but all water is recycled -- that includes urine from the toilet, moisture pulled out of the air by the house atmospherics (dehumidifier) from human breath, and all graywater (sink, shower, etc). Water collection is achieved by means of dew basins (an experimental design based on micro-textured alternating hydrophilic and hydrophobic surfaces), monsoon-season rainwater catchment, and atmospheric water generators based on a new type of ferroelectric polymer that allows for energy-efficient refrigeration without a heat-pump. I haven't had time to run the math yet, but water should not be a huge issue considering the efficiency of the recycling systems and AWG. Even in the deserts near Pakistan, there's at least 800 liters of water per cubic kilometer of air.

As far as growing underground vs. the surface, the desert environment makes farming the surface impractical. The aeroponics system is far more water-efficient than hydroponics, and the use of recycling tech makes it even better. It also allows for excellent use of space - certainly enough to feed a single vegan using the ~907 sqaure feet available in the growing environment. Grains might prove tricky, though, so you may have a point.

Either way, the question of how to feed the things is the problem. I need a time-efficient method to turn waste (human feces, compounds from urine, grease/oils, simple soaps, and organic matter from kitchen scraps) into usable nutrient. Due to the totally subterranean design, growing underground is a must, and so far aeroponics looks to be the only even partly viable option for this application.

[Shortpoet-GTD]

Did any of those links I posted help, or where they too general?

[TheArchitect]

I've actually seen all three before, while I was googling for information on this subject. They were helpful, though. The peecycling thing was the reason I re-designed the water filter for the house to slough off filtrate into the waste recycling tank instead of some other method of disposal; urine is filtered after it is separated at the source and back into water, and the compounds left behind (as the link proves) are a valuable source of many plant nutrients.

I've been doing more research, and I'm still stumped. A biological process would be ideal because it's stable, robust, and efficient, but I'm having trouble constructing one that is time and resource-efficient. The current design is to compost the waste materials at 140 degrees with ventillation and mechanical aeration in a large secondary tank, then leach any remaining moisture out of the mix and finely powder it, dissolving it in calculated amounts into the nutrient tank's water supply for the aeroponics system. But that process is whole-hog, and there isn't time for a lengthy wait between fertilizing cycles. I need some way to constantly process excrement and organic wastes into small amounts of usable nutrient on a constant and consistent basis. The only real upside to the first method is a gauranteed store of nutrient, since the size of each batch would be several times that necessary to fertilize the system. However, are there other sources of nutrients in this setup? that is, the house is built in the middle of the desert. Are there any other ways to obtain sufficient nutrients, in addition to the recycling of waste (if such a recycling system can be designed at all)?

[Shortpoet-GTD]

I don't beans about it but I would suggest herbs, spices and other natural substances.

Maybe not what you're talking about but when I was a kid (872 years ago- ) we had a septic system.
My Pop would drop in yeast cakes (about the size of a pack of cigarettes) into the tank but I can't
remember the time line-weekly, monthly?
Point being, the natural process may be the way to investigate it. Also plants.
Algae?
http://www.fitday.co...nd-facts.html#b

You'll have to put the words into the search box but try these site's too.
http://www.bobvila.com/find-info

http://www.motherearthnews.com/

Let us know how it's going because when you get the answer's, we can share it with
social media so they can use it too.

[TheArchitect]

I've read before about the use of various plants and algae to process waste -- and it's promising. In fact, it pretty much fits all my criteria, minus the fact that I'm not sure how to go about it. The problem is that I need a way to continuously break down waste, rather than in batches. Space is also an issue, as you may imagine. Ideally, I would use something vertical that's less than 9ft tall.

I suppose one could use separate chambers -- one for new waste, where it is treated aggressively by one class of micro-organisms to break down inorganics and soaps/oils/greases, one below that for further breakdown into usable nutrient, and some sort of mixing and pumping aparatus below that to move it all into the aeroponics plumbing. But the question then is how to move the nutrients by gravity or some other non-energy means between processing tanks. Hmmm.

The other problem is how to control nutrient amounts, but that can be taken care of by some careful math and a flow regulator. I'm having trouble coming up with data on this method of water treatment, oddly enough. I'll try popular science, I know they featured something similar several times in years past. Bless those tireless archivists.

[TheArchitect]

I found an article on geobacter -- a species that can break down oil and stuff like plutonium and produce electric current in the process. Here's my thought: a mutli-stage bioreactor. First stage is rapid aerobic decomposition similar to composting, second stage is to release usable compounds into solution, and third stage is anaerobic with geobacter and others that take care of whatever inorganics and such couldn't be broken down by the others. The problem is how to get the end products of each stage into the next without contamination, and how to make the process continuous. Maybe using some kind of media that absorbs only the end products, allowing them to pass into the next stage? I'd need some kind of mechanism to filter out oils, metals, and complex stuff like pharmaceuticals out of the collection tank so that they don't poison the cultures and divert them to stage 3. The good news is, if it can be done, the various cooperating species of geobacter may be able to generate power enough to offset the energy needed to keep the aerobic stages under favorable conditions. That would be something. Most of these bacterial processes create CO2 as a by-product, which could even be captured and piped into the growhouse to feed the plants. One might have to wear an oxygen mask when working in the growhouse, though, if that was the case.

I'd link to the geobacter article, but my browser is being finicky with copy and paste right now. I'll put up a link when that's fixed.

[TheArchitect]

Okay, I think I'm on to something. A culture of geobacter and methanosatea will produce electricity and methane, the latter being burned to produce more electricity (perhaps by heating a stirling engine?). The problem is where to place it. I could have a single tank, with geobacter and friends co-existing in oxygenated water with aerobic bacteria to break down waste efficiently -- but if I remember 10th-grade biology correctly, the aerobic organisms would out-compete the anaerobes and the system wouldn't work. A single chamber would be nice, but I can't see how to do it. The problem with a multi-stage is that it proves difficult to transfer the result of one to the other. Of course, this is a problem with the single-stage setup, too. How do I get the resulting nutrients to the plants? If an anaerobic culture could exist alongside an aerobic one, there's still the issue of their by-products, which tend to be toxic to plants (i.e. hydrogen sulfide, though preliminary research suggests that a second species of geobacter that breaks down sulfur compounds would mitigate this). Perhaps a third species could be used to mediate the waste products of the anaerobes? All of this is more microbiology than eco-engineering, but if anyone has a thought on the single-stage idea outlined above I'd be happy to hear it. I'm stumped beyond this point.

[Dustoffer]

The interior wetlands is outlined and directions for building in Reynold's "Earthship III".  Bio-reactor kits are available from  RealGoods.com and are in the "Solar Living Source Book", by them.  
If you want to just treat your tank and it is well vented, just pour in Rid-X or similar in enough quantity to totally break down the sewage which then can be pumped out to a leach field.  You can replace the toilet with a Biolet NE like I've got, or other brand of compost toilet, with or without power venting.

[TheArchitect]

As far as toilets go, I'm using a custom squat design. The bathroom is very small, so the toilet is in the middle of the room and the floor slopes towards it, allowing liquid to drain. It's recessed about an inch into the floor, and when not in use a slotted bamboo frame forms the floor of the shower above it. Water just drains through the toilet. Waste drops into a finely perforated vestibule, which allows liquids to drain into the collection tank for filtering into pure water. If there are solids, one simply pulls a lever which opens a valve, exposing the vestibule to the vacuum in the collection unit. Goodbye waste, and no water necessary. I set up a bidet hose instead of toilet paper, since the water is recycled and toilet paper is difficult to come by in a house in the middle of the Mojave. The problem is that if a vacuum is maintained in the pipes and collection chamber, it would present a problem for aerobic breakdown. I'm thinking of using something similar to an Envirolet, where the vacuum is on-demand and shreds waste as it passes through the unit, passing it along to the bioreactor.

Thanks for the info on the bioreactor, I'll definitely check that out. As it stands, if I can figure out a single-tank method to continuously produce nutrients for the plants, I'll be set. If I can incorporate geobacter into the process, it could even handle more complex compounds and produce power in the process. The idea I talked about in my above post concerning geobacter with a methane producer got scrapped when I remembered that burning methane produces CO2. Now I'm trying to think of ways to turn the CO2 into oxygen. I could use an algae mat or similar at the top of the tank; that could work. But the algae would end up feeding off the nutrients released from the aerobic breakdown process, which would defeat the purpose. Still, it's a thought. I like the idea of using geobacter for the above reasons, but it produces CO2 as a by-product. Must figure out a way to turn that into something more useful.

I'll keep researching. In the mean time, does anyone have any thoughts on the process I just outlined? A single tank, with both aerobic and anaerobic decomposition? Is that even possible? Common sense says otherwise, but I feel that there must be a way to do it.

[Shortpoet-GTD]

For readers that don't know much about this subject, a few info sites.

(6 pages)
http://home.howstuff.../aeroponics.htm

http://books.google....toilets&f=false