City Sewage and Food Supplies, as a combined topic


Yes and no, but i agree with your point. The problem with combining it all into one pipe is the different chemistry and physical characteristics. Even the sink flows could be considered black, but there’s the same reasons to not mix sink flow: it’s chemistry is likely to include many different cleansers and an assortment of slime molds from inside the (kitchen) pipes. Evaporation/distillation will go a long way towards cleaning up the liquid flow (containing fats, oils, detergents, etc) from sinks and showers, but i am at a loss for where the power would come from for heat sterilizing it (but if you have the heat, by all means use it here). By keeping the solids separate at the toilet, at least that portion is simplified, if for no other reasons than it’s a much smaller “waste” stream, and putting solids into a distiller isn’t going to recover purified solids.


would echo this. Cruise ships use a curious vacuum type system. And every cruise I’m on, there is some major repair going on because someone put something wrong into the toilet.

People don’t do what you expect. It would be good to anticipate that this is not survivor island, but a city of diverse people some of whom may have some unusual habits.


Granted. And be passing different medicines, and have different diseases.

On the other paw, the family-stead is likely not going to invest a ton of floatie-space and capital expenditure into a complicated system. I expect to go with small, easily repairs, no storage of “waste” past 48hours, and if i need to spend $1 per day on propane or diesel, i will. Or maybe i’ll cook over dehydrated seaweed, or a solar dish.


Matter of scale and end use. Most home-scale biogas is not scrubbed, or compressed, just used for cooking. Heat added can be solar. Thermophilic temps are body temperature with maybe a mild fever. Remember, a digester is basically an artificial stomach.
Probably the smallest simple and effective digester size is a 55 gallon plastic drum. A thermophilic digester will process faster and more efficiently, than a cold one, produces methane at a faster rate, and may even require a smaller capacity.
Also, remember, if you’re growing vegetables, the waste from those harvested plants should be ground-up, and go back into the system. When cleaning fish, the internal parts not consumed can be ground up and put into the system If you have a pet, its’ waste can go into the system. Almost anything that can be used as food, even if it’s fishing bait, can be digested. Paper is plant fiber.
One thing for certain, we don’t want to just dump untreated waste into the water around the seastead.
As for the diaper comment, The old way, when I was I kid, was to flush the part that would flush and then machine-wash.
I did include a separate aerobic system for the sink/shower water. Aerobics use chlorination (usually a/c electricity and a salt-brine addition), then waste is typically either filtered and reused, sent to a drain-field to filter back into the soil, or sprayed onto yards. Sprinkler is getting to be the most common method of disposal. If it isn’t safe enough to filter and reuse, it wouldn’t be safe enough to spray on a yard, where the whole family, the neighbors and all are potentially exposed.

How well you process waste is going to affect your environment. The cleaner the output, the cleaner your environment. Do you want to swim where you flushed the toilet? Would you want to fish there?

Incinerating toilets still create ash, which is alkaline, so now, dumping ash makes caustic lye, and alters the pH of the water you’re swimming and fishing in, plus you have ~85% of the liquid to treat and deal with, plus you’ve destroyed the mineral value. By dumping waste, you’ve lost mineral value and polluted the environment.

The system can certainly be simplified, for other scenarios, but, at city scale, waste management is going to HAVE to be a priority.

HOW complete is my system? As complete as I have thought through. Perhaps there is more that can be added…

Think of it as a space colony. The only thing you can do is import all your supplies and dump all waste, carry all supplies and dump waste, or take some supplies, recycle and provide a constant resupply. The better the system recycles, the less chance of a buildup of waste and the less space you have to dedicate to storing either future supplies, or toxic wastes.


Scale: The system I’ve described CAN be scaled for a family-sized unit, or maybe each block has its’ own central waste management and grow-dome system. Then we have decentralized waste management, decentralized food production, and fewer interconnections between platforms, also meaning fewer connections that can break, or leak, polluting the environment. Apartment/condo-scale structures will certainly need some form of central waste handling. My concept uses minimal storage, makes the most of mineral resources and recycles them. Purified Methane can be used as a heat source, whether it is for warmth, cooking, hot-water, or a backup generator, or other motorized process.

I’m not saying my way is best, or even perfect, but I don’t want the water at my location to be a cesspool, or toxic waste dump, and I want to be as self-sufficient as possible.

(Larry G) #93

7 tanks is pretty arbitrary- you’re thinking one per day? There’s no need for that. You’re correct in believing that you don’t want to directly empty the in-use system (“A” Tank) onto your plants while it is still in use. You want a period of time of anaerobic digestion to kill all pathogens with a set minim exposure period to minimum average heat.

So you want to use tank A for x period of time, switch to tank B while A finishes digestion for those safe minimums before emptying. Periodicity of that is flexible. A doesn’t have to be emptied until B is nearly full, so for example if it takes you a month to fill a tank, you get a month of non-use of the other tank for overkill. The first deposit in tank A will be two months old and the last deposit will be nearly a month old before you empty it, and the process goes faster the more mature the culture inside becomes.

I would personally want to size it to not have to empty a tank more often than every 6 months. I haven’t read or done experiments on exactly how long it continues to produce biogas (which will also obviously vary somewhat depending on feed stocks, more cellulose equals more biogas for longer) after you stop the waste deposits. To gain the maximum benefit of biogas production you would want to keep it working even after you have sterilized all pathogens, which generally only takes a few days at a reasonable temperature. You also want the material to be thoroughly composted to gain the max benefit of using it as fertilizer. Even if you stop adding human waste and only add plant material for your second month, it takes time for that material to break down.


Different system than my preferred design, due to expected mobility shaking and stirring. Based off so-called 'dry methane generator system, when a supernatant is used to initially displace the air, then pushed back to the supernatant tank using some of the previously produced biogas. Actually, I was thinking more along the lines of a series of smaller tanks to achieve the goal, based on 2 people, such as my wife and I. All our solid toilet and food waste, per week, should just about fill a 5 gallon container, based on my experience with composting toilet and long-term life in the woods. Each one is allowed to digest until it stops producing significant off-gassing, then goes into an aerated and heated composting phase, before using finished compost elsewhere.

That’s a conceptual idea based on a commercial design that is in use, miniaturized for our motorhome.

There are quite a few different methods for achieving the same goal, but, in the end, a sterile fertilizer is a sterile fertilizer, in my book.


I didn’t run the math, depends on the size of the tanks, how much is going into them, etc etc. So i would need only two large tanks of sewage? [cough] I am staying with the heat sterization alone for now, since i’d insist on heat sterilizing it after biogassing it anyhow. Later, i can add the biodigesters between the input and the heat sterilizer system. It’s all good, building the sterilizer alone now keeps me safe till i can add a biotank (or two).

Advantage of the heat sterilizer alone: if it can heat up a holding tank in an hour to 200F and keep it there for an hour, then it can process at least 12 tanks a day. Depending on storage and reheat space size. And it can do that as long as there is heat input. Meaning for a Drowning Man get together, it’s far more space and money efficient vs a 1000 gallon storage tank, and significantly lighter. Yes, in that scenario, i am assuming you have a baby diesel genny running to keep lights (radar, etc) on at night, and you can periodically tap some power off it. Or grab it’s exhaust pipe for heat.


Well, at 7-10 days per tank for filling, then another 7-10 days of digestion, then 35-50 days of aeration (additional heat from digestion through finishing), the goal is reducing fluid quantities, producing both biogas and sterile, finished compost. compost can be used as compost, or made into compost tea, or however.

Collecting and using solar and other heat is just a matter of doing whatever is appropriate for your situation.


Remember liquid (pending on what it is) can also be used as fertilizer (with treatment). Pee (Urea) makes great fertilizer, I believe it is high in nitrate. Also, since it’s mostly water, why bother wasting said water instead of using it to water crops. No point in wasting water when we don’t need to.


I must have missed this topic before, but I’d just like to say I very much agree with the OP. The TSI concept of building a floating housing estate and importing everything doesn’t seem sustainable to me. Aquaculture and dense hydroponic farms would probably be essential.

It’s been posted above, but by far the cheapest and most efficient waste recycling system I’ve seen before is separated composting toilets. The main reason municipal waste facilities are so expensive and hazardous is because the waste is mixed. If liquid and solid waste are kept separate, and the community is small enough that everything doesn’t have to be moved through pipes, it’s quite easy to produce completely sterile compost from human waste products, especially in a small country.

Alternately, mixed waste biodigesters might provide the answer, I’ve heard wonderful things, but I don’t know enough about them to say.

Another consideration which might have to be taken on board is cleansing. In the west we’re used to toilet paper, but it’s a bulky and expensive import which doesn’t compost or recycle very easily. We may have to give serious consideration to adopting the use of bidets as seen in the Islamic world and a few other regions such as Spain and India. It’s potentially just as clean, saltwater can be used and it would save alot of material imports or expensive manufacturing.


Urine is too concentrated to put directly where plants roots are. Some animal urine will flatout kill plants it touches. It’s got to be diluted, you can’t consider it a water source for plants. Well, maybe an ammonia plant, but that’s a different thread, i think.


It’s not hazardous because waste is mixed with waste, it’s hazardous because non-biodegradeables like paint and other chemicals are mixed with biodegradeables.


Urine is too concentrated to put directly where plants roots are. Some
animal urine will flatout kill plants it touches. It’s got to be
diluted, you can’t consider it a water source for plants. Well, maybe an
ammonia plant, but that’s a different thread, i think.

The solution I’ve heard of in permaculture groups is to filter it through a series of paddys containing hardy species of salt-march reeds. They filter the water and break down the urea. Plus you get reeds out of the bargain for making rope and furniture and paper and such.

It’s not hazardous because waste is mixed with waste, it’s hazardous
because non-biodegradeables like paint and other chemicals are mixed
with biodegradeables.

That too, but excrement mixed with urea creates a more friendly environment for pathogens than separated waste.

(Larry G) #102

Mostly because of the septic tank methodology or because of discharging partially-treated effluent. The mobility of pathogens in ground water is a big part of their spread. The slower the pathogen-containing groundwater moves, the less likely it is to spread viable pathogens.

They also usually age it. As the urea breaks down it forms some ammonia which evaporates. The aged urine can then be diluted and used for watering. There are other uses for urine in tradition crafts as well. The fact that it gives you ammonia and nitrogen compounds more or less for free (the cost of keeping it in a container) is a bonus. But you have to keep it separate from other waste for this.

(Larry G) #103

Bidets are a good solution but I’ve been over a good part of the the Islamic region of the world and only seen a couple bidets. More in Europe than the middle east. Most of the Islamic world has a trough in the floor with a filthy pull rope on an old-school wall-hanging water closet tank, if they are even that advanced. Outside of some expensive hotels in Dubai I haven’t seen much other than that.


I know it is too concentrated, and yeah, you got to dilute it. The point I was trying to make there was that we shouldn’t mix it with solid waste, treat it, suck the water out of it, and use it as fertilizer when we can just dilute the piss and use that (with treatment if need be). I just forgot to mention diluting it.

(Larry G) #105

I just contacted a few people on Criag’s List that had posted tanks of the appropriate types for me to set up a digester.

We’ll see what kind of deal I can get on one or two. So far it looks favourable to get something in the 200 to 1000 gallon range for under $500.


Ok, you confused me when you said these two lines:

The first line seems to say “use pee instead of water for plant irrigation, to save water”, but the 2nd line says “use water to dilute the pee first”. Naturally, for irrigation you’d use more water than pee, it’s like gallons of water vs a cup of pee, so any water savings is insignificant, near as i can tell. So i am still unclear what you are trying to tell us about the pee. I mean other than for the humans to deposit it into a separate recovery location, which i agree would be a good thing.


I figured those 40gal - 50gal drums that go for $10 on ebay would work? Is there an optomised drum type for use as a digester? I ask because i am currently getting educated separately on methane generators, and considering the use of assorted tanks -vs- 3" pvc -vs- 2" abs.