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MBR for domestic greywater

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I found this system almost serendipitously. I just searched “tinyhouse greywater recycle” to see if my own website was being indexed yet, an this caught my eye in the search results. Great… I had previously searched for “membrane bioreactor domestic” etc several times, an this never showed up. And this isn’t the first time this sort of thing has happened. I have officially lost all faith in Google’s supposedly leet ability to find what you are looking for.

Anyway, it’s interesting. They use flat plate modules, and it filters about 600 l per day, apparently. We only need 70 per person, so you can imagine if you divided the system size by 9 it would be a fairly manageable size. Just need to get a hold of one of the membrane modules they use. Maybe you could buy one from them as a spare part….
You would want some polishing with activated carbon and ion exchange resin to use it for showering, of course, and a redundant disinfection stage.

Written by gregor

September 21, 2010 at 14:40

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Greywater recycling system design up at mobile condo

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I like the way discussion sometimes happens in the blogosphere, so in that vein I’m gonna comment on someone else’s post here.

Mobile condo has another post up about a greywater recycling system. This is one of my main interests in this blog, because I think a greywater recycling system could be a substantial step to increase the practicality of tinyhouses.

‘k, so my read of the situation is that their planning on tossing the ozone for the recycling system, because of concerns about it’s toxicity. Sounds about right. More info about this is surely available from OSHA, especially regarding ozone in air, because it’s a common industrial air pollutant. Ozone can be removed from water by activated carbon. I don’t know if it can be removed from air in this way. It might be worth looking into. Ozone is also quite soluble in water, so I don’t know how much would escape from the water tank as the bubbles go through, especially if very small bubbles are used (eg 20 micron seems to be about the bubble size of the “aerator stones” often used in brewing wort and those consumer ozone things for ozonating water, but that might not be practical for a system running all the time, because they can get clogged by mineral scale etc.). Ozone can also be destroyed with UV, I have read about this being done in ozonated water generators, where they want to prevent ozone from being released from the system (ozonated water is used as a disinfectant in industry sometimes).

The amount of gas flow is pretty small, here, too, so a thin tube might work okay as an easy chimney, and it might get diluted satisfactorily fast, maybe worth looking into. Another thing in favor of ozone is that you can smell it well below the toxic level, so as long as you are aware of the hazard it poses, and aren’t lazy about remedying your exposure, it’s not so bad. At least you couldn’t get poisoned without knowing it, unlike e.g. carbon monoxide (unless you were asleep?) I don’t know exactly what it does to you, but damaged lungs are not good…

As I have mentioned elsewhere on this blog, I wonder if the plastic storage tanks etc. would get attacked by the ozone. Surely they would to some degree, but maybe the amount of ozone is small enough it’s not a problem.

Then there is the 0.5 micron carbon filter. This means a carbon block filter
with an nominal pore size of 0.5 micron between the carbon particles. The grain size (of the carbon) and type of the carbon will affect how well it adsorbs various contaminants, as I mentioned in the post about multifiltration (I think?). They are easy to obtain.

These filters tend to clog easily, so there must be some fairly good particle filtration elsewhere and/or experimenting with backflushing it. Also, particles going through the UV filter can shade bacteria from the full effect of the uv, so filtering out the particles real good might be a good idea anyway.

Having previously looked for a UV unit, I couldn’t find any small ones, but they must be available somewhere, certainly “Aerobic treatment systems”, used instead of septic tanks at cottages etc. use them. There are also those whole house units for about $500 a pop, but I don’t know if they would be very reliable.
Certainly they would put out a ton of UV light, as they are made for very high flow rates compared to a system like this, I assume the water would be pumped through the filters here relatively slowly, at several liters per hour, rather than 20 liters per second the whole house UV things are made for.

There is some evidence that UV-treated microorganisms can be re-activated by being exposed to sunlight, so that might be something to watch out for.

If I’m going to be totally honest, here, I have to admit, I would not try this without a residual disinfectant. Especially if the plan is to leave most of the dissolved salts in the water, that’s a lot of stuff, some of which is probably more toxic than chlorine. Biofilms, mold etc. can grow in the water tanks without disinfectant, they don’t need much to grow on. Legionella can grow in the condensate of air conditioners, for instance. It remains to be seen whether and how much digestible material will get through the carbon filter, for the bacteria to grow on, and towards the end of the filter life, how will you know if anything is getting through? They may grow on the plastic of the tanks, too.

Simply leaving the salts (not removed by the carbon filter and not digestible to bacteria) in the water is an interesting approach. You might get quite a few water cycles before the salinity gets annoying. However it also means that heavy metals (as salts) will get through, and accumulate.

At the end of the day, I guess water testing and some experimenting will be the only practical way to get some of these issues worked out.

Written by gregor

September 2, 2010 at 08:00

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Greywater recycling MBR system preliminary design

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Edit: I just realized I should probably explain what MLSS and MBR stand for, since reading all my previous posts might be a bit much. It is Mixed Liquor Suspended Solids, and refers to the amount, in grams, of particulate solids in the water, per liter. MBR stands for membrane bioreactor.
Some experimentation might be a good idea, and testing the water once or twice to make sure everything works as planned, by sending some off to a lab, is also a good idea. This system can, of course be scaled up, but let’s suppose it is made to filter 70 liters per day.

The mlss sensor here could be an optical turbidity sensor, but I chose the continuous level sensor with a long spring attached type.

Okay, now, going with the water flow, the first stage is the surge tank. This should be 80 liters, to accommodate worst case scenarios, and still have some headspace for bubbles to break. Water flows into chamber 1 by gravity of course, and bubbles also escape through the same opening, causing a limited amount of mixing and aeration in the surge tank. This matters because it is preferable that the the storage tank be aerated at least a bit, and there is another aerator foot inside the surge tank for that reason, because the bubbles here might not be enough to aerate the whole tank. Of course that depends partly on the shape of the tank. I’m thinking the tank would be a big piece of water pipe sideways, at a slight slope (which is not shown in the diagram) to ensure water heads toward the entry to chamber 1, even if the system is tilted slightly.

The aerator feet all have manual valves attached so you can adjust the air flow if you find it necessary. Remember, these aerator feet are just plastic tubes with holes poked in them with a thumbtack or something. That’s probably a good size of bubble, though finer bubbles will increase energy efficiency, I figure better to do things the easy way for a first generation prototype like this. BTW, water cannot flow into the aerator feet if the holes are small enough because of capillary forces. Otherwise a check valve on the air line would be a good idea.

The surge tank has the cutoff valve, which cuts off the water flow from the supply tank (which is also not shown in the diagram) to try to make sure that no water can flow out of the faucets etc. when the tank is full. You might make that a float switch instead, and have it turn off the drain valve or something. If there is a dishwasher or something, you need to account for that. You could have sensors in the halfway point of both the surge tank and the clean water storage tank, if the level is ever above the halfway tank in both tanks, the PLC knows there is too much water in the system, more than the 70 liters, and can sound a warning or something.

Okay, next is chamber 1, with the float switch so the plc knows when the surge tank is empty, and it can turn off the pumps etc. to save energy and avoid draining the MBR chambers. The aerator foot might as well be directly against the bottom of the chamber floor here.

Then there is the tube connecting chamber 1 to chamber 2, it passes through the float valve to cut off water flow when the level is too high in chamber 2. That makes sure there is some headspace in chamber 2. More importantly, this ensures that water doesn’t rush into chamber 2 in large quantities, reducing any spikes in the effluent output.

Next there is the MLSS sensor. In this case, there is a baffle nearby to reduce the amount of water flow and turbulence around the sensor, making it a bit easier to get a reading, though you might not need that. The PLC should read this intelligently, taking an average over a period of time, because I bet it would be a pretty noisy signal. As I mentioned, it is a continuous level sensor of some kind, could be through the wall if you want, whatever. The spring could be a stainless steel spring, or rubber, whatever, the more stretchy the material used (how long it can be stretched compared to it’s original length) the higher the sensitivity. Spandex from a sock? Hey it could work. Very small diameter Silastic tubing? You might also be able to use a weight attached in the right way. There might be a spring built into the float sensor that could also provide a force-displacement relationship that could be used.
Basically, the more dense the surrounding fluid is, the more upward force there is on the float sensor. It just has to change position when this happens. It should be able to sense a percent or two change in density.

Next is the membrane module, and the air scouring aerator foot, something I wrote about in a previous post.

Below that there is a baffle. It’s purpose is to reduce water flow and turbulence in the area below, where sludge is supposed to settle. The baffle might have to be more extensive than that, blocking off more of the pipe’s cross section, or you could put this area as a separate chamber. This is one of those discretionary things. Another advantage of a separate sludge settling chamber is that it can double as a pasteurization chamber. I chose to use the flow through pasteurizer, though.

The air output of this chamber goes into the top of the surge tank, so that water droplets have time to settle out a bit before going into the air exhaust line. That’s optional, but it might be a good idea to use a polypropylene air filter, which can withstand getting a bit wet. The air filter should probably be there, in case the MBR malfunctions and anaerobic bacteria grows and gets released out the air line. Aerobic sewage treatment systems don’t seem to filter the air, so this is probably optional.

The “airlift tube” is used to move some of the settled sludge back into the first chamber, which is done when the MLSS in the second chamber gets too low (since the sludge will flow into the second chamber anyway). When air escapes from the aerator, one way to thing of what it does is to reduce the effective density of the fluid in the column, so there is a net buoyancy force acting on the water in the column, and water flows into the column until the pressure at the bottom of the chamber in the airlift tube is the same as the pressure at the bottom of the secondary chamber. That equilibrium should never be achieved, though, because the water + bubbles escape from the top of the column before the height of the fluid in the airlift tube is achieved. How much air flow is required to do the airlifting depends on the bubble size, because small ones rise more slowly relative to the water. I noticed you can get 20 micron stainless steel aerators for aerating wort that would certainly produce plenty small bubbles, but I would be concerned that the holes are so small they might get clogged (mineral scaling might do that). I think just poking some holes with a sewing needle in some plastic tubing should be fine, anyway. A manual valve could be used for fine adjustment, maybe I should have included one, but it is optional, as long as the airflow is sufficient, there is no need to worry about it being excessive (except that the air pump has to be able to provide it.)

Next is the flow sensor, which is used by the plc to monitor the MBR’s performance, slow down the flow if it is too fast, by turning the pump off or down.

Next is the pump. What pump this is, I don’t know, but I have heard that aquarium pumps are usually made from food grade materials. Still, might be better to get a pump made for pumping potable water. The pump should not be capable of exerting too much suction force, or that could damage the membrane. How much exactly depends on the membrane used. You could run a DC pump at lower than the intended voltage or something, just run it off a wall wart.

Next is the sterilizing filter. Sound expensive, but you can get these for $50. There should be redundant disinfection at least, and this counts as one disinfection stage. The UF or MF membrane used in chamber 2 sort of counts, but it’s not a very good disinfection stage, because it will probably get a hole in it at some point, and when it does, the plan is to not fix it (since it will still work fine to filter almost all the sludge out). This can be checked periodically with the bubble point test, probably would have to buy a little hand air pump for that purpose, and keep it nearby the MBR.

Next is multifiltration. I mentioned that in a previous post. Deciding exactly how much of what filter media needs to go in here depends on what the output of the MBR proper is. See my previous post on multifiltration.

Next is ozonation. Again, you need to check this is working by smelling it or something. Don’t inhale too much, though, and the top of the column should be vented outside, for sure. I don’t know if the column and the contact tank after it should be made of metal or glass or something, but it’s probably a good idea. First the water goes into a column, it’s a column so the bubbles of ozone + air have a longish way to travel, ensuring a lot of the ozone is dissolved (though it doesn’t take much, actually). Then it travels through a tube for a while, that’s the contact tank. The ozone needs to be removed, too, which could be by passing it through a GAC filter.
Come to think of it, now, it might be a better idea to have way to ensure no bubbles enter the ozone contact tank, or the air will get around to the gac filter and cause minor malfunction after it accumulates (since it would not readily pass through the gac filter bed).

Last is chlorination, and you might optionally have a remineralization stage, or maybe you could add some salt to the chlorination solution, because demineralized water is fairly corrosive. But maybe there would be no need. I’ll try to put up another post about that later, an easy chlorinator that should be a bit more dependable than the other one I mentioned.

The chlorination could also be using in place of the ozone for the second redundant disinfection, with a few ppm of chlorine and a few liters of contact tank you could kill everything except crypto, but in a homemade system, maybe it wouldn’t do any harm to have the extra assurance of the ozone.

Then it goes to the clean storage tank.

Written by gregor

August 20, 2010 at 05:06

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Basic FO MBR design for greywater recycling

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Okay, so the electrical wiring is not shown here, nor is the disinfecting and clean water storage.

Basically let’s start with following the flow of the water. The water comes in, and the digestion tank is the surge tank, so the water level in the tank changes quite a bit. The float switch lets the programmable logic controller know when the water level is way down there, so it can turn off the water pumps, and that’s the MBR’s empty condition. The reason you can do this sort of thing, is that when the water is removed, the MLSS of course goes way up, and would be too high in a UF MBR, but for FO it is okay. Secondly, there is not really any need for more than one digestion chamber, since the FO membrane keeps 98% of the solutes in the digestion chamber.

The other float valve is to turn off the water flow to the taps and shower if the MBR is full. If there is something like a dishwasher that could dump a lot of water in at once, you’d have to accommodate that somehow, and maybe include an overflow tube.

Then you have the aerator foot. The programmable logic controller (PLC) can turn this on and off by turning the air pump on/off.

Okay, then you have the FO module, as previously discussed. It probably can’t withstand any real pressure differential across it, so the dirty water side and the draw solution side have to be about the same pressure. To accomplish that, the FO module is mounted in it’s own container. If the water level in the container gets too low, clean water gets let in from the clean water supply line. If the level gets too high, it spills over the edge into the digestion area. And then there’s just the recirculation pump to keep dirty water flowing around the membrane module. This could maybe be accomplished with an airlift thing, too, but when the water level is low in the digestion chamber, it’s a fairly high height to airlift to.

The draw solution (DS) side has a similar level regulating mechanism, except there is not really any need to compensate for a water level that is too low because that shouldn’t ever really happen unless there was a leak in the pipes or something, though you could add a float valve if you wanted to. The water gets pumped onto one chamber, flows through the membrane, then into the second. If the level is too high in the second chamber, if overflows in to the buffer chamber.

The buffer chamber has a float switch that could either turn the RO pump on automatically, or could be monitored by the PLC.

You could optionally add some sort of mlss sensor, which tells you when it is time to empty some of the sludge. A fairly small amount of sludge is produced anyway, and control of the mlss is not very critical, so a separate sludge collection chamber is optional. You could just check the mlss manually every couple months with one of those specific gravity things things they use for checking the density of beer, or even visually.

The FO membrane should reject 97% of all sorts of stuff, and the RO membrane will again reject something like 98% of all the different contaminants, so this could end up producing pretty clean water! Any polishing steps could be optional. You should have some sort of chlorination and maybe a way to make extra sure the water is redundantly disinfected, because the RO and FO membranes can get damaged, letting bacteria through. But that would be a separate system.

Anyway, the great thing about this is how wonderfully small it is. It could be 100 liters or something without trying. It would take more power than a UF MBR system, though, no doubt about that.

Written by gregor

August 15, 2010 at 03:41

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Total greywater recycling system (greywater to potable)

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A water recycling system that recycled every last drop of water, or very nearly, at least would be pretty awesome. Of course once you get to the level where water can be added by the rain and the (clean) water can be easily disposed of, there are going to be some diminishing returns. Nevertheless, let’s think about it – it might turn out that it isn’t that much harder to recycle all the water vs most of it.

If it was small enough, you could take it anywhere and still be able to take a shower, do laundry, cook, etc. Off grid power systems are well developed and well known, but off grid water seems to get a lot less attention. The usual approach is just rainwater, maybe with “recycling” some of the water to flush the toilet – so not exactly portable, and requires a pretty big roof (I estimate minimum 60 M2 for a single person in my area).

When I started thinking about this, of course you start reading about it, and there are just so many systems that clean water to various degrees. There’s usually primary, secondary, and tertiary treatment in the context of sewage treatment plants. Tertiary can mean different things in different contexts, but in the context of sewage treatment it means treating it past basic particulate removal (primary), past digesting the material with bacteria to reduce the Biochemical oxygen demand (BOD, sort of a measure of the amount of stuff present that is food to bacteria) (secondary), then removing the nitrogen compounds and some of the phosphorus with more bacterial digestion, or by adding various chemicals to precipitate the phosphorus, flocculate the particles, adjust the PH, disinfect, etc. That’s nowhere near the level where you can drink it, but sewage treatment lingo ends there. Anything beyond that is still a tertiary treatment method.

Then, on the supply side, the legal rules vary for what can and can’t be used in various situations (toilet flushing, irrigation, etc.) depending on where you live. The reality based rules are going to be based, of course, on bacterial and chemical contaminants. In municipal recycling there is a lot of concern that the standards used for deciding how safe water is, and what it would be safe enough to use it for, can’t list every compound known to humankind, and of course toxicology data is pretty scarce for a lot – nay, most – of the compounds in municipal sewage water, that may or may not make it past the various treatment stages. The water standards used right now focus on chemicals that were traditionally found and could pose a risk, in the water, when it came from rivers etc. rather than straight from the sewage lines.

Nevertheless, science certainly has some handle on these contaminants, like personal care products and pharmaceuticals (PCPPs), and like said in a previous post, municipalities can recycle the water if they want to. There are some docs about all this in the archive file. It is mostly the PCPPs and toxic stuff from cleaning solutions and industry etc. that are the big deal. I still need to read up more about this.

Anyway, you can see that at the end on the day, it can make a lot of sense to take a contaminant-based approach, rather than classifying water in broad categories, but it’s just that there are so many different contaminants to consider. Plus, sometimes it makes a lot of sense to say something like “Activated carbon can remove organic compounds pretty effectively”, even though it’s capacity to remove stuff will be different for different organic chemicals, and different types of activated carbon. You can also test for broad categories of stuff much more easily that specific chemicals, and of course saying that sewage is harder to treat and more dangerous and therefore belongs in a different category that greywater makes some sense (though they are more similar that I thought, I can tell you that).

Fortunately, things are simplified in a home treatment system, where, as I mentioned in a previous post, you can separate the water streams, on both the supply and disposal side, and there are other safety-enhancing factors. The main problem from a practical standpoint of building a home treatment system, especially one small enough to fit in a tinyhouse comfortably, is getting the parts, and monitoring the water quality, though the need for the latter is reduced by separating water streams.

I’ll put the ideas for a practical system in a separate post…

Written by gregor

August 14, 2010 at 19:02

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Existing greywater or sewage to potable systems

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In the references file you will see some stuff about municipal water recycling systems.  There are also a few patents on home water treatment systems to go in your basement.  I remember just hearing vague whispers about a basement system that was on the market there for a while back in the 60s (before they had laws against recycling water back to potable, I guess,) too, called the cyclet, cycle-let, or the cyclelet.

There are 2 examples I could find of cities practicing direct potable reuse:

Windoek, namibia

Cloudcroft, new mexico

and there is the Denver water recycling demonstration plant (it seems unclear whether that water is actually going back into the city supply system, though).  These systems always need a good deal of new water input, because people in the city will remove water from the system by using it for irrigation etc.

However,  there is also the past example of Chanute, kansas, that suffered a drought back in the 50s, and apparently had to recycle the exact same water some 5 to 18 times, all with 50s era technology.  Mind you, I have read that the level of water treatment they achieved would not be considered acceptable today.

But.  The thing is, they didn’t and couldn’t do any sort or segregation of the water streams, e.g. sewage from greywater and drinking water from everything else.  Plus there was water from many people mixed together and distributed to everyone, a major risk for outbreaks of disease, and there was probably some industrial waste and people flushing pharmaceuticals down the toilet etc.  A home based system can correct all those weaknesses, especially in a tinyhouse, where you probably don’t have very many people living there.

I did find one example of a guy in malta who had rigged up his house to treat the wastewater back to potable water, apparently, by the name of Marco cremona, who has a blog somewhere.  Maybe you can dig it up again from this page here (which itself details an interesting project): http://www.goodentrepreneur.com/The-Competition/Entries-Pool/Sustainable-Water-Recycling-for-Hotels-Large-Commercial-Buildings-and-Small-Communities

The page is about a system that recycles sewage to potable recycling for a hotel, but he says stuff about the system he set up for his own home, too.

Whether he did the segregating of the different water streams, I don’t know.  He does, however, point out on that page the issues with monitoring the quality of the water on a small scale, the sensors and so on could be hard to obtain or too expensive.  However, if we look at something like the life saver bottle (or jerrycan), or the lifestraw, or the HTI hydrowell and related products, which can render even the nastiest, most dangerous water drinkable, it is clear that there is technology out there capable of ensuring the water is pathogen free.  Putting more than one of these in series would produce an even more reliable system.  Straying from the immediate do-it-yourselfer-able realm, there are also some pretty amazing sensing technologies like cheap infrared spectrometers and microfluidics coming out now that could help a great deal with assuring the water is pathogen free, I bet.  When it comes to dissolved contaminants, I’m pretty sure there is nothing in sewage in concentrations so dangerous as to cause a major threat to life and health if you were exposed to it, even in drinking water, never mind the shower, unless maybe there were bacterial toxins or other biological (algal? fungal?) toxins in the water.  Which I haven’t ever heard of, anyway… Total dissolved solids sensors are cheap, and can be used to  check if there is a general malfunction with the chemical contaminant removal.  There are also total organic concentration sensors, as seen in that nasa paper I just blogged about, but they’re pretty expensive.

BTW, Marco Cremona’s system seems to be mainly an MBR system followed by reverse osmosis, a common combo (though there could be some activated carbon or something in there somewhere just not being mentioned).

In the reference file, there is also reference to the “komplete” (seems to be a German company), which recycles greywater back to potable and sewage back to flush the toilet, on a largish scale.

There are some water recycling (usually grey to potable, though maybe drinking it is not recommended) systems on cruise ships, too, I have noticed.  They are usually mbr and reverse osmosis, but some are just RO based, while still recovering 90% of the water (some is always wasted as brine in a reverse osmosis system).

You may be wondering why the NASA system supposedly cost $250 million to do exactly what some of these systems seem to be doing on a much larger scale on a much smaller budget.  Good question.  I seriously doubt the nasa system cost anywhere near that.  Otherwise, while the reliability of the system is of course more demanding for nasa, and as mentioned in some of the papers, they have a hard time using biological systems (which the paper says would be better than these physico-chemical systems) because of the microgravity, I don’t know how you would account for the cost difference.

I do think it’s interesting, that in some of the nasa press releases, they go on about how the system could be used here on earth some day, as if that is some sort of super futuristic idea.  But water recycling is already being done on earth without NASA’s help. While I’m sure the research on the nasa system is important and valuable (especially, as mentioned, for the water quality monitoring stuff,) the reason we can’t buy this sort of system is not because of the lack of technology.  It’s because of the unreasonable laws that prevent people from reusing wastewater in “potable” applications, and probably financial barriers.   E.g. I bet you still have to pay the cost of getting your house hooked up to the municipal system, which in an area like mine is something like $40k.

Written by gregor

August 11, 2010 at 19:30

Posted in Uncategorized

Greywater to ‘potable’ or nearly potable water recycling system

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The mobile condo blog, has a post up on their greywater system.  I’ve left a comment, but I want to make some less on-topic remarks on my own blog here, now that I have been reminded of the topic.

The system shown has a supply of rainwater available from the relatively large roof, so it does not need to recycle all the water.  Recycling even 50% of the water might be enough.  (Edit: apparently this is wrong, the system is intended to recycle most of the water, but in most climates, by my calculations, I seem t remember you might get away with 50% recycle rate) This simplifies things in many ways compared with a total water recycling system.  First of all, you don’t worry about certain dissolved contaminants accumulating in the system.  Second of all, you have some free water with which to backflush the particulate filters (although an air scoured/cross flow filter like used in membrane bioreactors could be even better, and as I mentioned in a previous post, obtaining a suitable membrane or two might be doable,) since you were going to throw it away anyway.  Plus, the rainwater can be used as drinking water, and the system’s excess water could used for evaporative cooling or watering plants.

You could also use it to flush the toilet, though you might have too much of it to use it all. 

BTW, I just want to take a moment to gripe here about the definition of “potable.”  Usually shower, sink, water for dishwashing, and drinking are all lumped together in this one category. When it comes to bacteria and other pathogens, obviously you want the water for all those applications to be pretty much free of any pathogens.  But when it comes to chemical contaminants, this categorization makes no sense at all.   Suppose you accidentally ingest 20 ml of water every day as a result of the shower and other non-drinking water, but still human-contact related, water uses.  Most people drink 1.5 liters a day or so of water, so that’s 75 times as much water.  Clearly what you care about is the total amount ingested from all these sources, and given the difficulty of removing chemical contaminants, it would not make sense to clean the non-drinking water so well.  It is okay to shower in water you wouldn’t drink, people do it all the time.  You can shower or swim in seawater and untreated river water.  On a municipal scale this might make sense, because it becomes pretty cheap to remove contaminants, probably cheaper than a dual-supply plumbing system.

But, as far as I can tell, almost all municipalities and regions in developed countries have explicit rules against using “wastewater,” including greywater, for any “potable” use.  So that’s why there are no commercial systems available that clean the water up to a suitable level for showering etc.

Lastly, I want to mention something I read about in a NASA paper, which is the possibility of segmenting the different water sources a bit more finely. We already see 3 categories of supply water here in this post: Toilet flushing, showering and other human contact but not drinking, and drinking water.  A fourth is obvious: irrigation, which can be done with untreated (not stored for any length of time) greywater.  There are also many categories of wastewater, shower water and water that comes from the kitchen not the same (esp. if you insist on putting food down the drain), sometimes these are referred to as “light grey” and “dark grey” (laundry is usually “dark grey” too.)

But you know what?  It makes much more sense to look directly at the different types and amounts of contaminants in every different water stream.  Laundry machine water, for instance, might have more and different types of detergent in it, than might kitchen water.  And water that comes from the dishwasher in a kitchen will not be the same as the water from the sink, and water from the sink is going to be a lot cleaner if you do not put food down the drain on purpose.

So if you are going to design a small scale treatment, supply, or recycling system, it might make sense to think this way.  Anyone reading this might be aware of the problems associated with mixing greywater and blackwater.  If you do that, now you pretty much have to treat all the water to the same high degree as the original blackwater before you can use it or dispose of it.  That makes the system a lot bigger and more expensive, but the same principle could be applied to other water streams, whether on the supply side or the wastewater side.

On the other hand, having a separate treatment system for all these streams might not make sense, you may be able to combine them at certain points to simplify the system.

Written by gregor

August 10, 2010 at 16:13

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Existing water treatment systems

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One of the big problems I have seen with water treatment systems is the companies behind them. Take the biolytix, for instance. Looks like a great technology, and maybe the concept could be used for a self contained toilet. The problem is the company won’t sell the proprietary filter media (I even contacted them, and they never answered,) they just want to sell this one type of system for cottages. And apparently, from reading a few forums, etc., they are lackadaisical about fixing the systems when they break; one guy had the worms die on him and had to wait 6 weeks for the replacement filter media (which you can’t just buy yourself because they won’t sell it to you.)

Same sort of deal with a lot of greywater filtering systems out there; the nubian and the perpetual water (which seems to have gone out of business,) are two. They won’t even tell you how the system works, so I guess you can forget about getting replacement parts for them. Membrane bioreactors, on the other hand, are not actually new, they have been used for more than 30 years for wastewater treatment, and ultrafiltration membranes are just as old, though fortunately they keep being improved (as shown by the lifesaver bottle.)

This is why I like the idea of using standard parts for stuff, and in developing the sort of system anyone could build and maintain. It’s like a Lister (diesel engine you can look up.) They are not fancy, or super efficient or blah blah, but they are incredibly popular and useful because they are simple, easy to maintain, and they area readily available.

Any sort of proprietary technology always costs way too much when it first comes out anyway, usually for many years until the patents expire. That’s fine in that the inventors deserve the profit for their hard work and obviously we need progress like that, but there’s a lot to be said for working with what we already have.

Written by gregor

May 3, 2011 at 00:09

Posted in Uncategorized

Toilet solutions for a tinyhouse roundup and roundaround.

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Yes, I just made up that word. It means speculation and stuff around existing solutions, in addition to existing ones.

Anyway, I’ve been following the “alternative toilets” thread on the tinyhouse forum, and a few days ago I read the Humanure Handbook (his term for human piss & crap is “humanure”). Interesting book, for sure, but I don’t agree with everything he says. He mentions a book, Compost Engineering, that sounds interesting, too, and I think I would have to read more about this before attempting homebrew improvements – or rather adaptation to a tinyhouse context – of the composting process.

But I was thinking of more general improvements:

1. Place whatever composter there is outside the habitable area, so if it does malfunction it is easier to clean up, while the receptacle is obviously better inside. To do this without water, you could use a Teflon toilet bowl and tube, to transfer the humanure outside. In a previous post, I posted a link to a site selling teflon sheet that could be used to make this. Teflon’s pretty amazing stuff, I wonder how well this would work. I wonder if you could figure out a “dry flush” mechanism, which prevented any humanure from sticking to any visible area of the toilet bowl automatically, that might be more acceptable to a lot of people, and non-stick materials would certainly help. I tried to find out more about Nasa’s air-flush toilet, but no dice.

2. Decide what you want (see below). If we can complete the nutrient cycle, that’s great, but if you just wanted disposal, an idea that occurs to me is that you could dry the piss and crap by evaporation, as an “air head” or “nature’s head” does (BTW, it is clear from the info in the humanure handbook, mainly because of the temperature and size of the storage chamber, that no meaningful decomposition is actually occurring in these toilets, rather they are just drying the material, i.e. they are, rather, desiccating toilets, and only the crap, not the piss), then pasteurize it, and it would be perfectly safe to put in the municipal garbage. You can get odor proof bags, made with foil-plastic laminate material, though as stated in the marketing material of these toilets, it does not smell when dry.

Or maybe you could find a gardener that would be happy to take it, but that seems like a hurdle. Crap takes up quite a small amount of space when dried – a human outputs about only 60 grams of solids per day in feces, and the rest of the crap is water.

Disposing of the (sterilized) urine on a lawn also seems like a very simple solution. The problem is that it might require a large lawn area for full time use. Would have to check that, If you have a drip or subsurface greywater system anyway, just increase the size, and, it could be perfect.

Bizarrely, the author of the humanure handbook does not mention pasteurization even once in the whole book . Yet from the data he gives about temperature-time treatments required to kill pathogens, it is clear that this would not be hard at all. I suggest the (dedicated) use of a kitchen appliance of some sort. A slow cooker might be good. I noticed you can get temp-resistant plastic slow cooker liners, basically plastic bags, you could line the storage chamber of the Nature’s head (or more practically a homebrew version for a fraction the cost) with a bag, then every month or two, you just tie it shut with a twist tie, and put it in the slow cooker for 10 minutes, and it is microbiologically safe. They are made to reliably reach the necessary temperatures, because they have to for food safety.

In all fairness, doing this on a large scale might not be a good idea, because some units would malfunction, some people would be too lazy to do the pasteurizaton step, etc, but you could certainly make a unit that performed the operations automatically, and refused to release the material until it had been pasteurized. In the Dymaxion house, a futuristic house by Buckminster Fuller, this approach of putting the humanure in the garbage rather than mixing it with water, was used, but I don’t know if they dried or even pasteurized it.

3. A water content sensor. One of the problems with dry composting is that it can only be done within a narrow water content range. You can get inexpensive sensors made to measure the water content of soil, so you might use one of these to measure the water content of the compost pile without user intervention, and water the pile if needed.

There are a lot of different toilet options out there for toilets of all sorts , looking something up on wikipedia, and following the links gives a view of some of the options. I think it’s fair to say we are talking about several different functions these toilets provide:

1. Waste disposal to avoid transmissible diseases.
2. Keeping the smell and mess down, or at least somewhere else from the habitable area.
3. Completing the nutrient cycle.
4. Preventing environmental pollution (undesirable release of nutrients, chemicals, and bacteria in the wrong place).
5. Prevent contraction of non-transmissible diseases like an e-coli infection.

These are not always connected that closely. Obviously it would be great to have all 5, but a compromise on some if you have to isn’t the end of the world. Traditional municipal systems are great at 1,2 and 5, but mostly fail at 3 and 4, and are ridiculously expensive, and social problems may prevent them from being used (regulations and stuff would fall in this category). A desiccating-pasteurizing toilet seems like it would be pretty cheap and safe. Commercial composting toilets actually look a lot less impressive to me now that I know more about them – because, despite what the manufacturer’s claim, they are not so safe after all from a microbiological standpoint. (And, according to reviews they don’t work very well for disposal either.) As far as I can tell they do not (could not) achieve the high temperatures needed to kill all pathogens in the timeframe in which they work (storing material for 3 to 6 months). It does help a fair bit, though.

In a tinyhouse, you also want to do it without:
1. Suffering from misunderstandings from bad neighbors.
2. Costing too much, including power consumption if off grid.
3. Needing a whole lot of maintenance.
4. Taking up much space.

So it seems like a thermophilic composter would be a lot better. But, like I said, I think I would have to read more to really make any decisions or try to design something.

Stepping outside the box for a second, you have to ask yourself why, exactly, people prefer flush toilets over dry. I assume it is because they flush the humanure completely away, and it is covered immediately while the toilet is being used, preventing any smell, and there is no exposed pile of other people’s crap below, which you are granted the privilege of gazing upon, and which kinda seems like it might splash up somehow or something (whether or not it actually could).

In Japan the toilets they have do not cover the crap, and this shows in the odor around the bathrooms, but by sucking air into the toilet bowl, smell could be prevented. It seems like it is just the possibility of stuff sticking to the bowl, really, and the pile of crap exposed below. And then there is the engineering problem of getting dry material from one point to another, which seems to be the only other point in favor of flush toilets, because fluids are easy to move around. Still, society already has municipal disposal, recycling, and in some cities even compost collection, so after you get over any fecophobia, as long as humanure is reliably pasteurized, and the process is semi automated, I think dry toilet collection could indeed catch on, if the right toilet mechanism were developed… I think the sticking point is the dry flush mechanism. A roots blower like mechanism made of non stick stuff, and maybe rinsed with just a very small amount of clean water, maybe? Or maybe 2 telfon bowls, one in use while the other is automatically emptied and cleaned. Edit on 2010/11/01: Maybe it would be better not to have a flush mechanism at all. Just a nonstick tube, twisted so you don’t see the pile of stuff below. Humanure slides away immediately after being deposited. No moving parts. Negative air pressure is used to prevent any escape of smell. If the Tube was flexible and you didn’t want to have the airflow associated with this approach to preventing smell form entering the habitable area, you might add a moving part that squeezes the tube shut. That way there are no hinges, seams or whatever, exposed to the humanure. You still need the urine separation ability, apparently the most common approach is to use a front receptacle, and a rear receptacle. Another approach that occurs to me is to try to use the adhesive properties of the water, the effect which is so annoying when trying to pour a beer, causing the water to run preferentially along the side of the bottle. I.e. You have a single tube, with mixed solids and liquids coming down, then at the output of the tube have a rounded piece of glass (or other hydrophilic material) of the right shape, which gets the water sticking to it, then guides the water away to s separate chamber. One problem with this is that you get fecal contamination of the urine, which in some circumstances could be bad. One pro is that the urine rinses the transfer tube, but if it was a good nonstick material this might be unneeded anyway. It could also be used in tandem with the 2-receptacle approach, attached to the dry-matter output tube, just in case water is inadvertently dumped into the dry-only receptacle, it still separates most of the water, and puts it in the right container.

Anyway, other options, some from the thread, some of which might not be very practical, seem to include

1. Anaerobic digester. While reading up for the greywater MBR, I read some about these. Basically they only make sense if you need the methane for running an internal combustion engine, cooking, or a lot of water is already mixed with the waste material from which you want to recover energy. The amount of methane you get per person of waste will not be near enough to do your cooking anyway. If you only want the heat and there was not too much water mixed in with the waste, it would make more sense to burn the waste directly, you would get more energy out, and it is a much more compact system, and easier to maintain. Anaerobic digesters take quite a bit of space. They also require various types of management sometimes, and the right input of nutrients and other conditions.

2. Nature’s head and Air head, like I said, these seem to be basically desiccating toilets, and they don’t even deal with the piss, except to store it.
3. Sawdust toilet, see the Humanure handbook for details, the problem with this is that it seems to entail a big compost pile, and yet more chores.
4. Biolet, sun-mar, clivus multrum, etc, there are a dozen commercial composting toilet, and they are are ridiculously expensive, and most seem to get bad reviews.
5. Incinerating toilets seem to get bad reviews, and require a lot of energy. Also expensive.
6. http://www.gocleanwaste.com/homepage So-called PETT, but this doesn’t seem practical for a tinyhouse.

Written by gregor

April 27, 2011 at 00:09

Posted in Uncategorized

Many in one tinyhouse support unit.

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The main reason I started this blog was because I had some ideas in a notes file that I thought were useful enough that I didn’t want them to just languish there, that they could potentially improve the situation if they were gotten out there. But it seems like I continue to find blogging fodder…

I was thinking, the tinyhousedesign blog put up a post a couple of days ago about a tinyhouse community, and how you could try to enable that with more sophisticated technology than septic tanks and generators (or grid) air conditioners etc., in a more practical way than asking everyone to show up with solar power systems etc. built in. (I can’t help but notice a lot of the motivation is to avoid the politics, I keep meaning to do a post on politics, boring as it is, it’s probably the most important issue).

I recently stumbled across these two systems, useless for a tinyhouse, and probably overpriced (if it doesn’t say it’s probably overpriced), but an example of how putting everything into one unit opens up some new opportunities for optimization.

Also, systems that stepped lightly on the land could make it easier to find land, potentially even leasing it, and if the systems could be picked up and moved, that opens up some interesting options. If people decide to invest in owning the land, then you can make the jump, but it reduces the initial cost; I mean, do you really want to invest $100k in an experiment like this right off the bat (if you can even get the financing)? Being able to ease into it could be useful.

Imagine an object that looked sort of like a stand-alone closet with 2 doors, in on the front, and one on the back. It’s about 0.5 meters by 0.5 meters at the base and 2 meters tall, bigger or smaller depending on how many people it is working for. Maybe you give it a nice appearance, like like one of those really small garden sheds. It’s heavy, though, maybe 150-230 kilos, because of the water, depending on how many people it needs to support. It might have wheels on it, or it might be designed to work with a separate heavy duty dolly, for when you want to move it. There is also a 7 square meter thermal flat panel collector sort of plonked on there or nearby. It has several tubes and hoses running out of it, and it’s made to handle greywater disposal, provide clean water including hot water, fresh air and heating, cooling, and electricity.

Inside there is all kinds of good stuff. There’s a bioreactor for greywater recycling, that’s why it’s so heavy, definitely one of the downsides of the MBR approach is that it could weight ~80 kg per person living in the tinyhouse.

There’s a programmable logic controller, which has the ability to communicate with x10 devices, those home automation system things that can communicate over the powerlines. This allows you to do load balancing by commanding the fridge to turn off etc. at the right time of day, or if excessive power is being used.

It’s got the heat exchanger for the ventilation system, and the necessary blowers or fans. It’s got all the heat exchangers and stuff for a high efficiency hot water system, but you might want to put the main storage tanks inside the tinyhouse due to the weight.

It’s got a 2 to 3 small (~90 watt) stirling engines for electricity generation, and the waste heat from the engines would by my reckoning be more than enough to supply all the hot water needs, and most or all of the space heating. Engines are turned on or off automatically as the demand for power changes (stirling engines have a bit of a problem with efficiently varying their output power, so several engines each of which could be turned on/off might be best).

It’s easy to couple the space heating to the engines for CHP, because it’s all right there. You could opt to connect into the radiant floor heating system if the tinyhouse is so equipped. Or you could have a small heat exchanger unit to transfer the heat to the airstream coming out of the ventilation system. The engines could run on nearly any fuel you want, wood, vegetable oil, whatever you have handy, with the right burner/feed mechanism. Defrosting the heat exchanger every couple of days when needed (which the plc can determine easily enough with temperature sensors) could also be done with this heat.

There are the power electronics, and a small solar panel to opportunistically harvest solar energy, as mentioned in the solar+stirling post, boosting the kwhr/day available, and reducing fuel use, however there is only one small battery, a Li-FePO4 or Li-ion battery to support high peak loads like a microwave, rice cooker etc., allowing you the convenience of such appliances. The panel might be 400W or something, or you could maybe omit it entirely, whatever is cheapest. The oven and stove should be propane, or whatever greener fuel you prefer, like methanol.

It takes care of air conditioning needs, too. That’s what the big solar thermal panel is for, I think that would be a minimum required size, funny that it would be comparable to a fridge’s, but it’s because the temperature drop across it is lower, and it is operating during much sunnier conditions, and you can do thermal closeting. The sizing might need to be revised though. The mechanism required could be adsorption, absorption, or evaporative plus a dessicant wheel, if you have disposable water available.

“Thermal closeting” could be done most nights, whenever the nighttime temperature is low enough, in which the water in the storage tanks are cooled down to the ambient temperature, then it absorbs heat during the day. In ontario here that might be sufficient alone, though you might still want the solar heat panel to provide power to remove humidity. How exactly the thermal closeting is arranged for is yet to be determined… maybe you could run a cooling coil through the water tanks, then have a big, slow fan blowing on an air-water heat exchanger, outside, to cool the coolant, then it goes back through the water tank coil to cool the main water supply. This is a lot like a whole house fan, but there is no concern about noise, because you can close the windows and the fan is outside. Or you could just open the windows or something, would beed to work out the details.

The MBR could handle waste from a washing machine, but you could also include a small washing machine and centrifugal drying machine for the user’s convenience, since most people would probably show up without them (got a post on laundry coming up).

In a village scenario it might make more sense to have a light industrial generator for power production, or a solar system shared by many people, and any heating can be solar heating, though in that case you need to have a way to store a considerable amount of heat to tide you over on cloudy days, or fuel burning backup so you don’t end up without hot water.

The 2 doors are to make maintenance easy, so you can access the insides from both sides. The walls would be insulated just a bit with foam to keep the MBR happy in cold weather.

Clearly there are both technical (experimenting on the water system) and practical problems (getting the heat exchanger for the ventilation and the engines, and the membrane for the reactor) to be solved here, but I bet after the first couple were built you could build it all for ~$2.5-$4k in parts.

Edit: See the post “tiny system” for a design outline for an off grid all in one system for a rural area.
Also, I have since posted a number of posts like “off air conditioning in a tinyhouse” and things like that that look at some of the issues here in more detail, which are in the archives.

Written by gregor

April 11, 2011 at 00:01

Posted in Uncategorized

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