Greywater recycling system design up at mobile condo
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.