Getting rid of residual black water

I think vermifilter flush toilet systems are nearly ideal.
They produce very little black water, but still some.

I don't want to use a contained bog/wetland to deal with it because of weather.
Unless the plants are grown in  under cover, rain is liable to over flow the bog and spread unremediated water .
Unless the bog is indoors,cold weather would kill the plants or stop the evapotranspiration we are counting on.

Instead of an indoor bog, I thought a solar still might work.
Just a simple insulated box with a glazed lid that would evaporate the water and heat up the residue.
Alternatively or in addition to the solar thermal evaporation, a solar pv powered fan and/or solar chimney could speed create air movement to accelerate evaporation.

Another choice could be aeration of the black water, as is done in some newer septic systems.
They all seem to use air stones and follow up with chlorine.
That doesn't sound good, but another less noxious chemical might be ok.
Road salt or borox added to the evaporator could mix with and disinfect the incoming water, but remain in place as the evaporation takes place.

Adding dark particles to the black water could aid in evaporation by absorbing radiant solar thermal and conducting the heat directly to the water it is suspended in.

I originally thought to immediately vent the evaporated water, but  solar stills are designed to collect the water.
I'm not sure which is more useful.
Storing the purified water directly under but physically separated from the incoming water would allow it to act as a thermal flywheel and preheat the black water as it cools off.

Interesting problem. How much black water is generated? How often does it need to be dealt with?

Heat always works. If you can collect the black water in a metal container and use concentrated solar or a small fire to bring it to the point of a boil (i.e., exceeding pasteurizing temperature), any disease causing organisms would be rendered inert. The result is funky water that can be used anywhere. (I would use it on trees rather than root vegetables, but that's mostly an aesthetic choice.)

Edit: If i was boiling black water, I think I would add a very generous dose of biochar and dry ash. This to satisfy the Department of Aesthetics, Olfactory Division.

William, as you point out, vermifilters do appear to provide a pretty amazing level of treatment, but whether or not it's sufficient depends on both the characteristics of the influent and the target thresholds.  Additional vermifilter stages can be used to continue to improve most parameters, including pathogen reduction.  If the intended use is close to the surface one potential weakness of vermifilters to be aware of is that there appears to be inconsistent data on whether roundworm eggs are treated.  One method to address that concern is the sump used in a recirculating vermifilter design which can double as a settling stage.  The performance of the combination of vermifilter treatment with certain types of plants is very impressive as they seem to provide complimentary treatments.  The Wastewater Gardens website suggests that for cold climates, for the type of plants they are working with, the treatment doesn't stop but can be compensated for by doubling the size of the wastewater garden.  As far as aeration, I'm going to try flowforms which eliminate the risk of pore clogging.

I really like the recirculating vermifilter and the website it's on.
The incorporation of aeration into the process is inspiring.
I don't quite get how the system prevents the water from exiting before it's "clean".

I visited Anna Edey's vermicomposting filter at her house and was really impressed.

Can you give a link to the one you're looking at now? I like learning about these topics.

Her effluent did not spend long in the wood-chip and worm box. It flowed straight through, leaving the solids on top of the wood chips. (Importantly, use coarse large chips to prevent clogging and drowning all the worms). The effluent went down into a perforated pipe in a gravel-filled trench. To avoid roots getting in and clogging the perforated pipe, either the pipe was covered with, or the trench was lined with, weed barrier cloth. The trench was gravel up to the surface so it looked like a gravel path, surrounded by grass. It had pine trees all along one side, and her sheep meadow on the other side. I think pine trees have very polite roots, but you wouldn't want this within 50 or 100 feet of willow, poplar, or other plants with aggressive water seeking roots.

She's on Martha's Vineyard, USDA zone 7, and I don't remember how deep she buried all this, but you just have to go below your frost line.

If I were doing this, I'd run it under a path, road or driveway, with annuals on both sides that won't extend their roots too aggressively. To avoid friends getting yucked out, I might plant only ornamental annuals and annuals for mulch over it.  

In my situation in the high desert, I'm happy with my dry composting toilet system, but I understand there are many places and situations where a flush toilet is necessary for various reasons.

Burton posted the link above, it's a quite nicely done open source design.
I would be pretty comfortable discharging the water anywhere that an outhouse is legal, but I both of my properties are in a typical city.
I would like a toilet solution over at my yarden, one that doesn't involve hauling buckets back to the house.
A flush toilet is really just a way to accommodate visitors, for just me, a dry toilet would be fine.
Open composting of humanure would be enough to get me in serious trouble.

I already have a large worm bin that needs to be moved to the yarden, so it got me thinking about how to use that.
It's a fridge,  laid on its back, with a reservoir in the bottom that has a drain already built in.
Open the drain and you pretty much have a vermifilter.
As long as I  don't dump the post filter water, it's no different than an RV having a blackwater tank.
I had thought about adding a recirculating pump to the worm bin, to aerate the water in the reservoir.
An air lift pump was what I was considering, because they use little energy, aerate as they operate and are resistant to clogging.

William, I was a bit confused as well, thinking I'd put the pump in the bottom of the sump, so I sent your question onto Dean who runs the vermifilter.com website.  Keep in mind that the pump is always circulating the tank even when there is no inflow.  In his response he used the example that "if the sump holds 200 litres of water and the pump flows 50 litres per hour, then over 24 hours the water in the sump is recirculated 6 times in a day".  So, if the inflow rate doesn't exceed the 200 liters (or more accurately the volume difference between the inlet and outlet) in 4hrs then everything should get passed through the vermifilter of that stage at least once.  Hence the need to size the system for your use.  Having multiple stages also factors into the treatment, so its really nice that the system is so modular.
He added, "The recirculation pump can be either submerged directly into the water in the sump, or the inlet connected into the outlet pipe (the image in your link), or the inlet can be inserted directly into the sump. Its all the same, but importantly the recirculation pump must be below the surface of the water. A few inches is enough. It should be near the top where there is less chance of solids entering it."  He also added more information on that recirculation page that shows settling tanks inserted in series before the recirculating tanks to eliminate the need for filters to prevent clogging of the pumps.  Feel free to reach out to him directly using the Contact Form on his site.  He has been very helpful to me.