This site collects and presents techniques for dealing with graywater in Black Rock City, home of the annual Burning Man event.  The focus here is on evapotrons: devices that get rid of graywater by evaporating it; and how to build one for your camp.

The  Gray-B-Gon  wind-powered evapotron

In 2005 I built such a device, one that used wind for its power source. It wasn't pretty, but it worked pretty well; I improved the design, found a name for it, and wrote a guide so other burners could build their own. I led workshops in the San Francisco area where burners built them from parts kits. At Burning Man 2010, evapotrons based on the Gray-B-Gon (let's shorten that to "GBG") design were in use in dozens of camps, eliminating about 800 gallons of wastewater per day.

On the Documents page you will find a downloadable  Construction Guide pdf, and on the Construction Guide page you will see the Introductory section. You can build a GBG evapotron using the Guide, various bought and repurposed materials, and common (mostly) tools.  (Note: downloading gives better images than the 'view' option.)

It's easier in a workshop, or using a parts kit; you get the materials at far below retail cost, then assemble the GBG with as much help, or as little, as you wish.

You may live far from the San Francisco area.  Consider joining forces with other burners in your region to build GBGs for your camps. Preparing a Workshop is a guide to producing parts kits in volume, and to conducting a workshop.

Graywater? Greywater? Gr[ae]y water?

[A lexicographic diversion.] Some people prefer A (the American spelling); others, E (the English).  To me, writing Grey seems to carry the hope that a refined-looking name will improve the toxic, smelly stuff we're dealing with.  I don't think it does.

I note that Google delivers hundreds of thousands of hits for each of Graywater, Greywater, Gray water, and Grey water.  When you say it, they all sound the same.

Toxic, smelly stuff        

You do want to avoid contact with untreated graywater.  It gets  more toxic with time, and also (statistically at least) as the size of your camp increases.  Here's some useful advice for disinfecting with chlorine bleach.  Heed it whether or not you use an evapotron.

Kerry Veenstra says,
 "That was my first evapotron.  I built it from 1/8" plywood and 2-by-2s.  You're right, the top is a Savonius vertical-axis wind turbine.  Green twine drives the evaporation wheel by running over several S hooks (because I forgot the pulleys at home).  All of those S hooks created a lot of friction.  In the end, the "pulley" at the bottom of the turbine was "polished" by the twine and completely lost friction!

"The spider-web-like wheel supports a ring of canvas that was cut from a painter's drop cloth.  Unfortunately, it turns out that this painter's drop cloth was coated!  And so the cloth did not absorb *any* water!  Also, you can see that the wind is blowing on the fabric loop and bunching it into one side of the support slots.

"A fun fact about the design is that it came from a single 4-ft x 4-ft sheet of plywood.  The rings all are different sizes so that they nest.  The "U"-shaped supports nest, too.  There actually are two wheels, the smaller one reducing the speed of the wind turbine.  So really, there are two twine loops. 

"This was a joy to make, but in the end, it evaporated nothing!

In 2009, I saw in the Alternative Energy Zone an evapotron very different in style, yet fundamentally similar to the Gray-B-Gon.  It was built by Rev Jester and Elise, of Camp Wabi,  who gave me a link to a short video of it: 

Elise describes their evapotron this way:

"2009 was the first year we had a real camp kitchen. Previous years we just didn't produce much graywater and what we did produce we carried home with us in a few 5-gallon barrels which we poured into our gardens at home. It was a hassle cleaning the barrels afterwards.

"Jesse and I did build the evapotron inspired by your instructable. We modified the design in a response to wanting to use only salvaged materials:

The blades are the only non-easy-to-salvage parts on the machine, they are blades left over from a friend's first attempt at making a wind turbine. Because our blades were designed to run at high speeds, we adjusted the gearing of the machine to account for this.
Wood came from taking apart a packing crate
Mesh barrel came from discarded window screens
Strapping and pulleys came from torn bike tubes and the border stripping from window screens
The square bucket holding the grey water was found in a dumpster years ago
Bike wheels were unused donations to the Bike Shack, a Seattle volunteer-run diy bicycle repair shop <http://www.bikeshack.org>http://www.bikeshack.org

"One advantage we discovered to building the contraption on wood boards tied down to the bucket with stretchy straps is that the whole machine floated on the grey water, so the barrel was always only sunk into the water about a couple inches, regardless of how much water was in the bucket at the time.

"Drum dimensions are about 44cm long with 42cm diameter. I don't know what the evaporation rate is because I didn't keep track of how much or how often people were dumping water into it, but I was pretty happy with the performance once we moved it where the wind stream wasn't blocked by a big tent :-)

Mike Robertson built this Gray-B-Gon variant:
 http://www.youtube.com/watch?v=ximAfbAHF9M .  He says,

"This is my 2010 Burning Man Greywater Evaporation Pond Windmill that I built solely from parts found at OSH. Worked great! Inspiration came from the Gray-B-Gon.  As for the evaporation rate, I didn’t really measure it. It did pretty well for two peoples worth of showering for nine days though and I think if it had been a little more windy this last year it would have done a lot better.

"The bearings I used were 1 3/8” bearings and 5/8” all-thread and 5/8” collars to attach the sprockets to as well as the rotating netting and blades. The blades were made by cutting 4” PVC in half and attaching to the all-thread with 1” PVC pipe and four way fittings. Sprockets were a 42 tooth off a kid’s bike and an 11 tooth I bought off a scooter shop (make sure the sprockets are for the same type chain though). Rotating barrel is made from 1” PVC with netting draped around it. To hold it all together I use self-tapping metal screws so I could take it apart and store it

From inception to working device, I struggled to understand the basics:   Ember's 2006 Evapotron report

Bonefire Bob started with a massive blower fan and built a wind-powered evapotron around it.  It lacked only a playa-legend wind to turn the blades.

Pumped Cascade -- the other evapotron design that really works

Another time-tested evapotron design uses a pump to spill water over a vertical cylinder of hardware cloth (1/4" metal screen).  Like the GBG, the evaporative surface doesn't clog up with playa dust or other graywater gunk.  This design seems to have no generally-accepted name, so I will call it the Pumped Cascade design. Look at the Flying Saucer page for a fuller description. 

Evapotron history

This is the first Pumped Cascade evapotron on the playa:

Subcomandante Marcos, since promoted to Comandante, writes:

"It was napkin engineering that wasn't supposed to work so well, and trying to protect the kiddie pool from long highway trips and storage wasn't exactly factored in. I still have the original tub from the 36" version of '04. We often found schwag  left atop the disc.

"The first 48" version had glow lighting attached to the screen. People couldn't stop fingering the Curtain of Fluid, so we kept warning all the peeps about the contamination hazard.

 The challenge for pumped cascades is to spread water evenly.  In 2007 Denise, Dillon, and JennyG brought this evapotron with a
nice mechanism for spreading water .

Justin Wright returns  to the playa in 2011 with the third iteration of his design, above.  He credits Comandante Marcos' design, five years ago,  as his inspiration.  A twin unit is in the works. He offered this description:

The whole thing is about four feet tall, 26 inches across. The tiers allowed me to create much more surface. Combined with the flexible-mesh wedding cake sides, there's about 225 square feet of surface area. 
The whole thing collapses down to fit inside the basin for easy transport and storage.

The terry-cloth strip around the edge of each tier
creates a small lip. That allows each one to keep about 1/4" of water in it, and helps ensure even flow over the sides. The terry cloth and mesh act as a filters for particulate matter.

The bottom of the basin has a stack of towels to act as a filter and allow for easier removal of dregs at the end of use. The pump is surrounded by a fine particulate matter filter, plus its own internal filter.

The unit sits in a small traditional "pond" style setup, about six feet square. Any water that splashes out of the basin is caught in the pond, keeping graywater off the playa.

The second one I'm building will sit next to this one, with a balance siphon between. All our graywater goes through several filters and a holding tank before entering the evap setup.

The cost, with all new parts, would be $75-120. The only new purchases I made
for this and its twin were the "whiskey barrel" pond liner (the basin) and matching pumps. The rest was scavenged/salvaged/reused.

Last year's MK II version got rid of about 200 gallons over 8 days in BRC. The current version is evaporating about 4/5ths of a gallon per hour in 60-70% humidity, 80 degrees and occasional cloud cover.
In BRC conditions I expect a substantial jump in performance. I'm tweaking it a little to add even more surface area.

This gives a new meaning to "Vaporware"

Gary Stadler wrote to describe an astonishingly high-performance evapotron that, unfortunately, no longer exists (nor do photos).  It perished in a way that left Gary unwilling to rebuild it, but someone else should surely give it a try.  Here's Gary's description.

"Two years ago we made an evap system that puts all others to shame, and I thought I'd at least describe it to you.

"It's basically this --  an 8 by 8 foot polyethylene "pond", the usual flat thing on the ground with poles or 2x2's bordering the edges so it becomes a 1-2" deep "lake".

"Then you put a little 2 foot diameter dimple in the center, about a foot deep.  A half horsepower motor that can handle being wet hangs over the hole, with a shaft extension that drops down into the hole, with a small (maybe 4-6 inch) propeller mounted on the end of the shaft. So the propeller is sumberged in the little place formed by the dimple, and when the motor turns on, the prop moves water "up" into the air with a lot of vigor and mess.

"Last, you make a cheezy  8 foot diameter by 4 foot tall geodesic (or other) dome out of PVC and cover it with three layers of Burlap.

"How does it work?  The gray water goes into the pond, the propeller splashes the crap out of it and makes the entire burlap dome get wet.  Being that the burlap offers mega-surface area, and it's up in the wind a bit, it evaporates like crazy.  Three layers of burlap insure that drops don't get out and make the area surrounding the system wet.

"This single 8 foot system took care of an entire camp of 100 two years ago, it never screwed up, and it could easily get rid of 10 gallons of water in around 20 minutes!  Absolutely the most amazingly small and efficient system I've seen or made...

"So there you are... enjoy... "

"Evapotron"  history

After I'd built several graywater evaporators, all different, I realized I was having difficulty talking about them because I didn't have a name for the category.  I devised several terms, none appealing, and then I thought "Evapotron!  That has a nice rhythm, and it's ludicrously self-important.  Perfect."

Later I thought to Google it.  What do you know.  Decades before Burning Man – in 1965, in fact – evapotrons of a different sort were being used in meteorology.  An evapotron was–

a device that uses eddy correlation to measure the turbulent vertical flux density of water vapor within a few meters of the surface of the earth. Evapotrons were originally designed with analog electronics to make the necessary covariance calculations in real time. This term is not in common use for systems that make the covariance calculations with modern digital electronics.

Well, of course.  These days, Googling still shows a few hits for the original device with the covariances and the vertical flux density, but they're outnumbered by pages for our desert devices.