Some folks have expressed interest in the simple grey water swamp cooler that I demo-ed during the 2006 solar tour. It’s a simple, low-tech device that can be built for under $50 in a few hours, and it evaporated the grey water from a 2-person camp, and at the same time cooled the interior of my camper van by 10-15 degrees.
I made it from an old rectangular plastic kitchen garbage container. On the 2 large sides I cut a hole app. 12″ square, and covered the hole with replacement pads from an evaporative cooler. A small fountain pump and some clear tubing runs water over these pads. The top of the garbage can is covered with a piece of plywood with a hole cut in the center, and over this hole is mounted a 12V fan (either large computer muffin fan, or a salvaged ventilation fan from an old car). This fan is set up so it pulls (exhausts) air from the trash container, pulling it over the wet pads. A piece of dryer vent hose directs this air into the vehicle, tent, or whatever space you want to cool. The whole thing is powered by a solar panel. The fountain pump draws less than an amp, so size your fan based on the amount of solar power you have available.
The key to making this work is to pre-treat your greywater. I collected the shower water in a blow-up kiddie pool, and then transferred it to a 5 gallon bucket. I treated the water in the bucket with Alum (a flocculant) and bleach. The alum causes the suspended particles of playa dust to clump together and settle to the bottom, and the bleach sterilizes the water. After a little experimentation, I found that a teaspoon of alum and about 15 drops of bleach per 5 gallons worked well when allowed to sit overnight. After the water has settled, it can be transferred to the swamp cooler. Be careful not to stir up the water while transferring it, and you can get almost all the clear water leaving only a couple of inches of muddy water in the bottom of the bucket.
Alum can be bought in small containers at the grocery store (look in spices, it’s used for pickling) or in larger containers at swimming pool supply stores.
I probably won’t be at BM 2007, but would be happy to loan my prototype to someone, or to answer questions.