The Freshmäkkur

How it Works

1. Flocculation and Settling

When we received greywater, the first thing we did was transfer it to a 5-gallon bucket (our "settling tanks"). Then we added a couple of teaspoons of alum and stirred quickly for half a minute or so, until we could see flocs (fluffy clumps of playa dust, soap precipitate and other particles) beginning to form. Then we stirred slowly for a few more minutes to aid the formation of the flocs. We let the flocs settle for at least 20 minutes, but longer if we had enough free buckets.

We bought alum at a plant nursery. One 2-lb bag was more than enough for all my experiments and for Burning Man. It’s used by gardeners to acidify (lower the pH of) soil. It’s also used in water treatment plants for flocculation. I found that it doesn’t floc playa dust unless the water has some soap in it. And it has to be hippy soap. Dr. Bronner’s is best, and Camp Suds and Planet brands also work for flocculation. Neither Palmolive nor Ivory work. From this I’m extrapolating that hippy soaps work and big brands don’t. It’s not political, it’s just because (I postulate) the hippy soaps have a high pH (are more basic) and the big brands have a low pH (are more acidic). Alum works by neutralizing the surface charge on the playa dust particles, and apparently hippy soaps help that and big brand soaps hinder that.

2. Sand Filtration.

We poured the top of the contents of our 5-gallon buckets into our sand filter, being careful not to disturb the settled flocs at the bottom. The flocs at the bottom were then disposed of as sludge. The water which came out of the sand filter was clear, but still coloured from the dissolved organic material in the dishwater. It looked like apple juice.

Our sand filter was a Rubbermaid wrapping paper container filled two-thirds with play sand. The Rubbermaid lid was inverted and had holes drilled in it to distribute the water evenly over its surface. The sand was covered with a piece of filter bag which took out any large particles that we accidentally poured into the filter. We replaced the filter bag once during the week. Another type of cloth would work too. During the week, we replaced the top few inches of the sand which had become clogged.

The outlet of the sand filter contained a sieved fitting to prevent the sand from coming out. The outlet was quite small, in order to slow the flow through the filter, since the slower the flow of water, the more efficient the filter. As filters are used, they start to clog and the flow slows down. They become better as filters, but that doesn't matter if the flow through is nearly nil. This was a problem we experienced this year, and we fiddled with the outlet to help solve it. However, in the future, the outlet will be large and have a valve on it to control the flow. That way, as the filter gets clogged, the valve can be opened wider and a constant flow can be maintained.

3. Chlorination

We added bleach to the filtrate. This was necessary, since the next step in the treatment train is the removal of organic compounds. Bacteria love to eat organic compounds and when they eat they multiply, so without chlorination, we faced a massive bacterial overgrowth, making our effluent turbid and stinky.

Disinfection efficiency is proportional to the product of the concentration of chlorine and the time the water sits with chlorine in it (contact time).

bugs killed a concentration x time

We aimed to add about ¼ cup of bleach to 5 gallons of water and let it sit for at least 10 minutes. However, we probably ended up with more of both time and bleach since there wasn’t any way to communicate to each other whether any given parcel of water in the chlorine contact basin had already been bleached, and the water sat around until someone pumped it up to the GAC.

Bleach is about 6% hypochloric acid. In order to be effective, its pH should be below 7, which is generally a problem on the playa, since as we all have drilled into us, playa dust is alkaline, which means it has a high pH. However, this is where the alum (discussed above) does double duty, since it also reduces pH.

4. Pump

Jon Fram built a really cool see-saw that was hooked up to a hand pump. This is how we pushed water through the GAC tubes. A warning however: if you’re going to pump water through a filter, be sure all of your plumbing connections are sound – broken connections was our other problem (besides the filter clogging) this year.

5. Activated Carbon – Removal of Organic Compounds

The water was pumped through six parallel 8’ long, 1.5" diameter tubes filled with granulated activated carbon (GAC). Activated carbon has a high affinity for organic molecules and a huge surface area (something like one square centimeter has the same area as a football field, which seems to be the standard American way of measuring area). The GAC removes the organic molecules which are the components of the water responsible for taste, colour and smell. It also gets out a lot of the chlorine. Emerging from the GAC tubes is water that’s like tap water to the senses.

6. Ultraviolet Disinfection

And just because we’re paranoid, we then use UV disinfection. We irradiate the water with a 25 Watt germicidal bulb. Ultraviolet light messes with the nucleic acid of microorganisms, making them unable to reproduce and make you sick.

Our disinfection unit is a catering tray with holes drilled in it to keep it shut, and to allow us to mount the brackets for the bulb. On the outside of the unit is a ballast for the UV bulb, and a DC to AC inverter leading to a deep cycle marine battery. At Burning Man, the battery was recharged with a solar panel. The inverter has a switch on which allows us to easily turn the UV bulb on and off.

-Lorien Fono, September 2003