We chose to install a traditional septic tank, rather a composting toilet, because of the difficulty of maintaining an off-the-grid composting toilet in our cold, damp Vermont climate. For a composting toilet to function properly, the waste must be churned and ventilated and kept quite hot; this process requires far more energy that we could reliably produce during the colder seasons, when the days are shorter and the clouds more frequent. Although we would prefer to use our waste to fertilize our own fields, we were happy to find that the solid waste pumped from our tank would be processed into fertilizer for animal crops.
We did install an alternative system for processing our black water. Instead of using a leachfield, we use a constructed wetlands. In this system, black water from the septic tank is piped to a constructed wetland, an aboveground sand and gravel pit seeded with wetlands plants and sealed from the environment by a layer of waterproof clay. As the wetland plants grow, they take up waste and convert it to plant matter. Well-functioning wetlands are so effective that water coming out of many wetlands is drinking water quality.
We chose a wetlands because leach fields are a very wasteful system, requiring a lot of perkable land that would be better used for growing food. In addition, one to two back up locations are required, because leach fields are known to clog and fail. Finally, digging the pit for a leach field consumes a lot of energy. With a wetland, less land is used, and the land that is used makes a wonderful home for a variety of animal life. Although we have chosen, to pipe the water from our wetlands into a leachfield for additional safety, this leachfield is only 25% of the size of a traditional one and we don’t need space for backups.
Unfortunately, for many years our wetland was not functioning as it should because it is far too big. The state of Vermont estimated that a home of our size would produce 400 gallons of water each day, and required us to build our wetland accordingly. Since our water usage averages only 85 gallons per day, our wetland was not wet enough to support wetlands plants, and for years only regular field plants were growing on our bone dry gravel filled “wetland”. In 2007 we reviewed our wetland and found that it was finally holding water at the height needed to maintain plant life, we suspect that over time a layer of organic matter had built up on the inside of the wetland thereby reducing it’s size and limiting any absorption into the clay that might have been occurring. It is also possible that with a second child, born in 2005, our cloth diaper washing may have increased our daily water usage.
Having brought in one of our original engineers and a wetland “expert” to analyze our wetland, we are now in the process of preparing it for new wetland plants and we look forward to seeing how the introduction of wastewater from our new building further enhances our wetland’s ability to support wetland plant life. The cattails we planted this fall of 2008 are thriving and we intend to plant more cattails and woolgrass in the spring of 2009. Once the state of Vermont sees evidence that our wetland water samples are coming out clean, our new building may use the wetland in lieu of a leachfield thereby saving us many thousands of dollars.
An additional benefit is that it has now been found that cattails are a wonderful source for ethanol. As we continually strive for greater energy efficiency and independence, we are excited at the prospect that our wetland may become the home a usable fuel crop.