Use greywater diversion to expedite the production of valuable mulch.
By Dave Jacke
Sponsored by Permaculture Design Publishing
Permaculture is more than advanced organic gardening—it’s a worldview, where human needs are met through holistic designs that follows the patterns of natural systems. For example, the language of Nature has no word for waste—one organism’s waste is another species’ food. Applying this principle, permaculture designers have used greywater from kitchens, showers, and laundry rooms to construct wetlands and fill biofilters that lead to greenhouses, aquaculture installations, or simple irrigation systems. Whatever the application, greywater systems are integral to reducing our reliance on well water or city water. Greywater diversion is also a key component in many composting systems, such as the one designed by Doug Clayton for New Hampshire’s Gap Mountain Permaculture in the late 1980s.
Doug Clayton’s interesting, accessible method turns woodchip waste into organic mulch for the garden or orchard. This system has been running for 30 years with minimal maintenance and illustrates the essence of permaculture: the design of human systems that mimic natural systems for nutrient cycling. Doug designed this system to “dispose of greywater in a safe and sanitary manner and to recycle this water to a second productive use,” which in this case is to hasten the decomposition of wood chip piles so the resulting humus can be used as a soil amendment. To install Doug’s simple system, you’ll need a 100-gallon grease trap, a 70-gallon tank with a dosing siphon, a simple switch mechanism, and two 40-inch long piles of wood chips, used alternately, with perforated PVC pipe suspended in the center.
The grease trap in Doug’s system allows warm greywater from washing to cool off so that oils and grease can float to the surface, and solids can settle to the bottom, essentially functioning as a mini septic tank. Next, the dosing siphon stores a set volume of liquid, which the system releases in one dose. This release occurs without any moving parts that could fail and without electricity by trapping an air bubble between a bell jar and a plumbing trap. This dosing ensures that the system evenly distributes effluent throughout the 40 inches of wood chips, rather than just trickling in at the pipe inlet. It also allows the pile to reaerate after being hit with a load of water, ensuring that the decay process will be aerobic, rather than anaerobic. The switch is a simple cast-in-place concrete chamber about one foot in diameter with two outlets. An elbow is fitted over one outlet and turned up to close that side of the switch and direct the water to the pile in use.
To construct the piles for mulching, rough in two swales with a bulldozer, skid steer, or front-end loader with the diggings piled up on the trench sides as berms to hold in water, and with fiberglass (non-rotting) stakes every few feet to hold the perforated distribution pipe level as the wood chips rot down around it. Allow the distribution pipes to surface at either end of the pile to permit airflow. If possible, locate this system on a hillside so that the composted wood chips can be simply loaded onto a cart and wheeled downhill into orchards for use as mulch. Good design makes for less work!